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Systems International Scanning tour. These systems tion of one of the initial implementations of the included (1) a precast composite slab span system PCSSS in Center City, Minnesota. Transverse load (PCSSS) for short to moderate span structures based transfer is achieved through the development of trans- on the French Poutre Dalle system, (2) full-depth pre- versely oriented reinforcement protruding from the fabricated concrete decks, and (3) deck joint closure precast members. Furthermore, improved quality of details [e.g., decked-bulb-T (DBT) flange connec- the main superstructure can be achieved because of tions] for precast prestressed concrete girder systems the rigid quality control associated with the fabrica- for long span structures. Each system uses precast tion of precast members, which may be difficult to elements that are brought to the construction site achieve in CIP bridge construction. ready to be set in place and quickly joined together. Figure 2 shows a representative cross section of Depending on the system, the connections are either a precast inverted-T section used in the construction transverse (i.e., across the width of the bridge) or lon- of the PCSSS. The precast sections are placed adja- gitudinal (i.e., along the length of the bridge). The first cent to each other such that the transverse hooked system, PCSSS, is an entire bridge system whereas bars protruding from the adjacent webs form a lap the other two systems investigated in the project rep- splice in the CIP region between the webs. resent transverse and longitudinal joint details that One of the issues investigated in the NCHRP transfer moment and shear in precast deck panels and Project 10-71 study was the durability of the PCSSS, flanges of DBTs. Because of the similarities in the lat- specifically its ability to control potential reflective ter two types of systems, they are grouped together cracks that might develop in the CIP concrete due to in this summary. Two types of connection concepts the discontinuity created at the interface between the were explored with these details: looped bar details adjacent flanges that abut or due to the corners of the and two layers of headed bar details. Although both precast web. A supplemental reinforcement cage is types of systems performed adequately in initial tests, dropped into the CIP region between webs to pro- the looped bar systems were deemed to be more prac- vide supplemental reflective crack control above the tical for construction purposes and were investigated interface between the adjacent flanges. Figure 3 shows a cross section of the PCSSS indicating the in the subsequent tests. potential locations where reflective cracking would Because this report covers two very different be expected to initiate. Figure 4 shows a typical systems: (1) the PCSSS, which is an entire bridge instrumentation plan used in the investigation to system, and (2) transverse and longitudinal CIP con- monitor initiation of any reflective cracks that might nection concepts that transfer moment and shear have developed. between precast deck panels and the flanges of pre- cast DBTs, this summary, as well as the report, is separated accordingly. The complete report includ- Research Methodology and Findings ing appendices is available on the TRB website as Several numerical and experimental investiga- NCHRP Web-Only Document 173 (http://www.trb. tions were completed and reviewed during the proj- org/Main/Blurbs/164971.aspx). ect that related to issues of importance to the design and performance of PCSSS bridges. Included in this PCSSS review was the work completed during a study com- missioned by Mn/DOT, which was the first DOT in Introduction the United States to implement this technology. The PCSSSs are a promising technology for the laboratory bridge specimen utilized during the Mn/ implementation of accelerated construction tech- DOT study was subsequently made available for use niques for bridge construction. These bridge sys- with the project described herein. tems are composed of precast, inverted-T sections, Numerical studies included an investigation of fabricated off-site and delivered to the jobsite ready bursting and spalling stresses in the end zones of pre- for erection. The inverted-T sections are assembled cast inverted-T sections, effects of spacing of trans- such that no formwork is required prior to the place- verse reinforcement in the joint region, and an ment of the CIP deck, which considerably reduces investigation of the applicability of current design construction time related to the placement and specifications for slab-type bridges to the design of removal of formwork. Figure 1 shows the construc- PCSSS bridges for live load distribution factors and 2

