钢筋混凝土梁冲击损伤后剩余抗弯承载力试验及评估方法研究

It’s very necessary to evaluate the behavior of structures damaged induced by blast and impact loading. For reinforced concrete (RC) beams, strong inertia effect and strain rate effect caused by blast and impact loading make the cracking mechanism in beam and the mechanical behaviors of materials damaged induced by impact very different from those under static load. So, it is infeasible to evaluate the behaviour of impact-damaged RC beam by using the evaluation method of behaviour of damaged structure under static loading. However, there is little research on the residual mechanical behavior of impact-damaged steel rebar, concrete and RC beam and their evaluation. Therefore, based on the experiment method and numerical analysis, the residual flexural capacity of impact-damaged RC beam and its evaluation method are investigated in the project. Firstly, the residual constitutive behaviors of impact-damaged steel rebar and concrete are investigated by experimental and numerical method, and the strength curve based on impact-echo method for evaluation of residual strength of concrete damaged induced by impact is experimentally studied. Secondly， experiment and numerical analysis of the residual flexural capacity of impact-damaged RC beam are conducted， including the parametric analysis and the mechanism of influence of impact loading on the residual flexural capacity, also the residual strength evaluation of steel rebar and concrete in tested beams after impact.Finally, based on the mechanism of influence of impact loading on the residual flexural capacity, the formulation of residual flexural capacity at ultimate state is derived，and the formulation is validated and modified by the experimental result. The achievements can provide a basis for repairing, strengthening and reasonable safety assessment of impact-damaged RC structures.

结构在遭受爆炸冲击荷载后，对其进行性能评估十分必要。就钢筋混凝土梁（简称“梁”）而言，爆炸冲击造成强惯性与应变率效应，使其开裂机理及材料冲击损伤后的力学性能与静载下完全不同，故其冲击损伤后性能评估不能采用受静载结构的性能评估方法。然而国内外对梁及钢筋、混凝土冲击损伤后的力学性能及评估方法研究甚少。因此，本项目采用试验和数值分析方法，研究梁冲击损伤后抗弯承载力及其评估方法。首先，开展钢筋与混凝土冲击损伤后本构行为试验与数值研究，以及冲击回波法检测混凝土剩余强度的测强曲线试验研究。然后，开展梁冲击损伤后的抗弯承载力试验及数值分析，进行参数分析及冲击对剩余抗弯承载力的影响机理研究，并对试验梁冲击损伤后的压区混凝土与钢筋强度进行评估。最后，根据冲击影响机理推导极限状态剩余抗弯承载力计算公式，并根据试验梁的材料强度评估数据与承载力验证和修正公式。本研究为梁冲击损伤后的修复加固和结构安全评估提供基础。

近年来，爆炸冲击事故频发，造成工程结构损伤和破坏。为了对受爆炸冲击损伤后的钢筋混凝土结构进行修复加固和安全性能评估，研究其损伤后的力学性能十分必要。本项目对钢筋混凝土梁冲击损伤后的受弯性能进行研究，开展了以下工作：对300MPa~600MPa不同强度等级的建筑钢筋进行了动态拉伸试验，应变率范围为2.5×10-4~900/s，得到了不同应变率下钢筋的应力-应变曲线；通过对400MPa与500MPa强度等级钢筋的动态拉伸试验数据进行分析，修正了描述动力增大系数的Cowper-Symonds和Mlavar模型及描述工程应力-应变关系的Mander模型，修正的模型与试验结果吻合良好；检验了常用的Johnson-Cook（J-C）模型对HRB400E和HRB500E钢筋的真实应力-应变曲线的适用性，表明J-C模型对描述HRB400E的真实应力-应变曲线不合适，但其可用于描述HRB500E钢筋的真实应力-应变曲线，更进一步地提出了新的本构模型用于描述HRB400E和HRB500E钢筋的真实应力-应变曲线；开展了HRB400E钢筋动态拉伸损伤后的残余静态拉伸力学性能的应变时效试验，应变时效完成时间不超过120天，其0天残余屈服强度与静态拉伸时接近，但残余抗拉强度比静态拉伸强度有所提高，当应变时效完成后，残余屈服强度能达到动态拉伸卸载时的应力，同时抗拉强度进一步提高；开展了静态弯曲破坏的梁受冲击损伤后的残余承载力试验，提出了一种考虑静态抗剪、抗弯承载力和冲击能量的残余承载力与抗弯刚度的计算公式。本研究所建立的钢筋率效应本构模型为混凝土结构抗爆抗冲击的准确分析提供基础，建立的梁冲击损伤后的残余受弯承载力计算公式为其修复加固和结构安全评估提供参考。