基于开裂荷载为界点的混凝土应力-应变关系新表达

Stress-strain relationships in a new expression for concrete based on the cracking loads as the boundary point

目前,混凝土常用的受压应力—应变关系大多采用以强度峰值为界的分段表达形式。这种以强度峰值为界的表达形式将会给CFRP加固混凝土梁正截面受弯承载力计算带来麻烦,尤其是在多种材料共同工作时,计算分析过于复杂,将加大研究及实际应用的工作量。为简化计算,根据混凝土受压应力-应变关系曲线的一般特征,以混凝土开裂为界,提出以混凝土开裂为界的应力-应变关系表达新方式,建议先直线后抛物线的组合方程式,混凝土出现裂缝前采用线弹性关系,开裂后采用二次函数曲线。将新方程用于CFRP外贴加固梁的不以混凝土压碎为破坏标志的弯曲破坏形态相应的承载力公式推导,给出相应的受弯承载力表达式。该计算式无需考虑混凝土的应变是否过了强度峰值,免去了以强度为界时的分段积分,因而可以采用统一的函数式进行计算,达到简化计算的目的,这样不仅考虑了混凝土的适应性,同时也可用作裂缝预判。此外还能减少受力全过程早期模拟的工作量。将采用新承载力公式计算的结果与实例中的试验结果对比分析,结果表明两者吻合较好,证明该曲线合理。

At present,the commonly used compressive stress-strain relationship of concrete is mostly expressed in the form of subsection bounded by peak strength.However,the commonly used expression is complex for the calculation of the flexural capacity in the normal section of CFRP reinforced concrete beams.Especially when multiple materials work together,the computational analysis is too complicated,which would increase the workload of research and practical application.To simplify the calculation,according to the general characteristics of concrete compression stress-strain curve,the stress-strain relation in a new expression of concrete was explored by using the concrete cracking as the demarcation point,and the combination equation with straight line in the first and parabola in the second was then suggested.The linear elastic relation was used before the concrete cracking,and the quadratic function curve was used after cracking.The new equation was used to derive the corresponding bearing capacity formula of the flexural failure form of the CFRP externally reinforced beam without crushed concrete as the damage mark,and the corresponding expression of flexural bearing capacity was given.The calculation formula without considering whether the strain of concrete exceeded peak strength and eliminated the segmented integral when the strength was bounded,thus the unified functional formula can be used for calculation to achieve the purpose of simplifying the calculation.Besides,the early-age simulation of whole process in the early stage was reduced.The results calculated by using the new bearing capacity formula were compared with the experimental results in the example,and the results showed that the two had a good match,which proves that the curve is reasonable.