持续荷载作用下疲劳损伤混凝土梁的变形性能分析

Deformation performance analysis of fatigue damage RC beams under sustained loading

为明确往复荷载和持载作用下混凝土梁变形的发展规律,本文通过弯曲疲劳加载引入疲劳损伤后采用堆载法对4根梁进行堆载徐变试验,研究疲劳损伤对梁受压区混凝土的徐变发展规律和持续荷载作用下梁变形性能的影响。研究结果表明:相较于无损梁,疲劳损伤梁受拉区混凝土最大裂缝宽度、受压区混凝土总应变和总挠度更大,且在堆载作用下的发展速率更快,随着疲劳损伤程度的增大,各指标也有增大的趋势;疲劳作用促进了混凝土微裂缝的产生和发展,提前并加速了梁徐变变形的发展,导致前期疲劳加载就已产生了部分徐变应变和徐变挠度;基于试验结果建立了疲劳损伤梁受压区混凝土总徐变应变和梁徐变挠度计算模型,发现疲劳循环寿命比为0.025、0.15和0.60时的疲劳残余挠度分别相当于无损梁128、800和1180 d的徐变挠度。

To clarify the development law of deformation of concrete beams under cyclic and sustained loads,the effect of fatigue damage on the creep development law of the compression concrete and the deformation properties of beams un-der sustained load were studied.First,fatigue damage was introduced by the bending fatigue test;next,four-beam creep tests with different degrees of fatigue damage were conducted by surcharge loading.Results showed that the maximum crack width of concrete in the tension zone,the total strain of concrete in the compression zone,and the total deflection of fatigue-damaged beams are larger and faster than those in the nondamaged beam under sustained load,and all indica-tors increase with increasing fatigue damage.The development of concrete microfractures is promoted under cyclic load.Fatigue advances and accelerates the development of creep deformation,implying that partial creep strain and creep de-flection are formed in the early fatigue loading.Based on the experimental results,the calculation models of total creep strain in the concrete compression zone and creep deflection of fatigue-damaged beams are established.When the cyclic loading cycles are 0.025,0.15 and 0.60 times the fatigue life,the residual fatigue deflections are equivalent to the creep deflection of the nondamaged beam for 128,800 and 1180 days,respectively.