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Development of a Precast Bent Cap System for Seismic Regions (2011)

Chapter: Chapter 3 - Interpretation, Appraisal, and Applications

« Previous: Chapter 2 - Findings
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
×
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Suggested Citation:"Chapter 3 - Interpretation, Appraisal, and Applications." National Academies of Sciences, Engineering, and Medicine. 2011. Development of a Precast Bent Cap System for Seismic Regions. Washington, DC: The National Academies Press. doi: 10.17226/14484.
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62 3.1 Overview This chapter provides interpretation, evaluation, and appli- cations of the findings of Chapter 2 in developing research deliverables for the precast bent cap systems investigated. In particular, this chapter presents design specifications, design examples, and design flow charts developed using specimen test results and related references. Design methodologies for emu- lative connections generally follow existing CIP methodologies, but changes are incorporated into new or revised design speci- fications. Presented construction specifications were developed using specifications previously developed together with results from test specimen fabrication and assembly (8, 21, 22, 23, 26). All research deliverables are also presented as attachments to this report, grouped in the following categories: proposed design specifications (new and revised), design flow charts, design examples, construction specifications, and example connection details. In addition, an implementation plan is provided. The attachments provide a detailed list of these deliverables (attachments available at www.trb.org/Main/ Blurbs/164089.aspx). Design specifications for the SDCs—SDCs C and D, SDC B, and SDC A—are given in appropriate format for incorpora- tion into a future edition of the AASHTO Guide Specifications for LRFD Seismic Bridge Design (LRFD SGS) (1). A major proposed change is to revise Article 8.13, “Joint Design for SDCs C and D” of the 2009 LRFD SGS to include precast bent cap connections (grouted duct and cap pocket). However, to address all seismic design categories, two new articles are also required. Therefore, current Article 8.13, “Joint Design for SDCs C and D” is renumbered as Article 8.15, “Joint Design for SDCs C and D.” This allows two new articles to be added: Article 8.13, “Joint Design for SDC A” and Article 8.14, “Joint Design for SDC B.” Design flow charts and design examples are presented to illustrate the proper use of design specifications for both grouted duct and cap pocket connections at all SDC levels (SDCs A, B, C, and D). Construction specifications are pro- vided as a new proposed article—Article 8.13.8, “Special Requirements for Precast Bent Cap Connections”—to be added to the AASHTO LRFD Bridge Construction Specifications (LRFD BCS) (35). 3.2 Development of Design Specifications This section presents the basis for the provisions proposed for incorporation into the LRFD 2009 SGS (1). For simplic- ity, the following sections generally use the same outline as that found in the 2009 LRFD SGS. Proposed specifications are given below. References to articles within this section refer to the LRFD SGS (2009 edition or proposed specifications). Proposed design specifications have been prepared in the format and language of the 2009 LRFD SGS with detailed com- mentary (1). In addition, detailed drawings are incorporated into the design specifications, including labeling of precast bent cap features and joint shear reinforcement. Many sections of this chapter are directly incorporated into the proposed design specifications, but not all sections of the specifications are shown herein. It is recommended that the accompanying attachments be reviewed together with this section. Chapter 3 refers extensively to 2009 LRFD SGS (1) provi- sions, which adopt the AASHTO convention of using units of ksi for f ′c. This practice results in different coefficients than those presented formerly using units of psi. For example, terms such as 3.5 psi (likely joint cracking) appear as 0.11 ksi for the same provision (likely joint cracking). This chapter adds clarifying units as needed. 3.2.1 Overview Based on specimen test results and analysis, the design spec- ifications presented in the following sections differ in some ′fc′fc C H A P T E R 3 Interpretation, Appraisal, and Applications

63 respects from the 2009 LRFD SGS provisions for nonintegral CIP bent caps (1). Precast bent cap connections conservatively require that the joint principal tensile stress be calculated to determine the additional joint shear reinforcement require- ment not only for SDCs C and D (as required for CIP design), but also for SDC B. Where the joint principal tensile stress, pt, indicates likely joint cracking (0.11 ksi or larger), grouted duct design specifications for joint shear reinforcement closely match CIP specifications. Cap pocket specifications, however, account for use of a single corrugated pipe that replaces trans- verse joint reinforcement, require a supplementary hoop at each end of the pipe and a smaller area of vertical joint stir- rups, and do not specify horizontal J-bars. Where the joint principal tensile stress indicates joint cracking is not expected (less than 0.11 ), precast bent cap connections in SDCs B, C, and D still require minimum transverse reinforcement and vertical stirrups within the joint. All precast bent cap connec- tions require bedding layer reinforcement, and specifications ensure proper design and placement of the column top hoop. SDC A joints also prescribe minimum transverse reinforce- ment and vertical joint stirrups within the joint. For hybrid bent cap connections, the experimental results indicated that many of the existing joint detailing provisions are reasonable for implementation. Therefore, the underly- ing joint transfer mechanism for CIP and emulative bent caps is employed for hybrid bent caps. New provisions were added to the LRFD SGS for the design of hybrid systems to ensure that the response characteristics of a hybrid system are achieved. In the 2009 LRFD SGS, there are some disparities between the joint design provisions for nonintegral systems and for transverse design of integral systems (1). The general mecha- nism for transverse response of a multicolumn nonintegral or integral structure is essentially the same. Therefore, recom- mended modifications are presented for integral systems to develop a consistent design specification. Furthermore, a variety of design and detailing provisions is recommended for integral precast systems in order to ensure that reliable and safe seismic response is achieved. 3.2.2 Displacement Magnification for Short Period Structures It is essential to consider the impacts on expected seismic demands when utilizing a system that has a significantly differ- ent mode of seismic response. The nonintegral emulative and integral details have been shown to perform in a similar man- ner to CIP structures. Therefore, these systems can be imple- mented using the same lateral seismic demand procedures that are currently employed in the LRFD SGS. However, the hybrid details investigated are aimed at providing a different mode of ′fc ′fc seismic response that has inherently less energy dissipation capacity when considering the hysteretic response. The series of nonlinear time history analyses conducted on hybrid sys- tems described in Chapter 2 indicate that the experienced seis- mic demands for hybrid systems designed in accordance with the provisions described herein are of similar magnitude to a CIP system. Therefore, the current provisions as specified in Article 4.3.3 can be implemented for hybrid systems. 3.2.3 Vertical Ground Motion Design Requirements The jointed nature of discontinuous integral precast super- structures with vertical joints at the bent cap face requires spe- cial attention when considering potential flexural and shear demands. The basic design philosophy for lateral loading is to use capacity design procedures to ensure the elastic response of the superstructure. However, vertical seismic loading cannot be handled with the same capacity design procedures because there is not a well-defined mechanism for inelastic response. The effects of vertical excitation can impose significant flex- ural and shear demands on the superstructure at the interface between the bent cap and girder whether it is a precast or CIP system. Therefore, seismic demands generated from vertical motions must be considered in seismic design. Additionally, seismically induced foundation movements such as relative settlement, lateral spreading, and liquefaction can induce sub- stantial demands on the superstructure. This topic is covered in more detail in the discussion of superstructure design pro- visions. For precast systems, the potential implications of ver- tical excitation are greater than comparable CIP systems due to possible concentrated joint rotations and the reliance on shear friction mechanisms to resist vertical shear demands across the joint. It is recommended that more refined vertical seismic demand provisions be developed for all bridge sys- tems; however, at a minimum, the following provision is rec- ommended for inclusion in Article 4.7.2 of the LRFD SGS for precast systems: For integral precast bridge superstructures with pri- mary members that are discontinuous at the face of the bent cap (i.e., precast segmental, integral spliced girder systems, etc.), vertical seismic demand shall be explicitly considered in superstructure design for both moment and shear using equivalent static, response spectrum, or time history analysis. Demands from vertical ground motion shall be combined with horizontal seismic demands based on plastic hinging forces developed in accordance with Article 4.11.2. Seismic demands shall be combined considering 100% of the demand in the vertical direction added with 30% of the seismic demand resulting from flexural hinging in one of the horizontal perpendicular directions (longitu- dinal) and 30% of the seismic demand resulting from

64 flexural hinging in the second perpendicular horizontal direction (transverse). A major obstacle that must be overcome is the development of improved provisions for the development of vertical seismic loadings. Current provisions in the 2009 LRFD SGS admit that there are shortcomings in the design requirements for vertical excitation that must be resolved for all bridge systems (1). 3.2.4 Analytical Plastic Hinge Length For integral bridge systems, it is desirable to have an under- standing of the expected rotation capacity of the superstructure when considering demands associated with vertical loading or potential seismically induced relative settlement. Similar to column systems, the use of moment-curvature analysis and an analytical plastic hinge length can provide an easy-to- implement method for the estimation of the inelastic response of a superstructure joint and its ultimate rotation capacity. Moment-curvature analysis for capacity protected superstruc- ture elements is already required for SDC C and D structures per the 2009 LRFD SGS Article 8.10 (1). The only obstacle in the determination of the inelastic flexural response is a reason- able estimate of the analytical plastic hinge length. For ele- ments that are flexurally dominated, the analytical plastic hinge length can be reasonably approximated as one-half of the element depth in the direction of loading. Therefore, the following is a recommended addition to the 2009 LRFD SGS as Article 4.11.6.2: where: Lps = analytical plastic hinge length for integral concrete superstructures (in) Ds = total depth of superstructure (in) 3.2.5 Reinforcing Steel Modeling Localized joint rotations associated with hybrid systems can cause increased straining in reinforcing bars due to geo- metric compatibility. As the joint opens, the rotation must be accommodated in the reinforcing bar with the bar being fixed at both ends. These additional strain demands caused by geo- metric loading can be accounted for by a conservative reduc- tion in the ultimate tensile strain considered. The following recommended addition to Article 8.4.2 of the 2009 LRFD SGS accounts for this geometric loading in combination with the traditional reduced ultimate tensile strain (1): For hybrid connections, the reduced ultimate tensile strain, Rsu, shall equal one-half the ultimate tensile strain,  su. L Dps s= 0 5. ProposedLRFD SGS Eq. 4.11.6.2-1 3.2.6 Plastic Moment Capacity for SDC B, C, and D The current provisions for the determination of plastic moment capacities of ductile concrete members are suf- ficient for CIP and precast emulative systems. However, the intentional debonding of post-tensioning and reinforce- ment within a hybrid system creates complications in the application of the existing provisions. With discrete joint rotations and distributed straining of steel elements, moment- curvature analysis cannot be directly implemented for hybrid concrete members. Therefore, additional provisions are required. Debonded elements and associated distributed straining can be accounted for using moment-rotation analyses. The prem- ise of moment-rotation analysis is similar to that of moment- curvature analysis where strain compatibility is used to perform sectional analysis of the member. In a moment- curvature analysis, the strain distribution is considered linear and identical for both steel and concrete elements at the same location. Moment-rotation analysis makes a similar plain sec- tion assumption, but allows for varying strain at a given section by considering a fixed length over which an element accumu- lates strain. To account for the analysis procedure required for hybrid members, a new Article 8.5.2 is recommended for addition to the 2009 LRFD SGS (1): For hybrid concrete members, the plastic moment capacity shall be calculated using a moment-rotation (M-θ) analysis based on the expected material proper- ties. The moment-rotation analysis shall include the axial forces due to dead load together with the axial forces due to overturning as given in Article 4.11.4. The M-θ curve can be idealized with an elastic per- fectly plastic response to estimate the plastic moment capacity of a member’s cross section. The elastic portion of the idealized curve passes through the point marking the first reinforcing bar yield. The idealized plastic moment capacity is obtained by equating the areas between the actual and the idealized M-θ curves beyond the first reinforcing bar yield point similar to as shown in Figure 1. In the execution of a moment-rotation analysis, the follow- ing are the recommended strain lengths for specific elements in the section. The concrete compressive strain length can be approximated as the neutral axis depth. In performing any strain-compatibility sectional analysis, the neutral axis depth is calculated to determine the cross-sectional deformation distribution. This depth can be used to define the region over which the concrete strain is approximately constant. The rein- forcement strain length can be approximated as the length over which the reinforcement is intentionally debonded. The post-tensioning strain length can be approximated as the dis-

65 tance between anchorages as the tendons are debonded for their full length. 3.2.7 Hybrid Performance Requirements To ensure that hybrid systems exhibit the desired lateral response characteristics of self-centering behavior and lim- ited damage, a variety of provisions are recommended for inclusion in the LRFD SGS. These provisions are intended to limit various design parameters within specific target ranges to produce the intended mode of lateral response. The aim of the first set of provisions is to ensure that the contribution of reinforcement is such that the system will be capable of a reduction in the residual deformations as com- pared to traditional bridge systems. A series of limits is rec- ommended for inclusion in Article 8.8.1 of the LRFD SGS as outlined below. The first of the three equations ensures that the effective axial load acting on the column following a seis- mic event is large enough to force the column reinforcement back to a zero strain state, thereby aiding in the self-centering response. The second equation limits the contribution of the reinforcement on the overall flexural capacity in order to limit the potential residual deformations associated with traditional bridge construction. Increases over this limit will produce lateral response that is similar to traditional CIP bridges with more noticeable damage and residual deformation. The third equation is a limit on the neutral axis depth that is intended to limit the magnitude of strain in the concrete compression toe due to joint opening. The maximum longitudinal reinforcement for hybrid compression members shall be proportioned to satisfy Equations 2 through 4: where: PD = dead load axial load action on column (kip) Ppse = effective force in post-tensioning tendon at end of service life (kip) Ts = resultant column reinforcement tension force associated with ultimate moment capacity (kip) where: Ms = flexural moment capacity provided by longitudinal reinforcement at reference yield moment (kip-ft) My = reference yield moment (kip-ft) c Dc ≤ 0 25. ProposedLRFD SGS Eq. 8.8.1-4 M M s y ≤ 0 33. ProposedLRFD SGS Eq. 8.8.1-3 0 9 1 0 . . P P T D pse s + > ProposedLRFD SGS Eq. 8.8.1-2 where: c = distance from extreme compression fiber to the neutral axis at the reference yield point (in) Dc = column diameter or smallest dimension in the direc- tion of loading (in) The next recommended modification is to Article 8.8.2 of the LRFD SGS. This provision specifies a minimum flexural contribution of mild reinforcement for hybrid systems to ensure that stable and predictable lateral response is achieved. The traditional minimum reinforcement requirements are not applicable to hybrid systems and therefore a new provi- sion is added. For hybrid systems, the minimum amount of reinforcement ensures that the response predictions for ref- erence yield are reasonable and the overall seismic demands as modified by Article 4.3.3 are valid. The recommended addition to Article 8.8.2 is the following: The minimum area of longitudinal reinforcement for hybrid compression members shall satisfy: where: Ms = flexural moment capacity provided by longitudinal reinforcement at reference yield moment (kip-ft) My = reference yield moment (kip-ft) To prevent the premature fracture of column reinforcement in hybrid systems, the reinforcement must be intentionally debonded to accommodate the localized joint opening at the ultimate displacement capacity. A provision is recommended for inclusion in the LRFD SGS as Article 8.8.14 to explicitly enforce this requirement: Longitudinal reinforcement in hybrid columns shall be intentionally debonded from the surrounding con- crete at hybrid column end connections. The minimum debonded length shall be such to ensure that the strain in the longitudinal reinforcement does not exceed the reduced ultimate tensile strain specified in Article 8.4.2 at the column ultimate rotation capacity. As was previously discussed, the current provisions for short period displacement amplification are acceptable for use with hybrid systems within the bounds of the provisions pre- sented in the LRFD SGS and herein. However, the influence of joint opening at the reference yield point must also be accounted for in the mathematical modeling of hybrid con- crete members to ensure that the added flexibility is consid- ered. The moment-rotation analysis performed in accordance with the recommended Article 8.5 modifications provides a means to approximate the added flexibility for equivalent M M s y ≥ 0 25. ProposedLRFD SGS Eq. 8.8.2-5

