Zhuojin Pipe Fitting Co., LtdShake Table Test of Partially Filled Circular Steel Tube Concrete Bridge Piers
Literature Overview
This paper by Xu Yan, Wang Zhen, Goto Yoshiteru, and Kaesar Kenji was published in the China Journal of Highway and Transport in 2019 (Volume 32, Issue 12, pages 177-185). The research was supported by the Ministry of Education's International Laboratory for Earthquake Engineering (ILEE) Program, the National Key R&D Program (Grant 2017YFC1500702), and the National Natural Science Foundation of China (Grant 51878492). The study investigates the seismic behaviour of partially filled circular steel tube concrete bridge piers through destructive shake table tests on scaled two-span elevated bridge models.
Experimental Configuration
Two scaled models of two-span elevated bridges (scale ratio 1:6.7) were tested under strong seismic excitation. One model featured a non-eccentric partially filled circular steel tube concrete pier, while the other incorporated an eccentric partially filled pier to simulate the effect of transverse permanent load eccentricity. The partial filling approach—where concrete is filled only up to a certain height within the steel tube—offers construction advantages by reducing the amount of concrete required and simplifying the filling process, while still providing adequate seismic performance.
| Model Feature | Non-Eccentric Pier | Eccentric Pier |
|---|---|---|
| Concrete fill height | Same as eccentric model | Same as non-eccentric model |
| Permanent load eccentricity | None | Transverse eccentricity present |
| Primary failure mode | Uniform local buckling near base | Concentrated buckling on centre-line side |
| Horizontal cracking | Significant horizontal cracks | No horizontal cracks observed |
| Residual displacement | Approximately 3 cm | Approximately 3 cm |
Key Findings on Seismic Behaviour
The non-eccentric pier exhibited uniform local buckling deformation of the steel tube near the pier base, accompanied by significant horizontal cracking. The eccentric pier, influenced by transverse permanent load eccentricity, did not develop horizontal cracks. This difference in cracking behaviour explains why the longitudinal bridge-direction top displacement of the non-eccentric pier is significantly larger than that of the eccentric pier.
The transverse permanent load eccentricity causes the top transverse displacement and base local buckling deformation of the eccentric pier to concentrate on the side closer to the centre line. The plastic development region is also larger in the eccentric pier, resulting in greater maximum transverse top displacement compared to the non-eccentric pier. However, because the eccentric pier did not experience cracking, the transverse residual displacement is comparable to that of the non-eccentric pier, both around 3 cm.
Energy Dissipation Asymmetry
A critical finding is that the permanent load eccentricity causes unequal energy dissipation on the two transverse sides of the eccentric pier. This asymmetry in energy dissipation may lead to differential cumulative plastic deformation on the two sides, which is detrimental to fully exploiting the pier's superior seismic performance and energy dissipation capacity. This asymmetry represents a potential vulnerability that must be addressed in design.
The study validates that eccentric partially filled circular steel tube concrete piers can meet seismic performance requirements if the cross-sectional design is appropriately selected. However, the design must carefully account for the adverse effects of permanent load eccentricity on seismic performance.
Design Recommendations and Engineering Practice
Based on the test results, the authors recommend that designers of eccentric partially filled circular steel tube concrete piers carefully select structural parameters such as concrete filling height and diameter-to-thickness ratio (D/t) to minimise the adverse effects of permanent load eccentricity on seismic performance. The filling height should be optimised to provide adequate confinement in the critical plastic hinge region while considering the asymmetric stress distribution caused by eccentricity.
From a steel tube fabrication perspective, the D/t ratio is a critical parameter that influences both local buckling resistance and confinement effectiveness. The steel tubes must be manufactured with high quality welds to ensure uniform wall thickness, as any local thinning would exacerbate the asymmetric buckling behaviour observed in the eccentric pier. The partial filling process also requires careful quality control to ensure complete and uniform concrete filling up to the specified height, with no voids or honeycombing that could reduce confinement effectiveness.
Summary
This shake table study provides valuable experimental evidence on the seismic behaviour of partially filled circular steel tube concrete bridge piers under both symmetric and eccentric loading conditions. The key engineering insight is that while eccentric partially filled piers can achieve acceptable seismic performance with proper design, the permanent load eccentricity introduces asymmetric energy dissipation that must be carefully managed through appropriate selection of filling height and D/t ratio. For fabrication quality control, maintaining high weld integrity and uniform wall thickness in the steel tubes is essential to ensure the confinement effectiveness that supports the pier's seismic performance, particularly in the critical base region where local buckling initiates.