铁路圆端空心墩抗震延性的拟静力试验研究

Quasi-static test on seismic ductility of round-end hollow-section railway piers

为研究高烈度地区铁路圆端空心墩的延性抗震性能,对5个1:6缩尺模型进行了低周往复加载试验,分析了圆端空心墩损伤行为和塑性铰演化机理,探讨了不同设计参数桥墩的滞回性能、位移延性、强度/刚度及等效阻尼比等。结合损伤状态,基于位移延性对圆端空心墩抗震性能目标进行量化,并通过回归分析建立了强度/刚度退化与圆端空心墩性能目标的联系。鉴于已有模型不能很好估算圆端空心墩等效阻尼比,给出了基于试验数据的等效阻尼比公式。试验及分析结果表明:桥墩由于墩底倒角处混凝土压溃剥落、钢筋屈曲或拉断而发生弯曲破坏,墩身弯曲裂缝范围约占墩高的0.61~0.75;墩底实心段、倒角过渡段和墩身变截面的共同影响使得塑性铰区延长并整体上移;随着配箍率增加,桥墩延性有较大提升;在一定范围内增大轴压比可以提高桥墩抗弯能力,但过大的轴压会使墩底混凝土提前压溃而降低延性性能;在现行铁路规范允许位移延性比4.8下桥墩处于中等损伤状态,表明按规范设计的桥墩具有较好的抗震安全性。

To investigate the ductile performance of round-end hollow-section railway piers in intensive seismic zone,five 1:6 scaled models were tested under low-cyclic loading.The damage behavior and plastic hinge evolution mechanism were analyzed,as well as the hysteretic performance,displacement ductility,strength/stiffness and equivalent damping ratio of the specimens with different design parameters.The quantification for seismic performance object was implemented using displacement ductility combined with damage assessment.The relationship between seismic performance objectives and strength/stiffness degradation was also established through the regression analysis of test data.Due to the existing models being not appropriate to evaluate the equivalent damping ratio of round-end hollow piers,a proposed model was regressed based on the test results.The experimental and analytical results show that all specimens have a flexural failure due to concrete spalling,buckling or fracture of longitudinal rebar at the region of solid-to-hollow section,and the flexural crack distribution nearly covers 0.61 to 0.75 of the pier height.The plastic hinge region is extended and moves up wholly due to the existing of solid-section part,the transition part of solid-to-hollow section and variable hollow-section.With the increase of stirrup ratio,the displacement ductility capacity is obviously improved.The increased axial load ratio can improve the flexural capacity to some extent,but excessive axial load will lead to decreasing ductility for premature concrete crushing.The pier is at medium damage state under the ductility factor limitation of 4.8 in the current seismic code of railway engineering,which indicates seismic safety of piers designed using the code.