66 elastic analysis. To account for the added flexibility, the effec- tive moment of inertia can be modified based on the effective section properties calculated using moment-rotation analysis. The recommended Article 5.6.6 of the LRFD SGS provides this requirement: The effective moment of inertia for calculation of elastic flexural deformations for hybrid bridge columns can be taken equal to the gross moment of inertia. For mathematical modeling, the increase in flexibility at reference yield due to joint opening shall be considered. The influence of joint rotation shall be determined in accordance with the provisions of Article 8.5 using moment-rotation analysis. For equivalent elastic analy- sis, Ieff shall be decreased to account for the additional flexibility due to joint rotation. 3.2.8 Superstructure Capacity for Longitudinal Direction, SDCs C and D Superstructure Demand As discussed in relation to the recommended modifica- tions to the 2009 LRFD SGS, vertical seismic demands can play a significant role in the performance of integral precast bridge systems (1). Therefore, additional recommendations were specified for the development and consideration of ver- tical ground motions in the design of integral precast bridges. For longitudinal response, seismic actions are distributed into the superstructure based on an effective width calculated in accordance with Article 8.10. However, for vertical demands, the seismic loading can be distributed across the entire width of the bridge. To account for this, the recommended addition to Article 8.10 is the following: Vertical seismic demands determined in accordance with Article 4.7.2 shall be distributed to the entire width of the superstructure. The demands associated with the column overstrength moment, Mpo, shall be considered concurrently with vertical seismic demands as specified in Article 4.7.2. Minimum Superstructure Rotation Capacity The use of capacity design procedures cannot ensure that a superstructure system does not experience loads in excess of the superstructure capacity when considering actual vertical seismic motions and seismically induced foundation move- ments. The potential for seismically induced relative settle- ments may induce substantial geometrically driven demands on a bridge superstructure system. These mechanisms can result in loadings in the superstructure that may cause inelas- tic superstructure action. To ensure that the superstructure can accommodate a limited amount of inelastic rotation demand, the superstructure to bent cap connection should be capable of experiencing a defined level of rotation demand. The intent of the following recommended Article 8.10.3 is to ensure that the superstructure can resist a limited amount of inelastic action: The superstructure to bent-cap connection shall have plastic rotation capacity equal to or greater than 0.01 radians. The plastic rotation capacity shall be calcu- lated using the moment-curvature analysis required per Article 8.9 and the analytical plastic hinge length for superstructures as defined in Article 4.11.6. Torsional Design for Open Soffit Superstructures CIP integral bridge systems traditionally have a top deck slab and bottom soffit slab that provide reliable distribution of column overstrength demands into the superstructure. However, precast systems without a soffit slab cannot trans- fer the seismic demands through the same mechanism. The column flexural overstrength demands must be transferred into the superstructure by way of torsional response of the bent cap. Commonly used torsional mechanisms cannot develop over the short distance between the face of the column and girder. Instead, a modified torsional response must be con- sidered. The following new Article 8.10.4 requires the explicit consideration of a torsional transfer mechanism for open soffit systems: The transfer of column overstrength moment, Mpo, and associated shear and axial load via torsional mecha- nisms must be explicitly considered in the superstructure design for open soffit structures. Shear Design for Integral Precast Superstructures The potential for inelastic superstructure response due to vertical motion and seismically induced settlement was men- tioned in the discussion of the minimum superstructure rota- tion capacity. The bottom flanges of precast girders in the superstructure should be detailed to accommodate the poten- tial inelastic actions without degradation of the compression zone. Therefore, the use of closed hoops is recommended as a means to enhance the integrity of the girder flanges in the event of inelastic loading. The recommended addition to the 2009 LRFD SGS (1) is the following: The bottom flange of integral precast girders shall be reinforced with closed hoops within the region from the face of the bent cap equal to a distance equal to the superstructure depth. These hoops shall be spaced with the girder shear reinforcement, with spacing not to exceed 8 in. The hoops shall be the same size as the girder shear reinforcement, with a minimum bar size of No. 4.

67 Experimental results highlighted in Chapter 2 and described in detail in the attachments, indicate the importance of a well-developed shear transfer mechanism at the girder to bent cap connection. The potential for concentrated joint opening during seismic loading will result in a significant decrease in the effective shear depth across the joint that must be considered in design. The shear reinforcement can be distributed in the superstructure based on an assumed strut mechanism with a 30-deg maximum compression strut angle. Most importantly, the shear reinforcement must be extended as close to the top of the deck as possible while still satisfying concrete cover requirements. The recommended shear detail- ing uses headed reinforcement to ensure the sufficient anchor- age of the reinforcement within the short distance allocated. The following is a recommended addition to the 2009 LRFD SGS (1) as Article 8.10.5: For integral precast superstructures with girders dis- continuous at the face of the bent cap, headed shear reinforcement shall be placed within a distance from the face of the bent cap equal to 1.75 times the neutral axis depth at nominal capacity as determined in accor- dance with Article 8.9. The headed shear reinforcement within this distance shall be capable of resisting the fac- tored shear demand including effects of vertical seismic loading in accordance with Article 4.7.2. The shear demand shall be calculated considering the direction of loading and shears generated during positive flexural loading of the superstructure. This reinforcement shall extend as close to the top of the deck as possible while maintaining required concrete cover dimensions. 3.2.9 Joint Definition Specimen test results and related research provide a suffi- cient basis for safe, constructible, durable, and economical design of nonintegral emulative precast bent cap systems using grouted duct or cap pocket connections and hybrid connections in all SDC levels. However, as shown in Chapter 2, testing was limited to interior joints of multicolumn bent caps. Therefore, proposed provisions for all SDCs follow the precedent for CIP joints found in Article 8.13.4.1 of the 2009 LRFD SGS (1) in limiting specifications to interior joints of multicolumn bent caps: Interior joints of multicolumn bents shall be consid- ered “T” joints for joint shear analysis. Exterior joints shall be considered knee joints and require special analysis and detailing that are not addressed herein, unless special analysis determines that “T” joint analysis is appropriate for an exterior joint based on the actual bent configuration. Specifications for knee joints in CIP and precast bent cap systems should be developed. 3.2.10 Joint Performance SDCs C and D The joint performance for SDCs C and D is stated as follows: Moment-resisting connections shall be designed to transmit the maximum forces produced when the column has reached its overstrength capacity, Mpo. This matches the existing provision for SDCs C and D in the 2009 LRFD SGS (1). SDC B The joint performance for SDC B is stated as follows: Moment-resisting connections shall be designed to transmit the unreduced elastic seismic forces in columns where the column moment does not reach the plastic moment, Mp, and shall be designed to transmit the col- umn forces associated with the column overstrength capacity, Mpo, where the plastic moment, Mp, is reached. Based on Article 8.3.2 of the 2009 LRFD SGS, this provi- sion requires that connections be designed to transmit the lesser of the forces produced by Mpo or the unreduced elastic seismic forces (1). However, when the elastic seismic moment reaches the plastic moment, Mp, significant plastic hinging may develop. Therefore, it is conservatively required in such cases that connections be designed to transmit the forces pro- duced by Mpo. For SDC B, the column section may be designed and governed by load cases other than seismic. This proposed article is an application of Articles 8.3.2 and C8.3.2 of the 2009 LRFD SGS, which recognize that SDC B bridges may be subjected to seismic forces that can cause yielding of the columns and limited plastic hinging, as they are designed and detailed to achieve a displacement ductility, µD, of at least 2.0 (1). According to Article C4.8.1, SDC B columns are targeted for a drift capacity corresponding to concrete spalling. Article 4.8.1 provides an approximate equation for local displacement capacity, providing an approach that lim- its the required seismic analysis (i.e., expands the extent of a “No Analysis” zone). Thus, based on Article 4.11.1, joint shear checks and full capacity design using plastic overstrength forces are not required. This more liberal practice, as stated in Article C4.11.1, may be adopted for CIP joints. However, owners may also choose to implement the more conservative capacity-protection requirements given in Article 8.9. Full and limited ductility specimen tests indicated initial concrete spalling of the column at drift ratios ranging from 0.9% to 1.8% (µ1.5 to µ3). Specimens used a moderate amount of column longitudinal reinforcement—1.58%. For this case, joint shear cracks developed at loads less than effective yield

68 (µ1) for all specimens at principal tensile stresses that ranged from 2.95 psi to 4.3 psi, close to the 3.5 psi assumed by the 2009 LRFD SGS (1). At µ2, all specimens had significantly exceeded 3.5 and reached forces that were 88% to 100% of the maximum overall force induced in the joint during testing. Furthermore, the CPLD specimen, designed accord- ing to SDC B detailing requirements (i.e., no joint reinforce- ment other than the steel pipe), exhibited extensive joint shear cracking. As reported in Matsumoto 2009 (26), the absence of joint stirrups—in accordance with SDC B design—was the main cause of the development and growth of joint shear cracks. This indicates that SDC B joint design for precast connections should be based on a check of principal tensile stresses and that all SDC B joints should include at least min- imum joint shear reinforcement, defined as transverse rein- forcement and joint stirrups. The proposed LRFD SGS adopts the more conservative provisions that principal tensile stresses be checked for SDC B and that joint design depend on this check. These provisions help ensure that the precast bent cap connections accommo- date forces in an essentially elastic manner and do not become a weak link in the earthquake resisting system (Articles 4.11.1 and C4.11.1, 2009 LRFD SGS) (1). SDC A The joint performance for SDC A is stated as the following: Moment-resisting connections shall be designed to transmit the unreduced elastic seismic forces in columns. According to the 2009 LRFD SGS, bridges designed for SDC A are expected to be subjected to only minor seismic dis- placements and forces; therefore, a force-based approach is specified to determine unreduced elastic seismic forces, in lieu of a more rigorous displacement-based analysis (Articles 4.1 and 4.2, 2009 LRFD SGS) (1). However, some SDC A bridges may be exposed to seismic forces that may induce limited inelasticity, particularly in the columns. For this reason, Article 8.2 states that when SD1 is greater than or equal to 0.10 but less than 0.15, minimum column shear reinforcement shall be provided in accordance with Article 8.6.5 for SDC B, subject to Article 8.8.9 for the length over which this reinforcement is to extend. Although Article 8.8.9 does not specify placement of transverse col- umn reinforcement into the joint, Articles 5.10.11.4.1e and 5.10.11.4.3 of AASHTO LRFD Bridge Design Specifications (4th edition) with 2008 and 2009 Interims, referenced by the alternative provisions in Articles 8.2 and 8.8.9, specify place- ment of transverse reinforcement into the joint for a distance not less than one-half the maximum column dimension or ′fc ′fc′fc′fc 15.0 in from the face of the column connection into the adjoining member (29). According to these alternative provisions, when SD1 is greater than or equal to 0.10 but less than 0.15, minimum transverse reinforcement is required for CIP joints. When SD1 is less than 0.10, transverse shear reinforcement is not required. For all values of SD1 in SDC A, the designer may choose to con- servatively provide joint reinforcement as specified for SDC B, although SDC A is typically considered a “No Analysis” region for which seismic analysis is not required (2009 LRFD SGS, Article C4.6) (1). Precast bent cap connections for SDCs B, C, and D are designed and detailed to provide sufficient reinforcement for force transfer through the joint and bent cap. The precast bent cap design provisions for SDC A, including minimum provisions, are more liberal than those for precast bent caps for SDC B and may be considered “No Analysis” requirements for SDC A precast bent cap systems. They are deemed appro- priate for all values of SD1 in SDC A. When SD1 is less than 0.10, alternative precast bent cap connections developed for nonseismic regions may be used. Figure 3.1 and Figure 3.2 show several nonintegral precast bent cap details developed by Matsumoto et al. (8) for grouted duct, grout pocket, and bolted connections (7). Other references such as Brenes et al. (36) provide additional recommendations for detailing nonintegral precast bent cap connections using grouted ducts. It is recommended that minimum vertical stir- rups within the joint be used, as required for SDC A details. In addition, column longitudinal reinforcement should be extended into the connection as close as practically possible to the opposite face of the bent cap. 3.2.11 Joint Proportioning Two provisions should be satisfied in proportioning bent cap joints: (1) provide cross-sectional dimensions to satisfy limits on principal tensile and compression stresses and (2) provide sufficient anchorage length to develop column longitudinal reinforcement in the bent cap joint under seismic demand. Principal Stress Requirements SDCs C and D. Principal tensile and compression should be checked for SDCs C and D as required by Article 8.13.2 of the 2009 LRFD SGS for CIP connections (1). SDC B. As mentioned previously, to ensure that SDC B structures using precast bent caps are designed and detailed to achieve a displacement ductility, µD, of at least 2.0 (Article C8.3.2, 2009 LRFD SGS) (1), the proposed provisions conser- vatively require that SDC B joints be proportioned based on a check of principal stress levels. The provisions of Article

(a) Grouted Duct (b) Bolted 69 8.13.2 of the 2009 LRFD SGS are thus used for joint propor- tioning, except that the design moment used in determina- tion of principal stresses should be the lesser of Mpo or the unreduced elastic seismic column moment. SDC A. Check of principal stresses is not required for SDC A. Minimum Anchorage Length Column longitudinal bars should be extended into joints a sufficient depth to ensure that the bars can achieve approxi- mately 1.4 times the expected yield strength of the reinforce- ment, i.e., a level associated with extensive plastic hinging and strain hardening up to the expected tensile strength. For SDCs C and D, Article 8.8.4 of the 2009 LRFD SGS requires that column longitudinal reinforcement be extended into cap beams as close as practically possible to the opposite face of the cap beam and that for seismic loads, the anchorage length into the cap beam satisfy the following (1): where: lac = anchored length of longitudinal column reinforcing bars into cap beam (in) dbl = diameter of longitudinal column reinforcement (in) fye = expected yield stress of longitudinal column rein- forcement (ksi) f ′c = nominal compressive strength of bent cap concrete (ksi) Prior research by Matsumoto et al. (7, 8) and Mislinski (9) on anchorage of reinforcing bars in grouted ducts—confirmed l d f f ac bl ye c ≥ ′ 0 79. 2009LRFD SGS Eq. 8.8.4-1 Figure 3.1. Alternative precast bent cap connections for SDC A (SD1 < 0.10) (7).

