弯曲荷载作用下PP-ECC梁裂缝发展规律试验研究

Experimental Study on the Crack Development Law of PP-ECC Beams Under Bending Load

本文通过四点弯曲试验,研究PP-ECC梁在弯曲荷载作用下的裂缝发展规律,并与RC梁进行对比.研究结果表明:新裂缝的产生几乎贯穿了PP-ECC梁的整个加载阶段,并且在极限阶段呈现出多条主裂缝共同发展的破坏状态,同时,裂缝的发展模式以及发展形态也更为多元化.而RC梁表面不再有新裂缝产生,在加载后期则会出现单条较为明显的主裂缝;相同配筋率下,PP-ECC梁破坏时产生的裂缝数量远高于RC梁,裂缝数量增长率分别为420%和780%,并且随着配筋率的提高,RC梁与PP-ECC梁受拉区产生的裂缝数量逐渐减小;RC梁受拉区底部裂缝的延伸率达到了100%,而PP-ECC梁底部受拉区裂缝的延伸率则随着配筋率的提高而逐渐提高,平均延伸率为66.83%,远低于RC梁,较低的裂缝延伸率说明了PP-ECC梁具备比RC梁更好的受拉区裂缝控制能力.PP-ECC梁的最大裂缝宽度远小于RC梁,其最大裂缝宽度分别为RC梁试件的35.3%和38.5%,主裂缝的宽度随着加载级别的提升而呈现出近线性发展规律,PP-ECC梁的主裂缝的发展更为均匀稳定,并且随着配筋率的提高,RC梁与PPECC梁的最大裂缝宽度不断增大;PP-ECC梁裂缝最大延伸高度小于相同配筋率下RC梁的裂缝最大延伸高度,同时,加载过程中,PP-ECC梁的主裂缝宽度和裂缝数量发展以及主裂缝延伸高度和开裂宽度发展均体现出较高的一致性和同步性.

In this study,the crack development law of PP-ECC beams under bending load is investigated through a four-point bending test,and the results are then compared with that of RC beams.Results show that the generation of new cracks occurs during almost the entire loading stage of the PP-ECC beam,and the failure state of multiple codeveloping main cracks is observed during the limiting stage.Moreover,the crack development mode and development form diversify further.No new cracks are generated on the surface of the RC beam,and a single evident main crack appears during the later stage of loading.At the same reinforcement ratio,the number of cracks generated when the PP-ECC beam is damaged is much higher than that of the RC beam,and the number of cracks increase to 420%and 780%,respectively.With the increase in reinforcement ratio,the number of cracks in the tension zone of the RC and PP-ECC beams gradually decreases,and the elongation rate of the cracks at the bottom of the RC beam tension zone reaches 100%.The crack elongation of the tensile zone at the bottom of the PP-ECC beam gradually increases with the increase in reinforcement ratio,with an average elongation rate of 66.83%,which is considerably lower than that ofthe RC beam.The low crack elongation indicates that the PP-ECC beam has better crack control ability in the tension zone in comparison with the RC beam.The maximum crack width of the PP-ECC beam is much smaller than that of the RC beam,and the maximum crack width is respectively 35.3%and 38.5%of the RC beam specimen.With the increase in loading level,the width of the main crack shows a nearly linear development law,and the development of the main crack of the PP-ECC beam improves in terms of uniformity and stability.With the increase in reinforcement ratio,the maximum crack width of the RC beam and the PP-ECC beam continues to increase.Moreover,the maximum extension height of the crack of the PP-ECC beam is smaller than that of the RC beam at the same reinforcement ratio.During the loading process,the development of the main crack width and the number of cracks and that of the main crack extension height and crack width show high consistency and synchronization.