预应力混凝土箱形连续梁桥裂缝成因分析及对加固方案的评价

预应力混凝土箱梁桥中出现剪力引起的斜裂缝的现象非常普遍。从设计方面寻找斜裂缝出现的原因,对现有的预应力加固方法的有效性进行探讨。从工程实例出发,利用虚拟层合有限单元法对桥梁加固前、后的空间计算做了分析,得出桥梁加固前、后两阶段的受力情况。经分析发现:竖向预应力的不足以及预应力筋的布置不妥所造成的过大局部应力是导致产生斜裂缝的主要原因。同时发现:现有的预应力加固方案中加固设计没有有效弥补原有方案的缺陷。经计算斜裂缝处的应力在加固后仍为拉应力,在设计荷载下裂缝将继续开展,试验结果也证明了这一点。

Analysis of cracks in continual box-girder with prestressed concrete bridge and assessment of reinforcement

The presence of cracks caused by shear in continual box-girder with prestressed concrete bridge is quite common. This paper deasls with the causes of these cracks in terms of design methods and the efficiency of the strengthening using prestressed concrete is discussed. The study is based on a real bridge which has crack of this kind. To find out the reasons which cause the cracks, the spatial analysis using the method of virtual laminated element(MOVLE) is done on the bridge. Two models of the bridge are set up for the analysis. One model is the bridge which has been strengthened and the other is the bridge which is not. From the results of the spatial analysis, lacking of vertical prestressed steel and improper disposition of prestressed steel which caused great local stress in concrete are the main reasons. The study also shows that the cracks will still develop under present prestressed reinforcement designing because the stress at the place of the cracks is tension stress after strengthening. The field experiment has also proved that.