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(a) (b) (c) (d) (e) (f) Figure 1 Sequence of construction of a PCSSS: (a) precast pier caps in place, (b) Inverted T-sections in place (elevation view), (c) Inverted T-sections in place (plan view), (d) drop-in cage placed between precast webs for potential crack control, (e) deck reinforcement in place, and (f) finished structure. for consideration of effects of skewed supports. The to the issue of reflective crack control, in addition to two primary considerations that distinguish PCSSS a numerical investigation as to the effect of the trans- bridges from slab-span bridges are (1) the required verse reinforcement, the issue was also studied in reinforcement to control reflective cracking above laboratory investigations of two large-scale labo- the longitudinal joint between the precast flanges and ratory specimens (i.e., Concept 1 and 2 bridges), as (2) the effect of time-dependent restraint moments well as in subassemblage test specimens specifically due to the composite nature of the system. With regard designed to investigate crack control. 3

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Figure 2 PCSSS precast inverted-T cross section. Reflective cracking Web corner of precast section Flange corners of precast sections Longitudinal precast joint Figure 3 Anticipated locations of reflective cracking in Minnesota Department of Transportation (Mn/DOT) PCSSS (Bell et al. 2006). Figure 4 Location of transverse concrete embedment gages in each of the three instrumented joints at midspan of the center span of the Center City Bridge (Bell et al. 2006) (VW = vibrating wire). 4

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The Concept 1 laboratory bridge was a two-span spaced at 18 in. to provide a maximum spacing of continuous bridge that included variations in a 9 in. between transverse reinforcement. number of parameters, including precast flange Figure 5 shows the instrumentation layout in the depth and end zone reinforcement details. It had plan view of the Concept 1 bridge. A similar instru- been instrumented in the study for the Mn/DOT to mentation configuration was used in the Concept 2 investigate the effects of restraint moment and bridge. potential development of reflective cracking. The The performance of both bridge specimens was Concept 1 specimen included No. 6 transverse hooked investigated under various types of loading, includ- reinforcement embedded into the precast webs to ing cyclic loading to simulate traffic, loading to provide load transfer and crack control in the joint simulate environmental effects, and loading to region, as well as No. 5 cage stirrups that con- investigate load transfer between adjacent precast tributed to the crack control reinforcement. The panels (both longitudinal and transverse). To sim- nominal maximum spacing between transverse rein- ulate the environmental (thermal gradient) effects-- forcement was 12 in., similar to the detail of one of as observed in the Center City Bridge that was the first implementations of PCSSS bridges in the instrumented for the Mn/DOT study--the struc- State of Minnesota, the Center City Bridge. The varia- tures were loaded to impose transverse strains tions in the detailing of the two spans in the Concept 1 above the longitudinal joint between the precast bridge are summarized in Table 1. The Concept 2 flanges. The structures were cycled at these strain bridge was a simply supported structure that included levels to simulate more than 100 years of service variations in the transverse reinforcement details life as exposed to thermal gradient effects, which across the precast joint. The horizontal shear rein- were found to be much more significant than strains forcement between the precast web and CIP topping due to traffic loading. Following the cyclic load was eliminated in this structure. In the Concept 2 tests, the bridges were loaded above the nominal specimen, No. 4 embedded hooked reinforcement design flexural strengths to the limiting capacities was used in the west half of the simple span, while of the actuators to investigate the effectiveness of No. 4 straight embedded bars mechanically con- composite action. Following the tests, cores and nected to reinforcement in the precast webs were slices of the bridge were examined to investigate provided in the east half span. See Figure 2 for illus- any residual cracks. tration of the precast inverted-T cross section used Figure 6 shows the location of the patch loads in in the west end of the precast beams 1N and 1S in the Concept 1 bridge used to investigate the effect of the Concept 2 laboratory bridge specimen. No. 3 cyclic loading to simulate approximately 2 million cage stirrups were staggered in the Concept 2 labo- cycles of vehicle loading over the joint. Relatively ratory bridge relative to the transverse reinforcement small strains were observed in those tests. As a Table 1 Original and modified design criteria in Spans 1 and 2 of the Concept 1 laboratory bridge. Span 1 (Modified Section) Span 2 (Original