某地铁桥梁箱梁下挠及开裂检测评估处治技术

某地铁高架桥为65 m+120 m+65 m预应力混凝土变截面连续梁桥，建成后运营不久发现主梁产生较大的竖向下挠，并且主梁跨中底板出现较多延伸至腹板的横向裂缝。为了解主梁下挠和裂缝产生的原因以及目前桥梁的技术状况，对该桥梁进行了专项检测，并采用有限元软件进行结构验算。检测及验算结果表明：该桥梁体下挠和开裂的主要原因主要是梁体跨中预应力的损失，特别是底板束预应力损失过大或张拉不足而导致的梁体抗弯承载力不足。根据检测评估结果主要采用了体外预应力钢束进行维修补强。维修处治后的荷载试验表明，桥梁强度、刚度及动力性能均满足规范要求，桥梁加固处治效果良好。

Detection, Evaluation and Treatment Technique of Down-warping and Cracking of a Subway Bridge Box Girder

A subway viaduct is a 65 m + 120 m + 65 m pre-stressed concrete variable cross-section continuous beam bridge. Soon after its completion, it is found that there is the larger vertical down-warping in the main girder, and there are more transverse cracks extending to the webs at the baseplate in the middle span of the main girder. In order to understand the causes of down-warping and cracks of the main girder, and the current technical conditions of the bridge, the special detection is carried out for this bridge, and the finite element software is used to check the structure. The detection and checking results show that the main causes of bridge down-warping and cracking the loss of mid-span prestressing of the bridge. Especially, the flexural capacity of the girder is insufficient due to excessive prestress loss or insufficient tension of baseplate beam. Based on the results of detection and evaluation, the external pre-stressing steel beam is used to maintain and reinforcement. The load test after the maintaining treatment shows that the strength, rigidity and dynamic performances of the bridge all meet the standard requirements. The reinforcing treatment effect of the bridge is good.