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From page 161... ... 162 Chapter 6 PCSSS: Subassemblage Investigation of Crack Control Reinforcement 6.0 Introduction Seven specimens were designed to investigate the effect of spacing, size, and placement of transverse reinforcement on the development and propagation of reflective cracking in the precast composite slab span system. This chapter describes the design and cracking behavior of these seven subassemblage specimens. Read the entire page →
From page 162... ... 163 The subassemblage specimens were designed to provide insight into the relative performance of variations in the transverse reinforcement details for crack control and load transfer. For this reason, the specimen designs were limited to the transverse reinforcement selection. Read the entire page →
From page 163... ... 164 Table 6.1.1: Subassemblage specimen design details Specimen Identification Width Depth Transverse Bars (Load Trans.) Cage (Crack Control) Read the entire page →
From page 164... ... 165 Figure 6.1.1: Elevation and plan views of subassemblage specimen. The x-axis was aligned along the North direction and corresponded with the longitudinal joint. Read the entire page →
From page 165... ... 166 Figure 6.1.2: Photograph of deck reinforcement utilized for the subassemblage specimens 6.1.1. Subassemblage 1 – Control Specimen 1 The first subassemblage was deemed the control specimen because it had detailing similar to that of the transverse hooked reinforcement in the Concept 2 laboratory bridge specimen. Read the entire page →
From page 166... ... 167 Figure 6.1.3: Layout for SSMBLG1-Control1, SSMBLG3-HighBars, SSMBLG4-Deep, SSMBLG5-No.6Bars, and SSMBLG7-Control2. Transverse hooked bars are shown in blue; cage reinforcement is shown in green 6.1.2. Read the entire page →
From page 167... ... 168 Figure 6.1.4: Layout for SSMBLG2-NoCage. Transverse hooked bars are shown in blue 6.1.3. Read the entire page →
From page 168... ... 169 An elevation view of SSMBLG3-HighBars with the increased depth of the deck is shown in Figure 6.1.5. The reinforcement ratios for crack control and load transfer were equal to 0.0031 and 0.0010, respectively. Read the entire page →
From page 169... ... 170 Figure 6.1.6: Failure of SSMBLG3-HighBars due to fracture of the transverse hooked reinforcement near the CIP - precast web interface 6.1.4. Subassemblage 4 – Increased Depth of Precast Section As the span length of the PCSSS increases, the depth of the precast section also needs to increase in order to meet stress requirements at transfer and service. Read the entire page →
From page 170... ... 171 6.1.5. Subassemblage 5 – Increased Transverse Hook Size The size of the reinforcement used for transverse load transfer must be sufficient to provide adequate flexural capacity after cracking. Read the entire page →
From page 171... ... 172 The reinforcement design for SSMBLG6-Frosch was selected such that the transverse reinforcement for load transfer (i.e., hooked bars protruding from the precast webs) was identical to that of the control specimen. Read the entire page →
From page 172... ... 173 6.1.7. Subassemblage 7 – Control Specimen 2 The seventh subassemblage specimen was originally designed to provide means to investigate a debonded flange surface. Read the entire page →
From page 173... ... 174 in., and the two respective bars from the opposite member were spaced at slightly less than 18 in., however the center to center distance between adjacent sets of transverse hooked bars remained constant, at 18 in. Figure 6.1.9: Photograph of SSMBLG7-Control2 to illustrate manufacturing error in placement of transverse hooked bars 6.2. Read the entire page →
From page 174... ... 175 specimen. The instrumentation layout for the subassemblage specimens is shown in Figure 6.2.1. Read the entire page →
From page 175... ... 176 locations between adjacent transverse hooked bars. The instrumentation at the origin face of SSMBLG7Control2, which was representative of all specimens, is shown in Figure 6.2.2. Read the entire page →
From page 176... ... 177 No.6Bars, which was instrumented with LVDTs with a nominal range of ±0.1 in. (referred to as LVDT050 or LVDT100 hereafter) Read the entire page →
From page 177... ... 178 Figure 6.2.4: LVDT layout on origin face of SSMBLG6-Frosch. Vertical line above precast joint is shown by series of dots; measurements were taken from bottom of the precast chamfer 6.3. Read the entire page →
