起波钢筋高速动态拉伸力学性能研究

针对提高混凝土梁抗冲击爆炸性能的起波配筋新技术，采用理论分析与动态冲击拉伸试验相结合的方法，揭示了起波钢筋的快速拉伸变形作用机理，分析了拉伸速度、起波矢高等因素对起波钢筋抗拉强度的影响规律，确定了起波钢筋静态弹性极限强度计算方法。提出了起波钢筋等效拉伸应变率新概念，建立了弹性极限强度动力放大系数（dynamic increase factors，DIF）计算模型。研究结果表明，预先弯折起波使得钢筋在受力拉直过程中产生截面弯矩，起波钢筋的力学性能存在明显的应变率效应；起波钢筋弹性抗拉极限强度DIF随起波矢高的增高先增大后减小，存在一个最优起波设计矢高，可以使起波钢筋抗拉强度动态放大系数达到最大。研究成果可为进一步推动起波配筋技术在防护工程中的应用提供依据。

Study on mechanical properties of the kinked rebar under high speed dynamic tension

Aiming at new technology of the kinked rebar which can improve the resistance of concrete beams to impact and blast loading, the mechanism of rapid tensile deformation of the kinked rebar was revealed through theoretical analysis combined with dynamic impact tensile tests. The influences of the tensile velocity and the bending height of the kinked rebar on its tensile strength were analyzed. According to the mechanism of tensile deformation, the calculation method of the static elastic ultimate strength of the kinked rebar was determined by using the classical plastic mechanics theory, and the proposed calculation method was modified based on the existing literature data to consider the error caused by the Bauschinger effect. A new concept of equivalent tensile strain rate of the kinked rebar was put forward, the kinked rebar was regarded as an equivalent material, and the average strain rate of the bending part of the rebar was defined as the equivalent tensile strain rate of the kinked rebar. Considering the influence of the tensile velocity and the bending height of the kinked rebar, the calculation model of dynamic increase factors (DIF) of the elastic ultimate strength was established, referring to the form of the Johnson-Cook material constitutive model. The results show that the pre-bending kink results in the section bending moment of the steel bar during force straightening and the mechanical properties of the kinked rebar have an obvious strain rate effect. The tensile yield strength first increases and then decreases with the increase of the bending height of the kinked rebar. There is an optimal bending height for the kinked rebar at high strain rates, which can maximize the dynamic amplification factor of the tensile strength of the kinked rebar. The research results can provide a basis for further promotion of the application of the kinked rebar technology in protection engineering.