徐变对增大截面法加固受弯构件的抗弯承载力的影响研究

Study on the influence of creep on flexural capacity of RC flexural members strengthened with increasing section method

基于线性徐变及平截面假定,在考虑应力滞后效应的基础上,研究徐变对增大截面法加固钢筋混凝土受弯构件抗弯承载力的影响,确定徐变影响下的新增钢筋强度利用系数,验证现行GB 50367-2013《混凝土结构加固设计规范》用新增钢筋强度利用系数0.9来考虑应力滞后效应、徐变和收缩等综合因素影响的适用性。本文根据增大截面法加固受弯构件开裂截面长期应力应变分布,推导了构件在长期荷载下的平衡方程并利用MTLAB编写程序求数值解,在此基础上推导受弯构件持荷后短期加载过程中的力与力矩平衡方程,确定徐变影响下加固构件承载力及新增钢筋强度利用系数。计算典型工况并将本文计算结果与采用加固规范公式及仅考虑应力滞后效应公式的计算结果进行对比分析,结果表明:在线性徐变范围内,徐变对受弯构件抗弯承载力影响较小,可不考虑;考虑应力滞后效应及徐变影响时新增钢筋强度利用率大于0.98,规范公式满足截面抗弯承载力要求,且有一定安全储备。

Based on the assumptions of linear creep and plane section,the influences of creep on the bearing capacity of reinforced concrete flexural members strengthened with increasing section method is studied,and the strength utilization coefficient of additional reinforcement under the influence of creep is determined.The applicability of the current"Code for Design of Reinforcement of Concrete Structures",which uses the strength utilization factor 0.9 of new reinforcement to consider the influence of stress lag,creep,shrinkage and other comprehensive factors is verified.According to the cracking section enlarged cross section method to reinforce flexural members long-term stress and strain distribution,component under long-term load balance equation is deduced and numerical solution using MTLAB program,on the basis of flexural member is derived after the charge in the process of short-term load force and moment balance equations,to determine the bearing capacity of the strengthened beam under the influence of creep and the reinforced strength utilization coefficient.The typical working conditions are calculated and the results are compared with those calculated by the reinforcement code formula and the formula only considering the stress lag effect.The results show that the creep has little effect on the flexural capacity of the flexural member in the linear creep range,so it is not considered.Considering the influence of stress lag and creep,the steel utilization ratio of the newly added reinforcement is greater than 0.98.The standard formula meets the requirements of section flexure bearing capacity and has a certain safety reserve.