Section) Decreased flange thickness (3 in.) Original flange thickness (51/4 in.) Smooth flange surface Original roughened flange surface Increased stirrup spacing for horizontal shear Original stirrup spacing for horizontal shear reinforce- reinforcement (No. 5 stirrups at 24 in.) ment (No. 5 stirrups at 12 in.) Increased clear spacing under hooks (13/8 in. nominal Original clear spacing under hooks (1/4 in. nominal clear clear spacing between horizontal shear reinforcement spacing between horizontal shear reinforcement stirrups and precast section) stirrups and precast section) Decreased transverse deck reinforcement (No. 4 bars Original transverse deck reinforcement (No. 5 bars at 12 in.) at 12 in.) The longitudinal deck steel in the south half of the bridge was two No. 7 and one No. 8 bars per 12 in. at the continuous pier (Original design) The longitudinal deck steel in the north half of the bridge was reduced to No. 6 bars at 6 in. spacing at the continuous pier (Modified design) 5

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Figure 5 Instrumentation layout for Concept 1 laboratory bridge specimen (Smith et al. 2008). consequence, the loads were subsequently increased to investigate the relative performance of various to induce similar strains in the cross section as those reflective crack control reinforcement details. Fig- observed in the Center City Bridge because of ther- ure 7 shows the elevation and plan views of a repre- mal effects. The figure shows the location of loads sentative subassemblage specimen. Table 2 lists the applied through a spreader beam to extend the reflec- variables investigated in each of the subassemblages. tive crack along the length of the joint. The reinforcement ratio for crack control, given in In addition to the two large-scale laboratory bridge Table 2, considered the area of all reinforcement specimens, six subassemblage specimens were tested crossing the precast joint near the bottom of the CIP Figure 6 Placement of patch loads during fatigue loading and extension of longitudinal reflective cracking (applicable in Span 1 only) for the Concept 1 laboratory bridge specimen. 6

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(a) Elevation view of subassemblage specimens (b) Plan view and directional orientation of subassemblage specimens Figure 7 Elevation and plan views of subassemblage specimen. trough. Therefore, the bottom leg of the cage stirrups cast flanges. The size, quantity, and location of crack- and all of the embedded transverse reinforcement ing were documented through a range of quasi-static were included in the calculation (i.e., for each pair of and cyclic load tests. Figure 8 illustrates the method transverse embedded bars, both were included in the for documenting the visual observations. The sub- calculation because both were assumed to be effec- assemblages were instrumented internally to investi- tive above the longitudinal joint between the adjacent gate the location of the cracking along the depth and flanges). Furthermore, the area of concrete used in the through the thickness of the structure. The results calculation was only that which was located between obtained from the internal instrumentation were com- the top of the precast flanges and the top of the pre- pared to visual observations of crack initiation, width, cast webs. It should be noted that this crack control and depth observed on the faces of the specimen. reinforcement would only be effective in the region Following the tests of the laboratory bridge and above the longitudinal joint between adjacent precast subassemblage specimens, a forensic examination of panels. For potential cracks that may develop at the the specimens was conducted. Cores were taken in the precast web-CIP interface, only the reinforcement region over the longitudinal joint between the adjacent protruding from the precast webs would be effective. precast flanges and above the CIP-precast web inter- The specimens were loaded to flexurally induce face, as shown in Figure 9, to look for evidence of any cracking above the longitudinal joint between the pre- residual reflective cracks under no loading. 7

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Table 2 Subassemblage specimen design details. Transverse Bars R/F (Load Trans.) Cage (Crack Control) Ratio Specimen Width Depth Max ID [in.] [in.] Size Spacing Depth1 Presence Size Spacing Spacing2 cr SSMBLG1- 62.75 14 #4 18 in. 41/2 in. Cage #3 18 in. 9 in. 0.0031 Control1 OC OC SSMBLG2- 67.25 14 #4 18 in. 41/2 in. No Cage 0 0 18 in. 0.0025 NoCage OC SSMBLG3- 62.75 14 #4 18 in. 7 in. Cage #3 18 in. 9 in. 0.0031 HighBars OC OC SSMBLG4- 62.75 18 #4 18 in. 41/2 in. Cage #3 18 in. 9 in. 0.0022 Deep OC OC SSMBLG5- 62.75 14 #6 18 in. 41/2 in. Cage #3 18 in. 9 in. 0.0061 No.6Bars OC OC SSMBLG6- 64 14 #4 18 in. 41/2 in. Cage #3 4.5 in. 4.5 in. 0.0052 Frosch OC OC SSMBLG7- 62.75 14 #4 18 in. 41/2 in. Cage #3 18 in. 9 in. 0.0031 Control2 OC OC 1 The depth of the transverse reinforcement was taken from the bottom of the precast section to the center of the reinforcement. 