From page 178... ... 179 in the longitudinal clamping members, which tended to concentrate the compressive force at the ends of the members. This served to better simulate the effects of restraint in the bridge system (i.e., clamping the subassemblage specimens near the ends simulated the effect of the bridge supports transverse to the longitudinal joint, and relieved the compressive stress across the subassemblage) Read the entire page →
From page 179... ... 180 Figure 6.3.2: Section view of clamping assembly and subassemblage specimen, parallel to joint, illustrating exaggerated curvature of L-section (top) and wide flange section (bottom) Read the entire page →
From page 180... ... 181 Figure 6.3.3: Separation of East precast section from CIP concrete during testing of SSMBLG3-HighBars before the implementation of the vertical clamping assembly Separation at the precast – CIP interface Read the entire page →
From page 181... ... 182 Figure 6.3.4: Clamping system used to provide rotational restraint of the precast members from the CIP concrete during the subassemblage tests and loading apparatus consisting of 1 in. HSS and neoprene bearing pad 6.4. Read the entire page →
From page 182... ... 183 from the third truck. All the specimens were prewetted with water and allowed to reach a surface dry condition prior to the placement of the CIP concrete. Read the entire page →
From page 183... ... 184 Table 6.4.2: Measured subassemblage CIP concrete material properties on first day of specimen testing Specimen # Description CIP age on 1st day of testing fc [psi] Read the entire page →
From page 184... ... 185 Table 6.5.1: Subassemblage specimen measured modulus of rupture and predicted cracking moment and load Specimen # Description ft [psi] MCR-pred [in-kip] Read the entire page →
From page 185... ... 186 tabulated and plotted as percentages of the predicted cracking load. The use of 55 percent of the observed cracking load was selected to provide an adequately small base level (i.e., small enough such that initial cracking was reasonably expected not to have occurred prior to exceeding the base level load) Read the entire page →
From page 186... ... 187 Table 6.5.2: Subassemblage loading plan for example specimen with predicted cracking load of 40 kips Predicted Cracking Load PCR-pred = 40 k Applied load when cracking was observed PCR-meas= 24 k ( = 60% of PCR-pred) Read the entire page →
From page 187... ... 188 6.5.1. Data Acquisition The primary instrumentation utilized during the subassemblage tests were resistive-type concrete embedment strain gages and LVDTs, and also included a single transversely oriented concrete embedment VW gage. Read the entire page →
From page 188... ... 189 6.6.1. Transverse Strains Near Joint Region due to Shrinkage and Handling of Subassemblage Specimens The transverse strain near the joint region was monitored during the curing process, as well as during handling of the specimens, to provide an estimate of the state of strain near the joint at the initiation of load testing. Read the entire page →
From page 189... ... 190 Figure 6.6.1: Measured transverse mechanical strains in the subassemblage specimens based on the number of days after the placement of the CIP concrete The sign of the transverse strain data remained "compressive" indicating shortening or shrinkage throughout the curing and handling periods for each specimen. No evidence of cracking was visually observed on either the origin or end faces of the specimens after placement of each subassemblage into the load frame. Read the entire page →
From page 190... ... 191 6.6.2. In the discussion regarding visually measured crack widths and lengths in the following sections, the crack width was taken to be equal to the largest observed crack on each face when two cracks were present (i.e., when the load was large enough such that a second crack had formed) Read the entire page →
From page 191... ... 192 In some cases, at loads near the maximum applied to each specimen, diagonal cracking was also observed in the CIP region, initiating at the outside edge of the bottom wide flange section of the clamping assembly, and extending to the vertical precast web-CIP interface, as noted in Figure 6.6.3. Figure 6.6.3: Photograph of cracking near the vertical precast web-CIP interface, including cracking through the precast flange and diagonal cracking due to the clamping assembly in SSMBLG6-Frosch 6.6.3. Read the entire page →
From page 192... ... 193 The detail near the joint and location of crack measurement is shown in Figure 6.6.4. A representative image of the crack width measurement is shown in Figure 6.6.5. Read the entire page →
