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From page 82... ... 83 Chapter 5 PCSSS: Large-Scale Laboratory Bridge Investigation of System Behavior 5.0 Introduction The performance of the precast composite slab span system in a global sense depends on the interaction between neighboring precast panels as well as panels in the adjacent spans. This interaction between components of the PCSSS warranted the development of two large-scale laboratory test specimens constructed and tested in the University of Minnesota Structures Laboratory. Read the entire page →
From page 83... ... 84 concrete considered in the calculation was taken as that between the top of the precast flanges and the top of the section. An illustration of the area of steel and concrete considered for the calculation of the reinforcement ratio for transverse load transfer is highlighted in yellow in Figure 5.1.1. Read the entire page →
From page 84... ... 85 Figure 5.1.2: Reinforcement and depth of concrete considered in the calculation of the reinforcement ratio for reflective crack control (highlighted in yellow) Read the entire page →
From page 85... ... 86 flange surface was used in Span 1. The smooth flange was designed to reduce the stress concentration above the flanges directly at the joint, as well as aid in the removal of the formwork during fabrication. Read the entire page →
From page 86... ... 87 Figure 5.1.3: Bursting reinforcement details used in the Concept 1 laboratory specimen. Configuration numbers correspond to the discussion on bursting in Section 4.5 Read the entire page →
From page 87... ... 88 A simplified plan view of the Concept 1 laboratory bridge, including support locations and relevant dimensions is included in Figure 5.1.4; the transverse reinforcement near the longitudinal precast joint region is not shown for clarity. The reinforcement present in each unique cross section (i.e., east, west, or midspan) Read the entire page →
From page 88... ... 89 Figure 5.1.5: Cross section and individual reinforcement details for the east end of precast beam 1N Read the entire page →
From page 89... ... 90 Figure 5.1.6: Cross section and individual reinforcement details for west end of precast beam 1N Read the entire page →
From page 90... ... 91 Figure 5.1.7: Cross section and individual reinforcement details for midspan of precast beam 1N Read the entire page →
From page 91... ... 92 Figure 5.1.8: Elevation and plan views of reinforcement layout for precast beam 1N Read the entire page →
From page 92... ... 93 Figure 5.1.9: Cross section and individual reinforcement details for east end of precast beam 1S Read the entire page →
From page 93... ... 94 Figure 5.1.10: Cross section and individual reinforcement details for west end of precast beam 1S Read the entire page →
From page 94... ... 95 Figure 5.1.11: Cross section and individual reinforcement details for midspan of precast beam 1S Read the entire page →
From page 95... ... 96 Figure 5.1.12: Elevation and plan views of reinforcement layout for precast beam 1S Read the entire page →
From page 96... ... 97 Figure 5.1.13: Cross section and individual reinforcement details for east end of precast beam 2N Read the entire page →
From page 97... ... 98 Figure 5.1.14: Cross section and individual reinforcement details for west end of precast beam 2N Read the entire page →
From page 98... ... 99 Figure 5.1.15: Cross section and individual reinforcement details for midspan of precast beam 2N Read the entire page →
From page 99... ... 100 Figure 5.1.16: Elevation and plan views of reinforcement layout for precast beam 2N Read the entire page →
From page 100... ... 101 Figure 5.1.17: Cross section and individual reinforcement details for east end of precast beam 2S Read the entire page →
From page 101... ... 102 Figure 5.1.18: Cross section and individual reinforcement details for west end of precast beam 2S Read the entire page →
From page 102... ... 103 Figure 5.1.19: Cross section and individual reinforcement details at midspan of precast beam 2S Read the entire page →
From page 103... ... 104 Figure 5.1.20: Elevation and plan views of reinforcement layout for precast beam 2S Read the entire page →
From page 104... ... 105 Figure 5.1.21: Photograph of the Concept 1 laboratory bridge shortly after completion of the continuity pour The reinforcement ratios for each span were not identical because of the reduction in the flange thickness in Span 1. The reinforcement ratio for transverse load transfer and crack control in Span 2 (which was similar to the Center City Bridge) Read the entire page →
