地震作用下拱肋-一字撑损伤模式与抗震性能评价

Arch rib-straight brace damage pattern and the seismic performance evaluation under earthquakes

横撑是肋拱桥在地震作用下最易发生损伤的部位之一。为了研究地震作用下拱肋与横撑之间的相互作用及其对两者损伤模式的影响规律,首先基于某原型肋拱桥构建拱肋−一字撑简化分析模型,研究横撑刚度、布设位置和数量对结构动力特性和弹性稳定性的影响,设置总计20组对比分析工况;然后基于静力弹塑性分析,根据塑性铰形成路径和分布特点,识别5类典型的拱−撑损伤模式;最后采用非线性时程分析法,通过定义协同耗能指标ϕ、综合评价指标ξ等,对比分析各类损伤模式的动力响应特征和抗震性能。研究结果表明:静力弹塑性分析和非线性时程分析可以得到相互验证的5类拱−撑损伤模式;当拱−撑结构发生横撑→拱肋→拱脚(BRS)损伤模式时,结构的地震响应规律、抗震性能均明显优于其余4类损伤模式,且横撑、拱肋和拱脚的应变曲线峰值非常接近,三者可协同参与结构整体塑性耗能;所提ϕ和ξ可准确表征各类拱−撑损伤模式的抗震性能,当ϕ的绝对值越接近0或ξ越小时,拱−撑结构的协同耗能机制越好,整体抗震性能更优;当一字撑设计使拱−撑系统满足BRS损伤模式时,结构具有最优的抗震性能。所提出的损伤模式识别方法和量化评价指标可为今后同类拱桥一字型横撑的设计和结构抗震性能评价提供参考。

Transverse braces are one of the most vulnerable parts of rib arch bridges under earthquakes.In order to study the interaction between arch rib and braces under earthquakes and its influence on the damage pattern of the arch rib-brace structure,a simplified arch rib-straight brace analysis model which based on a prototype arch bridge was firstly established.Twenty comparison groups were set to study the influence of brace stiffness,layout position and quantity on the dynamic characteristics and elastic stability of the arch rib-brace structure.Five typical arch rib-brace damage patterns were identified based on the formation path and distribution of plastic hinges which were obtained through the static nonlinear analysis.The nonlinear time-history analysis method was applied to comparatively investigate the dynamic response characteristic and seismic performance in different damage patterns through the proposed energy dissipation coordinating indexϕand comprehensive evaluationξ.The results indicate that both static elastic-plastic analysis and nonlinear time-history analysis can obtain 5 types of arch rib-brace damage patterns that are mutually verified;the seismic responses and performance of the arch rib-brace structure are obviously superior when subjected to the brace→rib→springing(BRS)damage pattern compared to the other four damage patterns,and the peak strain values of the brace,arch rib and springing are very close to each other in the BRS damage pattern,indicating a coordinated mode of energy dissipation among the three components.The proposed indexesϕandξcan efficiently represent the seismic performance of the identified arch rib-brace damage patterns.When the absolute value ofϕis closer to 0 or the value ofξis smaller,the arch rib-brace structure can develop a more coordinated mechanism of energy dissipation and thus gain a better overall seismic performance.When the design of straight braces makes the arch-brace system meet the BRS damage pattern,the structure has the optimal seismic performance.The damage pattern identification approach and the evaluation indexes that proposed in this research can provide a reference for the design of straight braces and seismic performance evaluation of similar arch bridges in the future.