聚丙烯纤维混凝土梁裂缝发展的试验研究与模型计算

Experimental Study and Model Calculation on Crack Development of Polypropylene Fiber Reinforced Concrete Beams

为探究PP-ECC梁在弯曲荷载作用下的裂缝发展规律,制作了8根PP-ECC梁和2根RC梁,首先通过四点弯曲加载研究了其裂缝发展形态、裂缝宽度和延伸高度,并与RC梁进行对比;然后,在考虑梁构件受弯时ECC的抗拉能力的基础上,基于粘结滑移理论和平截面假定建立了裂缝平均间距模型、裂缝最大宽度模型及裂缝最大延伸高度模型,并通过模型计算结果与试验结果的对比对各模型的合理性和准确性进行了验证。结果表明:PP-ECC梁在单轴拉伸时具有明显的应变-硬化特性,呈现多条微裂缝发展的破坏模式;PP-ECC梁在弯曲荷载下的裂缝数量显著多于RC梁,且裂缝发展贯穿整个试验过程;PP-ECC梁主裂缝宽度和延伸高度均小于RC梁,且随荷载增加而呈现较均匀的发展状态;基于粘结滑移理论建立的PP-ECC梁裂缝平均间距模型的精度系数在0.95~1.05之间,裂缝最大宽度模型的精度系数在0.85~1.2之间,基于平截面假定建立的裂缝最大延伸高度模型的精度系数在0.95~1.1之间。

Eight PP-ECC beams and two RC beams were fabricated in order to investigate the crack development law of PP-ECC beams under bending load.Firstly,the crack development pattern,crack width and crack extension height of PP-ECC beams were studied by four-point bending load,and compared with those of RC beams.Then the average crack spacing model,the maximum crack width model and the maximum crack extension height model were established based on the bond-slip theory and plane cross-section assumptions,considering the tensile capacity of the ECC beam when the beam was flexed.And the rationality and accuracy of each model were verified by comparing the model calculation results with the test results.The results show that PP-ECC has obvious strain-hardening characteristics under uniaxial tension,showing a mode of multiple micro-cracks development.The number of cracks in PP-ECC beams under bending load is significantly more than that in RC beams,and cracks develop through the whole test process.The width and extension height of main cracks in PP-ECC beams are smaller than that in RC beams,and cracks show more uniformity with the increase of load.The accuracy coefficient of PP-ECC beam average crack spacing model based on bond-slip theory is between 0.95 and 1.05,the accuracy coefficient of the maximum crack width model is between 0.85 and 1.2,and the accuracy coefficient of the maximum crack extension height model established based on plane cross-section assumption is between 0.95 and 1.1.