Unified Truss-Arch Model for the Analysis of Bending-Shear Interaction in Reinforced Concrete Members

The compatibility strut-and-tie method (C-STM) is a well-established nonlinear modeling tool to efficiently and accurately predict the overall load-deformation response of shear-critical RC members subjected to combined bending and shear. Such a high-performance tool, however, is computationally demanding. In this paper, a simplified limit analysis model based on C-STM is presented to predict the load-carrying capacity of RC beams. Amenable for hand methods of analysis, the approach is called the truss-arch model unified (TAMU). The TAMU approach accounts for the failure mechanism of the diagonal concrete strut that is softened because of the transverse tensile strain. Instead of providing overall force-deformation behavior, this model focuses on evaluating the ultimate load-carrying capacity by assuming the failure mechanism occurs when the principal diagonal strut reaches its softened strength in shear-critical beams. An explicit equation for the principal strain ratio is derived to evaluate the softened concrete strength and is used to develop formulas for the ultimate load-carrying capacity. The validity of the formulas is verified through a comparison of the predicted ultimate load-carrying capacities with maximum measured strengths from previous experimental results on large-scale physical tests representing bridge piers. The TAMU approach is then compared with other code-based strength analysis methods and shows better predictions of the maximum load-carrying capacity.