2 The maximum spacing was the maximum nominal distance between reinforcement traversing the longitudinal joint, regardless of type (i.e., transverse hooked bars or cage). NOTE: R/F ratio = reinforcement ratio, cr = reinforcement ratio for crack control, OC = on center. There were a few considerations not included in Bursting, Splitting and Spalling Stresses the laboratory research or numerical study, such as the connection between the precast elements and the Significant changes have been made to the bridge substructure. These details were investigated pri- design specification since 2007 with regard to end marily by means of examination of structural plans zone stresses, specifically in the terminology. Up for existing PCSSS structures. to and including the 2007 specifications, the term "bursting" was used to describe the end zone stresses and was associated with design requirements likely Conclusions and Recommendations developed specifically for I-girders, but also applied The conclusions and recommendations are sum- to other shapes. The 2008 Interim specifications marized by topic. relaxed the placement requirements for wide-shallow Figure 8 Measurement of width and length of crack observed on origin and end faces of subassemblage specimens. 8

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Cores at the Longitudinal Joint Cores at the Web/C.I.P. Interface C.I.P. Composite Deck Precast Inverted-Tee Up Reference Line Down Figure 9 Location of cores removed from the test specimen and reference line for measurement of vertical location of cracking in subassemblage core specimens. sections by allowing the designer to spread the end on the precast prestressed inverted-T sections used zone reinforcement, termed "splitting" reinforcement, in the PCSSS. The experimental results from the over a larger distance. In the case of pretensioned solid Concept 1 and 2 laboratory bridge investigations or voided slabs, the designer can substitute the sec- indicated that the 12-in. deep concrete sections had tion width for "h," rather than using the section depth sufficient strength to resist tensile stresses induced for "h." According to this study, this may not be in the transfer zone of the precast inverted-T sections appropriate when trying to control spalling stresses. at the time of release. Four unique end regions of In addition, the terminology for the reinforcement the Concept 1 laboratory bridge specimen precast described in this section of the design specifications members did not exhibit any evidence of cracking, is more correctly termed "spalling" reinforcement even in the absence of vertical reinforcement. These rather than "splitting" or "bursting" reinforcement findings were corroborated with the results of numer- (Uijl 1983). Figure 10 illustrates the correct terminol- ical studies. ogy to describe the end zone stresses in prestressed Results from the finite element study (Eriksson members. 2008) revealed that the relationship between e2/(h * db) Experimental and numerical studies were com- (where e stands for prestress eccentricity, h stands for pleted to investigate the effects of end zone stresses section depth, and db stands for strand diameter) and 1 Beam 2 3 1 - Spalling Stress 2 - Bursting Stress 3 - Prestress Force Figure 10 End zone stresses in prestressed members. 9

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0.10 0.09 Uniform Bond Stress Distribution Linear Bond Stress Distribution 0.08 Design Recommendation Spalling Force/ Strand Force 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 2 e /(h*d b ) Figure 11 Ratio of spalling force to prestress force for varying e2/(h * db ). the ratio of tensile spalling force to prestress force is as the product between h/12 and the distance between reasonably approximated by a straight line as shown the outermost prestress strands (bs) and can be writ- in Figure 11. Because the true bond stress distribu- ten as tion is somewhere between uniform and linear bond stress, an average between these two assumptions h Tc = 0.24 fc bs (2) was developed, as shown in Figure 11. The equation 12 for this straight line approximation is where Tc is the tensile force that can be resisted by the e2 concrete, fc is the concrete compressive strength at T = P 0.02 - 0.01 0 (1) 28 days, h is the height of the member (the precast hdb slab), and bs is the distance between the outermost where T is the spalling force and P is the strand pretension strands. If the design tensile force is force. smaller than the tensile force resisted by concrete Vertical steel reinforcement does not carry the (T < Tc), it is reasonable to assume cracking will not vertical tensile stress until the concrete cracks. If the occur and vertical tensile steel is not needed in the spalling stresses are small enough in a member