From page 105... ... 106 restraint, and therefore simulate a roller connection. Lateral stability at the end supports was provided via bracing between the wide flange sections and the strong floor, as shown in Figure 5.1.22. Read the entire page →
From page 106... ... 107 threaded into the anchors embedded in the precast sections. The development length of the straight bars was calculated to be 28.5 in. Read the entire page →
From page 107... ... 108 Figure 5.1.23: Threaded connection and adjacent termination detail of straight bars in east half span of the Concept 2 laboratory bridge specimen Figure 5.1.24: Conceptual section illustrating continuous nature of embedded reinforcement utilized in conjunction with mechanical anchors when threaded transverse reinforcement is present; figure shown represents configuration in east half span of the Concept 2 laboratory bridge specimen (transverse reinforcement in joint region to be mechanically anchored to reinforcement in precast web is not shown) Read the entire page →
From page 108... ... 109 As for the Concept 1 specimen, a supplementary cage was used in the joint region to control potential reflective cracks that could originate over the longitudinal joint between the adjacent precast flanges. The reinforcement cage in the Concept 2 laboratory bridge was reduced in size to No. Read the entire page →
From page 109... ... 110 horizontal shear stress that was expected to be developed in the Concept 2 laboratory bridge was unlikely to result in loss of composite action. A simplified plan view of the Concept 2 laboratory bridge specimen, including support locations and relevant dimensions is included in Figure 5.1.25; the transverse reinforcement near the longitudinal precast joint region is not shown for clarity. Read the entire page →
From page 110... ... 111 Figure 5.1.26: Cross section and individual reinforcement details for the east end of the precast beam 1N in the Concept 2 laboratory bridge specimen Read the entire page →
From page 111... ... 112 Figure 5.1.27: Cross section and individual reinforcement details for the west end of the precast beams 1N and 1S in the Concept 2 laboratory bridge specimen Read the entire page →
From page 112... ... 113 Figure 5.1.28: Cross section and individual reinforcement details at midspan of precast beam 1N in the Concept 2 laboratory bridge specimen Read the entire page →
From page 113... ... 114 Figure 5.1.29: Elevation and plan views of the reinforcement layout for precast beam 1N in the Concept 2 laboratory bridge specimen Read the entire page →
From page 114... ... 115 Figure 5.1.30: Cross section and individual reinforcement details for the east end of the precast beam 1S in the Concept 2 laboratory bridge specimen Read the entire page →
From page 115... ... 116 Figure 5.1.31: Cross section and individual reinforcement details at midspan of precast beam 1S in the Concept 2 laboratory bridge specimen Read the entire page →
From page 116... ... 117 Figure 5.1.32: Elevation and plan views of the reinforcement layout for precast beam 1S in the Concept 2 laboratory bridge specimen Read the entire page →
From page 117... ... 118 Figure 5.1.33: Photograph of the Concept 2 laboratory bridge specimen prior to placement of CIP concrete The Concept 2 laboratory bridge specimen occupied the same space in the University of Minnesota Structures Laboratory as Span 2 of the Concept 1 laboratory bridge specimen. The west end of the Concept 2 laboratory bridge specimen was located a distance of 2 in. Read the entire page →
From page 118... ... 119 The instrumentation layout for the Concept 1 laboratory bridge specimen is shown in Figure 5.1.34 (Smith et al. Read the entire page →
From page 119... ... 120 Figure 5.1.35: Typical instrumentation layout near precast joint in the Concept 1 laboratory bridge specimen The instrumentation layout developed for the Concept 2 laboratory bridge closely followed the original instrumentation plan for the Concept 1 laboratory bridge. Additional transversely oriented instruments were added at the eighth points to allow for increased refinement in detection of the extent of longitudinal reflective cracking. Read the entire page →
From page 120... ... 121 Figure 5.1.36: Instrumentation layout for the Concept 2 laboratory bridge specimen Read the entire page →
From page 121... ... 122 Figure 5.1.37: Typical 9 and 6 gage transverse instrumentation layout in Concept 2 laboratory bridge specimen Figure 5.1.38: Location of origin and definition of positive x and y ordinates for instrumentation layout in the Concept 1 and Concept 2 laboratory bridge specimen Read the entire page →