From page 193... ... 194 Figure 6.6.5: Measurement of crack width during subassemblage testing Because the performance of the transverse hooked bars and cage reinforcement was of primary interest in the subassemblage specimens, and the presence of cracking near the vertical precast web face was undesirable and could have an influence on the crack width measurement above the longitudinal joint between the precast flanges, the observed crack widths were tabulated up to and including the load step in which the first crack or separation of the vertical precast web was observed. Figure 6.6.6 shows the width of the crack observed near the joint on the origin face before each set of cycles in the selected specimens. Read the entire page →
From page 194... ... 195 SSMBLG6-Frosch was consistently loaded to higher levels of load in comparison with some of the other test specimens. This was also the case for the SSMBLG5-No.6Bars, for which results are not present in Figure 6.6.6 because crack width measurements were not recorded on the origin face of that specimen. Read the entire page →
From page 195... ... 196 improved overall PCSSS because if a reflective crack would initiate at the vertical precast web-CIP concrete interface, the cage reinforcement would not contribute to the crack control resistance. The only reinforcement crossing such a crack would be the transverse hooked bars protruding from the precast webs. Read the entire page →
From page 196... ... 197 Figure 6.6.7: Maximum1 crack widths measured on the end face2 1Maximum crack width was measured at the horizontal precast flange -CIP interface; and in the case of SSMBLG6-Frosch, where two vertical cracks were observed at high loads, the largest crack width was recorded 2Reinforcement spacing from end face of specimen was half of the maximum reinforcement spacing of selected specimens before each set of cycles According to Figure 6.6.7, SSMBLG5-No.6Bars, SSMBLG6-Frosch, and SSMBLG7-Control2 appeared to outperform the other specimens, especially at higher levels of load in the case of SSMBLG6-Frosch and SSMBLG7-Control2. Also, in the case of SSMBLG6-Frosch, recall two vertical cracks were observed on each face of the specimen, which was generally preferred because the development of many, smaller cracks is often favored to the development of few, larger cracks, especially when the ingress of water and corrosive materials are of concern. Read the entire page →
From page 197... ... 198 the other specimens due to the increase in member depth while the section contained similar reinforcement details as were used in the control specimens. The overall performance of the six subassemblage specimens based on the crack widths measured using a crack gage was good. Read the entire page →
From page 198... ... 199 Table 6.6.1: Increase in the measured crack width on the end face as a result of cyclic loading at each load step 1No cracking was visually observed at associated load step 2Measurements were not available at given load step due to error in data collection 3Delamination was observed at vertical precast web – CIP interface The relative performance between each face of a given specimen was also of interest. Each face had reinforcement located a specified distance away. Read the entire page →
From page 199... ... 200 specimens shown other than SSMBLG6-Frosch, the proximity of the reinforcement to the origin face (3.1 in.) was smaller than the proximity of the reinforcement to the end face, and therefore the crack widths on the origin face would be expected to be smaller than those on the end face, resulting in negative values in Figure 6.6.8. Read the entire page →
From page 200... ... 201 6.6.4. Width of Cracking Near Joint Region Measured with LVDTs The origin and end face of each specimen was instrumented with LVDTs oriented across the joint to measure the total displacement, or opening, within their gage lengths. Read the entire page →
From page 201... ... 202 Figure 6.6.9: LVDT displacement measured via the Mid LVDT at the origin face 0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 0 0.005 0.01 0.015 0.02 Pe rc en t o f C ra ck in g Lo ad [% ] Measured Displacement of Mid LVDTs 1-Control1-9" 2-NoCage-18" 4-Deep-9" 5-No.6Bars-9" 6-Frosch-4.5" 7-Control2-9" Read the entire page →
From page 202... ... 203 Figure 6.6.10: LVDT displacement measured via the Mid LVDT at the end face 0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 0 0.005 0.01 0.015 0.02 Pe rc en t o f C ra ck in g Lo ad [% ] Measured Displacement of Mid LVDTs 1-Control1-9" 2-NoCage-18" 4-Deep-9" 5-No.6Bars-9" 6-Frosch-4.5" 7-Control2-9" Read the entire page →
