某桥主桥为主跨400 m的斜拉桥，1995年建成通车。在交通量激增、荷载超载、预应力损失等因素作用下，部分桥跨主梁呈现下挠加剧，主梁混凝土出现剥落、露筋及开裂等病害。为抑制主梁下挠不断发展的趋势，采用结构自重减载方式（将混凝土人行道板置换为轻型钢人行道板）来部分减缓主梁下挠，并对箱梁顶板底面粘贴碳纤维布进行加固。采用有限元软件建立主桥模型，计算结构自重减载及粘贴碳纤维布对改善主梁下挠的作用效应。结果表明，将混凝土人行道板置换成轻型钢人行道板后，主梁下挠程度相对减小；碳纤维布与主梁共同参与受力，在一定程度上抑制了混凝土病害进一步发展，也避免了因混凝土开裂而造成的主梁下挠，验证了该加固方案的可行性。%A Bridge was opened to traffic in 1995 .Its main bridge is a cable‐stayed bridge with a main span of 400 m .According to the inspection report ,the downwarping of main girder in some spans had been exarcebated ,the main girder concrete began to spalling ,deteriations including con‐crete spalling ,reinforcement exposure and concrete cracking were also found ,the causes of which can be attributed to the surge of traffic ,over load and prestress loss .To curb the exarcerbation of main girder downwarping ,the way of relieving the self weight of the structure was used to partial‐ly slow down the main girder downwarping ,specifically by replacing the concrete slabs in the side‐walks by the ligh weight steel plates ,and the main girder was strengthened by gluing carbon fiber sheet on the base of the top plate of the box girder .The finite element software was used to estab‐lish the model of the main bridge ,to calculate the effect of structural self weight reduction and car‐bon fiber sheets strengthening on the enhancement of main girder downwarping .The results of the calculation indicate that when the concrete slabs in the sidewalks were replaced by light weight steel plates ,the downwarping of side spans adjacent to the main span and the main girder showed the sign of abating .T he carbon fiber sheets joined the main girder to bear loads ,w hich suppressed the progress of the concrete deteriotation and prevented the occurrence of main girder downwarping induced by concrete cracking ,verifying the feasiblity of the retrofit scheme .
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