变高度预应力箱梁桥合龙段底板纵向裂缝的成因

Causes of Longitudinal Cracks at Bottom Slab in Closure Segment of Prestressed Box Girder Bridge with Variable Height

从对变高度预应力混凝土箱梁桥跨中合龙段底板位置出现的多种纵向裂缝形态的分类出发,分析了跨中底板在自重和预应力作用下所特有的多重荷载效应,通过对某桥梁的有限元数值模拟对多种纵向裂缝形成的原因进行了验证。结果表明,变高度预应力混凝土箱梁桥跨中合龙段底板纵向裂缝不仅是合龙索径向力与梁体自重作用下的横向框架效应耦合作用导致的,而且合龙索锚固力和梁体自重引起的空间折角效应、合龙索锚固力引起的深梁局部效应也是合龙段底板纵向裂缝形成的重要因素。并进一步对影响合龙段底板横向应力分布的因素进行了参数化分析,提出了控制合龙段底板纵向裂缝出现的设计建议。

Based on the classification of various forms of longitudinal cracks at bottom slab in midspan closure segment of prestressed concrete continuous box girder bridge with variable height,the special multiple load effect of bottom slab in midspan closure segment under prestress and dead load were analyzed,and the causes of longitudinal cracks was verified through numerical simulation of a bridge with finite element method.It is proved that the longitudinal cracks are not only caused by the coupling of horizontal framing effects under radial force of prestressed cables and dead load of box girder,but also caused by the spatial bending angle effect resulted from anchorage force of prestressed cables and dead load of box girder,and the deep-beam effect resulted from anchorage force of prestressed cables.Some parameters were analyzed to research the factors that affect transverse stress distribution in closure segment,and the design improvement of controlling the cracks was proposed.