Adjacent precast prestressed concrete box girder bridges transversely post-tensioned at top flanges only
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Date
2021-04
Authors
Labib, Shady Nasry Badie
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Abstract
Adjacent precast, prestressed concrete box girders are widely used in short and medium span bridges in North America. Adjacent box girders are connected at their interface using partial- or full-depth grouted shear keys. Typically, transverse post-tensioning (TPT) is applied through diaphragms at discrete locations along the bridge span to improve the transverse load distribution and control differential deflections. Nevertheless, diaphragms only reduce the differential deflection between girders and do not eliminate it. In addition, the provision of transverse diaphragms is associated with an increased cost and time. The main objective of this research program is to investigate the feasibility of eliminating the transverse diaphragms by applying TPT in the top flange of the girders. The effect of applying TPT in the top flange of the girders, instead of being accommodated in discrete rigid diaphragms, on the transverse load distribution is studied.
The research program comprised two phases: experimental and numerical. The experimental phase consisted of four different tests on a one-third scale bridge model, (1) Strain distribution test – uncracked shear key, (2) Load distribution test – uncracked shear key, (3) Load distribution test – cracked shear key, and (4) Ultimate load test. On the other hand, the numerical phase included the construction of a finite element model (FEM) to validate the experimental results of the tested bridge. The validated FEM was then used to study the influence of varying several parameters including the presence of concrete topping, wheel load location and the width of the bridge on the transverse load distribution behavior of box girder bridges.
Results demonstrated the efficiency of distributing the TPT force at a shorter spacing along the length of the bridge in producing the minimum required concrete prestress. In addition, the influence of TPT force and spacing on the transverse load distribution behavior was found insignificant during the simulated service condition (fully-intact or partially-cracked shear keys). However, at failure, the presence of TPT added redundancy to the bridge model and mitigated any sudden failure when shear keys were fully cracked. Furthermore, the presence of concrete topping reduced mid-span deflection up to 25%.
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Keywords
Adjacent box girders; Transverse post-tension; Diaphragm; Shear key; Prestress, Finite-element analysis
Citation
Labib, S., El-Gendy, M., and El-Salakawy, E. (2021). “Adjacent Concrete Box Girders Transversely Post-Tensioned at Top Flanges Only: Experimental Investigation." ASCE, Journal of Bridge Engineering, 26(4): 04021017. DOI: 10.1061/(ASCE)BE.1943-5592.0001699.