低周反复荷载作用下PVA-FRCC柱曲率与塑性铰长度研究

Study on the curvature and plastic hinge length of PVA-FRCC column under low cyclic load

为研究柱端掺加聚乙烯醇纤维(PVA)的水泥基中长柱在地震作用下柱端截面绝对曲率与塑性铰长度,对11根PVA纤维水泥基复合材料(PVA-FRCC)柱进行低周反复荷载试验。结果表明,掺入PVA纤维后,柱的裂缝控制能力明显提高,PVA纤维在改善柱裂缝形态方面的作用明显优于纵筋与箍筋;增大纤维体积掺量、PVA-FRCC设置高度、体积配箍率及纵筋配筋率,试件的曲率延性系数增大,下部截面的转动能力提高,此提高作用在加载后期表现得更加充分;纵筋配筋率一定时,采用掺加纤维并设置较少箍筋的方式比单纯设置较多箍筋的方式对提高构件截面延性和改善裂缝形态更有效。最后通过线性回归分析,给出曲率延性系数和塑性铰长度的拟合公式。实际设计中,根据结构抗震等级,PVA-FRCC柱端箍筋加密区或PVA纤维加强区的长度可取为(1.0~1.5)h、柱净高的1/4及500mm三者的最大值。

In order to study the section absolute curvature and plastic hinge length of medium and long cement-based columns with polyvinyl alcohol fiber(PVA)at the column end under seismic action,11 PVA fiber cement composite(PVA-FRCC)columns are tested under low-cycle repeated loading.The results show that the crack control ability of the column improves obviously after adding PVA fiber,and the effect of PVA fiber on improving the crack shape of the column is obviously better than that of longitudinal reinforcement and stirrup.Increasing the fiber volume ratio,the setting height of PVA-FRCC,the volume stirrup ratio and the longitudinal reinforcement ratio,the curvature ductility coefficient of the specimen increases,and the rotational capacity of the lower section increases,which is more fully manifested in the later stage of loading.When the ratio of longitudinal reinforcement is constant,the method of adding fiber and setting less stirrup is more effective than the method of setting more stirrup to improve the ductility and fracture morphology of the member.Finally,through linear regression analysis,the fitting formula of curvature ductility coefficient and plastic hinge length is given.In the actual design,according to the seismic grade of the structure,the length of PVA-FRCC column end stirrup infill area or PVA fiber reinforced area can be taken as the maximum value of(1.0-1.5)h,1/4 of the net height of the column and 500mm.