China’s high-speed railway network keeps pushing into seismically active territory, and the concrete piers that carry its tracks are increasingly being scrutinized for how they hold up when the ground shakes. A new quasi-static laboratory study, published in Advances in Bridge Engineering, reports that round-ended gravity piers of the type widely used on these lines lose their lateral stiffness earlier in the loading history when their shear-span ratio is larger, reaching equivalent damage states at smaller drift ratios.
The research team, led by Hanyu Wang and Yu Hong with Linbai Shen and Qianhui Pu, tested five 1:8-scale round-ended pier specimens designed from the Chinese standard bridge catalogue. The specimens carried longitudinal reinforcement ratios between 0.3 and 0.7 percent and stirrup ratios in the same range, values that mirror the deliberately sparse surface mesh reinforcement typical of high-speed railway gravity piers. A constant axial load of 450 kilonewtons, corresponding to an axial compression ratio of 0.05, simulated the fixed weight of the superstructure. The specimens were split into two parameter sets: one holding the reinforcement configuration constant while varying the shear-span ratio from 1.5 to 3.0, and another holding the shear-span ratio at 2.0 while trading longitudinal steel against transverse steel.
Testing took place at the National Engineering Laboratory in Geohazard Prevention Technology for Land Transportation at Southwest Jiaotong University. Two servo-controlled hydraulic actuators applied the axial load and then imposed cyclic lateral loading along the weak axis of the cross section, the direction that governs the stringent transverse displacement limits in high-speed railway design. The loading followed a hybrid strategy: force control before the reinforcement yielded, then displacement control in a drift-ratio sequence, with each drift level repeated for three full cycles until the lateral strength dropped to 80 percent of its peak. Marker-based image tracking with a high-resolution camera captured shear deformation, while arrays of linear variable differential transformers recorded displacement profiles and curvatures along the pier height.
The damage progression told a clear story. Initial horizontal cracking appeared at lateral loads of 270, 200, 210, 200, and 130 kilonewtons for the specimens P-1.5-0.5-0.5, P-2.0-0.3-0.7, P-2.0-0.7-0.3, P-2.0-0.5-0.5, and P-3.0-0.5-0.5 respectively. After yielding, diagonal cracks intersecting into X-shaped patterns at roughly 45 degrees formed in four of the five specimens, with the specimen carrying the highest longitudinal reinforcement ratio showing the most extensive diagonal cracking. All specimens eventually experienced longitudinal bar buckling on the tension face, and reinforcement rupture accompanied by audible snapping occurred in the lowest shear-span specimen and in the specimen with the least longitudinal steel.
The failure modes diverged in instructive ways. Three specimens with intermediate or high longitudinal reinforcement showed progressive diagonal cracking, bar buckling, and spalling after peak load, a signature of flexure-shear failure. The specimen with only 0.3 percent longitudinal reinforcement yielded early, stayed dominated by a single horizontal crack, and failed in a brittle flexural mode. The tallest specimen, with a shear-span ratio of 3.0, developed multiple widening horizontal cracks and pronounced base spalling, confirming a flexure-governed failure with significant plastic capacity.
Quantitatively, the shear-span ratio dominated the stiffness response. Raising it from 1.5 to 3.0 cut the peak lateral strength from 392.66 kilonewtons to 199.34 kilonewtons and reduced the initial effective stiffness by 54 percent, from 110.63 kilonewtons per millimeter in the stubbiest specimen to 50.89 kilonewtons per millimeter in the most slender one. Yet the more slender piers also displayed flatter load-displacement curves and greater post-peak displacement growth, indicating improved deformation capacity even as their stiffness faded sooner. Within the constant shear-span group, increasing the longitudinal reinforcement ratio from 0.3 to 0.7 percent boosted peak load capacity by about 43 percent and raised ultimate rotation from 1.86 to 2.55 percent of drift.
Energy dissipation proved to be governed by longitudinal steel rather than by geometry. The specimen with 0.7 percent longitudinal reinforcement dissipated a cumulative 245.7 kilonewton-millimeters, 165 percent more than the 92.9 kilonewton-millimeters absorbed by its 0.3 percent counterpart, despite carrying a lower stirrup ratio. Meanwhile, the three specimens sharing an identical reinforcement configuration but different shear-span ratios dissipated nearly the same cumulative energy, suggesting that within the tested range the reinforcement layout matters more than the shear-span ratio for the overall energy dissipation performance of these piers. A higher stirrup ratio, for its part, mainly stabilized the post-peak response, mitigating rapid strength decline without greatly extending deformation capacity.
By decomposing the total lateral displacement into flexural, shear, and bond-slip components using segmental curvature measurements, digital image tracking of diagonal targets, and base rotation transducers, the team quantified each mechanism’s share. Flexural deformation dominated throughout, contributing roughly 60 percent of total displacement in the early stages and rising above 85 percent later in some specimens. Shear deformation stayed near 10 percent of the total, rarely exceeding 13 percent, but grew as the shear-span ratio shrank: from 5.91 percent in the most slender specimen to 12.73 percent in the stubbiest, with the highest value, 13.00 percent, recorded in the specimen whose prominent shear cracking matched a distinct shear failure mode. Base slip contributed a stable, non-negligible share, exceeding 20 percent in two specimens and holding near 10 percent in the rest.
When the secant stiffness of each cycle was normalized by the initial stiffness at reinforcement yielding, the resulting degradation coefficient followed a clean exponential decay with drift, fitted by least squares with a coefficient of determination of 0.862. Specimens with larger shear-span ratios degraded earlier, their curves shifting leftward on the drift axis. The authors attribute this to two mechanisms: a higher shear-span ratio produces larger absolute displacements at the same drift, intensifying local strain concentrations, and the sparse longitudinal reinforcement in the curved end regions sits far from the confined core, allowing spalling and buckling to initiate sooner. Four additional validation specimens tested under the same protocol followed the same regression closely, supporting the model’s robustness within the tested parameter range.
The authors caution that the framework rests on 1:8-scale specimens, where scaling effects, unreplicated reinforcement detailing, and a coupled-variable test design in the reinforcement group constrain direct extrapolation to prototype structures, and they recommend further validation through larger-scale experiments and high-fidelity numerical simulation before engineering application. Within those limits, the study offers designers of high-speed railway bridges a quantitative basis for seismic damage assessment, performance-based design, and targeted maintenance of the round-ended gravity piers that anchor the network’s transverse stiffness.
Subject of Research: Seismic behavior and stiffness degradation of round-ended high-speed railway gravity bridge piers with low-to-medium shear-span ratios
Article Title: Experimental study on seismic behavior and stiffness degradation of round-ended gravity piers with low-to-medium shear span ratios
Article References: Wang, H., Hong, Y., Shen, L., & Pu, Q. (2026). Experimental study on seismic behavior and stiffness degradation of round-ended gravity piers with low-to-medium shear span ratios. Advances in Bridge Engineering, 7(1), Article 19. https://doi.org/10.1186/s43251-026-00208-5
Image Credits: AI Generated
DOI: 10.1186/s43251-026-00208-5
Keywords: high-speed railway, bridge piers, seismic behavior, stiffness degradation, quasi-static testing, shear-span ratio, flexure-shear failure, energy dissipation, deformation components, damage classification, reinforced concrete, performance-based design
News Source: Denise Maddox. (November 5, 2026). Round-Ended Railway Bridge Piers Show Earlier Stiffness Loss at Higher Shear-Span Ratios. Scienmag.
