地震作用下RC薄壁空心墩抗剪强度比较研究

Comparative study on shear strength of RC thin-walled hollow bridge piers under seismic effect

开展钢筋混凝土薄壁空心桥墩抗震问题的研究,对保证大型桥梁结构抗震安全具有重要意义。首先设计2个矩形薄壁空心墩试件,分别进行定轴力和变轴力下的拟静力试验,发现试件前期破坏以弯曲和剪切开裂为主,其后发生混凝土压碎脱落,纵筋屈曲等现象;最终试件薄壁发生突然的失稳破坏,引起桥墩倒塌。基于薄壁空心墩试验结果对国内外主要桥梁抗震设计规范和学者们提出的抗剪分析模型进行对比分析,认为我国《公路桥梁抗震设计细则》和欧洲Eurocode 8规范较为准确的计算了各试件抗剪强度或得到偏于保守的结果,可用于薄壁空心墩的抗剪设计;UCSD模型和Aschhiem模型高估了试件的抗剪能力,不适合于对薄壁空心桥墩的抗剪强度分析,而提出的改进的UCSD模型很好的预测了薄壁空心墩的抗剪强度。修正的压力场理论(Modified Compression Field Theory,MCFT)计算的薄壁空心墩抗剪强度最为准确。

Research on seismic behavior of RC thin-walled hollow bridge piers is of great significance to the seismic safety of large bridges. Two rectangular RC thin-walled hollow pier specimens were designed and tested. One specimen was subjected to constant axial load and cyclic lateral displacements, and the other was subjected to varying axial load and cyclic lateral displacements. The test results indicate that flexural and shear concrete cracks developed firstly and then concrete spalling and longitudinal bar buckling were observed in regions close to the bottom of specimens. The ultimate performance of specimens is dominated by local compression flange buckling failure of pier walls and specimens may collapse suddenly. The shear strength analysis models from bridge seismic design codes and literatures were evaluated and compared based on available test results for RC thin-walled hollow bridge piers. It is found that both Chinese bridge seismic design code and Eurocode 8 code give good or conservative predictions for shear strength of specimens, and hence they are applicable to the seismic design of thin-walled hollow bridge piers. However, the UCSD and Aschhiem models may overestimate the shear strength of specimens so that they could be inappropriate to the shear strength analysis of piers. Comparatively, the proposed modified UCSD model may predict the shear strength of thin- walled piers very well, while the Modified Compression Field Theory （MCFT） gives the most accurate predictions of shear strength for the piers with thin walls.