Hysteresis decomposition and nonlinear coupled modeling of RC hollow piers: Experimental characterization of flexural-shear-bond interaction for seismic response prediction

Accurate prediction of lateral displacement of bridge piers is essential for performance-based seismic design, whereas the deformation behavior of reinforced concrete circular hollow piers under flexural-shear interaction has not been insufficiently studied, particularly for configurations with double-layer reinforcement. Quasi-static tests were performed on five circular hollow piers with a shear span ratio of 2.81 to investigate their deformation characteristics and the effects of flexural-shear coupling. The test results show that pronounced flexural-shear coupled failure is observed, with flexural and diagonal cracks densely intersecting within the base plastic hinge region. Through refined decomposition of the three deformation components, it is revealed that at the ultimate state, flexural, shear, and bond-slip deformations contribute 40%-60%, 20%-30%, and 20%-50%, respectively. With increasing axial ratio, the flexural-shear interaction mode transitions from flexure-slip dominance to flexure-shear dominance, whereas higher stirrup ratios effectively mitigate the strength of flexural-shear coupling. Based on the test observations, modified models for three-component deformations are developed. In the flexural model, an ultimate curvature reduction factor χ ϕ and a flexural-shear coupled plastic hinge length L p ,fsi are introduced; in the bond-slip model, an axial ratio factor α η , a shear level factor β V , and a failure mode differentiation factor γ mode are incorporated; and in the shear model, a moment level factor δ m , an axial ratio-dependent crack angle θ s ( η ), and a failure mode coefficient ζ mode are introduced. Finally, the three component models are integrated into a unified framework to propose a comprehensive prediction approach for pier-top displacement. The validation results indicate that the prediction error ranges from −0.01% to +1.16%, with a mean absolute error of 0.55% and a standard deviation of 1.60%; compared to conventional methods, the prediction accuracy is improved by approximately 97%, the dispersion is reduced by 82%, and a slightly conservative trend is observed, making the proposed approach suitable for seismic deformation evaluation of circular hollow piers considering flexural-shear interaction.