70 by the NCHRP Project 12-74 grouted duct specimen (22)— indicates that the following equation can be conservatively used for seismic applications: where: lac = anchored length of longitudinal column reinforc- ing bar into grouted duct (in) dbl = diameter of longitudinal column reinforcement (in) fye = expected yield stress of longitudinal column rein- forcement (ksi) fcg = nominal compressive strength of grout (cube strength) (ksi) l d f f ac bl ye cg ≥ ′ 2 ProposedLRFD SGS Eq. 8.15.2.2.2-1 The maximum grout compressive strength used in Eq. 8.15.2.2.2-1 should be limited to 7,000 psi, even where the specified grout compressive strength (based on 2-in cubes) exceeds 7,000 psi. In addition, this equation applies #11 col- umn reinforcing bars or smaller ones. Anchorage of reinforcing bars in cap pocket connections can be based on prior precast bent cap research on grout pocket connections using trapezoidal prism-shaped pockets without a stay-in-place form (7, 8). Anchorage equations were modi- fied by removing a 0.75 factor that accounted for extensive splitting cracks at reentrant corners of grout pockets. Such cracking did not develop for the cylindrical-shaped cap pocket connections for CPFD and CPLD that used steel pipes as stay- in-place forms. The following equation—confirmed by CPFD (a) Grouted Pocket (Double Line) (b) Grouted Pocket (Single Line) Figure 3.2. Alternative precast bent cap connections for SDC A (SD1 < 0.10) (7).

71 and CPLD results—can be used for cap pocket connections (7, 8, 23, 26): where: lac = anchored length of longitudinal column reinforc- ing bars into cap pocket (in) dbl = diameter of longitudinal column reinforcement (in) fye = expected yield stress of longitudinal column re- inforcement (ksi) f ′c = nominal compressive strength of cap pocket con- crete fill (ksi) The anchored length includes the length of bar within the steel pipe and within the portion of the bent cap between the bottom of the steel pipe and the bent cap soffit. Maximum compressive strength for the concrete fill used in Eq. 8.15.2.2.2-2 should be limited to 7,000 psi, even where the specified concrete fill compressive strength exceeds 7,000 psi. In addition, this equation applies to #11 column reinforcing bars or smaller ones. As for CIP connections, the proposed specifications for grouted duct and cap pocket connections require that col- umn longitudinal reinforcement be extended into precast bent caps as close as practically possible to the opposite face of the bent cap. Only minor slip of column longitudinal bars was observed in the full ductility test specimens (CIP, GD, and CPFD). For example, for the CPFD specimen, bar slip contributed less l d f f ac bl ye c ≥ ′ 2 3. ProposedLRFD SGS Eq. 8.15.2.2.2-2 than 7% to fixed end rotation, and bar slip was comparable to that of the CIP specimen (21, 23). However, significant bar slip was observed in the CPLD specimen, as summarized in Chapter 2 and detailed in Matsumoto 2009 (26). The level of bar slip observed is attributed to significant shear cracking in the joint that developed due to the lack of joint reinforce- ment, especially vertical stirrups. The proposed LRFD SGS requires at least minimum joint reinforcement (both trans- verse confinement and vertical stirrups) for all SDC levels. In addition, the embedment depth of the CPLD column bars into the cap pocket was 26% less than that required by Eq. 8.15.2.2.2-2, due to the relatively low compressive strength of the concrete fill. Article 8.13.8.3 of the proposed LRFD Bridge Construction Specifications (4) requires a minimum 500-psi margin between the compressive strength of the bent cap and precast connection concrete fill (or grout). This margin accounts for the likelihood that the actual bent cap compressive strength will exceed its specified strength and the possibility of a low compressive strength of the grout or concrete fill. This provision is intended to ensure that the connection does not become a weak link in the system and helps limit bar slip. Comparison of Anchorage Length Equations. Figure 3.3 compares seismic anchorage (or development) length require- ments for anchoring column longitudinal reinforcement into bent cap joints, based on the equations given in Table 3.1. For simplicity, anchorage length, lac, is used herein for both anchorage and development lengths (lac and ld) applied to anchorage of column bars in a joint. Provisions in the 2009 0 10 20 30 40 50 60 4000 5000 6000 7000 8000 A nc ho ra ge L en gt h/ Ba r D ia m et er (l a c /d b) Compressive Strength of Concrete or Grout (psi) 2009 LRFD SGS AASHTO LRFD *1.25 UT Matsumoto, CP (GP*0.75) UT/CSUS Matsumoto, GD UT Brenes, GD (γ=.75, β=1) UT Brenes, GD (γ=.75, β=1.3) UW Steuck *1.5, GD Figure 3.3. Anchorage length versus compressive strength—comparison of equations.

72 LRFD SGS (Article 8.8.4) and LRFD BDS (Article 5.10.11.4.3) apply to CIP connections (29, 1). The grouted duct and cap pocket column bar anchorage equations (Eq. 8.15.2.2.2-1 and Eq. 8.15.2.2.2-2) are recommended for use in precast bent cap connections. Additional equations for grouted duct con- nections based on recent research are also provided (28, 37). Table 3.1 also compares the ratio of anchorage length to bar diameter (lac/db) for #11 rebar and compressive strength of 6,000 psi (grout or concrete) as an example. In addition, the lac/db ratio for each equation is compared to that of the 2009 LRFD SGS (Eq. 8.8.4-1), which is taken as a reference (1). Figure 3.3 and Table 3.1 indicate that the LRFD BDS equation is extremely conservative, requiring nearly twice the anchorage length required by the 2009 LRFD SGS. The proposed grouted duct and cap pocket (CP) equations are slightly more conser- vative (4% and 17%, respectively) than the 2009 LRFD SGS equation for the example, although Figure 3.3 shows the change in anchorage length with compressive strength. The proposed grouted duct equation is based on both tension cyclic and monotonic tension tests and includes a factor of safety of at least 2.0. In addition, this equation can be conservatively used for epoxy-coated bars. The use of f ′cg rather than in the denominator is explained in Matsumoto et al. (7). ′fcg Brenes et al. (36) extended the grouted duct research of Matsumoto et al. (8), examining group effects (γ factor) and plastic ducts (β factor), among other variables. Values of γ range from 0.45 to 0.9 for typical configurations of bars in a grouted duct connection. The case of γ = 0.75 and β = 1.0 shown in Figure 3.3 represents bar anchorage that accounts for group effects based on a moderate number of grouted column bars simultaneously subjected to tension under the design load combinations (γ = 0.75) as well as galvanized steel duct mater- ial (β = 1.0). The equation in Brenes et al. for grouted ducts is slightly more conservative than that of Matsumoto et al. for the assumed values of γ and β. Significantly, Brenes et al. found that the required anchorage length increased by 30% when polyethylene or polypropylene (plastic) ducts are used instead of steel. Tension cyclic tests were not conducted. The University of Washington equation, which is multiplied by the recommended 1.5 seismic factor (37), results in an exceptionally short development length and is not recom- mended for use in precast bent cap design. SDCs B, C, and D. Based on the foregoing development, Eq. 8.15.2.2.2-1 and Eq. 8.15.2.2.2-2 are proposed for anchorage of column bars in grouted duct and cap pocket connections, respectively. Table 3.1. Comparison of anchorage length equations. Reference Anchorage Length, or , (#11; or , 6000 psi) 2009 AASHTO LRFD SGS [15] 30.9 1.00 AASHTO LRFD BDS1 [27] 59.8 1.94 UT Matsumoto, Cap Pocket2 [3, 4] 36.0 1.17 UT/CSUS Matsumoto, Grouted Duct [3, 4] 32.0 1.04 UT Brenes, Grouted Duct3 [34] 36.7 ( ) 1.19 ( ) 47.7 ( ) 1.54 ( ) UW Steuck, Grouted Duct4 [35] 14.9 0.48 1Includes 1.25 seismic factor 2Embedment includes 0.75 factor 3 fs,cr taken as fye.; ; for galvanized steel; for plastic duct 4Includes 1.5 seismic factor; taken as 1.5 in.  / / /

73 SDC A. SDC A incorporates the same requirements as those for SDCs B, C, and D except that the nominal yield stress of the column longitudinal reinforcement may be used in lieu of the expected yield stress. This allows for a slightly reduced safety margin due to the significantly lower seismic demand and limited inelasticity in the columns. 3.2.12 Minimum Joint Shear Reinforcement SDCs C and D. Minimum joint shear reinforcement refers to transverse reinforcement within the joint region in the form of column reinforcement, spirals, hoops, intersect- ing spirals or hoops, or column transverse or exterior trans- verse reinforcement continued into the bent cap. For precast connections, minimum transverse joint reinforcement is required to help ensure that the connection does not become a weak link in a precast bent cap system. Transverse reinforce- ment for a grouted duct connection is the same as that for a CIP connection. However, for a cap pocket connection, the steel pipe serves as the transverse reinforcement. For SDCs C and D, the minimum joint shear reinforce- ment for precast and hybrid connections is determined using essentially the same basis as that used for CIP connections. If the nominal principal tensile stress in the joint, pt, is less than 0.11 , then the transverse reinforcement in the joint, ρs, must satisfy the following equation and no additional rein- forcement within the joint is required: where: fyh = nominal yield stress of transverse reinforcing (ksi) f ′c = nominal compressive strength of concrete (ksi) ρs = volumetric reinforcement ratio of transverse rein- forcing provided within the cap Where the principal tensile stress in the joint, pt, is greater than or equal to 0.11 , then transverse re- inforcement in the joint, ρs, must satisfy both Eq. 8.13.3-1 and the following equation: where: Ast = total area of column longitudinal reinforcement anchored in the joint (in2) lac = length of column longitudinal reinforcement embedded into the bent cap (in) For this case, additional joint reinforcement is also required. The 2009 LRFD SGS requires only Eq. 8.13.3-1 to be satis- fied (1). However, the proposed specifications require that ρs st ac A l ≥ 0 40 2 . 2009LRFD SGS Eq. 8.13.3-2 ′fc ρs c yh f f ≥ ′ 0 11. 2009LRFD SGS Eq. 8.13.3-1 ′fc the larger of Eq. 8.13.3-1 and Eq. 8.13.3-2 be used because the transverse reinforcement requirement of Eq. 8.13.3-2 can become less than that of Eq. 8.13.3-1 in some cases, as shown in this research. SDC B. The proposed provisions for precast connections in SDC B require the same check of principal tensile stress to determine transverse reinforcement in the joint as is required for SDCs C and D. However, the 2009 LRFD SGS does not include provisions for minimum transverse reinforcement for CIP structures in SDC B (1). The SDC B design requirement for CIP would then default to Article 5.10.11.3 of the 2009 LRFD BDS for Seismic Zone 2, which refers the designer to Article 5.10.11.4.3 (Seismic Zones 3 and 4). Article 5.10.11.4.3 requires the following: Column transverse reinforcement, as specified in Article 5.10.11.4.1d, shall be continued for a distance not less than one-half the maximum column dimension or 15.0 in from the face of the column connection into the adjoining member. It is judged that this reinforcement is not adequate for CIP limited ductility connections. It is therefore recommended that minimum joint transverse reinforcement requirements also be established for CIP bridges in SDC B. For limited or simplified seismic analysis (i.e., a “No Analysis”-type approach), mini- mum reinforcement satisfying Eq. 8.13.3-1 of the 2009 LRFD SGS is recommended (1). SDC A. For SDC A, principal stresses are not checked, but minimum joint shear reinforcement is proposed for pre- cast connections. This is simple, yet conservative and should be considered good detailing practice. Such reinforcement is not required for CIP joints per the 2009 LRFD SGS, but is rec- ommended (1). Grouted Duct Connections SDCs B, C, and D. Grouted duct connections use the same basis as CIP connections in SDCs C and D, with the additional requirement that spacing of transverse reinforcement not exceed 0.3Ds nor 12 in. This is intended to provide a reason- able number of hoops within the joint when the minimum requirement governs. SDC A. Joint transverse reinforcement provisions con- servatively match minimum requirements for SDC B. Cap Pocket Connections SDCs B, C, and D—Basic Equation for Pipe Thickness. For cap pocket connections, the thickness of the corrugated

74 steel pipe, tpipe, is based on providing shear resistance to the joint that is approximately the same as that provided by the hoops required for CIP joints: Cap pocket connections shall use a helical, lock-seam, corrugated steel pipe conforming to ASTM A760 to form the bent cap pocket. A minimum thickness of cor- rugated steel pipe shall be used to satisfy the transverse reinforcement ratio requirements specified in Article 8.15.3.1. The thickness of the steel pipe, tpipe, shall not be taken less than that determined by Eq. 1: In which: where: FH = nominal confining hoop force in the joint (kips) Hp = height of steel pipe (in) fyp = nominal yield stress of steel pipe (ksi) θ = angle between horizontal axis of bent cap and pipe helical corrugation or lock seam (deg) nh = number of transverse hoops in equivalent CIP joint Asp = area of one hoop reinforcing bar (in2) fyh = nominal yield stress of transverse reinforcement (ksi) The derivation of this equation is provided in the CPT Attachment. As shown in the design examples provided in the attachments, the spacing of transverse joint hoops can be directly related to the number of hoops, nh, by the volumet- ric reinforcement ratio for transverse joint hoops, ρs, using Eq. 8.6.2-7 of the 2009 LRFD SGS (1). F n A fH h sp yh≥ ProposedLRFD SGS Eq. 8.15.3.2.2-2 t F H f H p yppipe in. ProposedLR ≥ ⎧ ⎨⎪ ⎩⎪ max cos . θ 0 060 FD SGS Eq. 8.15.3.2.2-1 The maximum spacing requirements of 0.3Ds and 12 in do not apply to the determination of nh. The minimum thickness of the steel pipe, tpipe, of 0.060 in corresponds to 16-gage steel pipe, which was used for the 18-in nominal diameter pipe in the cap pocket specimens (with a 20-in diameter column). As shown in Table 3.2, this is the thinnest gage typically available off the shelf for corrugated steel pipe. Other pipe thicknesses (nominal and tolerance range) are shown in Table 3.2, with specified and minimum values for coated steel sheet per ASTM A929 (25). Thicker pipes (gages 8, 7, and 5) are usually available through special order. Material costs increase roughly according to the weight shown in the last column of Table 3.2. SDCs B, C, and D—Alternative Equation for Pipe Thickness. The following simplified equations, Eq. C8.15. 3.2.2-1 and Eq. C8.15.3.2.2-2, may be used to conservatively determine pipe thickness, tpipe, in lieu of calculating the num- ber of hoops in an equivalent CIP joint, nh, as the basis for determining pipe thickness. This avoids iteration in design cal- culations, but may result in thicker gage pipe used in design. Where the principal tensile stress in the joint, pt, specified in Article 8.15.2.1, is less than 0.11 , the thickness of the steel pipe, tpipe, may be determined from the following: where: f ′c = nominal compressive strength of the bent cap concrete (ksi) D ′cp = average diameter of confined cap pocket fill between corrugated pipe walls (in) fyp = nominal yield stress of steel pipe (ksi) θ = angle between horizontal axis of bent cap and pipe helical corrugation or lock seam (deg) t f D f Cc cp yp pipe ProposedLRFD SGS Eq.≥ ′ ′ 0 04. cosθ 8.15.3.2.2-1 ′fc Table 3.2. Steel corrugated pipe thicknesses. Thickness (in) Gage Number Nominal Tolerance Range Specified† Minimum† Pounds per Square Foot 16 0.0598 0.0648 to 0.0548 0.064 0.057 2.439 14 0.0747 0.0797 to 0.0697 0.079 0.072 3.047 12 0.1046 0.1106 to 0.0986 0.109 0.101 4.267 10 0.1345 0.1405 to 0.1285 0.138 0.129 5.486 8* 0.1644 0.1742 to 0.1564 0.168 0.159 6.875 7* 0.1838 0.1883 to 0.1703 No value No value 7.500 5* 0.2092 0.2162 to 0.2022 No value No value 8.750 *Nonstandard size available by special order †Values refer to coated steel sheet thicknesses per ASTM A929 (25)

