自重对混凝土三点弯曲梁断裂性能的影响

自重对三点弯曲梁试件的断裂性能有重要影响，而以往基于三点弯曲梁研究混凝土的断裂性能时，很少考虑自重引起的试件初始裂缝张口位移（CMOD_ini）的影响。为了研究CMOD_ini对三点弯曲梁断裂性能的影响规律，给出了CMOD_ini及考虑CMOD_ini影响的有效裂缝长度（a_c）和失稳断裂韧度（K_ICun）的计算公式，并用不同试件尺寸及不同初始缝高比的三点弯曲梁试验数据进行了对比分析。结果表明:当试件初始缝高比为0.4时，CMOD_ini受试件尺寸影响较小，即使试件尺寸达到2200 mm×550 mm×240 mm时，自重对其CMOD_ini、a_c及K_ICun的影响均小于5%。CMOD_ini受初始缝高比的影响较大，且随着初始缝高比的增大而增大，对于尺寸为1143 mm×305 mm×76 mm，初始缝高比为0.818的三点弯曲梁试件，自重对其CMOD_ini、ac及K_ICun的影响分别为24.26%、1.73%和17.31%。可见，当三点弯曲梁试件尺寸及初始缝高比均较大时应该考虑自重引起的CMOD_ini的影响。

INFLUENCE OF SELF-WEIGHT ON THE FRACTURE PROPERTIES OF THREE-POINT BENDING CONCRETE BEAMS

Self-weight has a significant influence on the fracture properties of beams under three-point bending(TPB).However,the influence of initial crack mouth opening displacement(CMODini)caused by self-weight was rarely considered in previous research on concrete fracture properties based on TPB beams.To investigate the influence of CMODmi on the fracture properties of TPB beams,a calculation formula of CMODini,effective crack length(a)and unstable fracture toughness(KIC^un)considering the influence of CMODini are presented.The calculated results of the formula were compared with the experimental data of specimens of different sizes and initial crack-depth ratios.The results indicate that CMODini is slightly influenced by the specimen sizes.The influence of the self-weight on CMODini,ae and KIC^un is less than 5%even if the specimen size is 2200 mm×550 mm×240mm and the initial crack-depth ratio is 0.4.CMODini is greatly influenced by the initial crack-depth ratio.The influence increases with the increase of the initial crack-depth ratio.Moreover,the influences of the self-weight on CMODini,ae and KIC^un 24.26%,1.73%and 17.31%,respectively,when the specimen size is 1143 mm×305 mm×76 mm and the initial crack-depth ratio is 0.818.Therefore,the influence of CMODmi caused by the self-weight of TPB beams should be taken into account when both the specimen size and the initial crack-depth ratio are large.