Improving the accuracy of camber predictions for precast pretensioned concrete beams.

PDFTech Reporthttp://ntl.bts.gov/lib/55000/55600/55683/IADOT_TR_625_InTrans_Honarvar_Improving_Camber_Predictions_Precast_Pretensioned_Concrete_Beams_Appendices_2015.pdfIHRB Project TR-625InTrans Project 11-390CurvaturePrecast concretePrestressed concreteBeamsAccuracyCreepShrinkageFinite element methodThermal analysisIowaIowa State University. Institute for TransportationHonarvar, EbadollahNervig, JamesHe, WenjunSritharan, SriRouse, Jon MattIowa State University. Bridge Engineering CenterIowa. Highway Research BoardUS Transportation CollectionThe discrepancies between the designed and measured camber of precast pretensioned concrete beams (PPCBs) observed by theIowa DOT have created challenges in the field during bridge construction, causing construction delays and additional costs. Thisstudy was undertaken to systematically identify the potential sources of discrepancies between the designed and measured camberfrom release to time of erection and improve the accuracy of camber estimations in order to minimize the associated problems inthe field.To successfully accomplish the project objectives, engineering properties, including creep and shrinkage, of three normalconcrete and four high-performance concrete mix designs were characterized. In parallel, another task focused on identifying theinstantaneous camber and the variables affecting the instantaneous camber and evaluated the corresponding impact of this factorusing more than 100 PPCBs. Using a combination of finite element analyses and the time-step method, the long-term camber wasestimated for 66 PPCBs, with due consideration given to creep and shrinkage of concrete, changes in support location andprestress force, and the thermal effects.Utilizing the outcomes of the project, suitable long-term camber multipliers were developed that account for the time-dependentbehavior, including the thermal effects. It is shown that by using the recommended practice for the camber measurementstogether with the proposed multipliers, the accuracy of camber prediction will be greatly improved. Consequently, it is expectedthat future bridge projects in Iowa can minimize construction challenges resulting from large discrepancies between the designedand actual camber of PPCBs during construction