75 Where the principal tensile stress in the joint, pt, is greater than or equal to 0.11 , the thickness of the steel pipe, tpipe, may be determined from the larger of Eq. C8.15.3.2.2-1 and the following equation: where: Ast = total area of column longitudinal reinforcement anchored in the joint (in2) D ′cp = average diameter of confined cap pocket fill between corrugated pipe walls (in) fyh = nominal yield stress of transverse reinforcing (ksi) lac = anchored length of longitudinal column reinforc- ing bars into precast bent cap (in) fyp = nominal yield stress of steel pipe (ksi) θ = angle between horizontal axis of bent cap and pipe helical corrugation or lock seam (deg) The derivations of these equations are provided in an attach- ment together with a comparison of the influence of different variables in these equations. For example, Figure 3.4 com- pares the pipe thicknesses required by Eq. 8.15.3.2.2-1, Eq. C8.15.3.2.2-1, and Eq. C8.15.3.2.2-2. For comparison, column diameters range from 24 in to 60 in; equivalent hoop sizes vary according to the column diameter; the column is assumed to have a longitudinal steel ratio, Ast/Acol, of 0.015; and the bent cap compressive strength is assumed to be 6,000 psi. Figure 3.4 reveals that (1) using the general (refined) equation results in t A D f l f st cp yh ac yp pipe ProposedLRFD ≥ ′ 0 14 2 . cosθ SGS Eq. 8.15.3.2.2-2C ′fc the thinnest required pipe; (2) using the approximate equa- tions (larger of the two equations, where principal tensile stress is greater than or equal to 0.11 ) usually results in a pipe thickness one gage size larger than that required by the general equation, using the gage sizes given in Table 3.2; (3) a reasonable pipe thickness results in all cases; and (4) Eq. C8.15.3.2.2-1 governs over Eq. C8.15.3.2.2-2 for all but the largest column diameter (60 in). Figure 3.5 compares the pipe thicknesses for column lon- gitudinal steel ratios, Ast/Acol of 0.010, 0.015, and 0.020. This figure shows the expected significant impact of Ast/Acol on required pipe thickness. It also shows that Eq. C8.15.3.2.2-2 results in thick gage pipes for larger columns, indicating that the designer may prefer to use the general equation in such conditions to minimize the required pipe thickness. The CPT Attachment provides additional plots that show the effect of f ′c on pipe thickness for 4,000 psi, 6,000 psi, and 8,000 psi bent cap concrete. The required pipe thickness increases approximately 10% to 30% with f ′c based on Eqs. C8.15.3.2.2-1 and C8.15.3.2.2-2. For example, for a 36-in diameter column with #6 hoops (Ast/Acol = 0.015), the pipe thickness increases 18% as f ′c increases from 4,000 psi to 8,000 psi. Eq. C8.15.3.2.2-1 results in a larger increase of 41% (pro- portional to ). Eq. C8.15.3.2.2-2 is not dependent on f ′c. SDC A. Cap pocket pipe thickness for SDC A is based on the minimum provision for transverse reinforcement, as given in Eq. 8.15.3.2.2-1. Eq. C8.13.3.2.2-1 may be alterna- tively used. ′fc ′fc 0.00 0.05 0.10 0.15 0.20 0.25 0.30 #3 #4 #4 #5 #6 #5 #6 #8 #6 #8 Pi pe T hi ck ne ss (in ) Eq. 8.15.3.2.2-1 Eq. C8.15.3.2.2-1 Eq. C8.15.3.2.2-2 Dc = 36 in Dc = 48 in Dc = 60 in Dc = 24 in Gage 16 Gage 14 Gage 12 Gage 10 Gage 8 Gage 7 Gage 5 Figure 3.4. Pipe thickness versus column diameter (Dc) and equivalent hoop size (Ast/Acol = 0.015, f ′c = 6,000 psi for bent cap).

76 3.2.13 Integral Bent Cap Joint Shear Design Per 2009 LRFD SGS, joint shear design is required for SDCs C and D, but not SDC B (1). Where the principal tensile stress, pt, is greater than or equal to 0.11 , additional joint shear reinforcement is required. The 2009 LRFD SGS requires placement of joint shear reinforcement based on assumed force transfer mechanisms in the longitudinal and transverse direc- tions. Based on a review of the testing presented in Chapter 2 and other previous research on precast integral bridge systems, the assumed force transfer mechanism for longitudinal load- ing is adequate for the system considered. However, the requirements presented in the 2009 LRFD SGS for transverse response vary from the requirements for nonintegral transverse response (1). The mechanism for trans- verse response is the same whether an integral or nonintegral connection is used. Therefore, there are recommended mod- ifications to the integral design provisions to account for these differences. Vertical Stirrups Requirements specified in the 2009 LRFD SGS for vertical stirrups in integral bridge systems are based on longitudinal and transverse loadings. Per Figure 8.13.4.2.1-1 of the 2009 LRFD SGS, for single column bent caps only vertical stirrups are required along both faces of the bent cap extending one- half the column dimension on both sides of the column (1). ′fc This requirement is based on an assumed longitudinal force transfer mechanism and is appropriate for use in both CIP and precast integral bridge connections. In accordance with Figure 8.13.4.2.1-1, for multicolumn bent caps additional reinforcement is required on both sides of the column based on an assumed transverse force transfer mechanism. These requirements vary from those presented for nonintegral bent caps and must be updated for consistency. The recommended modifications to this provision elimi- nate the second portion of Figure 8.13.4.2.1-1 for multicolumn bent caps. Instead, this article should reference the recom- mended provisions of LRFD SGS Article 8.15.5 for vertical stir- rups inside and outside of the joint. The transverse provisions for nonintegral bent caps are described in more detail in sub- sequent sections of this report. Horizontal Stirrups The 2009 LRFD SGS requires the placement of horizontal stirrups around the vertical stirrups within the bent cap (1). These provisions are adequate for integral systems in the longi- tudinal direction but must also be updated to be in agreement with the nonintegral transverse requirements. The provisions of Article 8.13.4.2.2 of the 2009 LRFD SGS provide a minimum quantity of horizontal stirrups required in addition to spacing requirements. The provisions for nonintegral bent caps specify only spacing and size requirements. The recommended modi- fication for integral bent caps is the addition of a provision to 0.010 0.015 0.020 0.010 0.015 0.020 0.010 0.015 0.020 Ast/Acol Eq. 8.15.3.2.2-1 Eq. C8.15.3.2.2-1 Eq. C8.15.3.2.2-2 Dc = 36 in Dc = 48 in Dc = 60 in Gage 16 Gage 14 Gage 12 Gage 10 Gage 8 Gage 7 Gage 5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Pi pe T hi ck ne ss (in ) Figure 3.5. Pipe thickness versus column diameter (Dc) and column flexural reinforcement ratio (#6 hoop, f ′c = 6,000 psi for bent cap).

77 ensure that the horizontal stirrups for multicolumn bent caps also satisfy the nonintegral provisions. Additional Longitudinal Cap Beam Reinforcement Provisions for nonintegral bent caps per the 2009 LRFD SGS require the placement of additional longitudinal rein- forcement within the cap beam (1). There is currently no requirement for the placement of this reinforcement for multi- column integral bent caps. Therefore, it is recommended that a provision for integral bent caps that requires the placement of additional longitudinal cap beam reinforcement for multi- column bent caps be added. The adequacy of this requirement for transverse response of nonintegral bent caps is discussed in more detail in a subsequent section. 3.2.14 Nonintegral Bent Cap Joint Shear Design Per the 2009 LRFD SGS, joint shear design is required for SDCs C and D, but not SDC B (1). For SDCs C and D, where the principal tensile stress, pt, is less than 0.11 , minimum joint shear (transverse) reinforcement is required. Where pt is greater than or equal to 0.11 , the additional joint shear reinforcement (Ajvis , A jvo s , A jl s , and horizontal J-bars) is required. ′fc ′fc The proposed joint shear design approach for nonintegral precast bent caps and integral bent caps in the transverse direc- tion follows the same approach, but conservatively requires the principal tensile stress check for SDC B as well as SDCs C and D. In addition, the additional joint shear reinforcement differs in certain regards from CIP requirements. Although vertical joint stirrups, horizontal J-bars, and additional longitudinal bent cap reinforcement are addressed, other provisions, such as bedding layer reinforcement and supplementary hoops, are included. In addition, minimum joint shear reinforcement— both transverse joint reinforcement and vertical joint stir- rups inside the joint—is conservatively required for all SDC levels. The proposed joint shear reinforcement provisions are based on precast bent cap specimen response reported in the work of Matsumoto (21, 22, 23, 26) as well as additional analysis presented herein. Table 3.3 compares the joint rein- forcement used in the full ductility specimen design to that required by the 2006 LRFD RSGS, which was the original design basis of specimens, and the 2009 LRFD SGS, the current AASHTO seismic guide specifications (2, 1). The proposed LRFD SGS for precast bent caps for SDCs C and D is also listed and compared to the test specimens (Proposed Specification/ Test Specimen) and to the 2009 LRFD SGS (Proposed Specification/2009 LRFD SGS). Table 3.3. Comparison of joint reinforcement for various seismic guide specifications—SDCs C and D. Reinforcement Type Term Specimen Quantity 2006 LRFD RSGS 2009 LRFD SGS   Proposed Guide Proposed Specification Specification Proposed Specification 2009 LRFD SGSTest Specimen Transverse Hoop -A max of - A, B 1.00B Vertical Joint 0.27 0.20C 0.175 0.175 0.65D 1.00 0.089E - 0.135 GD: 0.135 CPFD: 0.12 GD: 1.52 CPFD: 1.35 GD: 1.00 CPFD: 0.89 Additional Bent Cap Longitudinal 0.0 0.0 0.245 0.245 - F 1.00 Horizontal J-bar 0.13G 0.10G Every other intersection in joint Every other intersection in joint - G GD: 1.00 CPFD: - H Bedding Layer Hoop - - - - Reinforcement per specification - I - I Notes: A GD test specimen used hoops close to minimum per 2006 LRFD RSGS, and CPFD used a steel corrugated pipe thickness based on 2006 LRFD RSGS. B Typically this will be 1.0, except that the proposed specification requires the larger of 2009 LRFD SGS Eq. 8.13.3-1 and Eq. 8.13.3-2 be used. C Placed transversely within Dc from either side of column center line per 2006 LRFD RSGS. Placement was adjacent to joint. D Difference was due to change in design requirements and rounding of bar sizes in specimen. E Specimen used construction stirrups; 2006 LRFD RSGS did not require jvi sA . F Not used because 2006 LRFD RSGS did not require jl sA . G Proposed Guide Specification and 2009 LRFD SGS require jh sA in joint for GD; GD specimen used jhsA adjacent to joint per 2006 LRFD RSGS. H Horizontal J-bars are not used for cap pocket connections. I Specimen did not use hoop in scaled 1- in bedding layer. Bedding layer hoop applies only to precast connections.

78 From Table 3.3, it is evident that the joint design require- ments became considerably more conservative from the 2006 LRFD RSGS to 2009 LRFD SGS and that the differences between the test specimens and the 2009 LRFD SGS reflect this (2, 1). As a whole, the proposed joint reinforcement is conservative compared to that used in the test specimens. In addition, there is considerable consistency (i.e., a ratio of 1.00 for Proposed Specification/2009 LRFD SGS) between the proposed specifications and 2009 LRFD SGS for SDCs C and D where principal tensile stress, pt, is greater than or equal to 0.11 . However, there are still considerable differences in design specifications between nonintegral CIP and precast bent caps, as shown in the following sections. Limits on Bent Cap Depth Nonintegral precast bent caps are subject to the same bent cap depth limitations and the alternative design basis required by Article 8.13.5 of the 2009 LRFD SGS (for CIP bent caps) (1). The proposed provision is the following: Cast-in-place, emulative precast and hybrid bent cap beams satisfying Eq. 1 shall be reinforced in accordance with the requirements of Articles 8.15.5.1 and 8.15.5.2. Bent cap beams not satisfying Eq. 1 shall be designed on the basis of the strut and tie provisions of the AASHTO LRFD Bridge Design Specifications and as approved by the Owner. where: Dc = column diameter (in) d = total depth of the bent cap beam (in) Vertical Stirrups Inside and Outside the Joint SDCs C and D—Principal Tensile Stress, pt, 0.11 or Larger. The 2006 LRFD RSGS used for the design of the prototype bridge and full ductility test specimens did not dis- tinguish between integral and nonintegral bent cap systems, nor between the design of vertical stirrups inside the joint region and outside (i.e., adjacent to) the joint region (2). Based on the work of Sritharan (38), the 2009 LRFD SGS (1) for nonintegral bent caps increased the required total area of vertical joint stirrups (inside and outside the joint) approxi- mately 21% over the 2006 LRFD RSGS requirement. In addi- tion, Articles 8.13.5.1.1 and 8.13.5.1.2 of the 2009 LRFD SGS require placement of 0.175Ast outside the joint (adjacent to each side of the column) as well as 0.135Ast inside the joint. These are major changes in joint stirrup requirements over the 2006 LRFD RSGS provisions. These provisions should also be required for the design of integral bent cap systems in the trans- verse direction as the response mechanism is the same. ′fc D d Dc c≤ ≤ 1 25. ProposedLRFD SGS Eq. 8.15.5-1 ′fc The full ductility specimens used the more liberal (and constructible) placement of joint stirrups outside the joint as the more severe condition for investigating joint response, permissible by the 2006 LRFD RSGS (2). Rounding stirrup bar diameters to practical sizes for the test specimens resulted in a larger area of vertical stirrups outside the joint region than required. However, two 2-leg construction stirrups with a total area of 0.089Ast were included within the joint region, as mentioned in Matsumoto (21). As shown in Table 3.3, this resulted in an area 66% of that required by the 2009 LRFD SGS (0.135Ast) (1). As shown in the strain profiles of Figure 2.48 (CIP), Figure 2.54 (GD), and Figure 2.59 (CPFD), vertical joint stirrups were highly effective for the CIP and GD specimens for which maximum joint crack widths were 0.025 in and 0.040 in, respectively. This confirms the importance of such stirrups in achieving emulative response. Smaller joint stirrup strains were evident for the CPFD specimen, which exhibited much smaller crack widths and a crack pattern that differed from the CIP and GD specimens. In contrast, the CPLD specimen exhibited severe joint cracking, which is attributed to the absence of joint reinforcement, especially joint stirrups. Figure 2.46 and Fig- ure 2.64 portray the significant effect of the CPLD joint shear cracking on joint shear stiffness and system displacement, even though the specimen achieved an exceptionally large drift of 5.0% in the presence of cracks up to 0.080 in wide. Outside the joint, the GD and CPLD stirrup strains were the largest, 68% of yield and 61% of yield, respectively. Based on a comparison of GD and CIP results and the overall GD emulative response, the proposed specification requires full ductility grouted duct connections to use the same joint stirrups inside the joint as required by the 2009 LRFD SGS (1). Based on a comparison of the CPFD and CIP response, it is deemed reasonably conservative to require 0.12Ast—12% less than the CIP requirement (0.135Ast) but 35% more than that used in the CPFD specimen (0.089Ast), which exhibited min- imal joint distress and exceptional joint performance: Vertical stirrups inside the joint with a total area, Ajvis , spaced evenly over a length, Dc , through the joint shall satisfy: Vertical stirrups inside the joint shall consist of dou- ble leg stirrups or ties of a bar size no smaller than that of the bent cap transverse reinforcement. A minimum of two stirrups or equivalent ties shall be used. Due to the presence of the pipe, overlapping double-leg vertical stirrups are not practical. Figure 3.6 shows the minimum number of two-leg vertical joint stirrups required for values of Ajvis /Ast ranging from 0.08 A As jvi st≥ 0 12. ProposedLRFD SGS Eq. 8.15.5.2.3a-1