From page 122... ... 123 5.2. Construction of Laboratory Bridge Specimens and Material Properties Fabrication of the precast panels for both bridges was completed at County Materials in Roberts, Wisconsin. Read the entire page →
From page 123... ... 124 The yield strength of the No. 4 hooked bars that provided transverse reinforcement continuity and crack control reinforcement above the longitudinal joint between the precast panels in the Concept 2 laboratory bridge specimen was found to be approximately 70 ksi through the testing of three representative samples. Read the entire page →
From page 124... ... 125 As discussed in Section 3.2 reflective cracking was observed in two of the three instrumented joints in the Center City Bridge via transversely oriented concrete embedment VW strain gages located at midspan of the center span. Furthermore, cracking in the field bridge was observed to occur during the first spring after construction was completed, revealing the potential for reflective cracking to be present during the majority of the service life for the precast composite slab span system (PCSSS) Read the entire page →
From page 125... ... 126 Figure 5.3.1: 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 Figure 5.3.2: Placement of patch loads during fatigue loading and extension of longitudinal reflective cracking for the Concept 2 laboratory bridge specimen Read the entire page →
From page 126... ... 127 The vertical location of the transversely oriented concrete embedment resistive strain gages varied between each span of the Concept 1 laboratory bridge and the Concept 2 laboratory bridge due to the variations in the thickness of the precast flange and the vertical depth of the transverse reinforcement traversing the longitudinal precast joint. The measured vertical locations of the bottommost layers of transversely oriented strain gages that were monitored during initiation of cracking in the laboratory bridge specimens, as well as the relative instrumentation in the Center City Bridge, are given in Table 5.3.1. Read the entire page →
From page 127... ... 128 The largest strain that was developed in the west quarter point of the Concept 2 laboratory bridge was 85 µε, when a total load of 210 kips was applied to a spreader beam and a transverse strain of 150 µε was measured at the east quarter point. A second million cycles of fatigue loading were subsequently completed on each specimen after reflective cracking was introduced in each section. Read the entire page →
From page 128... ... 129 (a) Concept 1 Span 1; patch load at midspan (b) Read the entire page →
From page 129... ... 130 Good fatigue behavior was observed for both the Concept 1 and Concept 2 laboratory bridge specimens. No significant degradation of the joint was observed. Read the entire page →
From page 130... ... 131 fluctuations, assuming that a total of 150 days a year were expected to induce considerable thermal gradients. Each of the three test spans were subjected to similar levels of transverse strains throughout the testing procedure. Read the entire page →
From page 131... ... 132 load, spreader load, or both (in which case the order shown is that applied to the specimen) during the quasi-static cracking process. Read the entire page →
From page 132... ... 133 the outer (i.e., east) quarter point of Span 2, however the crack was not observed to have extended to the instrumentation at the interior quarter point, which may have been attributed to transverse restraint provided by the proximity to the nearby interior support. Read the entire page →
From page 133... ... 134 Table 5.3.5: Measured load and transverse strain, and number of cycles completed during environmental effect simulation on Span 2 of the Concept 1 laboratory bridge specimen Concept 1, Span 2 Prior to cracking at 1M cycles of fatigue load After cracking at 1M cycles of fatigue load After cracking to target strain of 160µε After cycling to target strain of 160µε After cycling to enviro. strain level A After cycling to enviro. Read the entire page →
From page 134... ... 135 of a spreader beam during two separate load cycles, the first with bearing points symmetrically located 2.5 ft. from midspan, and the second with bearing points symmetrically located 5 ft. Read the entire page →