From page 203... ... 204 Table 6.6.2: Maximum crack widths via crack gage (from Section 6.6.3) and LVDT displacements measured on the origin and end faces Specimen Description 1 Percent of predicted cracking load applied2 Origin Face End Face Measured with crack gage Measured with LVDTs Measured with crack gage Measured with LVDTs 1-Control1-9" 100% 0.016 in. Read the entire page →
From page 204... ... 205 Figure 6.6.11: Difference in LVDT displacements between the origin and end face (origin minus end) Read the entire page →
From page 205... ... 206 Figure 6.6.12: Measurement of the length of crack during subassemblage testing. Red dots illustrate path of crack Crack length is approx. Read the entire page →
From page 206... ... 207 Figure 6.6.13: Normalized crack length on the origin face of selected specimens before each set of cycles Figure 6.6.14: Normalized crack length on the end face of selected specimens before each set of cycles 0% 20% 40% 60% 80% 100% 120% 140% 160% 0 0.2 0.4 0.6 0.8 Pe rc en t o f P re di ct ed C ra ck in g Lo ad Normalized Crack Length 1-Control1-9" 2-NoCage-18" 4-Deep-9" 6-Frosch-4.5" 7-Control2-9" 0% 20% 40% 60% 80% 100% 120% 140% 160% 0 0.2 0.4 0.6 0.8 Pe rc en t o f P re di ct ed C ra ck in g Lo ad Normalized Crack Length [in] 1-Control1-9" 2-NoCage-18" 4-Deep-9" 5-No.6Bars-9" 6-Frosch-4.5" 7-Control2-9" Cracked NA location for SSMBLG6-Frosch Cracked NA location for SSMBLG4-Deep Cracked NA location for SSMBLG5-No.6Bars Cracked NA location for SSMBLG4-Deep Read the entire page →
From page 207... ... 208 Table 6.6.3: Predicted locations of the subassemblage cracked section neutral axes Specimen Cracked Section Neutral Axis Depth measured from the compression fiber Normalized Depth of Cracked Section Neutral Axis (measured from bottom of section) 1-Control1 1.74 in. Read the entire page →
From page 208... ... 209 Figure 6.6.15: Difference in normalized crack length between the origin and end face (origin minus end) of selected specimens 6.6.6. Read the entire page →
From page 209... ... 210 Figure 6.6.16: Slope of linear fit line for load versus 1.0 level strain data at middle cross section in SSMBLG1Control1 Cracking was detected in the middle gage (directly over the precast joint) at an applied load of 50 percent of PCR-pred Read the entire page →
From page 210... ... 211 Figure 6.6.17: Slope of linear fit line for load versus 1.5 level strain data at middle cross section in SSMBLG1Control1 Cracking was detected in the middle gage (directly over the precast joint) at an applied load of 50 percent of PCR-pred Read the entire page →
From page 211... ... 212 Figure 6.6.18: Slope of linear fit line for load versus 2.0 level strain data at middle cross section in SSMBLG1Control1 Cracking was detected in the middle gage (directly over the precast joint) at an applied load of 50 percent of PCR-pred Read the entire page →
From page 212... ... 213 Figure 6.6.19: Slope of linear fit line for load versus 1.0 level strain data at origin cross section in SSMBLG1Control1 Cracking was detected in the middle gage (directly over the precast joint) at an applied load of 45 percent of PCR-pred Read the entire page →
From page 213... ... 214 Figure 6.6.20: Slope of linear fit line for load versus 1.5 level strain data at origin cross section in SSMBLG1Control1 The load at which cracking was first observed was taken as the first data point where a clear difference in the slope of the data occurred. For example, in Figure 6.6.16, the crack was assumed to be present at the 1.0 location at the midspan cross section at a load of 50% of the cracking load, with cracking observed only in the gage centered over the joint. Read the entire page →
From page 214... ... 215 Figure 6.6.21 and Figure 6.6.22 illustrate the load at which cracking was observed for each specimen at the gages through the depth at the midspan and origin cross sections, respectively. A specimen exhibiting superior performance would have a steeper slope at each gage level, that is, larger levels of load would be required to drive a crack to a given depth. Read the entire page →
From page 215... ... 216 Figure 6.6.22: Load at which cracking was first observed in gages at origin cross section as determined from strain gages The improved performance of SSMBLG5-No.6Bars and SSMBLG6-Frosch based on the analysis of the strain gage data supported the results from the previous sections. Furthermore, SSMBLG5-No.6Bars outperformed the Frosch specimen as larger levels of load were applied as the crack was driven up towards the top level of instrumentation. Read the entire page →
