Innovative Bridge Designs for Rapid Renewal (2014)

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582 Recommended ABC Design Specifications 5.14.6— Provisions for Design of Prefabricated Systems for Accelerated Bridge Construction 5.14.6.1—General The design of most modular systems for rapid renewal follows traditional LRFD design specifications. The requirements specified herein shall supplement the requirements of other sections of the LRFD Design Specifications for the design of prefabricated modular systems for rapid renewal. These requirements apply to precast concrete components and prefabricated composite steel girder systems. The design of bridges built using large-scale prefabrication is not specifically covered in the AASHTO LRFD Bridge Design Specifications. When lifting prefabricated components, the location of the support points need to be identified and accounted for in the design, including dynamic effects. 5.14.6.2—Design Objectives 5.14.6.2.1—Rideability The provisions of LRFD 2.5.2.4–Rideability shall be applicable with the following additions: Construction tolerances, with regard to the profile and crossslope of the finished deck, shall be indicated on the plans or in the specifications or special provisions. Where concrete decks without an initial overlay are used, consideration should be given to providing an additional minimum thickness of 0.5 in. to permit correction of the deck profile by grinding, and to compensate for thickness loss due to abrasion. For precast decked concrete girder bridges, where the deck is part of the initial precast section, consideration should be given to either increasing this allowance or providing a variable thickness deck to permit correction of the deck profile due to effects of camber. 5.14.6.2.2—Deformations Stresses and deflections shall be computed to control the integrity of the modular compo- nents during lifting and transportation. The Engineer of Record (EOR) shall define defor- mation controls suitable for each span. For steel or prestressed concrete modular systems, for the purposes of monitoring the structure under fabrication, lifting, transportation and setting in the final location, it is A P P e n D i x G

583 recommended that the EOR determine the anticipated deflection profile for the following conditions when spanning the temporary supports or pick points: –– Under the self-weight (and prestress) of the composite beams and diaphragms. –– Of the composite superstructure and with addition of superimposed dead load from barriers, parapets, medians or sidewalks. The above deflection conditions can be calculated using any appropriate calculation tech- nique based upon elastic analysis. For all the above, for precast prestressed or post-tensioned beams, take into account the age of the concrete at the time the operation is assumed to take place. Under the initial lift condition, ensure that the anticipated flexural tensile stress induced in the top of the structural concrete slab for the assumed support locations is no greater than 0.125 ksi or 0.19÷f′cm (ksi) where f′cm = anticipated strength of concrete at the time of the initial lift operation. If the above conditions cannot be satisfied, then it is recommended that the assumed locations of the lifting points be revised. 5.14.6.3—Loads and Load Factors 5.14.6.3.1—Definitions •– Camber Leveling Force—A vertically applied force used to equalize differential camber between prefabricated elements in a prefabricated modular structural system prior to establishing continuity or connectivity between the elements. •– Dynamic Dead Load Allowance—An increase or decrease in the self-weight of compo- nents to account for inertial effects during handling and transportation of prefabricated elements. 5.14.6.3.2—Load and Load Designation CL = Camber leveling force (kip) C = Locked-in force effects due to load applied to erected prefabricated elements to correct misalignment due to differential camber prior to establishing continuity 5.14.6.3.3—Load Factors and Combinations When camber leveling forces, CL, are considered and they increase the critical effect in the design of the member, the load factor in all Service Load Combinations shall be taken as specified for DC in Table 3.4.1.1-1. Where camber leveling forces act to reduce the critical effect being considered, the load factor shall be taken as 0.0. 5.14.6.3.4—Load Factors for Construction Loads This AASHTO LRFD Section 3.4.2 addresses the Strength Limit State and Service Limit State checks for construction loads. The following additional requirements for LRFD Section 3.4.2 are extended to apply to prefabricated elements and modular systems (concrete and steel composite). These addi- tional requirements are invoked to guard against damage or permanent distortions to the modular system during handling and placement. 1. The Designer shall analyze spans on the assumed temporary/lifting supports based on the Strength I Limit State with a load factor equal to 1.25.