for end region to resist the spalling force. Otherwise, the concrete tensile strength to prevent cracking, steel must be placed within the end region of the vertical tensile steel is not necessary for the member. member to resist the tensile force found in Equation To calculate the concrete area to be considered (1). The area of steel needed to resist the predicted for providing tensile resistance, the area over which spalling force is given by spalling forces act must be determined. Based on the slab span sections studied, the shortest distance T As = (3) into the member the spalling stress extends is h/12. fs This becomes a conservative estimate as the section increases in height and e/h. The area of concrete to where As is the area of steel and fs is the allowable resist this tensile strength is conservatively estimated working stress of vertical reinforcement. 10

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The numerical studies showed that certain precast members at the time of continuity, and thermal inverted-T members did not require spalling rein- gradients. Positive and negative restraint moments are forcement, specifically those with depths less than illustrated in Figure 12. 22 in. for which the expected concrete tensile strength Negative restraint moments are caused by differ- was larger than the expected vertical tensile stresses ential shrinkage of the CIP concrete, where the rate of due to the development of prestress. shrinkage of the CIP concrete is larger than the rate of It was also found through numerical studies that shrinkage and creep of the precast member. When the the existing design requirements may not be conser- precast member is at a relatively old age, defined as vative for deep inverted-T sections (i.e., greater than greater than 90 days by AASHTO, the shrinkage of 22 in.). Larger amounts of spalling reinforcement the newly placed CIP concrete will tend to "shorten" than specified by the 2010 design specifications were the top fiber of the bridge structure and subsequently found to be required. It was also found that the rein- induce longitudinal tensile stresses in the top of the forcement should be placed as close to the end of the bridge at the piers. The reinforcement included in the member as possible (i.e., within h/4 of the end of the deck of the structure over the piers in continuous sys- member, where "h" represents the depth of the mem- tems provides the tension ties necessary to counteract ber). The end region was the most critical region for negative restraint moments. the reinforcement to be located to address spalling Positive restraint moments at the piers in contin- stresses, even for the case of wide sections. uous systems may be due to both time-dependent and thermal effects. When the precast member is at Restraint Moment a relatively young age at the time of continuity, the Multispan precast composite bridge structures rate of shrinkage of the precast member and the CIP made continuous with CIP concrete develop time- may be similar; however, the precast member would dependent and thermal restraint moments at the con- also undergo creep. The creep of the precast section tinuous piers. The size and magnitude of restraint would tend to "shorten" the bottom fiber of the bridge moments are affected by shrinkage, creep, age of the structure and subsequently induce longitudinal tensile Negative restraint moment induces tension near the top surface at the pier. (a) Positive restraint moment induces tension near the bottom surface at the pier. (b) Figure 12 Positive and negative restraint moments in continuous bridge superstructures (Molnau and Dimaculangan 2007). 11

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stresses in the bottom of the bridge at the pier. In distribution tests on the laboratory bridge speci- addition, thermal gradients in the section cause the mens (i.e., Concept 1 and Concept 2) to determine top surface of the structure to expand, again induc- the applicability of current live load distribution fac- ing a positive restraint moment in the structure. For tors in the bridge design specification for slab-type this reason, both time-dependent and thermal gradi- bridges to the PCSSS. ent effects must be considered in the design of pos- The numerical models illustrated that the longi- itive restraint moments. Because positive restraint tudinal curvatures measured in the precast slab span moments induce longitudinal tensile stresses near the system with a reflective crack extending to within bottom of the section, reinforcement must be pro- 3 in. of the extreme compression fiber and a tandem vided to carry the tensile force at the piers. Because load greater than that which could be physically of the sectional geometry of the PCSSS, all rein- applied in the field resulted in longitudinal curvatures forcement provided for positive restraint moments that were only 84% of the longitudinal curvatures must be