分级不连续循环载荷作用下混凝土的疲劳特性

Fatigue performance of ordinary concrete subjected to stepwise discontinuous cyclic loading

为研究混凝土在不连续周期荷载作用下的疲劳特性,在常规疲劳加载路径中加入时间间隔,对比开展了混凝土的常规疲劳试验和不连续疲劳试验.研究结果表明:在不连续疲劳试验中,加入时间间隔后的应力循环产生的残余应变(塑性变形)明显大于加入时间间隔前的应力循环产生的残余应变;时间间隔效应从0.062的应力水平开始影响混凝土的疲劳性能,并逐步增强,至应力水平为0.25后趋于稳定;时间间隔后循环内混凝土的弹性模量大于时间间隔前循环内混凝土的弹性模量;不连续疲劳损伤累积速度明显大于常规疲劳损伤,混凝土的不连续疲劳寿命远小于常规疲劳寿命;混凝土不同组分间的残余应力在时间间隔内持续作用,致使裂隙持续扩展,造成时间间隔后循环内残余变形较快发展.

In order to study the fatigue performance of concrete under discontinuous cyclic loads,time intervals were added into the conventional fatigue load path,and the conventional fatigue test and discontinuous fatigue test were carried out.Results show that in the discontinuous fatigue test,the residual deformation (plastic deformation) produced in the stress cycles after adding intervals is larger than that in the stress cycles before adding intervals.The time intervals start to affect the fatigue performance of concrete when the stress ratio (defined as the ratio of maximum stress to the compression strength) is 0.062,and the effect enhances gradually with the stress ratio increasing to 0.25,after which the effect tends to be stable.The elasticity modulus in the cycles after adding intervals is larger than that in the cycles before adding intervals.The cumulative rate of discontinuous fatigue damage is obviously higher than that of conventional fatigue damage,and the discontinuous fatigue life of concrete is much shorter than that of the conventional fatigue.The residual stress between different materials of concrete continues to act during time intervals,causing the crack to continue to expand,resulting in the rapid development of residual deformation in the cycle after adding intervals.