79 to 0.135, based on several stirrup sizes. Results are shown for 36-in and 48-in diameter columns and for column longitudi- nal reinforcement ratios, Ast/Ag, of 0.01, 0.015, and 0.02. The height of the bar indicates the number of required stirrups, subject to the proposed specification minimum of two stir- rups. Additionally, the number in parentheses at the top of the bar indicates the calculated stirrup requirement (i.e., without rounding or the 2-stirrup minimum). Figure 3.6 shows that both the 0.135Ast requirement for grouted ducts and the 0.12Ast requirement for cap pocket connections pro- duce a number of stirrups that can be reasonably satisfied in design and construction. Although the design requirement can become significant for larger percentages of column longitudinal reinforcement (Ast), potential congestion can be alleviated by the use of larger stirrup bar sizes. Grouted duct connections require a larger area of vertical stirrups than cap pocket connections, and as shown in Figure 3.6, this sometimes results in a larger number of stirrups; however, the area requirement can be satisfied by using overlapping two-leg stirrups. Cap pocket connections accommodate only two-leg stirrups; therefore, it is important that the designer carefully consider using larger stirrup sizes and possibly bundling stirrups, especially when a larger column reinforcement ratio is used. In addition, care should be taken in design to ensure that the number and placement of stirrups over the top opening of the pocket does not unduly interfere with concrete placement in the pocket during the assembly operation. For both connection types, stirrups should be placed symmetrically. Three sets of stirrups can be placed symmetri- cally when column bars are rotated a half turn (to avoid con- flict); however, conflict between bent cap longitudinal bars and column bars and/or corrugated ducts should also be avoided. Based on a comparison of CIP results with GD and CPFD response and the overall GD and CPFD emulative response, the proposed specification requires grouted duct and cap pocket full ductility connections to use the same joint-related vertical stirrup area outside the joint (Ajvos ) as required by the 2009 LRFD SGS (1). SDCs C and D—Principal Tensile Stress, pt, Less than 0.11 . Per the 2009 LRFD SGS, where the principal tensile stress, pt, for a CIP connection is less than 0.11 , only minimum joint transverse (hoop) reinforcement is required; vertical joint stirrups are not required (1). As men- tioned previously, additional joint shear reinforcement for precast bent caps should be based on principal tensile stress exceeding 0.11 (i.e., likely joint shear cracking). How- ever, given the inherent variability in actual bridge fabrica- tion, assembly, and seismic response and the potentially severe impact of joint shear cracking on intended emulative response, the proposed specifications conservatively require a minimal area of vertical joint stirrups in grouted duct and cap pocket connections in SDCs C and D, even where the principal tensile stress, pt, is less than 0.11 . This provision is expected to be more commonly associated with SDC B and ′fc ′fc ′fc ′fc (2.04) (1 31) (0 93) (2.54) (1 64) (1 16) (3.05) (1 97) (1 39) (3.44) (2.22) (1 56) 4 6 8 Ast/Ag = 0.01 Dc = 36 in .. .. .. . 0 2 6#5#4# M in im u m N o. o f 2 - le g St irr u ps Rebar Size (No.) 0.08 Asjvi/Ast 0.10 Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast (3.05) (1 9 ) (1 39) (3.82) (2 46) (1 4) (4.58) )80.2()69.2( (5.15) (3.32) (2.34) 4 6 8 Ast/Ag = 0.015 Dc= 36 in .7. 7.. 0 2 6#5#4# M in im u m N o. o f 2 -le g St irr up s Rebar Size (No.) 8% Asjvi/Ast 10% Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast (4.07) (2.63) (1 85) (5.09) (3.28) (2.31) (6.11) (3.94) (2.78) (6.87) (4.43) (3.12) 4 6 8 Ast/Ag = 0.02 Dc= 36 in . 0 2 6#5#4# M in im um N o. o f 2 -le g St irr u ps Rebar Size (No.) 0.08 Asjvi/Ast 0.10 Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast )60.2()29.2()33.2( (3.50) (2.47) (3.94) (2.78) 4 6 8 Ast/Ag = 0.01 Dc= 48 in )29.0()56.1( (1.15) (1.37) (1.55) 0 2 8#6#5# M in im um N o. o f 2 -le g St irr u ps Rebar Size (No.) 0.08 Asjvi/Ast 0.10 Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast (3.50) (2.47) (4.38) (3.08) (5.25) (3.70) (2.06) (5.91) (4.16) (2.32) 4 6 8 Ast/Ag = 0.015 Dc= 48 in (1.37) (1.72) 0 2 8#6#5# M in im u m N o. o f 2 -le g St irr u ps Rebar Size (No.) 0.08 Asjvi/Ast 0.10 Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast (4.67) (3.29) (5.84) (4.11) (2.29) (7.00) (4.94) (2.75) (7.88) (5.55) (3.09) 4 6 8 Ast/Ag = 0.02 Dc= 48 in (1.83) 0 2 8#6#5# M in im u m N o. o f 2 -le g St irr up s Rebar Size (No.) 0.08 Asjvi/Ast 0.10 Asjvi/Ast 0.12 Asjvi/Ast 0.135 Asjvi/Ast Figure 3.6. Minimum number of 2-leg stirrups inside the joint—36-in and 48-in diameter columns.

80 is therefore addressed in the next section (SDC B). Vertical stirrups outside the joint are not required. SDC B. Where the principal tensile stress, pt, for an SDC B bridge using a precast bent cap connection is 0.11 or larger, the joint shear design provisions for SDCs C and D are conservatively required. Where the principal tensile stress is less than 0.11 , the following minimum provision for ver- tical stirrups in the joint must be satisfied for grouted duct connections: Vertical stirrups with a total area, Ajvis , spaced evenly over a length, Dc, through the joint shall satisfy: Vertical stirrups inside the joint shall consist of dou- ble leg stirrups or ties of a bar size no smaller than that of the bent cap transverse reinforcement. A minimum of two stirrups or equivalent ties shall be used. This limited provision, which still results in a highly con- structible joint region, provides reinforcement to restrict joint shear effects in the event of joint shear cracking. As shown in Figure 3.6, joints will typically require only two to three 2-leg stirrups. Vertical stirrups outside the joint are not required. The Ajvis requirement for cap pocket connections is identi- cal to that for the grouted duct connections. SDC A. For SDC A, the principal tensile stress, pt, is not calculated. However, the following minimum provision for vertical stirrups in the joint conservatively applies for grouted duct connections: Vertical stirrups with a total area, Ajvis , spaced evenly over a length, Dc, through the joint shall satisfy: Vertical stirrups inside the joint shall consist of dou- ble leg stirrups or ties of a bar size no smaller than that of the bent cap transverse reinforcement. A minimum of two stirrups or equivalent ties shall be used. As shown in Figure 3.6, the minimum 2-stirrup require- ment is expected to govern. The provision for cap pocket connections is identical to that for the grouted duct connections. Additional Longitudinal Cap Beam Reinforcement SDCs C and D. The 2006 LRFD RSGS (2) used in the design of the prototype bridge and emulative test specimens did not include the significant additional longitudinal bent A As jvi st≥ 0 08. ProposedLRFD SGS Eq. 8.13.4.2.2a-1 A As jvi st≥ 0 10. ProposedLRFD SGS Eq. 8.14.5.2.2a-1 ′fc ′fc cap reinforcement, which is prescribed in the 2009 LRFD SGS (1) for nonintegral bent caps as follows: Longitudinal reinforcement, Ajls, in both the top and bottom faces of the cap beam shall be provided in addi- tion to that required to resist other loads. The addi- tional area of the longitudinal steel shall satisfy: Maximum bent cap longitudinal bar strains for the speci- mens were limited to 46% of yield for CIP and 53% of yield for GD, but exceeded yield for CPFD and CPLD. The area of the CPLD bent cap longitudinal reinforcement was reduced 30% from the CPFD, which contributed to the extent of yielding, as discussed in Matsumoto (26). Based on specimen response, the proposed specifications do not modify the 2009 LRFD SGS (1). Therefore, this addi- tional reinforcement is required where the principal tensile stress, pt, for a precast bent cap connection is 0.11 or larger. As shown in the example connection details for cap pocket connections for SDCs B, C, and D provided in the attachments, inverted U-bars or hairpins may be placed within the pocket to help restrain potential splitting cracks and buckling of top bent cap flexural bars within the joint. This additional conservative measure is optional but recommended where the principal tensile stress, pt, is 0.11 or larger. It is not required for grouted duct connections where overlapping vertical stirrups within the joint can serve the same purpose. SDC B. As for other additional joint shear reinforcement, the additional longitudinal bent cap reinforcement stipulated in the previous section for SDCs C and D is conservatively required for SDC B where the principal tensile stress, pt, for a precast bent cap connection is 0.11 or larger. SDC A. For SDC A, additional longitudinal cap beam reinforcement is not required. Horizontal J-Bars SDCs C and D. In accordance with the 2006 LRFD RSGS (2), horizontal J-bars with an area, Ajks , of at least 0.10Ast was used in the CIP and GD specimens together with Ajvs re- inforcement adjacent to the joint (within Dc/2 of column face). The 2009 LRFD SGS for nonintegral bent caps modified this requirement as follows (1): Horizontal J-bars hooked around the longitudinal reinforcement on each face of the cap beam shall be provided as shown in Figure 8.15.5.1.1-1. At a mini- mum, horizontal J-bars shall be located at every other vertical-to-longitudinal bar intersection within the joint. ′fc ′fc ′fc A As jl st≥ 0 245. ProposedLRFD SGS Eq. 8.13.5.1.3-1

81 The J-dowel reinforcement bar shall be at least a #4 size bar. This provision is included in the proposed LRFD SGS for grouted duct connections, when the principal tensile stress, pt, for a precast bent cap connection is 0.11 or larger. How- ever, based on specimen response, cap pocket connections were shown not to require horizontal J-bars. SDC B. Where the principal tensile stress, pt, for a precast bent cap connection is 0.11 or larger, J-bars stipulated for SDCs C and D are similarly required for grouted duct con- nections in SDC B. SDC A. For SDC A, horizontal J-bars are not required. Supplementary Hoops for Cap Pocket Connections SDCs C and D. The CPFD specimen response demon- strated the effectiveness of a supplementary hoop placed at each end of the steel pipe to limit dilation and potential unraveling. This reinforcement, which matched the column hoop bar size, reached up to 52% of yield during the test, indicating its contribution to joint performance. Therefore, where the principal tensile stress, pt, is 0.11 or larger, cap pocket connections in SDCs C and D require the use of supplementary hoops: A supplementary hoop shall be placed one inch from each end of the corrugated pipe. The bar size of the hoop shall match the size of the bedding layer rein- forcement required by Article 8.15.5.2.1. The hoop area meeting the requirement of the bedding layer reinforcement (and column hoop) is considered sufficient. Where the principal tensile stress, pt, is less than 0.11 , hoops are not required but may be conservatively included. SDC B. As for the additional joint shear reinforcement, supplementary hoops stipulated in the previous section for SDCs C and D are conservatively required for SDC B where the principal tensile stress, pt, for a precast bent cap connection is 0.11 or larger. Where the principal tensile stress, pt, is less than 0.11 , supplementary hoops may be optionally in- cluded as a simple, inexpensive, and conservative measure. SDC A. For SDC A, supplementary hoops are not required. Reinforcement at the Bedding Layer and Top of Column Bedding Layer Reinforcement. A bedding layer between the bent cap soffit and the top of column is used to accom- ′fc ′fc ′fc ′fc ′fc ′fc modate fabrication and placement tolerances. Transverse reinforcement around the column bars within the bedding layer provides confinement and reduces the unsupported length of column bars, thereby reducing the potential for buck- ling during plastic hinging of the column. Accurate place- ment of reinforcement is, therefore, essential to achieving the expected system ductility capacity. Reinforcement should nor- mally be placed evenly through the depth of the bedding layer. However, in some cases, an uneven bedding layer (e.g., a slop- ing bent cap on top of a large diameter column) or a bedding layer of an unusual shape may be encountered, requiring place- ment of bedding layer reinforcement that is not uniformly dis- tributed, to minimize the unsupported length of column bars. In all cases, plan sheets should show the intended placement of the bedding layer reinforcement. The associated requirement for shop drawings is addressed in proposed Article 8.13.8.4.4 of the AASHTO LRFD Bridge Construction Specifications (LRFD BCS) (35). Adequate flowability of the concrete fill or grout should not be prevented by the size and placement of the bed- ding layer reinforcement. Matsumoto et al. (8) present an alter- native approach to accommodating tolerances and enhancing durability by embedding the column or pile into the bent cap. The proposed design specification is as follows: Bedding layers between columns and precast bent caps shall be reinforced with transverse reinforcement, as shown in Figure 8.15.5.2.2-1 and Figure 8.15.5.2.3-1. Bedding layer reinforcement shall match the size and type of transverse reinforcement required for the col- umn plastic hinging region and shall be placed evenly through the depth of the bedding layer. Grout bedding layer heights shall not exceed 3 in. For seismic loading scenarios, the bedding layer thickness is limited to 3 in when constructed of a cementitious grout material. Grout properties do not show the same improve- ment with lateral confinement that concrete materials show. Increasingly large grout bedding layer thicknesses can result in the development of poor lateral response due to the degrada- tion of the bedding layer. Therefore, the use of grout materials is limited to joints 3 in or less in dimension. Lateral Reinforcement Requirement for Columns Connecting to a Precast Bent Cap. Uniform spacing between hoops at the top of the column and the bedding layer is crit- ical to ensuring that system ductility is not compromised. Hoop spacing is addressed in Article 8.8.14 of the proposed LRFD SGS and Article 8.13.8.4.4 of the proposed LRFD BCS. A smaller cover than that used for typical column applications is permitted for the top hoop because the placement of the bedding layer concrete or grout will provide additional cover after the precast bent cap is set. Plan sheets and shop draw- ings are required to show the intended placement of the first hoop at the top of the column.

