钢-UHPC-NC组合梁负弯矩区受力性能试验研究

Experimental Study of Fatigue Performance of Steel-UHPC-NC Composite Beam in Negative Moment Zone

为解决钢-混组合梁负弯矩区混凝土面板的开裂问题,采用薄层超高性能混凝土(UHPC)替代部分普通混凝土(NC),制作钢-UHPC-NC组合梁,对组合梁负弯矩作用下的受力性能进行研究。设计制作了2根钢-UHPC-NC组合梁(21cm厚的C50混凝土+4cm厚的UHPC)和1根钢-NC组合梁试件(25cm厚的C50混凝土),通过负弯矩静力加载对组合梁的裂缝特征、开裂荷载、承载力等进行对比分析。结果表明:采用薄层UHPC替代部分组合梁负弯矩区混凝土翼缘的表层,与C50混凝土层相比,UHPC层裂缝分布呈现数量多、宽度小、长度短的特征;同等配筋率下刚度提升7%,对极限承载力影响不大;钢-UHPC-NC组合梁开裂荷载为1400 kN,远高于钢-NC组合梁300kN的开裂荷载。采用UHPC薄层可提高混凝土的开裂荷载,可有效解决组合梁负弯矩区混凝土面板的开裂问题。

A thin course of ultra-high performance concrete(UHPC)can be placed to substitute part of the normal concrete to address the cracking of concrete slabs in the negative moment zone of steel-concrete composite beam.In this paper,the fatigue performance of the composite beam under the action of negative bending moment is investigated.Two steel-UHPCNC composite beam specimens(each with 21cm-thick C50concrete course and 4cm-thick UHPC course)and a steel-NC composite beam specimen(with 25cm-thick C50concrete course)were prepared,to which static loads were applied to the negative moment zones to examine and analyze the cracking loads,cracking property and load bearing capacity of the composite beams.The results demonstrate that the steel-UHPC-NC composite beam cracks when the applied load reaches 1400kN,which is far greater than the 300kN that is for the steel-NC composite beam.When a thin course of UHPC is placed to substitute part of the surface of concrete flanges in the negative moment zones of the composite beams,in contrast to C50concrete course,the cracks in the UHPC course are larger in amount,with smaller widths and lengths.With the same reinforcement ratio,the stiffness of the concrete slabs is improved by 7%,but the ultimate load bearing capacity shows no obvious change.Placing a thin course of UHPC can improve the cracking resistance of concrete and can effectively resolve the cracking issue of concrete slabs in the negative moment zone of composite beam.