Seismic shear strength of thin-walled circular hollow RC bridge piers considering flexural-shear interaction

The thin-walled circular hollow reinforced concrete (RC) bridge piers provide favorable material efficiency, but their seismic shear strength is difficult to evaluate because hollow-section geometry and post-yield flexural damage can jointly reduce the available shear-transfer capacity. To address this problem, a mechanics-informed semi-empirical shear-strength formulation is developed for thin-walled circular hollow RC piers considering flexural-shear interaction. The shear resistance is decomposed into concrete, transverse-reinforcement, and longitudinal-reinforcement contributions. Circular hollow-section effects are represented through modifications of stirrup effectiveness, compression-zone depth, and effective shear area, while the average influence of accumulated flexural plastic deformation is incorporated through a displacement-ductility degradation coefficient. A database of 58 circular hollow RC pier specimens from previous studies is used to calibrate the data-dependent model terms. The formulation is subsequently evaluated using five quasi-static specimens from the present experimental program and six additional literature hold-out specimens. The mean prediction-to-test ratios are 0.97 and 1.09, with standard deviations of 0.06 and 0.07 for the two evaluation datasets, respectively. For the common six-specimen comparison with existing shear-strength models, the proposed formulation shows lower overall prediction error and dispersion, with the clearest improvement observed for the limited high-hollow-ratio specimens. The experimental observations are qualitatively consistent with progressive deterioration of the effective compression region and shear-transfer mechanisms after flexural yielding. However, the available validation remains limited and does not establish uniform superiority, failure-mode-independent accuracy, or extrapolation capability beyond the experimental envelope. The proposed formulation therefore provides a preliminary, computationally convenient framework for estimating the seismic shear strength of thin-walled circular hollow RC bridge piers within the parameter range represented by the available data.