From page 135... ... 136 Table 5.3.6: Measured load and transverse strain, and number of cycles completed during environmental effect simulation on Span 1 of the Concept 1 laboratory bridge specimen Span 1, Concept 1 Prior to cracking at 1M cycles of fatigue load After cracking at 1M cycles of fatigue load After cracking to enviro. strain level A After cycling to enviro. Read the entire page →
From page 136... ... 137 a quasi-static load controlled load test, however the transverse strains measured at the midspan cross section reached the target values prior to the indication of the cracking at the west quarter point, and therefore no additional load was applied in this modified setup. The lack of observed cracking was attributed to three possible explanations. Read the entire page →
From page 137... ... 138 Figure 5.3.6: Transverse strains measured with 35 kip patch load applied at quarter points during environmental effect simulation in the Concept 2 laboratory bridge 0 20 40 60 80 100 120 Tr an sv er se S tr ai n [u e] Mid-Span Outer (east) Read the entire page →
From page 138... ... 139 Table 5.3.7: Measured load and transverse strain, and number of cycles completed during environmental effect simulation at the quarter points of the Concept 2 laboratory bridge specimen Concept 2, load applied at quarter points Prior to cracking at 1M cycles of fatigue load After cracking at 1M cycles of fatigue load After cracking to enviro. strain level A After cycling to enviro. Read the entire page →
From page 139... ... 140 midspan tests, with the revised target strain to be the maximum transverse strain measured at the quarter points (i.e., 253µε at the east quarter point) Read the entire page →
From page 140... ... 141 Table 5.3.8: Measured load and transverse strain, and number of cycles completed during environmental effect simulation at midspan of the Concept 2 laboratory bridge specimen Concept 2, load applied at midspan Prior to cracking at 1M cycles of fatigue load After cracking at 1M cycles of fatigue load After cracking to enviro. strain level A After cycling to enviro. Read the entire page →
From page 141... ... 142 Figure 5.3.8: Transverse strains measured at midspan under the 35 kip patch load applied at midspan during the 15,000 cycles completed during the environmental effect simulation In summary, Span 2 of the Concept 1 laboratory bridge showed excellent crack control during the cycling procedure at the environmental simulation strain level B, which corresponded to a measured value of approximately 233µε. Span 1 of the same bridge, which would be expected to have superior crack control capabilities because of the reduced flange depth, showed a degradation of the joint under the same target strain level, which corresponded to an approximate transverse strain of 303µε. Read the entire page →
From page 142... ... 143 inelastic strains during the load tests. Because the forensic exam was conducted following the tests, the cracks may have closed due to the load removal. Read the entire page →
From page 143... ... 144 (a) Load placement during transverse load distribution tests for Concept 1 laboratory bridge (b) Read the entire page →
From page 144... ... 145 Figure 5.3.10: Longitudinal curvature in north and south panels in Span 2 of Concept 1 laboratory bridge under 35 kip patch load applied at midspan centered over south panel The curvature at each data point was calculated using three longitudinally oriented strain gages in a vertical line. The coefficient of variation (R2) Read the entire page →
From page 145... ... 146 Figure 5.3.11: Longitudinal curvature in north and south panels in Concept 2 laboratory bridge under 35 kip patch load applied at the quarter points centered over south panel. The longitudinal curvatures were observed to increase in the Concept 2 laboratory bridge. Read the entire page →
From page 146... ... 147 specification (2004) , the maximum stirrup spacing at the ends of the precast beam was 15 in., which could be reduced to 24 in. Read the entire page →
From page 147... ... 148 laboratory. For this reason, load tests were conducted on each span to determine the maximum capacity of each specimen, and subsequently to determine whether composite action was maintained throughout each test. Read the entire page →
From page 148... ... 149 Figure 5.3.13: Photograph of tri-actuator load setup and transverse loading beam utilized during ultimate load tests; shown for the Concept 2 laboratory bridge test The calculation of the sectional ultimate moment capacity for each span was completed using Response2000. The assumed tensile strength of the prestressing strand was taken to be 270 ksi, the yield strength of the mild reinforcement as 60 ksi, and the concrete compressive strain at crushing was assumed to be 0.003. Read the entire page →
