考虑梁受弯损伤轴向伸长效应的RC框架结构强震破坏模式及易损性研究

The elongation of beams in RC frames due to flexural cracking and yielding is restrained by the surrounding structural components, thereby leading to axial force and significantly enhanced flexural strength. According to capacity design philology, the flexural capacity of beams in a RC moment frame is the basis for the shear design of beams and the flexural design of columns. The unexpected enhanced beam flexure capacity would result in unacceptable failure mechanism and structural collapse under strong earthquakes. Extremely limited research has been carried out on this effect. In this project, experiments will be conducted on interior beam-column subassemblies to study the mechanism of the axial elongation effects and the influence on flexural performance of RC frame beams. The test setup permits applying axial restraint at beam ends and measuring the compressive axial force passively generated in the beams. Combined with the force transfer mechanism of the plastic hinge zone, a flexure-shear-axial fiber model which can capture beam elongation effects and its effect on other aspects of RC members will be proposed. Based on beam-column subassemblies experiments and nonlinear time history analysis, a modified flexure-axial interaction method will be suggested for computing the beam flexural strength considering the axial elongation effects. Finally, the seismic fragility method is employed to study the influence of beam elongation effects on seismic performance, collapse fragility and typical failure mechanisms. The research results provide theoretical foundation for improving the failure mechanism design of RC frames under strong earthquakes.

周边构件对RC梁受弯损伤轴向伸长的约束作用会在梁中产生不可低估的轴力，显著提高其抗弯承载力。作为能力设计法的起点，梁抗弯承载力非预期超强可能导致结构在强震中难以出现预期的破坏模式，造成结构倒塌破坏。有关梁轴向伸长效应对RC框架结构抗震性能影响的研究极为有限。本课题采用等效约束刚度法等效考虑周边构件的约束作用，将实际超静定结构简化为静定梁柱子结构，进行拟静力试验，揭示梁轴向伸长的机理及影响因素，探索轴向伸长效应对梁抗弯性能的影响规律，结合梁塑性铰区力传递机制，构建考虑梁受弯损伤轴向伸长效应的数值分析模型。综合梁柱子试验研究和整体结构非线性动力时程分析，提出考虑轴向伸长效应的弯-轴耦合的梁抗弯承载力计算方法。最后基于地震易损性分析方法，获得考虑梁轴向伸长效应对整体结构各级性能水准的超越概率、抗倒塌能力及典型破坏模式失效概率的影响规律。研究成果为完善RC框架结构强震破坏模式设计提供研究基础。

强震中预期合理的破坏模式是结构实现抗震设防目标的决定性因素之一。作为预期损伤部位，梁抗弯性能是实现包括强柱弱梁在内的所有“能力设计法”的起点，是保证结构强震抗震性能的关键。周边构件对RC梁受弯损伤轴向伸长的约束作用会在梁中产生不可低估的轴力，显著提高其抗弯承载力。梁抗弯承载力非预期超强可能导致结构在强震中难以出现预期的破坏模式，造成结构倒塌破坏。有关梁轴向伸长效应对RC框架结构抗震性能影响的研究极为有限。. 本项目采用等效约束刚度法等效考虑周边构件的约束作用，将实际超静定结构简化为静定梁柱子结构，进行了梁柱子结构拟静力试验，揭示了梁轴向伸长的机理及影响因素，探索了轴向伸长效应对梁抗弯性能的影响规律，结合梁塑性铰区力传递机制，构建了考虑梁受弯损伤轴向伸长效应的数值分析模型。综合梁柱子试验研究和整体结构非线性动力时程分析，提出了考虑轴向伸长效应的弯-轴耦合的梁抗弯承载力计算方法。最后基于地震易损性分析方法，获得了梁轴向伸长效应对整体结构抗震性能的影响。重要结果：1）揭示了梁受弯损伤轴向伸长的机理；2）构建了考虑梁受弯损伤轴向伸长效应的数值分析模型；3）提出了考虑梁受弯损伤轴向伸长效应的梁抗弯承载力计算方法；4）获得了梁受弯损伤轴向伸长约束效应对RC框架结构整体抗震性能的影响。研究成果为完善RC框架结构强震破坏模式设计提供研究基础。