The seismic fragility of reinforced concrete (RC) bridge piers is critical for urban rail transport systems, as severe pier damage may interrupt post-earthquake operation and threaten network safety. Compared with conventional highway bridge piers, urban rail transport RC solid piers usually have lower axial load ratios, larger cross-sections, and stricter serviceability requirements. However, the combined effects of geometric parameters, reinforcement detailing, and material strength on their cyclic behavior, dynamic response, and seismic fragility remain insufficiently understood. To address this issue, seven 1/4-scale RC solid pier specimens were tested under quasi-static cyclic loading to examine the effects of pier height, transverse reinforcement ratio, and longitudinal reinforcement ratio on damage evolution, hysteretic response, skeleton curves, and energy dissipation. A fiber-based OpenSees model considering bond-slip effects was then established, validated against the tests, and extended to a full-scale prototype pier for parametric analysis. The effects of aspect ratio, axial load ratio, longitudinal reinforcement ratio, stirrup ratio, steel yield strength, and concrete strength were evaluated under cyclic loading and nonlinear dynamic time-history excitations. An incremental dynamic analysis-based probabilistic seismic demand model was further developed using 30 near-fault ground motions, with peak ground acceleration as the intensity measure and displacement ductility as the engineering demand parameter. The results showed that increasing the aspect ratio changed the failure mode from flexure-shear-dominated to flexure-dominated behavior, increasing the ultimate displacement from 122 mm to 155 mm while reducing the peak lateral strength from 263 kN to 248 kN. Increasing the longitudinal reinforcement ratio improved both peak strength and ultimate displacement, from 226 kN to 262 kN and from 120 mm to 160 mm, respectively. The numerical results indicated that aspect ratio, axial load ratio, and longitudinal reinforcement ratio had more pronounced effects on seismic demand and fragility than stirrup ratio. Increasing steel yield strength generally reduced seismic fragility, whereas increasing concrete strength enhanced lateral resistance but did not necessarily improve fragility performance. These findings suggest that the seismic performance of urban rail transport RC solid piers should be evaluated by combining cyclic response, dynamic demand, and fragility-based performance, rather than by maximizing any single design parameter.

Evaluating the seismic resilience (SR) of water distribution systems (WDSs) can support decision-making in optimizing design, enhancing reinforcement, retrofitting efforts, and accumulating resources for earthquake emergencies. Owing to the complex geological environment, buried water supply pipelines exhibit varying degrees of corrosion, which worsens as the pipelines age, leading to a continuous degradation of their mechanical and seismic performance, thereby impacting the SR of WDSs. Consequently, this study proposes an SR evaluation method for WDSs that takes into account the corrosive environment and the service age of buried pipelines. Utilizing the analytical fragility analysis method, this research establishes seismic fragility curves for pipelines of various service ages and diameters in diverse corrosive environments, in combination with the Monte Carlo simulation method to generate seismic damage scenarios for WDSs. Furthermore, the post-earthquake water supply satisfaction is utilized to characterize the system performance (SP) of WDSs. Two repair strategies are employed for damaged pipes: assigning a single repair crew to address damages sequentially and deploying a repair crew to each damage location simultaneously, to assess the minimum and maximum SR values of WDSs. The application results indicated that the maximum decrease in SP across 36 conditions was 32%, with the lowest SR value of WDSs being 0.838. Under identical seismic intensities, the SR value of WDSs varied by as much as 16.2% across different service ages and soil conditions. Under rare earthquake conditions, the effect of the corrosive environment significantly outweighs the impact of service age on the SP of WDSs. Post-disaster restoration resources can minimize the impact of the corrosive environment and service age on the SR of WDSs.

