Strength of reinforced concrete pier caps-experimental validation of strut-and-tie method

The strut-and-tie method (STM) is commonly used to design reinforced concrete (RC) pier caps, where the traditional methods of shear and flexural design cannot be used due to nonlinear strain distribution. This paper presents experimental studies on scaleddown pier cap specimens subject to four concentrated loads, to study the influence of various parameters and the applicability of STM. The STM prescribed by ACI 318 and AASHTO are found to give reasonably conservative results only when the beneficial effect of triaxial confinement near the bearing node is invoked; otherwise, the predictions are overly conservative. Variations in bearing plate size, distributed reinforcement, and loading eccentricity did not have much influence on the load capacity, but distributed reinforcement was seen to be beneficial in limiting crack widths. The formation of the assumed STM is validated using strain measurements in concrete and steel, and it is observed that this develops only after significant cracking.