大跨径梁式桥的主要病害

论述了预应力混凝土大跨径梁式桥的两种主要病害,一是跨中下挠,二是梁体开裂。分析了跨中下挠、垂直裂缝、斜裂缝、纵向裂缝的原因,并叙述了预防对策。这些对策主要是:梁有足够的正截面和斜截面强度;设计中要控制恒载挠度(包括徐变挠度)在一个较小值;在梁纵向两悬臂端施加水平力对顶后合龙;三维分析箱梁主拉应力并布置预应力束;预留体外备用钢束;混凝土加载龄期不小于7天;竖向预应力应两次张拉以保证有效预应力。

Main Faults in Large Span Beam Bridges

Two kinds of main faults in large span prestressed concrete beam bridges are discussed.The first one is excessive deflection in the midspan of the beam,and the second one is the cracking in the beam.The reasons of producing excessive deflection and cracking including vertical cracking,skew cracking and longitudinal cracking are analysised in the paper,and the prevention countermeasures are also discussed.These prevention countermeasures are mainly as follows.The beam has enough strength in the normal cross sections and skew cross sections.The deflection of dead load(including the deflection due to creep)is controlled within a defined smaller value.Before beam clousure,the horizontal forces are applied from one cantilever end to the other.The main tensile stresses are analysed with 3D method,and prestressed strands are arranged correspondingly.External prestressed strands are prepared in advance.The loading age of the concrete is not less than 7d.The vertical tendon had to be prestressed twice to ensure effective prestressing.