Shearing in High Strength Concrete Bridge Girders: Technical Report

TLDR: In this article, a semi-empirical equation was developed at the University of Houston (UH) to predict the shear strength of reinforced concrete I-girders with normal strength concrete through the project Texas Department of Transportation (TxDOT) 0-4759.

Abstract: Prestressed Concrete (PC) I-girders are used extensively as the primary superstructure components in Texas highway bridges. A simple semi-empirical equation was developed at the University of Houston (UH) to predict the shear strength of PC I-girders with normal strength concrete through the project Texas Department of Transportation (TxDOT) 0-4759. The UH-developed equation is a function of shear span to effective depth ratio, concrete strength, web area and amount of transverse steel. This report intends to: (1) validate the UH-developed equation for high strength concrete by testing ten 25-ft long full-scale PC I-girders with different concrete strength; and (2) validate the UH-developed equation for different sizes of PC girders and study the possibility of having premature failure due to local failure in end zone. Ten modified Tx28 PC girders were tested for the first objective. The girders were divided into three groups (namely Groups A, C and F) based on the concrete compressive strength. Group A consisted of two girders with a concrete compressive strength of 7000 psi. Group F had four girders with a concrete compressive strength of 13000 psi and Group C included four girders with a compressive strength 16,000 psi. Girders in Group A were designed to have a balanced condition in shear. A pair of girders each belonging to Group F and Group C were designed to have a balanced condition while remaining girders were designed as over-reinforced sections. Each group of the PC girders was tested with different shear span to effective depth ratio so as to get two types of shear failure modes, i.e., web-shear and flexure-shear. The validity of the proposed UH-developed equation was ascertained using the girders test results. UH-developed equation was found to accurately predict the ultimate shear strength of PC girders having concrete strength up to 17,000 psi with enough ductility. Six PC girders of Tx-series with three different sizes were tested for the second objective. The girders were divided into three groups (namely Groups D, E and G) based on the girder depth. The test data shows that the PC girders of the new Tx-series has no cracks under service loads and can reach the maximum shear capacity without having a shear bond failure. Also, these girders’ test results ensured the validity of the UH-developed equations for PC girders with different sizes. Simulation of Concrete Structures (SCS), a finite element program recently developed at UH, was used to predict the shear behavior of the tested girders. Analytical results presented in this report proved the validity of SCS to predict the behavior of PC girders with different concrete strength up to 17,000 psi and with different depth up to 70 inches.