Double-column reinforced-concrete (RC) hollow bridge piers are often assessed using flexure-dominated models, although their thin walls can develop shear-related deterioration. This study reanalyzes seven previously reported cyclic tests on scaled square hollow-pier columns and extends the assessment to a full-scale double-column system in OpenSees. The tests varied the shear-span ratio and transverse and longitudinal reinforcement. A flexure-only fiber model and an axial–flexure–shear interaction membrane–beam–truss element model (AFSI-MBTEM) were evaluated using six response indicators before cyclic and nonlinear time-history analyses of the prototype system. Lower shear-span ratios increased resistance but intensified inclined cracking, stiffness loss, and post-peak deterioration; increasing L/D from 3.9 to 7.9 reduced peak strength from 320.5 to 145.9 kN. AFSI-MBTEM reduced the mean absolute errors in peak strength, yield displacement, and effective stiffness to 3.08%, 11.83%, and 12.86%, respectively, but did not improve residual-displacement or mean hysteretic-loop-energy predictions. At the system level, shear-span ratio most strongly affected cyclic stiffness and peak base shear; wall-thickness ratio, width-to-depth ratio, and longitudinal reinforcement were also influential. Under three near-fault records, AFSI-MBTEM predicted 5.31–10.32% lower peak base shear, while displacement changes remained record-dependent. Shear-sensitive modeling improves force and deformation assessment, but the system-level trends remain conditional on the adopted prototype, parameter ranges, and records.

An innovative symmetrical hysteresis model for reinforced concrete (RC) rectangular hollow columns is presented. The Bouc–Wen–Baber–Noori (BWBN) model was selected to depict the inelastic restoring forces and was improved by introducing a coefficient to describe the relationship between stiffness degradation and peak displacement. Sensitivity analysis was conducted at the local and global levels to clarify the importance of each parameter in the improved BWBN model. As such, a hybrid intelligence algorithm named PSOGSA was employed to identify the parameters of the BWBN model utilizing quasi-static tests of 16 hollow columns. The empirical formulas were regressed to bridge the connection between the BWBN model and design parameters of hollow columns. The results showed that the hysteresis curves of the improved BWBN model calibrated by the PSOGSA agreed well with the measured loops. In addition, the accuracy of the empirical prediction method of hysteretic parameters was checked through comparison with other hollow members. The calibrated improved BWBN model produced more precise hysteretic responses for RC hollow columns, since the peak and residual performance levels were simultaneously considered.

Rectangular reinforced concrete (RC) hollow bridge piers may exhibit significant shear participation after flexural cracking and yielding, whereas their seismic responses are commonly evaluated using flexure-dominated numerical models. This study investigates the effects of axial–flexure–shear interactions on the cyclic response and seismic fragility of rectangular RC hollow bridge piers. Cyclic loading tests on seven one-eighth-scale specimens were analyzed to characterize the effects of the shear-span ratio and reinforcement configuration. The experimental results were then used to assess a conventional flexure model and an axial–flexure–shear interaction model, denoted as AFSI–MBTEM. Full-scale piers with heights of 16, 24, and 32 m were subsequently analyzed under cyclic loading and representative near-fault ground motions. Finally, 7200 nonlinear time-history analyses were conducted using 80 records divided into non-pulse and short-, medium-, and long-period pulse-like groups, while seismic fragility curves were developed using displacement ductility as the demand parameter. The tests indicated flexure-dominated but distinctly shear-sensitive behavior, particularly for specimens with low shear-span ratios. Compared with the flexure model, AFSI–MBTEM reproduced pinching, post-peak deterioration, and hysteretic energy more accurately, reducing the mean absolute error in hysteretic energy from 23.57% to 13.29%. For the full-scale piers, model differences generally decreased as the pier height and shear-span ratio increased together, although the effects on large-deformation stability and seismic response remained configuration- and ground-motion-dependent. AFSI–MBTEM predicted higher fragility in 46 of the 48 height–motion–damage-state comparisons. At the upper analyzed intensity of PGA = 1.5 g, it also produced higher DS4 exceedance probabilities in the examined critical cases. Within the investigated section configurations, axial-load ratios, and coupled height–shear-span cases, the results indicate that neglecting axial–flexure–shear interactions may lead to nonconservative fragility estimates, particularly for configurations with greater shear participation.