located within the longitudinal trough regions predicted using the AASHTO Load and Resistance between precast panels. Consequently, this reinforce- Factor Design (LRFD) (2010) load distribution fac- ment must be placed in groups centered between pan- tors for monolithic concrete slab span bridges. This els, generally 6 feet apart, thereby prohibiting the suggests that PCSSS-type superstructures could rea- distribution of the reinforcement along the face of the sonably and conservatively be designed using the bottom surface. current live load distribution factors for monolithic Research completed during the Mn/DOT study slab-type bridges. and the current study has shown that restraint Furthermore, the live load truck tests on the Cen- moments that develop due to thermal gradients can ter City Bridge suggested that the measured longitu- be significant and should be considered in either dinal curvatures were approximately three times less case (i.e., whether or not time-dependent effects than those calculated using monolithic slab span generate positive or negative restraint moments). equations. And the measured longitudinal curvatures The positive restraint moment effects attributed to were consistently conservative when compared to the design thermal gradients can be an order of monolithic slab span finite element (FE) models. The magnitude larger in some climates than the positive conservatism in the factors for monolithic slab span restraint moments due to time-dependent effects. bridges was sufficient to cover the cases of the The thermal gradients provided by the bridge design PCSSS bridges even considering the potential effects specification should be taken into consideration by of reflective cracking as discussed above. calculating the resulting expected curvatures of each Load distribution tests on Span 2 of the Concept 1 span treated as simply supported and then determin- and Concept 2 laboratory bridges included an inves- ing the moment required to overcome the end rota- tigation of the transverse load distribution between tions and provide continuity. There may be little or adjacent precast panels. Both spans showed good load no economic gain in continuity because of the large transfer capabilities across the longitudinal joint dur- thermal restraint moments that develop and, in some ing intermittent tests to extend the reflective crack, cases, continuity may require additional reinforce- conducted throughout the investigation of the labo- ment in the precast sections (i.e., larger than would ratory bridge specimens. In both cases, little variation be required for a simply-supported design). As a in the measured longitudinal curvatures with crack consequence, it is not conservative to design the growth was observed in the unloaded panels, which PCSSS bridges as simply supported and add positive suggested that load was effectively transferred across moment reinforcement across the piers for integrity the longitudinal joint from the loaded panel despite the reinforcement without considering the effects of the presence and increase in the size of reflective cracking restraint moments that can be generated due to the induced in/near the joint. thermal gradient effects. In summary, the numerical and experimental stud- ies in regards to live load distribution factors indi- Live Load Distribution Factors cated that the PCSSS was well represented by monolithic FEM models, suggesting that the discon- Numerical modeling was combined with obser- tinuity at the precast joint did not significantly affect vations from a live load truck test on the field- the load distribution characteristics of the system. instrumented Center City Bridge along with load Also, the performance of the large-scale laboratory 12

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bridge specimens reinforced the notion that the sys- with fewer horizontal shear ties than were used in tem provided sufficient transverse load distribution, Span 2 and in the Center City Bridge, which did not with and without the presence of reflective cracking satisfy the minimum horizontal shear reinforcement near the joint region. requirements of the 2005 bridge design requirements. The Concept 2 laboratory bridge was designed and Skew constructed with no horizontal shear ties. In both Numerical modeling was applied to simply sup- bridges, the surface condition of the precast mem- ported monolithic and jointed (to simulate the PCSSS ber was roughened to a surface consistent with a 1 discontinuity at the adjacent precast flange interface) /4-in. rake. bridge models with skewed supports ranging up to In the tests on both spans of the Concept 1 labo- 45 degrees. Three independent load cases were inves- ratory bridge and on the Concept 2 laboratory bridge, tigated, including a 35-kip load individually applied the sections were observed to remain composite well over a 12- by 12-in. patch at both quarter points and beyond service