584 2. When investigating Strength Load Combinations I during construction, load factors for the weight of the structure and appurtenances, DC and DW, as well as applied camber leveling load, CL, shall not be taken to be less than 1.25. 3. When evaluating prefabricated components or individual elements of modular systems during construction, a dynamic dead load allowance of 15 percent, acting up or down, shall be applied to all dead load present at the time of handling and transportation. A reduced value may be used at the discretion of the Owner or when measures are taken to minimize inertial effects during transportation. 4. The Designer shall also check the spans to be brought into service for displacements based on Service I Limit State. Service stresses in the span while being handled and placed shall have a service load factor on dead load of 1.30 (handling impact factor). If a rigor- ous structural analysis allowing for the three-dimensional effects of inadvertent twist during transportation is undertaken and included, the service load handling impact fac- tor may be reduced to 1.05. No factored loads shall be used for deflection calculations. 5. No permanent distortion (twist) as a result of handling and placement will be allowed. 6. Contract Documents shall include a completed table of “anticipated deflections” as discussed in LRFD Section 3.4.2.2. 7. Plan notes for construction loads shall include “the magnitude and location” of con- struction loads considered in the design as outlined in LRFD Section C3.4.2.1. 8. The bridge is not subject to Service III limit state while under construction. Bridges analyzed carrying construction equipment shall utilize Service I with a 5% impact factor. 5.14.6.4—Analysis LRFD Section 4.5, Mathematical Modeling, provides general guidance for mathematical modeling of bridges. The following additional requirements are extended to apply to pre- fabricated concrete and steel composite modular systems: 1. Prefabricated elements and modular systems are to be analyzed based on elastic behavior for handling and placement. Inelastic analysis will not be permitted. 2. The analysis may consider the influence of continuous composite precast barriers and rails on the behavior of modular systems during handling and placement. 3. Analysis of modular systems may be based on approximate or refined methods in accor- dance with AASHTO LRFD Bridge Design Specifications. 4. Contract Plans shall state that all formwork for the deck shall be supported from the longitudinal girders similar to conventional construction methods. Shored construction shall not be assumed. Decked girder systems shall be designed to accommodate future deck replacement without the use of shoring during deck removal and replacement operations. 5.14.6.5—Control of Cracking (Non-Prestressed Components) LRFD Section 5.7.3.4, Control of Cracking by Distribution of Reinforcement, addresses requirements for all reinforced concrete members. It is extended to apply to prefabricated elements and systems. 1. Provisions specified in LRFD Article 5.7.3.4 for the distribution of tension reinforcement to control flexural cracking shall apply to all prefabricated elements and systems at the Service I Limit State. 2. The longitudinal reinforcement in the deck and superimposed attached items like side- walks, parapets, and traffic railings shall be analyzed.

585 5.14.6.6— Lifting and Handling Stresses (Non-Prestressed Components) Specify maximum tensile stress in non-prestressed precast concrete components during transportation, handling and erection under the Service I load combination. A 30% handling impact factor on dead loads shall be assumed. As an alternate, we can specify that precast components be handled in a manner that restricts the crack widths to acceptable limits. The lifting inserts should be so arranged that when the element is lifted it remains stable and the bottom edge remains horizontal. The positions of lifting inserts are calculated to limit lifting stresses and to ensure that the precast element hangs in the correct orientation during lifting. Check the potential for lateral instability during transportation and erection. Analysis of lifting and handling stresses shall be based on the recommended lifting points shown on the plans. The minimum concrete strength at which precast elements can be lifted should be specified on the plans. 5.14.6.7—Prestressed Components Requirements of LRFD Section 5.9.4, Stress Limits for Concrete, shall be modified as follows for modular systems: Minimum compressive strength at time of handling f′cm should be specified on the plans. 5.9.4.1—For Temporary Stresses Before Losses—Fully Prestressed Components 5.9.4.1.2—Tension Stresses Modify second bullet of Table 5.9.4.1.2-1 for “Other Than Segmentally Constructed Bridges”: 1. In areas other than the precompressed tensile zone and without bonded reinforcement, and in top flanges of noncomposite prestressed components that will serve as the riding surface in the finished bridge Add to Table 5.9.4.1.2-1 for “Other Than Segmentally Constructed Bridges”: 2. For handling stresses in the top flange of noncomposite prestressed components that will serve as the riding surface in the finished bridge 0.24 ÷ f′cm (ksi) 5.9.4.2—For Stresses at Service Limit State After Losses—Fully Prestressed Components 5.9.4.2.1—Compression Stresses This section addresses compression stresses in Prestressed Concrete members. It is extended to apply to prefabricated elements and systems. LRFD Table 5.9.4.2.1-1, the third bullet shall apply to prestressed girder elements and modu- lar systems during shipping and handling with a Fw = 1.0. 5.9.4.2.2—Tension Stresses This section addresses tension stresses in prestressed concrete. It is extended to apply to prefabricated elements and systems.