From page 149... ... 150 A numerical analysis of the continuous two-span Concept 1 laboratory bridge suggested that the ultimate capacity of the specimen would not be reached, as the maximum load available during the Concept 1 ultimate tests was approximately 420 kips, which corresponded to an applied maximum moment of 1272 ft.-kips, which was considerably less than the ultimate sectional capacities of either Span 1 or 2. The continuous bridge was modeled as a three-span system, with the center span modeled with an 18 in. Read the entire page →
From page 150... ... 151 (i.e., the CIP top section and the precast bottom section) Read the entire page →
From page 151... ... 152 Figure 5.3.14: Longitudinal strains measured through the section depth at midspan of north panel 20 in. from precast joint with 458 kip applied Load in Concept 2 laboratory bridge specimen The compression force developed in the section was calculated by integrating the stress profile using the measured strain profile and assuming the modified Kent and Park (Park et al., 1982) Read the entire page →
From page 152... ... 153 5.4. Destructive Testing of Large-Scale Laboratory Specimens At the conclusion of the tests, cores were taken at locations of interest through the laboratory bridge specimens to investigate the location and extent of cracks that were believed to have developed during the tests based on the strain measurements. Read the entire page →
From page 153... ... 154 Figure 5.4.1: Location of reference line for measurement of vertical location of cracking in core specimens Core samples were extracted from both spans of the Concept 1 large-scale laboratory bridge. A total of five cores were removed from Span 1, while four cores were extracted from Span 2. Read the entire page →
From page 154... ... 155 Table 5.4.2: Summary of maximum height and width of cracks measured in core specimens from the Concept 1 laboratory specimen Specimen x-Coordinate of Core (in.) Read the entire page →
From page 155... ... 156 Table 5.4.3: Summary of maximum height and width of cracks measured in core specimens from the Concept 2 laboratory specimen Specimen x-Coordinate of Core (in.) y- Coordinate of Core (in.) Read the entire page →
From page 156... ... 157 5.4.2. Visual Inspection of Internal Surfaces after Sectioning the Laboratory Bridge Specimens by Means of Saw Cutting Capacity constraints of the overhead crane system present in the University of Minnesota Structures Laboratory necessitated that both the Concept 1 and Concept 2 laboratory specimens be split into segments of no more than 30,000 lbs in total weight for removal. Read the entire page →
From page 157... ... 158 of delamination at the horizontal interface was observed in all cross-sectional cuts, regardless of the presence of the smooth or roughened precast flange. No evidence of delamination or cracking was observed at the vertical PC web interface on any of the cut surfaces of the Concept 1 laboratory bridge. Read the entire page →
From page 158... ... 159 Figure 5.4.4: Concept 2 laboratory bridge specimen partitioning for saw cutting procedure Evidence of reflective cracking was not observed in any of the cross sections in the Concept 2 laboratory bridge specimen. As observed in the Concept 1 laboratory bridge specimen, some delamination of the horizontal PC – CIP interface was observed at midspan on both the west face of panel 3 and the east face of panel 2, as illustrated in Figure 5.4.5. Read the entire page →
From page 159... ... 160 Figure 5.4.6: Evidence of diagonal cracking in the trough region on the east face of panel 2 in the Concept 2 laboratory bridge PC flange interface Diagonal crack Corner of PC web Cage reinforcement Read the entire page →
From page 160... ... 161 Figure 5.4.7: Close up view of diagonal crack identified on east face of panel 2 in the Concept 2 laboratory bridge Precast – CIP interface Diagonal cracking Read the entire page →

From page 82...

... 83 Chapter 5 PCSSS: Large-Scale Laboratory Bridge Investigation of System Behavior 5.0 Introduction The performance of the precast composite slab span system in a global sense depends on the interaction between neighboring precast panels as well as panels in the adjacent spans. This interaction between components of the PCSSS warranted the development of two large-scale laboratory test specimens constructed and tested in the University of Minnesota Structures Laboratory.