load levels through the full range of at midspan for each model. For each load case, the loading to the maximum capacity of the loading sys- largest horizontal shear stress in the plane above tem, which was in excess of the predicted nominal the precast joint nearest the loading was determined. capacity of the Concept 1 and 2 bridges. The hori- The small variation and consistency between the zontal shear stress estimated in the Concept 2 system models considering a joint between precast sections at the precast-CIP interface was subsequently calcu- with a 3-in. flange and a monolithic structure sug- lated to be 135 psi. As the bridge had not yet been gested that the impact of the joint in precast com- loaded to failure due to the limited capacity of the posite slab span construction was not expected to actuators, it may have been possible to generate even significantly affect the performance of the system in larger horizontal shear stresses. skewed applications, and the design of skewed PCSSS The results of the laboratory tests are consistent bridges could be completed assuming a monolithic with those of Naito and Deschenes (2006) and suggest slab span system. that the bridge design specification should allow for the design of precast slab span structures without Composite Action and Horizontal Shear Strength horizontal shear ties, and allow for the development of a maximum factored horizontal shear stress of To conclude the laboratory tests, the large-scale 135 psi in sections with intentionally roughened sur- bridge specimens were loaded above the nominal faces (i.e., 1/4-in. rake as shown in Figure 13 for the flexural capacities to the limiting capacities of the Concept 2 bridge) unreinforced for horizontal shear. actuators in order to investigate the ability for the precast slab span sections to remain composite with Reflective Crack Control across the Longitudinal the CIP concrete topping. Placement of reinforce- Joint between Precast Flanges ment for horizontal shear was observed to be difficult and time consuming for the fabricator, especially Reflective cracking was intentionally induced when finishing the top web surfaces. Furthermore, in the Concept 1 and Concept 2 large-scale labora- the reinforcement extending from the precast webs tory specimens to investigate the performance of the for horizontal shear extended out of the precast sec- PCSSS through a range of loading that was designed tion with minimal clearance between the hook and to simulate both fatigue performance due to vehicu- the precast web surface in order to avoid interfer- lar loading as well as the influence of environmental ence with placement of the deck reinforcement in effects. The performance of both spans of the Con- the field. In initial field applications of the PCSSS, cept 1 laboratory bridge and the Concept 2 laboratory the low clearance of this horizontal shear reinforce- bridge was observed to adequately control cracking ment may have limited its effectiveness because in the precast joint region throughout the loading. aggregate was unable to flow below the returned Reflective cracking was also monitored through- stirrups. Span 2 of the Concept 2 laboratory bridge out the range of testing for seven subassemblage was designed with the same horizontal shear lay- specimens in order to quantify the relative perfor- out utilized in the Center City Bridge, which sat- mance of the respective design details for reflective isfied the 2005 bridge design requirements. Span 1 crack control in each specimen. The ability for of the Concept 1 laboratory bridge was designed each specimen to control the width of cracking was 13

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Figure 13 Intentionally roughened surface, by means of raking, of top web of precast beam used for the construction of Concept 2 laboratory bridge specimen. desirable, as large cracks were expected to cause de- the ends of the members. This served to better simu- gradation of the longitudinal joint region. This degra- late the effects of restraint in the bridge system (i.e., dation included providing a potential avenue for the clamping the subassemblage specimens near the ends ingress of moisture and chlorides. simulated the effect of the bridge supports transverse It was found during the testing of the first speci- to the longitudinal joint and relieved the compressive men, SSMBLG3-HighBars, that the stiff flanges of stress across the subassemblage). the precast section rotated and caused delamination Each of the subassemblage specimens performed between the precast flange and CIP concrete, result- adequately throughout the range of loading, though ing in propagation of a crack at the precast-CIP variations in the extent of cracking indicated some concrete interface. The test setup was subsequently relative differences. The two specimens with the modified by developing a system to clamp the pre- largest reinforcement ratios for