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From page 21... ... 22 Chapter 3 PCSSS: Background 3.0 Introduction to Background Interest in the development of precast composite slab span system (PCSSS) bridges in Minnesota led to research on the topic at the University of Minnesota prior to the initiation of the NCHRP 10-71 project. Read the entire page →
From page 22... ... 23 others who should be contacted. The respondents represent bridge engineers (including many individuals who serve as State Bridge Engineers) Read the entire page →
From page 23... ... 24 designed and thought out. The overwhelming consensus that durability was a primary concern regarding the PCSSS was a major driver in the fact that the control of reflective cracking was an essential objective of the project. Read the entire page →
From page 24... ... 25 webs was reinforced with typical deck reinforcement in both the longitudinal and transverse directions. The plan view and construction stages of the Center City Bridge are shown in Figure 3.2.1. Read the entire page →
From page 25... ... 26 Figure 3.2.2: Anticipated locations of reflective cracking in Mn/DOT PCSSS (Bell et al. Read the entire page →
From page 26... ... 27 transverse hooks, contained five gages, while the upper row, placed just above the precast web consisted of ten gages. The instrumentation layout, which was identical at each of the instrumented joints, is shown in Figure 3.2.4. Read the entire page →
From page 27... ... 28 Figure 3.2.5: Lower level of concrete embedment and spot-weldable VW gages utilized in observation of reflective cracking in the Center City Bridge Furthermore, the bridge was instrumented with longitudinally oriented spot-weldable gages to investigate the behavior of the structure in terms of longitudinal live load distribution over a continuous pier. Because of symmetry, only one pier was considered, as shown in Figure 3.2.1. Read the entire page →
From page 28... ... 29 Figure 3.2.6: Plan view of longitudinal instrumentation locations for investigation of live load distribution over the continuous pier (Bell et al. Read the entire page →
From page 29... ... 30 analyzed. Due to the different values of the coefficient of thermal expansion between the concrete itself and the steel wire inside of the concrete embedment VW gages, taken to be 5.67 µε/°F and 6.78 µε/°F, respectively, a correction based on the difference between the values of the coefficients of thermal expansion was required to determine the mechanical strain, which was calculated as shown in Eqn. Read the entire page →
From page 30... ... 31 19-Sep-2005 11-Mar-2006 03-Sep-2006 26-Feb-2007 21-Aug-2007 13-Feb-2008 06-Aug-2008 29-Jan-2009 24-Jul-2009 -200 0 200 400 600 S tr ai n ( 10 -6 in /in ) Read the entire page →
From page 31... ... 32 of the design assumptions made with respect to transverse live load distribution and continuity over the shared piers. A total of seven single truck and five paired truck configurations were selected for the truck tests, however due to time constraints associated with the single night test, the various configurations were prioritized, with the authors designating the primary test configurations with numbers, and the secondary configurations with letters. Read the entire page →
From page 32... ... 33 (a) Single truck positions (b) Read the entire page →
From page 33... ... 34 had the rear tandem of the two trucks spaced laterally at 12 ft. on center at midspan of the center span. Read the entire page →
From page 34... ... 35 the relative values of transverse strain observed during the live load truck tests were significantly less than the daily strain fluctuations observed in the same Joints during the long term observation, where, as discussed in Section 3.2, daily transverse strain fluctuations of more than 220 µε were observed. This suggests that transverse strains induced due to thermal gradients can be an order of magnitude larger than those observed due to traffic loading, and therefore should be considered carefully in the design of precast composite slab span systems. Read the entire page →
From page 35... ... 36 Hook End Center Embedded End Embedded End Hook End Off-Center Off-Center 0 2 4 6 8 10 12 14 16 -8 -6 -4 -2 0 2 4 6 8 Transverse Distance from Joint (in) Read the entire page →
From page 36... ... 37 City Bridge. The authors included the parapets in their model, however found that the results were affected only locally by the parapets, and therefore were able to superimpose the data for each of the six configurations onto the single plot. Read the entire page →
From page 37... ... 38 slab span systems. It can be assumed that longer spans would behave similarly because they would have a deeper overall section, and the height of the gap at the flange tips would be unchanged, so longer span bridges should behave more like monolithic systems than shorter ones. Read the entire page →
From page 38... ... 39 (a) Negative restraint moment induces tension near the top surface at the pier (b) Read the entire page →
From page 39... ... 40 was observed] should not have varied significantly from the previous day, researchers speculated thermal effects may have played a role in the crack development. Read the entire page →
From page 40... ... 41 Figure 3.3.2: Ratio of 20-year positive restraint moment (due to time-dependent effects only) to cracking moment comparison 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0 15 30 45 60 75 90 Precast Age at Continuity (days) Read the entire page →
From page 41... ... 42 Figure 3.3.3: Ratio of 20-year positive restraint moment (due to time-dependent and thermal effects) to cracking moment comparison AASHTO (2010) Read the entire page →
From page 42... ... 43 where α is the coefficient of thermal expansion, T(y) is the temperature gradient (°F) Read the entire page →
From page 43... ... 44 Figure 3.3.4: Comparison of calculated and TPbeam results for ratio of 20-year restraint moment (due to thermal effects only) to cracking moment The magnitude of the positive restraint moments, with the inclusion of the effects of thermal gradient, may negate any benefit from continuity at service. Read the entire page →

From page 21...

... 22 Chapter 3 PCSSS: Background 3.0 Introduction to Background Interest in the development of precast composite slab span system (PCSSS) bridges in Minnesota led to research on the topic at the University of Minnesota prior to the initiation of the NCHRP 10-71 project.