钢筋混凝土柱失效模式的随机演化竞争与概率能力模型研究

How to avoid the brittle failure of reinforced concrete (RC) columns truly and assure the effective realization of seismic design principle in strong shear capacity and weak bending capacity to prevent the serious damage or sudden collapse of RC structures plays a key role on the seismic performance investigation of building structures. This project aims to consider the influence of the randomness of concrete materials to study the flexural failure, shear failure and flexural-shear failure mode of RC columns. The random fluctuation characteristics on the nonlinear mechanical behavior of RC columns at the sectional level and component level under different failure modes is first investigated by conducting the stochastic nonlinear mechanical experiment of RC columns, where the stochastic evolutionary characteristic and the mutual competition relationship of bending mechanism and shear mechanism in nonlinear full range are analyzed in details. Then the truss and arch model representing the stochastic evolutionary characteristic and mutual competition relationship of bending mechanism and shear mechanism is developed to derive the probabilistic capacity model of mechanical characteristic parameters of RC columns such as the bending capacity and shear strength capacity etc., where the mean prediction model and standard deviation prediction model are derived based on the probabilistic capacity model. Finally, the critical variables affecting the transformation of failure mode of RC columns are investigated based on the simplified truss and arch model and the corresponding seismic design index as well as its probabilistic capacity model are established, which improve the research of earthquake resistant mechanism of RC columns and provide the technical support for the performance-based seismic design theory of RC structures.

如何切实避免钢筋混凝土柱发生脆性破坏，保证“强剪弱弯”抗震设计准则的有效实现，防止钢筋混凝土结构发生严重破坏或突然倒塌，是结构抗震性能研究的关键与基础。本项目重点关注混凝土材料随机性的影响，围绕钢筋混凝土柱的弯曲失效、剪切失效和弯剪失效，通过开展钢筋混凝土柱的随机非线性力学行为试验，深入研究不同失效模式下钢筋混凝土柱截面尺度和构件尺度非线性力学行为的随机涨落特征，分析非线性受力全过程中抗弯机制和抗剪机制的随机演化特征与相互竞争关系；发展能够表征抗弯机制和抗剪机制随机演化与竞争关系的桁架-拱模型，推导钢筋混凝土柱抗弯承载力、抗剪承载力等力学特征参数的概率能力模型，建立相应的均值预测方程和标准差预测方程；基于简化的桁架-拱模型，研究影响钢筋混凝土柱失效模式转换的关键控制参数，提出相应的抗震设计指标，推动钢筋混凝土柱抗震失效机理的研究，为基于性能的钢筋混凝土结构抗震设计理论提供技术支持。

深入开展钢筋混凝土柱失效模式的随机演化特征与相互竞争关系研究，刻画和控制钢筋混凝土柱的弯曲失效、剪切失效和弯剪失效模式转换，对于避免钢筋混凝土柱发生剪切脆性破坏，进而满足钢筋混凝土结构的抗震性能要求，具有十分重要的理论意义与应用价值。本项目围绕钢筋混凝土柱的弯曲失效、剪切失效和弯剪失效，系统开展了钢筋混凝土柱非线性受力全过程中不同失效模式下的外观损伤表征、受力机制构成、随机演化特征、相互竞争关系和概率能力模型研究。研究结果表明：混凝土材料的随机性对于钢筋混凝土柱截面尺度和构件尺度的非线性力学行为具有十分显著的影响。其中，截面尺度的随机性大于构件尺度的随机性；剪切失效的随机性大于弯曲失效的随机性。基于桁架-拱机制，将钢筋混凝土柱简化为一个由抗剪机制与抗弯机制构成的串并联系统，建立了表征钢筋混凝土柱抗弯机制和抗剪机制随机演化特征与相互竞争关系的的简化计算模型。在此基础上，推导了钢筋混凝土柱抗弯承载力和抗剪承载力的概率模型，提出了钢筋混凝土柱失效模式的概率判别指标，同时建立了控制钢筋混凝土柱失效模式转换的抗震设计指标，如最小配箍率、最大轴压比和最小剪跨比。项目研究成果不仅可为我国基于性能的钢筋混凝土结构抗震设计理论提供技术支持，而且可以推动钢筋混凝土结构基本理论的研究由半经验半理论建模向概率化理论化建模方向发展。