82 GD and CPFD specimen tests confirmed the importance of accurate placement of the column top hoop and the unsup- ported column bar length (22, 23). Figure 3.7 shows column bar buckling at the interface between the cap and column for the CPFD specimen (post-test). The unsupported column bar length was considerably larger than the regular column hoop spacing. Although this did not affect the maximum force induced in the joint and the specimen achieved over 4% drift, system ductility was limited by buckling of column lon- gitudinal reinforcement. The proposed specification addresses this issue as follows: The spacing between the first hoop at the top of the column and the bedding layer hoop shall not exceed the spacing used for hoops in the plastic hinge region. The concrete cover above the first hoop at the top of the column shall be permitted to be less than that specified in Article 5.12.3 of the AASHTO LRFD Bridge Design Specifications. Transverse reinforcement used for piles shall be similarly detailed. 3.3 Proposed Changes to AASHTO Guide Specifications for LRFD Seismic Bridge Design and AASHTO LRFD Bridge Design Specifications Based on the test results and development of design speci- fications, proposed design specifications have been prepared and are provided as attachments to this report (available online at www.trb.org/Main/Blurbs/164089.aspx). Proposed addi- tions or revisions to the AASHTO Guide Specifications for LRFD Seismic Bridge Design, 1st Edition (1), are as follows: • Attachment DS1: Revised Article 2.1 Definitions – Revision of current article to include definitions of emu- lative and hybrid systems • Attachment DS2: Revised Article 4.3.3 Displacement Magnification for Short Period Structures – Revised Article to account for hybrid systems • Attachment DS3: Revised Article 4.7.2 Vertical Ground Motion, Design Requirements for SDC D – Expanded Article to include explicit requirements for consideration of vertical excitation with integral precast bent caps discontinuous at bent • Attachment DS4: Revised Article 4.11.6 Analytical Plastic Hinge Length – Revised Article to account for integral concrete super- structures • Attachment DS5: Proposed Article 5.6.6 Ieff for Hybrid Systems – New Article for hybrid systems • Attachment DS6: Revised Article 8.4.2 Reinforcing Steel Modeling – Revised Article for hybrid systems • Attachment DS7: Proposed Article 8.8.14 Lateral Re- inforcement Requirement for Columns Connecting to a Precast Bent Cap – New Article to ensure spacing between the hoop at top of column and the bedding layer hoop does not com- promise system ductility • Attachment DS8: Revised Article 8.5 Plastic Moment Capacity for SDC B, C, and D – Revised Article for hybrid systems • Attachment DS9: Revised Article 8.8.1 Maximum Longi- tudinal Reinforcement – Revised Article for hybrid systems • Attachment DS10: Revised Article 8.8.2 Minimum Longi- tudinal Reinforcement – Revised Article for hybrid systems • Attachment DS11: Proposed Article 8.8.14 Minimum Debonded Length of Longitudinal Reinforcement for Hybrid Columns – New Article for hybrid systems • Attachment DS12: Revised Article 8.10 Superstructure Capacity Design for Longitudinal Direction for SDC C and D – Revised Article for integral precast systems • Attachment DS13: Proposed Article 8.13 Joint Design for SDC A – New Article for SDC A precast bent cap connection design • Attachment DS14: Proposed Article 8.14—Joint Design for SDC B – New Article for SDC B precast bent cap connection design • Attachment DS15: Revised Article 8.15—Joint Design for SDCs C and D Figure 3.7. View of column bar buckling at interface between the bent cap and column–CPFD (after removal of concrete post-test).

83 – Revision of current Article 8.13 for SDCs C and D to Article 8.15 for precast bent cap connection design Other proposed articles for the AASHTO LRFD Bridge Design Specifications (4th Edition) are as follows (29): • Attachment DS16: Revised Article 5.10.11.4.3—Column Connections – Revised Article to ensure AASHTO LRFD SGS is used for emulative precast bent cap to column connection design. • Attachment DS17: Proposed Article 5.11.1.2.4—Moment Resisting Joints – Revised Article to ensure AASHTO LRFD SGS is used for emulative precast bent cap to column connection design. 3.4 Design Flow Charts and Design Examples Design flow charts and design examples have been devel- oped for the systems and connections investigated under this project. The design flow charts and design examples illustrate the design process, including proper application of the design specifications, for all SDC levels using precast bent cap to col- umn connections with practical reinforcement and detailing. Two design flow charts are provided, one for SDC A and another for SDCs B, C, and D. Consolidation of SDCs B, C, and D into one flow chart highlights the fact that the amount and type of joint shear reinforcement are based on the deter- mination of the principal tensile stress and that, even for SDC B, the likelihood of joint shear cracking should be determined. Finally, as required, the effects should be mitigated through the use of joint shear reinforcement. Design examples are provided for SDC A, SDC B, and SDCs C and D. The examples include extensive commentary and figures and list applicable references to the LRFD SGS and LRFD BCS. The design examples for SDCs C and D illus- trate the case in which additional joint shear reinforcement is required (i.e., principal tensile stress, pt, 0.11 or larger). The SDC B and SDC A examples illustrate the case in which minimum joint reinforcement governs. Special consideration is given to clarity, completeness, and accuracy. Design flow charts and design examples are provided as attachments to this report (available online at www.trb.org/ Main/Blurbs/164089.aspx), as follows: • Attachment DE1: SDC A Design Flow Chart – Flow chart for design of precast bent cap connections in SDC A • Attachment DE2: SDC A Design Example—Grouted Duct Connection ′fc – Design example for grouted duct connection in SDC A (minimum joint reinforcement) • Attachment DE3: SDC A Design Example—Cap Pocket Connection – Design example for cap pocket connection in SDC A (minimum joint reinforcement) • Attachment DE4: SDCs B, C, and D Design Flow Chart – Flow chart for design of precast bent cap connections in SDCs B, C, and D • Attachment DE5: SDC B Design Example—Grouted Duct Connection – Design example for grouted duct connection in SDC B (minimum joint reinforcement) • Attachment DE6: SDC B Design Example—Cap Pocket Connection – Design example for cap pocket connection in SDC B (minimum joint reinforcement) • Attachment DE7: SDCs C and D Design Example—Grouted Duct Connection – Design example for grouted duct connection in SDCs C and D (additional joint reinforcement) • Attachment DE8: SDCs C and D Design Example—Cap Pocket Connection – Design example for cap pocket connection in SDCs C and D (additional joint reinforcement) • Attachment DE9: SDCs C and D Design Example—Hybrid Connection – Design example for hybrid connection in SDCs C and D • Attachment DE10: SDCs C and D Design Example— Integral Connection – Design example for integral connection in SDCs C and D 3.5 Development of Construction Specifications This section provides the basis for proposed Article 8.13.8— Special Requirements for Precast Bent Cap Connections to be added to AASHTO LRFD Bridge Construction Specifications, 2nd Edition, 2004 with 2006, 2007, 2008, and 2009 Interims (LRFD BCS) (35) to address nonintegral precast bent cap sys- tems using grouted duct and cap pocket connections. Proposed construction specifications are based on specifica- tions developed by Matsumoto et al. (8) together with results from the experimental test results. Major sections of the construction specification address the following: • Materials – portland cement concrete for the precast bent cap and cap pocket fill – hydraulic cement (non-shrink) grout

84 – corrugated metal duct – lock-seam, helical corrugated steel pipe – connection hardware • Contractor submittal including a precast bent cap place- ment plan • Construction methods including grouting of grouted duct connections and concreting of cap pocket connections (trial batch, placement, material testing) In addition, a grout specification for the grouted duct con- nection from Matsumoto et al. (8) is presented. Most of this section is incorporated within the proposed specification as code and commentary. Proposed specifica- tions are set off from the main text. The following sections use the same outline as that used in the proposed specifications. References to articles within this section refer primarily to existing or proposed Articles of the LRFD BCS. 3.5.1 General This article addresses construction of precast bent cap connections: This article describes special requirements for integral and nonintegral emulative and hybrid precast bent cap connections using the grouted ducts or cap pockets. These special requirements are intended to ensure pre- cast bent cap connections studied are constructible and also provide the expected seismic performance, durability, and economy. The grouted duct connection uses corrugated ducts embed- ded in the precast bent cap to anchor individual column lon- gitudinal bars. The ducts and bedding layer between the cap and column or pile are grouted with high-strength, non-shrink cementitious grout to complete the precast connection. Ducts are sized to provide adequate tolerance for bent cap fabrication and placement and should be accounted for in sizing the bent cap to minimize potential congestion. The cap pocket connection uses a single, helical, corrugated steel pipe embedded in the precast bent cap to form the cap pocket, which anchors the column longitudinal bars. This pipe, placed between top and bottom bent cap longitudinal re- inforcement, serves as both a stay-in-place form and as joint transverse reinforcement. Special forming is required above and below the pipe to form the cap pocket void through the full depth of the bent cap. A flowable CIP concrete is used to fill the void and complete the precast connection. The pipe diameter is sized to provide adequate field tolerance for placement of the precast bent cap over column longitudinal bars, and the pipe thickness is sized to satisfy transverse joint reinforcement requirements. Hybrid connections use grouted duct connections to anchor column longitudinal reinforcement. Unbonded post- tensioning is also used in the section to resist lateral demands. The integral connections must provide a stable flexural con- nection between the superstructure and substructure. These connections can include systems with discontinuous girders at the bent cap made continuous through longitudinal post- tensioning. In Article 8.13.8, the term “column bars” refers to column bars, column dowels, and pile dowels. 3.5.2 Materials Materials used for precast bent cap connections include Portland cement concrete for the precast bent cap, connec- tion hardware, and materials specific to each connection type. Grouted duct connection materials include hydraulic cement grout (non-shrink) and corrugated metal ducts. Cap pocket connection materials include Portland cement concrete for the cap pocket fill and the steel (corrugated) pipe. Hybrid connections use grouted duct connections in combination with post-tensioning. The proposed specification states the following: The materials and manufacturing processes used for precast concrete bent caps shall conform to the require- ments of Article 8.13.3 except as those requirements are modified or supplemented by the provisions that follow. Portland Cement Concrete for Precast Bent Cap Bent cap concrete is required to satisfy provisions for normal-weight Portland cement concrete and provide a strength margin between the cap and the connection. The specified compressive strength of the connection grout or con- crete fill is required to exceed the expected bent cap concrete compressive strength by at least 500 psi to help ensure that the connection does not become a weak link in the system: Portland cement concrete for the precast bent cap shall conform to the provisions of Article 8.2.2 for normal-weight concrete. The concrete mix design for the precast bent cap shall conform to the requirements of Articles 8.13.8.3.2a and 8.13.8.3.3a to achieve the required 500 psi strength margin between the bent cap compressive strength and the specified compres- sive strength of the connection grout or cap pocket concrete fill. Lightweight concrete can provide significant advantages for a precast bent cap system. However, its use should be based on relevant research including research on its effect on the seismic performance of the connection.

85 Use of lightweight concrete shall be based on appli- cable research of connection performance, including seismic effects, and approval by the Engineer. Grouted Duct Connection Hydraulic Cement Grout (Non-Shrink). Grout for the grouted duct connection is carefully specified: Grout used in grouted duct connections shall consist of prepackaged, cementitious, non-shrink grout in accor- dance with ASTM C1107 and the additional perfor- mance requirements listed in Table 8.13.8-1, including the following properties: mechanical, compatibility, constructability, and durability. Table 8.13.8-1 require- ments shall govern over ASTM C1107 requirements. Grout shall contain no aluminum powder or gas- generating system that produces hydrogen, carbon dioxide, or oxygen. Grout using metallic formulations shall not be permitted. Grout shall be free of chlorides. No additives or admixtures, including retarders, shall be added to prepackaged grout. Extension of grout shall only be permitted when recommended by the manu- facturer and approved by the Engineer. At a minimum, grout compressive strength and flowa- bility shall be established during trial batches per Article 8.13.8.5.4a. Laboratory testing shall be permitted to establish other properties listed in Table 8.13.8-1. Grouted joints shall not exceed 3 in. in thickness for structures located in Seismic Design Categories B, C, and D. Proposed LRFD BCS Table 8.13.8-1 is shown as Table 3.4 of this report. This table includes provisions intended to ensure that the grout used in the connection develops mechanical, compatibility, constructability, and durability properties that help ensure that the grout is placed efficiently, achieves per- formance for rapid construction, and does not become a weak link in the system under the various limit states. For example, Table 3.4 requires the 28-day grout compressive strength to have a minimum 500-psi margin over the 28-day expected bent cap concrete compressive strength. This margin accounts for the likelihood that the actual concrete strength will exceed its specified strength as well as the possibility of a low grout strength. The 1.25 factor applied to f ′ce_cap in Table 3.4 accounts for the higher 2-in grout cube compressive strength compared to standard concrete cylinder compressive strength. Grout should be selected with a compressive strength based on water required for fluid consistency using the ASTM C939 Flow Cone Test. Grouts mixed to a flowable or plastic consis- tency in accordance with ASTM C230 achieve a higher com- pressive strength but possess inadequate fluidity for filling voids in a precast bent cap system and therefore should be avoided. Prepackaged grouts are proprietary mixes, and thus no addi- tives should be used in the grout. Additives may adversely affect grout properties and void manufacturer warranties. Modification of prepackaged grout, including extension with small-size aggregate, is discouraged because of the additional uncertainty introduced in achieving the required Property Value Mechanical Age Compressive strength (psi) Compressive strength (ASTM C109, 2” cubes) 1 day 3 days 7 days 28 days 2,500 4,000 5,000 Maximum [6000, 1.25 ( ) + 500] Compatibility Expansion requirements (ASTM C827 & ASTM C1090) Modulus of elasticity (ASTM C 469) Coefficient of thermal expansion (ASTM C 531) Grade B or C⎯expansion per ASTM C1107 2.8-5.0×106 psi 3.0-10.0×10-6/deg F Constructability Flowability (ASTM C939 Flow Cone) Set Time (ASTM C191) Initial Final Fluid consistency efflux time: 20–30 sec 2.5–5.0 hrs 4.0–8.0 hrs Durability Freeze Thaw (ASTM C666) Sulfate Resistance (ASTM C1012) 300 cycles, relative durability factor 90% Expansion at 26 weeks < 0.1% Table 3.4. Grout specification for grouted duct connection (8).

