弯剪破坏与轴力附加弯矩对钢筋混凝土柱极限变形能力的影响综述

A critical review of influence of flexural-shear failure mode and P-Δ effect on ultimate deformation capacity of RC columns

钢筋混凝土(RC)柱变形能力计算是实现基于性能的抗震设计的基本条件。为此结合我国规范,针对弯剪破坏模式相关研究成果进行总结与评述。讨论了以经验公式为主的RC柱极限变形计算方法,揭示了参数模型的不足;指出对于弯剪破坏模式,剪切作用和轴力二阶效应是造成变形计算离散的重要原因。塑性铰长度不是一个典型的统计量,基于等效塑性铰长度模型得到的极限变形计算值离散性大。考虑塑性铰区弯剪相互作用,才能正确反映柱的抗剪需求,但简化计算方法存在争议,且缺乏有效方法评价剪切作用对柱变形性能的影响。GB 50010-2010《混凝土结构设计规范》中,对考虑地震作用的受剪承载力计算公式的修正能够有效避免RC柱在大位移下发生剪切破坏,但对不同位移延性下剪切破坏构件的安全储备不同且离散性增大。轴力二阶效应导致相同的试验柱在不同试验装置下剪力需求和极限变形不同,对弯剪破坏柱与弯曲破坏柱的影响也不相同。最后,结合极限变形计算的现状,建议我国规范补充基于回归方法建立的极限变形下限值经验公式,以完善基于性能设计方法。

The prediction of deformation capacity of reinforced concrete(RC)columns is the foundation to realize performance-based seismic design.This paper presented a critical review of flexural-shear failure of columns based on Chinese design codes.The empirical formulas of ultimate deformation of RC columns were discussed,and the deficiencies of parametric model were revealed.The failure mode of flexural-shear,shear behavior and P-Δeffect are the main reasons for the scattering of the prediction of ultimate displacement.The length of plastic hinge is not a specific statistical sample.The prediction of ultimate displacement on the basis of equivalent plastic hinges method shows large scatter.In order to reveal the real shear demand in RC columns subjected to seismic loadings,the interaction between shear and flexural behaviors in plastic hinge zone should be taken into consideration.However,the corresponding simplified methods need to be improved.An effective method to evaluate the effect of shear on the deformation performance of columns is not available.In the GB 50010-2010‘Code for design of concrete structures’,the correction of the shear capacity formula for seismic design can effectively avoid the shear failure of columns under large displacement reversals,but the safety margin is different under varying ductility levels of ultimate displacement.The scatter of the prediction of GB 50010-2010 is larger than that of the original formula.Shear demand of identical columns under different test setups is not same due to the variety of P-Δeffect.The influence of P-Δeffect on the ultimate deformation capacity of RC columns depends failure modes.Finally,according to the relevant research in ultimate deformation,it is suggested that Chinese building code should be supplemented with an empirical formula for lower limit value of ultimate displacement by regression methods to improve performance-based design methods.