开裂预应力混凝土梁的检测、评估和加固

应用钢筋混凝土基本理论,分析预应力混凝土结构开裂的力学成因。以3座典型有裂缝预应力混凝土桥梁为例,论述检测、评估和加固方法。从梁体跨中挠度和支点转角的大小及影响线、结构变形的协同性判断裂缝对结构整体受力状态的影响。从开裂截面的应变分布、实测应变与加载弯矩关系、应变值大小以及截面中性轴的稳定性综合判断开裂截面的工作状态和承载能力。当评定结果为梁体的预应力度满足要求时,对主要起受压作用的混凝土开裂区采用高标号钢筋混凝土在梁肋两侧增加断面的方法予以加固,对其他混凝土开裂区采用灌缝处理,对受拉区,可在局部加贴钢板加固。当评定结果为梁体的预应力度严重不足时,先对裂缝进行灌缝处理,然后采用在受拉区表面大面积粘贴10 mm钢板加固。

Inspection, Evaluation and Reinforcement of Fissured Prestressed Concrete Girder

The mechanical cause for forming fissures in prestressed concrete structure is analyzed by employing the basic theory of reinforced concrete. Inspection, evaluation and reinforcement methods are illustrated by taking 3 typical prestressed concrete bridges with fissure as examples. The influences produced by fissures on the stressed condition of the overall structure is judged in terms of the deflection of girder mid-span, the size of the intersection angle of the support point, and the coordinative factors affecting line and structure deformation. The working status and the bearing capacity of fissure section are judged synthetically by strain distribution, the relation between field test strain and the applied moment, size of strain value and the stability of section neutral axis. When the evaluation result of girder prestressing force meets the requirement, for concrete fissure area under main compression, high grade reinforced concrete will be adopted to strengthen both sides of girder rib by the method of adding section. For other concrete fissure area, crack pouring method is employed. Steel plate will be locally used to strengthen the area under tension. When the evaluation result of girder prestressing force is severely insufficient, fissures will be first treated with the method of crack pouring. Then 10 mm steel plate is used massively to strengthen the surface of the area under tension.