86 properties and the potential risk in resolving liability if the quality of grouted connections is believed to be deficient. For example, ASTM C33 No. 8 Hard Pea Gravel or Hard Aggregate Chips may contain excessive fines that adversely affect the flow of the prepackaged grout. Clear spacing between the reinforcing and the formed sur- faces should be at least three times the top size of the aggre- gate to ensure adequate flow of grout to fill all voids. Corrugated Metal Duct. Corrugated metal ducts used to anchor column bars within the bent cap are specified as follows: The use of ducts in a grouted duct connection shall conform to the requirements of Article 10.8.1 except as those requirements are modified or supplemented by the provisions that follow. Ducts used to provide holes in the precast bent cap concrete shall be formed with semi-rigid steel ducts that are cast into the concrete. Ducts shall be galva- nized ferrous metal per ASTM A653 and shall be fab- ricated with either welded or interlocked seams. Ducts shall be corrugated with a minimum wall thick- ness of 26 gage for ducts less than or equal to 4-in diameter and 24 gage for ducts greater than 4-in diameter. Rib height of the corrugation shall be at least 0.12 in. Plastic ducts shall only be used based on applicable research and when approved by the Engineer. Duct diameter shall be based on fabrication and place- ment tolerances established for the job. Placement and anchorage of ducts shall conform to the requirements of Article 10.4.1.1. Corrugated galvanized steel ducts for grouted duct connec- tions have been successfully used in seismic and nonseismic research as well as in practice. Steel ducts provide excellent mechanical interlock with the bent cap concrete and connec- tion grout as well as confinement for the grouted column bar. When steel ducts with the minimum specified duct thickness and corrugation rib height are used together with grouts satis- fying Table 8.13.8-1, excellent bond develops and column bars can be safely anchored in a grouted duct within the relatively short anchorage length given in Article 8.15.2.2.2 of the 2009 LRFD SGS (1). Use of plastic ducts can have a significant impact on the behavior, failure mode, and strength of grouted duct con- nections and should not be used without investigation and approval of the Engineer. Brenes et al. (36) provide guide- lines for use of high-density polyethylene and polypropylene ducts in grouted duct connections, including minimum duct wall thickness, corrugation rib height, and maximum spac- ing between ribs. An increase in development length of approx- imately 30% was recommended for plastic ducts tested under monotonic tension. However, tension cyclic tests were not conducted. Cap Pocket Connection Portland Cement Concrete for Cap Pocket Fill. Portland cement concrete for the cap pocket fill has additional require- ments beyond that of typical normal-weight concrete: Portland cement concrete for the cap pocket fill shall follow the provisions of Article 8.2.2 for normal-weight concrete and Article 8.3 for associated materials. The mix design for the concrete fill shall be based on achiev- ing a concrete compressive strength at least 500 psi greater than the expected concrete strength of the precast bent cap. Lightweight concrete shall not be used. Concrete shall satisfy Article 8.13.8.5.5a to ensure pocket and bedding layer are completely filled and without voids. The probable concrete strength for the cap pocket fill is required to provide a minimum 500-psi margin over the expected bent cap concrete compressive strength to ensure that the cap fill concrete is not the weak link in the connection. This margin accounts for the likelihood that the actual bent cap compressive strength will exceed its specified strength as well as the possibility of a low compressive strength of the fill. Use of lightweight concrete is not permitted in the cap pocket because it may pose an unnecessary risk in the seismic performance of the connection. Concrete should be sufficiently flowable to fill the pocket and bedding layer and to flow out of air vents at the top of the bedding layer. In addition, clear spacing between the reinforc- ing and the formed surfaces should be at least three times the top size of the aggregate to ensure adequate flow of concrete to fill all voids, including the bedding layer. Steel Pipe. The steel pipe, which serves a critical dual purpose in fabrication and seismic reinforcement, is specified as follows: The steel pipe used to form the void in the precast bent cap concrete shall be a lock seam, helical corrugated pipe cast into the concrete. The steel pipe shall satisfy the requirements of ASTM A760, Standard Specification for Corrugated Steel Pipe, Metallic-Coated for Sewers and Drains, and the lock seam shall satisfy the requirements of AASHTO T 249, Standard Method of Test for Helical Lock Seam Corrugated Pipe. The pipe shall satisfy the thickness required by Article 8.15.3.2.2 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. Where required, coupon testing to determine ma- terial properties shall be conducted in accordance with ASTM A370. Plastic pipe shall not be used. The pipe diameter shall be based on fabrication and placement tolerances established for the job. Placement and anchorage of steel pipe shall conform to the requirements of Article 10.4.1.1.

87 Lock seam, helical corrugated steel pipe has been successfully used in seismic research as well as in practice for precast cap pocket connections. These pipes provide excellent mechanical interlock with the bent cap concrete and connection concrete fill and also serve as joint reinforcement. When the steel pipe is designed in accordance with Article 8.15.3.2.2 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design and is used together with concrete satisfying Article 8.13.8.3.3a, excellent bond is expected to develop and column bars are expected to be anchored in the pipe within the relatively short anchorage length given in Article 8.15.2.2.2 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design (1). Plastic pipe should not be used because it cannot serve as seismic reinforcement. Connection Hardware. Connection hardware is speci- fied as follows: All connection hardware such as friction collars, shims, falsework, or other support systems shall be in accor- dance with the requirements shown in the plans. Friction collars and shims may be used to support the cap during placement. When shims are used, compressible shims such as those made of plastic are preferred over steel shims to help ensure that load eventually transfers to the hardened bed- ding layer grout. Plastic shims should be made of engineered multipolymer, high-strength plastic with a modulus of elastic- ity slightly less than the hardened grout at the time of load transfer. Steel shims have a stiffness at least five times that of the bedding grout and therefore can act as hard points between the column and bent cap. Calculations should be made to determine the potential effect of shims in the com- pression zone of the bedding layer. Where steel shims are used, additional cover should be provided for corrosion protection. Specific measures to prevent movement of shims during cap placement should be detailed in the plan sheets. To facil- itate complete grouting of the bedding layer, the total shim plan area should be limited and shims should be placed away from the exposed surface of the bedding layer unless shim removal is planned. Hybrid Precast Concrete Connections Hybrid connections constructed with precast components use a combination of column longitudinal reinforcement and unbonded post-tensioning. The connection of column longi- tudinal reinforcement is traditionally made using a grouted duct connection. The construction specifications for grouted duct connections shall therefore be implemented for these connections. However, experimental testing described in Chapter 2 indicated a need to place fibers within the bedding layer for hybrid precast connections. Therefore, the following article is recommended for hydraulic cement grout in hybrid precast connections: Grout used in grouted duct connections in conjunction with hybrid precast connections shall meet the require- ments of Article 8.13.8.3.2a. Polypropylene fibers shall be added to the grout matrix during mixing at a 3 lb/cu yd fraction. Fibers shall meet the requirements of ASTM C1116. Integral Precast Connections with Vertical Joints The integrity of vertical closure joints in integral precast connections is essential to satisfactory flexural response. To promote joint integrity, a high-quality, non-shrink grout containing fiber reinforcement is necessary. The following article is therefore recommended: Grout used in grouted duct connections shall consist of prepackaged, cementitious, non-shrink grout in accordance with ASTM C1107 and the additional per- formance requirements listed in Table 8.13.8-1, includ- ing the following properties: mechanical, compatibility, constructability, and durability. Table 8.13.8-1 require- ments shall govern over ASTM C1107 requirements. Grout shall contain no aluminum powder or gas- generating system that produces hydrogen, carbon diox- ide, or oxygen. Grout using metallic formulations shall not be permitted. Grout shall be free of chlorides. No additives or admixtures, including retarders, shall be added to prepackaged grout. Extension of grout shall only be permitted when recommended by the manufac- turer and approved by the Engineer. At a minimum, grout compressive strength and flowa- bility shall be established during trial batches per Article 8.13.8.5.4a. Laboratory testing shall be permitted to establish other properties listed in Table 8.13.8-1. Polypropylene fibers shall be added to the grout matrix during mixing at a 3 lb/cu yd fraction. Fibers shall meet the requirements of ASTM C1116. Grouted joints shall not exceed 3 in for structures located in Seismic Design Categories B, C, and D. 3.5.3 Contractor Submittal As explained in Matsumoto et al. (8), the contractor should provide a detailed submittal to ensure successful construction of the precast bent cap connection: In advance of the start of precast bent cap placement operations in the field, to allow the Engineer not less than a 30-calendar-day review period, the Contractor shall submit the following documents: (1) Precast Bent Cap Placement Plan per Article 8.13.8.4.2, (2) Design Calculations for Construction Procedures per Article 8.13.8.4.3, and (3) Shop Drawings per Article 8.13.8.4.4.

Bent caps shall not be set until the Engineer has approved all required submittals. Any subsequent devi- ation from the approved materials and/or details shall not be permitted unless details are submitted by the Contractor and approved by the Engineer in advance of use. Two sets of the Precast Bent Cap Placement Plan, calculations, and required drawings shall be submitted and resubmitted if and as necessary until approved by the Engineer. The specified number of distribution copies shall be furnished after approval. Precast Bent Cap Placement Plan The Precast Bent Cap Placement Plan is specified as follows: The Precast Bent Cap Placement Plan, at a minimum, shall contain the following items: (a) Step-by-step description of bent cap placement for each bent, including placement of the bent cap on the columns or piles and the proposed method for form- ing the bedding layer, placing grout in ducts or concrete in cap pockets, and ensuring that grout or concrete is properly consolidated in the connection and bedding layer. (b) Method and description of hardware used to hold bent cap in position prior to connection grouting or concreting. Hardware shall be permitted to consist of friction collars, plastic or steel shims, shoring, or other support systems. A hardware submittal shall consist of product information, material descriptions, and draw- ings for friction collars and shims and shop drawings for shoring if used. (c) For grouted duct connections, manufacturer’s product information for at least two candidate grouts, including a description of the performance characteris- tics as specified in Table 8.13.8-1, mixing requirements, working time, curing requirements, and other informa- tion related to grouting of precast connections utilizing ducts. For cap pocket connections, concrete fill mix design, description of the method to achieve concrete consistency for filling the pocket and bedding layer, cur- ing requirements, and other information related to con- creting precast connections using a steel pipe should be provided. (d) Hardware and equipment associated with grout- ing grouted duct connections or concreting cap pocket connections. (e) A mitigation plan to repair any voids observed within the bedding layer, coordinated and approved by the Engineer. (f) Other required submittals shown on the plans or requested by the Engineer relating to successful instal- lation of precast bent caps and associated hardware. Design Calculations for Construction Procedures Design calculations related to construction procedures are specified as follows: 88 Design calculations shall be submitted for friction col- lars, shims, falsework, erection devices, formwork, or other temporary construction that will be subject to cal- culated stresses. Design of the friction collars, shims, and falsework or erection devices for all bent cap concrete, duct grout, or cap pocket concrete shall be completed under the direction of and sealed by a registered Professional Engineer. Post-tensioned precast bent caps shall also follow the provisions of Article 8.16.3.2. Shop Drawings Detailed shop drawings are specified as follows: The Contractor shall submit detailed shop drawings for approval in accordance with the contract docu- ments. The shop drawings shall follow the provisions of Article 8.16.3.3, with the following additions: (a) Shop drawings shall completely describe the pro- posed construction sequence and shall show enough detail to enable construction of the bent cap without the use of the plan sheets. (b) Size and type of ducts or pipes for all bent cap connections shall be clearly detailed. Duct or pipe sup- ports, tremie tubes, air vents, and drains shall be shown, including size, type, and locations. (c) Bedding layer reinforcement, as well as its loca- tion within the bedding layer and its location relative to the first hoop at the top of the column or pile, shall be shown. (d) Spacing between the first hoop at the top of the column or pile and the bedding layer hoop shall be shown. This spacing shall not exceed the spacing used for hoops in the plastic hinge region. The concrete cover above the first hoop at the top of the column shall be permitted to be less than that specified in Article 5.12.3 of the AASHTO LRFD Bridge Design Specifications. (e) A table showing elevations and geometry to be used in positioning the bedding layer collar for bent cap placement shall be provided. (f) For the grouted duct connection, details of grout- ing equipment, grout mix design, and method of mix- ing, placing, and curing grout shall be provided. (g) For the cap pocket connection, details of concrete fill mix design and method of mixing, placing, and cur- ing concrete fill shall be provided. (h) Other required submittals shown on the plans or requested by the Engineer relating to successful instal- lation of precast bent caps and associated hardware shall be provided. As discussed in Chapter 2, uniform spacing between hoops at the top of the column and the bedding layer is critical to ensuring that system ductility is not compromised. A smaller cover than that used for typical column applications is permit- ted for the top hoop because the bedding layer provides addi- tional cover after placement of the precast bent cap. Plan sheets

should show the intended placement of the first hoop at the top of the column. This requirement for design is addressed in the proposed Article 8.8.14 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. 3.5.4 Construction Methods General Construction of precast bent cap systems must account for tolerances: All tolerances shall be established on a project- specific basis. Combined tolerances shall include, but are not limited to, fabrication of the bent cap and columns or piles and placement of the bent cap over the columns or piles, including location of column bars or other dowels within the corrugated metal ducts or steel pipe. All form release agents and curing membranes shall be completely removed from areas of the cap that will be in contact with bearing seat and connection grout. Combined fabrication and placement tolerances should be established for each project. The following issues should be con- sidered: differences in tolerances for longitudinal and transverse directions; accuracy of column bars or dowels within corru- gated ducts or steel pipes; size, type, location and orientation of ducts or pipe to account for cap slope; plumbness of column bars or dowels; and provisions for out-of-tolerance substruc- ture elements. Handling and placement are specified as follows: Handling of precast bent caps shall satisfy the provi- sions of Article 8.16.7.4. The Contractor is solely responsible for ensuring the stability of the bent cap prior to and during grouting or concreting operations. All grades, dimensions, and elevations shall be deter- mined and verified before the bent cap is placed. The contractor shall verify proper alignment between the columns or piles, including column bars, dowels, corru- gated metal ducts, steel pipes, and other connection hardware cast into the bent cap. All loose material, dirt, and foreign matter shall be removed from the tops of columns or piles before the cap is set. Grouting of Grouted Duct Connection Grouting is a crucial operation for use of a precast bent cap system using the grouted duct connection. Because it involves procedures, operations, and equipment that may not be famil- iar to the Contractor, specifications provide sufficient detail to ensure that connections are properly made in the field. Specifications address general grouting issues, trial batches, grout placement, and grout testing. Matsumoto et al. (8) pro- vide further background and details on these provisions. General Issues. General issues are specified as follows: The preparation and use of grout for precast bent cap connections shall conform to the requirements of Article 10.9 except as those requirements are modified or supplemented by the provisions that follow. Prepackaged, cementitious, non-shrink grout shall be used in strict accordance with manufacturer’s recommendations. Per Article 8.13.8.3.2a, additives or admixtures, includ- ing retarders, shall not be added to grout. However, it shall be permitted to adjust the temperature of mixing water or substitute ice for water to extend the working time and pot life. Addition of water to previously mixed grout or remix- ing of grout shall not be permitted. Water exceeding manufacturer’s recommendations shall not be added to the grout to increase flowability. Trial Batch. The trial batch is a key step in achieving the required installation and performance of a grouted duct con- nection. The purposes of a trial batch are to do the following: • Determine the required amount of water to be added to a particular grout brand to achieve acceptable flowability per Table 3.4 and pot life under the temperature and humidity conditions expected in the field; • Determine the grout cube strength corresponding to the flow achieved; • Examine grout for undesirable properties such as segregation; • Establish the adequacy of proposed grouting equipment such as the mixer, pump, tremie tubes, and vent tubes; • Provide jobsite personnel experience in mixing and han- dling grout prior to actual connection grouting; and • Help the contractor to make a judicious decision regarding grout brand and its use. The trial batch is specified as follows: At least 2 weeks prior to grouting of connections, a trial batch of grout shall be prepared to demonstrate grout properties per Article 8.13.8.3.2a and adequacy of equipment and to familiarize job site personnel with grouting procedures. A batch of grout shall be the amount of grout sufficient to complete an entire connection or number of connec- tions and is limited to the amount of grout that can be placed within the pot life determined in the trial batch. For continuous placement using a grout pump, a batch shall be defined as one connection or one bent cap. Partial batches will not be allowed and shall be discarded. The Contractor shall establish grout flowability by measuring efflux (flow) time of the grout with a standard 89

