基于纵向钢筋屈曲的高墩桥梁地震倒塌机理研究

Recently many bridges with high piers have been constructed crossing deep valleys at mountain area in western China, where the geotechnical condition is more complicated and the earthquake is more active. It is necessary for much research on the collapse mechanism of them from initial failure of bridge piers, progression of damage and degradation of stiffness and strength, to ultimate collapse of the bridge. The collapse-resistant capacity of the bridge will be severely decreased by the damage and degradation of strength and stiffness of piers due to cumulative damage under earthquake. It is a key work that taking the degradation of strength of the reinforcement into account. This project therefore aims at the simulation of earthquake disaster process and collapse mechanism of high pier bridge with buckling of longitudinal reinforcement. Research on pseudo-static collapse experiments of RC hollow rectangular thin-walled piers is performed. The refined finite element model is developed and utilized to perform parameters analysis. The stress-strain relationship of reinforcement with buckling is proposed on the basis of experiments and finite element analysis and utilized to develop the analysis model of high piers with the damage of reinforcement buckling. The results of experiments and numerical simulation are also used to study the collapse mechanism of bridge piers to propose a criterion of collapse. Finally, the numerical simulation of earthquake disaster process is performed to reveal the collapse mechanism of high pier bridge. The influence of P-Δ effect, pier height, direction of ground motion on the collapse-resistant capacity of high pier bridge is investigated in detail. This project can provide scientific basis for the important engineering construction which has great theory and application value.

高墩桥梁结构近年来在地震灾害频繁的我国西部多山谷地区得到了广泛的应用，开展地震作用下高墩桥梁的抗倒塌性能研究是一项重要的科学与工程任务。地震作用下桥梁墩柱在变形过程中刚度、强度会随着损伤积累而出现退化特性，严重影响墩柱的抗倒塌能力。将钢筋后期强度退化引入到墩柱的退化特性中，是桥梁结构抗倒塌能力评估的关键工作。本项目将研究考虑纵向钢筋屈曲的高墩桥梁地震灾变数值模拟及倒塌机理。采用矩形薄壁空心墩柱拟静力倒塌试验研究，建立考虑纵筋屈曲的精细有限元模型并进行参数分析，提出考虑受压屈曲的钢筋应力应变模型；基于该模型建立模拟高墩墩柱纵向钢筋受压屈曲破坏的有限元模型；进而结合试验研究和数值模拟探明墩柱倒塌破坏机理，提出高墩桥梁倒塌破坏判别准则；在此基础上研究P-Δ效应、墩高、地震动输入方向等因素对高墩桥梁抗地震倒塌能力的影响，从而揭示高墩桥梁地震灾变倒塌机理。预期成果能为相关重大工程的建设提供科学支撑。

本课题围绕高墩桥梁在地震作用下的倒塌问题开展了相关研究工作。.结合申请人在桥梁抗地震倒塌能力关键问题方面的前期研究工作和该学科的最新成果，针对地震作用下桥梁墩柱在变形过程中刚度、强度随着损伤积累而退化的问题，探索高墩桥梁在地震作用下抗倒塌能力，重点研究了高墩桥梁中桥墩纵向钢筋屈曲导致结构在地震作用下倒塌破坏的地震灾变机理，并对桥梁劣化对地震作用下高墩桥梁的抗倒塌能力的影响进行了初步研究。取列得了一系的研究成果。主要工作包括：.1）对墩柱中纵向钢筋的屈曲进行了深入分析。提出了能考虑纵向钢筋屈曲的钢筋应力应变模型，通过考虑纵向钢筋屈曲压应变的方式计入纵向钢筋屈曲的影响。基于该钢筋模型建立了模拟高墩墩柱纵向钢筋受压屈曲破坏的高墩桥梁有限元分析精细模型； .2）对高墩桥梁在地震作用下的响应进行了深入分析，提出了高墩刚构桥倒塌破坏的判断准则，通过墩顶节点的竖向位移来反映结构承受竖向荷载的能力，以此判定高墩桥梁在地震作用下是否发生倒塌破坏..3）对地震作用下高墩桥梁发生倒塌破坏的机理进行了深入分析，揭示了结构发生倒塌破坏的机理。梁桥结构的墩柱先后进入弹塑性状态，混凝土保护层发生剥落，随后纵向钢筋屈曲而逐渐丧失承受竖向荷载的能力，继而发生倒塌破坏。.4）研究了高墩桥梁在地震倒塌极限状态点的塑形变形特征，破坏模式以及P-Δ 效应对极限承载能力的影响力。.5）研究了劣化对高墩桥梁结构抗倒塌能力的影响。混凝土剥落、钢筋截面减少、和钢筋强度降低等劣化在一定程度上影响了结构在地震作用下的抗倒塌能力，其中钢筋截面减少对极限承载能力影响最大。