From page 216... ... 217 to provide a stress field that was constant along the length of the precast joint over which the reinforcement details of each particular specimen could be investigated. Furthermore, uniform loading applied along the structure above the longitudinal joint between the precast elements was necessary to provide an unbiased investigation of the crack mapping completed on the origin and end faces of each specimen, where the influence of the proximity of the embedded reinforcement on surface cracking was monitored. Read the entire page →
From page 217... ... 218 The results of the above analysis for each of the subassemblage specimens are shown in Figures 6.6.24 – 6.6.29. Figure 6.6.23: Strain gage identification utilized for investigation of uniformity of cracking along the length of the precast joint. Read the entire page →
From page 218... ... 219 (a) Load at which cracking was detected at various locations along the length of the precast joint (b) Read the entire page →
From page 219... ... 220 (a) Load at which cracking was detected at various locations along the length of the precast joint (b) Read the entire page →
From page 220... ... 221 (a) Load at which cracking was detected at various locations along the length of the precast joint (b) Read the entire page →
From page 221... ... 222 (a) Load at which cracking was detected at various locations along the length of the precast joint (b) Read the entire page →
From page 222... ... 223 specimens where the internal instrumentation and external visual measurements better correlated in terms of crack initiation. Also observed in SSMBLG5-No.6Bars was that the crack traversed two gages at each of the two multiinstrumented cross sections. Read the entire page →
From page 223... ... 224 (a) Load at which cracking was detected at various locations along the length of the precast joint (b) Read the entire page →
From page 224... ... 225 observations suggest that the relatively large reinforcement ratio provided in SSMBLG6-Frosch (which was accomplished through a tight spacing of No. 3 cage stirrups) Read the entire page →
From page 225... ... 226 precast flanges, as shown in Figure 6.6.29(b) , at roughly the same applied load despite the presence of the smooth surface condition. Read the entire page →
From page 226... ... 227 The predicted tensile reinforcement stress in each specimen is shown in Figure 6.6.30. The vertical axis represents the applied loading, and is given as the ratio of the applied load to the predicted cracking load. Read the entire page →
From page 227... ... 228 Table 6.6.4 summarizes the maximum tensile reinforcement stress predicted for each of the specimens associated with the maximum loads applied during each of the tests. Table 6.6.4: Maximum applied loading and associated predicted tensile reinforcement stresses in subassemblage specimens Specimen Tensile Reinforcement Area, including cage [in2] Read the entire page →
From page 228... ... 229 Figure 6.7.1: Coring locations in subassemblage specimens Each of the core specimens was examined both with the naked eye and the aid of an Olympus SZX12 stereo-microscope to identify the extent of cracking on the core surface. The level of magnification used to examine the cores ranged between 2.1X to 27X, which was the full capacity of the microscope. Read the entire page →
From page 229... ... 230 Table 6.7.1: Crack width classification categories for analysis of core specimens Crack Classification Crack Width (W) Read the entire page →
From page 230... ... 231 Table 6.7.2: Summary of maximum height and width of crack measured in core specimens Specimen Location of Core Maximum height of crack1 Maximum width of crack2 Crack length measured on face3 Crack width measured on face4 (class designation) Origin Face End Face Origin Face End Face 1-Control19" Joint 7.5 in. Read the entire page →
From page 231... ... 232 to develop a Class C crack, crack width larger than 0.023 in., was SSMBLG1-Control1, in which no specific perturbation in the history of the specimen was known to be the cause. Cracking or separation of the CIP concrete at the vertical precast web interface was observed on nearly every specimen. Read the entire page →

From page 161...

... 162 Chapter 6 PCSSS: Subassemblage Investigation of Crack Control Reinforcement 6.0 Introduction Seven specimens were designed to investigate the effect of spacing, size, and placement of transverse reinforcement on the development and propagation of reflective cracking in the precast composite slab span system. This chapter describes the design and cracking behavior of these seven subassemblage specimens.