crack control, SSM- cast flanges to the CIP concrete on either side of the BLG5-No.6Bars (cr = 0.0061) and SSMBLG6- longitudinal joint as shown in Figure 14. Although Frosch (cr = 0.0052), performed well relative to the the test setup induced compressive forces through the remaining specimens. In these two specimens, mea- depth of the section at the faces, it was believed to sured crack widths were consistently smaller than the better emulate the field conditions because in a remaining specimens. SSMBLG7-Control2 (cr = bridge system, the pier supports would be normal to 0.0031) also indicated better than average perfor- the longitudinal joint, thereby preventing the relative mance through visual observations, however, the rotation of the precast flanges with respect to the CIP analysis of the embedded instrumentation suggested in the trough above the precast flanges at the ends of that the behavior of this specimen was similar to the the sections. specimens in the group not including SSMBLG5- The vertical rods that connected the top and bot- No.6Bars and SSMBLG6-Frosch. The behavior of tom steel members used to clamp the section were SSMBLG7-Control2 was attributed to a relatively located a clear distance of between 2 in. and 3 in. from smooth precast flange surface achieved prior to the the face of the specimen. Consequently, curvature placement of the CIP concrete (done in anticipation was induced in the longitudinal clamping members, of studying a debonded flange surface, which was which tended to concentrate the compressive force at abandoned to allow for a second control specimen 14

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A A Figure 14 Clamping system developed to simulate restraint near joint region on subassemblage specimens. to be tested). The relatively smooth flange surface imum transverse reinforcement spacing provided was expected to better distribute transverse stresses in the Concept 2 laboratory bridge did not correlate across the precast flanges in the joint region, thereby with an improvement in the control of cracking near reducing the potential stress concentration at the inter- the longitudinal trough area relative to the 12-in. face between the adjacent precast flanges that created maximum spacing provided in the Concept 1 spans. a longitudinal joint. However, it was observed via an Therefore, an economical design may favor 12-in. analysis of the horizontal crack propagation using the transverse reinforcement spacing to 9-in. spacing with concrete embedment resistive strain gages that a no expected reduction in performance. An increase in single crack was present internally in the specimen the maximum transverse reinforcement spacing to suggesting that the smooth flange surface did not dis- 18 in. is not recommended, primarily because crack- tribute the transverse stress adequately enough so ing in SSMBLG2-NoCage (which was reinforced as to promote the development of multiple cracks. with only transverse No. 4 bars spaced at 18 in.) was A completely debonded surface, however, was not generally largest. The crack widths in SSMBLG2- expected to be desirable as it would likely promote NoCage increased with the least increase in the delamination of the horizontal precast flange-CIP applied load relative to the other subassemblage interface, which was expected to promote cracking at specimens that had transverse reinforcement spac- the vertical precast web where cage reinforcement ings no larger than 9 in. The subassemblage speci- was not present to aid in the control of cracking. men with transverse reinforcement spacing no larger In the subassemblage study, the maximum trans- than 9 in. were observed to provide acceptable crack verse 9-in. spacing for crack control appeared to be control. sufficient as long as enough reinforcement was pro- Furthermore, little difference was observed vided to ensure that the reinforcement did not yield between the performance of the sections of the Con- upon cracking. This was evident through the good cept 1 laboratory bridge with No. 6 transverse hooked performance of the SSMBLG5-No.6Bars and SSM- bars where reflective cracking was observed and the BLG6-Frosch specimens. These results are consis- performance of the Concept 2 laboratory bridge with tent with those of Frosch et al. (2006). No. 4 transverse hooked bars where reflective crack- The maximum transverse reinforcement spacing ing was observed. There was, however, a noticeable was further investigated by evaluating the perfor- increase in the relative performance of SSMBLG5- mance of the Concept 1 and 2 laboratory bridges, No.6Bars compared to SSMBLG1-Control1, in which provided more realistic boundary conditions which the only nominal difference was the larger in the longitudinal joint region above the precast bars in the former specimen. Because the increased flanges. In this study, it was found that the 9-in. max- performance observed in SSMBLG5-No.6Bars, 15