586 Prestressing losses may be calculated by either the Approximate or Refined method in AASHTO LRFD Articles 5.9.5.3 and 5.9.5.4. Service III is for tension limits subject to normal anticipated highway “traffic loading.” These loadings do not include nor do they apply to construction vehicles. Use Service I for construction loadings. During design, the actual scheduling of construc- tion is not known. Since the age of the members can have a significant effect on the stresses early on, conservative assumptions must be made to ensure that the design stresses are for the worst case scenario. Add to Table 5.9.4.2.2-1 for “Other Than Segmentally Constructed Bridges”: 3. For components subjected to locked-in effects due to application of camber leveling forces No tension 5.11.5.3.1—Lap Splices in Tension This section specifies a minimum of 12″ length for lap splices in tension. The minimum length requirement may be waived if demonstrated by test results on a specimen represent- ing the proposed joint design using UHPC. An experimentally determined development length may be used as the basis for the joint design. 5.14.6.8—Design of the Grouted Splice Coupler The AASHTO LRFD Bridge Design Specifications Article 5.11.5.2.2 requires that all mechanical reinforcing splice devices develop 125% of the specified yield strength of the bar. Several manufacturers produce grouted splice couplers that can meet and exceed this requirement. If this requirement is met, the coupler can be treated the same as a reinforc- ing lap splice. 5.14.6.9—Provisions for Joints The following sections modify applicable section of Section 5 of the LRFD Bridge Design Specifications: 5.14.4.3.3d—Longitudinal Construction Joints For longitudinal joints designed as shear-flexure joints without transverse post-tensioning that are also required to resist forces due to differential camber between adjacent compo- nents, the key shall be filled with an approved concrete. Minimum compressive strength and time required to attain the minimum compressive strength shall be specified on the plans. The applied camber leveling force shall not be removed until the joint is capable of resisting shear due to differential camber. Grinding for profile or cross-slope correction shall not begin until the concrete has attained the specified minimum compressive strength. 5.14.4.3.3e—Cast-in-Place Closure Joint Concrete in the closure joint should have strength comparable to that of the precast compo- nents. The width of the longitudinal joint shall be large enough to accommodate develop- ment of reinforcement in the joint. Where development sufficient for anchorage of the reinforcement can be demonstrated by test results on a specimen representing the proposed joint design, the width of the joint can be based upon an experimentally determined devel- opment length plus a clear distance between the joint reinforcement and the nearest

587 concrete surface adequate for concrete placement in the joint. Otherwise, the joint width shall not be less than 12.0 in. 5.14.6.10— Provisions for Steel Composite Systems This AASHTO sub-section addressing requirements for the design of composite steel modu- lar systems. The following sections modify applicable section of Section 6, Steel Structures, of the LRFD Bridge Design Specifications: 6.7.4.1—Diaphragms and Cross Frames This section addresses the location of diaphragms and cross frames in steel structures. The following additional requirements are extended to apply to prefabricated elements and systems. 1. In interior lift points for composite modular system shall be considered an interior support. 2. At interior supports provide either a diaphragm or a cross-frame with necessary stiffen- ers as appropriate for bracing, connections and local bearing. The designer should address suitable diaphragm or cross-frame details to provide the necessary compression flange stability under temporary handling conditions. 3. Investigation shall include the stability of compression flanges during handling and placement. Diaphragms or cross-frames required for the construction condition may be specified to be temporary bracing. 6.10.1.1.1a—Sequence of Loading This section addresses loads applied to a steel structure. The following additional require- ments are extended to apply to prefabricated steel modular systems. 1. Shored construction as allowed in the last sentence of this section is not allowed for spans assembled using steel modular systems. 2. Contract Plans shall state that forming and shoring of the deck shall be supported from the longitudinal girders similar to conventional construction methods.