循环荷载作用下植筋混凝土梁优化设计研究

Experimental research on optimal design of rebar-planting concrete beam under cyclic load

植筋混凝土梁在达到规定的植筋深度时,经循环荷载作用后植筋端头处截面因抗剪能力不足出现斜裂缝,引起构件脆性破坏。针对此问题,提出了一种优化设计方案,即在植筋端头处设置箍筋。设计6组试件,对比优化前后植筋梁的破坏特征、延性系数、承载力、钢筋应变和疲劳损伤的差异。结果表明：在设计时将植筋端头置于原构件箍筋处能够明显提高植筋混凝土梁的延性系数和承载力,降低疲劳损伤。植筋深度决定了植筋梁的破坏特征,植筋深度小于20d,经优化后的试件仍发生脆性破坏。锚固深度达到25d时,经优化的试件疲劳破坏特征由脆性破坏转为塑性破坏。推导出了与植筋深度和混凝土残余应变相关的疲劳损伤计算公式,经优化设计后试件的疲劳损伤可以降低13.93%-19.24%。

Brittle failure may occur on rebar-planting concrete beam under cyclic load because of shear crack near the end of rebar-planting section even if rebar-planting concrete beam fulfills requirement of rebar-planting depth. A structural optimization measure was put forward to set stirrup at the end of rebar-planting section. Six groups of rebar-planting concrete beams were analyzed through experiments. Parameters before and after optimal design were contrasted,including failure mode,ductility coefficient,ultimate loads,strain of post-installed rebar and fatigue damage. Results show that setting stirrup at end of rebar-planting section can improve the ultimate bearing capacity and deformability effectively and reduce fatigue damage. The failure mode of the rebar-planting beam mainly depends on the planted depth. With the rebar-planting diameter less than 20 d,the brittle fracture occurs for the optimized specimen. With the rebar-planting diameter more than 25 d,the fatigue failure mode of the optimized specimen changed from brittle failure to ductile failure. A formula for calculating the fatigue damage related to the planted depth and the concrete residual strain was deduced. It is shown that the fatigue damage of the specimen can be reduced by 13. 93% ~ 19. 24% after the optimal design.