90 flow cone according to the Corps of Engineers Flow Cone Method, CRD-C 611 and ASTM C939. The flow time shall be determined twice: (1) immediately after mixing and (2) at the expected working time corresponding to the pot life of the grout. The ambient temperature and mixing water temperature at the time of trial batch mixing shall be within +/− 5 deg F of that expected at the time of grout placement. The Contractor shall estab- lish that the grout flow time satisfies the limits prescribed in Table 8.13.8-1. Observation of segregation, clumps of grout, or other anomalies in the final trial batch shall be cause for rejec- tion of the proposed brand of grout. Samples used for testing shall be taken from the middle of the batch. One set of six (6) grout cubes shall be prepared as specified in Article 8.13.8.5.4c to verify the compressive strengths shown in Table 8.13.8-1. The Contractor shall validate the proposed grout placement technique by using the trial batch grout and grout equipment in a sample grouting operation simi- lar to the proposed connection grouting. Pumping shall be validated in the trial batch in cases where it is pro- posed for field placement. Adequacy of the mixer, pump, tremie tubes, vent tubes, and other grouting equipment shall be established. The contractor shall demonstrate that the equipment is adequate for mixing the grout and grouting the connection within the pot life of the batch and does not introduce air into the grout or con- nection. A wire mesh shall be used to filter out poten- tial clumps when transferring grout between the mixer and containers. Grout Placement. Grout placement is specified as follows: All equipment necessary to properly perform grouting operations shall be present before actual grouting oper- ations begin. All grouting operations shall be performed in the presence of the Engineer in accordance with the Precast Bent Cap Placement Plan. Grouting operations shall be performed under the same weather limitations as cast-in-place concrete and as required by the grout manufacturer. Grout pumping shall be required for con- nections that cannot be completed by other methods within the pot life established for the grout during the trial batch. All additional materials required to ensure proper connection of bent cap to column, such as but not lim- ited to bedding layer hoops, shall be properly placed according to shop drawings. All surfaces to be in contact with the grout shall be cleaned of all loose or foreign material that would in any way prevent bond prior to setting bedding layer forms. Bedding layer forms shall be drawn tight against the existing concrete to avoid leakage or offsets at the joint. All previously hardened concrete surfaces that will be in contact with the grout shall be pre-wetted to a surface- saturated moist condition when the grout is placed. Drain ports or holes shall be provided to allow residual water from pre-wetting to drain prior to grouting. Forms for the closure pour between the cap and column shall be adequately vented to allow air to escape during grouting. Vent tubes shall have a minimum 1⁄2-in. inner diameter and shall be flush with the top of the bedding layer. Vents shall not be plugged until a steady stream of grout flows out. Grout shall be deposited such that all voids in the bedding layer and bent cap are completely filled. Grout shall be consolidated at intervals during placement operations as needed. All connections shall be grouted in a manner that deposits the grout from the bedding layer or bottom of connection upward. When pumping is used, grout shall be placed through ports located at the bottom of the bedding layer. To prevent introduc- ing air into the system, when continuous flow grouting is not possible, shutoff valves shall be required. All exposed grout surfaces shall be cured in accor- dance with manufacturer’s recommendations. All grout surfaces shall be inspected post-grouting in coordination with the Engineer. Any voids shall be repaired as specified in the mitigation plan in Article 8.13.8.4.2. Grout shall not be disturbed and connections shall not be loaded until final acceptance of the connection. Final acceptance of the connection shall be after the grout has reached a compressive strength in accordance with the “Final Strength” shown in the plans or as approved by the Engineer. Grout Testing. Grout testing is specified as follows: The compressive strength of the grout for “Beam Setting Strength” and “Final Strength” shall be deter- mined using grout cubes prepared and tested in accor- dance with ASTM C109. The contractor shall prepare a minimum of six (6) cubes per batch. A Commercial Testing Laboratory approved by the Engineer shall test the specimens for “Beam Setting Strength” and “Final Strength.” Grout failing to meet the minimum required compressive strength may be cause for rejection of the connection, grout removal, and re-grouting of the con- nection by means approved by the Engineer. Protection of the grout cube specimens in the field is criti- cal and should be performed as required by ASTM C942. Prior to testing, all cubes should be measured for mass determina- tion. The typical break pattern is also to be noted. Curing and ambient temperatures are to be reported as well as flow deter- minations per ASTM C939. Concreting of Cap Pocket Connection Concreting of cap pocket connections addresses similar issues as grouting of the grouted duct connection: trial batch, concrete placement, and concrete testing. The handling and placing of concrete for the cap pocket fill in precast bent cap connections shall con- form to the requirements of Article 8.7 except as those

91 requirements are modified or supplemented by the provisions that follow. Trial Batch. The trial batch is a key step in achieving the required installation and performance of a cap pocket connection. The purposes of a trial batch are to do the following: • Determine the required amount of water and admixtures required to achieve acceptable flowability and pot life under the temperature and humidity conditions expected in the field; • Determine the corresponding cylinder strength; • Examine the concrete for undesirable properties; • Establish the adequacy of proposed concreting equipment such as the mixer, pump, tremie tubes, vibrators, and vent tubes; • Provide jobsite personnel experience in mixing, placing, and consolidating the concrete in the connection prior to actual connection concreting; and • Help the contractor to make a judicious decision regarding concrete mix and associated operations. The trial batch for cap pocket concrete is specified as follows: At least 2 weeks prior to concreting of connections, a trial batch of concrete shall be prepared to demon- strate concrete properties per Article 8.13.8.3.3a and adequacy of equipment and to familiarize jobsite per- sonnel with concreting procedures. A batch of concrete shall be the amount of concrete sufficient to complete an entire connection or number of connections and is limited to the amount of concrete that can be placed within the pot life as determined in the trial batch. For continuous placement using a con- crete pump, a batch shall be defined as one connection or one bent cap. Partial batches will not be allowed and shall be discarded. The Contractor shall establish concrete flowability using AASHTO T 119, Slump of Hydraulic Cement Concrete. The Contractor shall establish that the slump satisfies the requirements of Article 8.13.8.3.3a during all stages of placement of the concrete fill. Observation of segregation or other anomalies in the final trial batch shall be cause for rejection. Samples used for testing shall be taken from the middle of the batch. One set of six (6) cylinders shall be prepared and tested in accordance with Article 8.5.7 to verify the compressive strengths required by Article 8.13.8.3.3a. The Contractor shall validate the proposed concrete placement technique by using the trial batch concrete and concreting equipment in a sample concreting oper- ation similar to the proposed connection concreting. Pumping shall be validated in the trial batch if it is to be used in the field placement. Adequacy of the mixer, pump, tremie tubes, vibrators, vent tubes, and other concreting equipment shall be established. The contrac- tor shall demonstrate that the equipment is adequate for mixing, placing, and consolidating the concrete in the connection within the pot life of the batch and does not introduce air into the connection. Concrete Placement. Concrete placement in the cap pocket is specified as follows: All equipment necessary to properly perform con- creting operations shall be present before actual con- creting operations begin. All concreting operations shall be performed in the presence of the Engineer in accordance with the Precast Bent Cap Placement Plan. Concreting operations shall be performed under the same weather limitations as cast-in-place concrete. Concrete pumping shall be required for connections that cannot be completed by other methods within the pot life established for the concrete during the trial batch. All additional materials required to ensure proper connection of bent cap to column, such as but not lim- ited to bedding layer hoops, shall be properly placed according to shop drawings. All surfaces to be in contact with the cap pocket con- crete shall be cleaned of all loose or foreign material that may in any way prevent bond prior to setting bed- ding layer forms. Bedding layer forms shall be drawn tight against the existing concrete to avoid leakage or offsets at the joint. All previously hardened concrete surfaces that will be in contact with the cap pocket concrete shall be pre-wetted to a surface-saturated moist con- dition when the concrete is placed. Drain ports or holes shall be provided to allow residual water from pre-wetting to drain prior to concreting. Forms for the closure pour between the cap and column shall be adequately vented to allow air to escape during con- creting. Vent tubes shall be flush with the top of the bedding layer and have an inner diameter adequate for venting air and allowing concrete to flow out. Vents shall not be plugged until a steady stream of concrete flows out. Concrete shall be deposited such that all voids in the bedding layer and bent cap are completely filled. Concrete shall be deposited through the top opening of the cap pocket in a manner that deposits the con- crete from the bedding layer or bottom of connection upward. Concrete in the pocket shall be vibrated in accordance with Article 8.7.3. All exposed cap pocket concrete surfaces shall be cured in accordance with Article 8.11. All concrete surfaces shall be inspected post-concreting in coordination with the Engineer. Any voids shall be repaired as specified in the mitigation plan in Article 8.13.8.4.2. Concrete shall not be disturbed and connections shall not be loaded until final acceptance of the con- nection. Final acceptance of the connection shall be after the cap pocket fill concrete has reached the

92 “Final Strength” shown in the plans or as approved by the Engineer. Testing of Cap Pocket Fill Concrete. Testing of the cap pocket fill concrete is specified as follows: The compressive strength of the concrete for “Beam Setting Strength” and “Final Strength” shall be deter- mined using concrete cylinders prepared and tested in accordance with Article 8.5.7. The contractor shall prepare a minimum of six (6) cylinders per batch. A Commercial Testing Laboratory approved by the Engineer shall test the specimens for “Beam Setting Strength” and “Final Strength.” Concrete failing to meet the minimum required compressive strength may be cause for rejection of the connection, concrete removal, and re-concreting of the connection by means approved by the Engineer. Beam Placement Placement of beams on the precast bent cap is specified as follows: The top surface of any precast bent cap anchorage shall be finished and waterproofed as shown in the plans. Lifting loops shall be burned off 1 in below the sur- face of surrounding concrete and patched using material approved by the Engineer. Beams shall not be set until the grout for grouted duct connections or concrete for cap pocket connec- tions has reached a compressive strength equal to the “Beam Setting Strength” shown on the plans. 3.5.5 Measurement and Payment Measurement and payment are specified as follows: The measurement and payment processes used for precast concrete members shall conform to the require- ments of Article 8.17. 3.6 Proposed Changes to AASHTO LRFD Bridge Construction Specifications Based on the work of Matsumoto et al. (8) and the results presented in this report, the proposed Article 8.13.8—Special Requirements for Precast Bent Cap Connections for the AASHTO LRFD Bridge Construction Specifications (35) has been prepared. This construction specification is provided as an attachment to this report. Major sections of the construction specification address the following: • Materials – portland cement concrete for the precast bent cap and cap pocket fill; – hydraulic cement (non-shrink) grout; – corrugated metal duct; – lock seam, helical corrugated steel pipe; – connection hardware; • Contractor submittal including a Precast Bent Cap Place- ment Plan; and • Construction methods including grouting of grouted duct connections and concreting of cap pocket connec- tions (trial batch, placement, and material testing). In addition, a grout specification for the grouted duct con- nection from Matsumoto et al. (8) is presented. The proposed addition to the AASHTO LRFD Bridge Construction Specifications, 2nd Edition, is as follows (35): • Attachment CS1: Proposed Article 8.13.8—Special Require- ments for Precast Bent Cap Connections (AASHTO LRFD Bridge Construction Specifications, 2nd Edition, 2004 with 2005–2009 Interims) – New Article that adds specifications for precast bent cap connections. 3.7 Example Connection Details Based on test results and design and construction specifi- cations, a set of example precast bent cap connection details have been prepared—three for the grouted duct connection (SDC A, SDC B, and SDCs B, C, and D), three for the cap pocket connection (SDC A, SDC B, and SDCs B, C, and D), one for hybrid connection, and one for integral connection. To address the possibility that additional joint shear rein- forcement may be required for SDC B, two sets of details are shown for the emulative connections related to SDC B: (1) SDC B: principal tensile stress, pt, less than 0.11 and (2) SDCs B, C, and D: principal tensile stress, pt, greater than or equal to 0.11 . Details similar to the SDC B example apply for SDCs C and D where additional joint reinforcement is not required. The following drawings are provided as attachments to this report: • Attachment ECD1: SDC A—Grouted Duct Connection – Example bent cap details for grouted duct connection in SDC A • Attachment ECD2: SDC A—Cap Pocket Connection – Example bent cap details for cap pocket connection in SDC A ′fc ′fc

93 • Attachment ECD3: SDC B—Grouted Duct Connection – Example bent cap details for grouted duct connection in SDC B (minimum joint reinforcement used) • Attachment ECD4: SDC B—Cap Pocket Connection – Example bent cap details for cap pocket connection in SDC B (minimum joint reinforcement used) • Attachment ECD5: SDCs B, C, and D—Grouted Duct Connection – Example bent cap details for grouted duct connection in SDCs B, C, and D (additional joint reinforcement required) • Attachment ECD6: SDCs B, C, and D—Cap Pocket Connection – Example bent cap details for cap pocket connection in SDCs B, C, and D (additional joint reinforcement required) • Attachment ECD7: SDCs B, C, and D—Hybrid Connection – Example bent cap details for hybrid connection in SDCs B, C, and D • Attachment ECD8: SDCs B, C, and D—Integral Connection – Example bent cap details for integral connection in SDCs B, C, and D

Next: Chapter 4 - Conclusions »
Development of a Precast Bent Cap System for Seismic Regions Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Report 681: Development of a Precast Bent Cap System for Seismic Regions explores the development and validation of precast concrete bent cap systems for use throughout the nation’s seismic regions.

The report also includes a series of recommended updates to the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications, Guide Specification for LRFD Seismic Bridge Design, and AASHTO LRFD Bridge Construction Specifications that will provide safe and reliable seismic resistance in a cost-effective, durable, and constructible manner.

A number of deliverables are provided as attachments to NCHRP Report 681, including design flow charts, design examples, example connection details, specimen drawings, specimen test reports, and an implementation plan from the research agency’s final report. These attachments, which are only available online, are titled as follows:

Attachment DS—Design Specifications

Attachment DE—Design Examples

Attachment CS—Construction Specifications

Attachment ECD—Example Connection Details

Attachment SD —Specimen Drawings

Attachment TR—Test Reports

Attachment CPT—Corrugated Pipe Thickness

Attachment IP—NCHRP 12-74 Implementation Plan

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