重度疲劳开裂钢桥桥面的UHPC加固技术

武汉军山长江大桥在服役17年后，桥面板出现了严重的疲劳开裂问题，难以修补，为此提出一种钢桥面板不修补，上铺带横向钢板条的UHPC桥面加固方案。以军山长江大桥为研究背景，应用子模型技术对比计算了钢面板重度开裂时纯钢梁和加固后钢面板的应力状态；制作了双层钢筋网+UHPC的传统轻型组合桥面结构与钢板条+UHPC及三层钢筋网+UHPC两类新型加固结构，开展了横向抗弯静力试验及疲劳试验。研究结果表明：采用UHPC加固技术后，正交异性钢桥面的疲劳应力大幅度下降，其中钢面板-U肋焊趾处的横向拉应力沿纵、横桥向的分布降幅达78.8%～86.4%；UHPC拉应力方面，由于钢面板不修补，UHPC层下缘拉应力高达12.9MPa，UHPC层下缘布置80mm宽间距200mm的钢板条后，其底面名义开裂应力可达43.2MPa，远高于设计拉应力，钢板条+UHPC的钢桥面加固方案经过应力幅22MPa的1000万次疲劳试验，UHPC层具备800万次疲劳寿命(裂缝宽度小于0.05mm)，且刚度无折减，因此可作为永久结构层与重度开裂的钢桥面构成轻型组合桥面结构，经UHPC加固后，原钢桥面的疲劳裂缝有望不再发展。

UHPC-based strengthening technique for significant fatigue cracking steel bridge decks

Wuhan Junshan Yangtze River Bridge has experienced significant fatigue cracking on the deck plates after a service period of six years, and they are difficult to repair. Thus, a novel UHPC-based strengthening technique with steel strips for repairing the OSDs with significant fatigue cracks is proposed. Two types of bridge deck systems, OSD and conventional lightweight steel-UHPC deck (LWCD), were analyzed with the submodel technology to get the stress. The conventional LWCD specimens with two-story bars and two types of modified LWCD specimens with steel strips and three-story bars were manufactures, and the static and fatigue tests were performed. The analysis results indicate that the conventional LWCD can significantly reduce the fatigue details stress, and the transverse tensile stress distribution around the rib-to-deck welded joints can be reduced by 78.8%-86.4%. Under the vehicle load, the maximum design tensile stress at the bottom of UHPC layer was 12.9MPa. The tensile strength of UHPC layer strengthened by 80mm-width steel strips could reach 43.2MPa, which is much higher than the designed stress. Basing on the 10 million fatigue-loading cycles test results of the steel strips strengthening scheme, it is concluded that the UHPC layer has 8 million cycles fatigue life (the crack width is less than 0.05 mm), therefore the permanent UHPC structure layer and the severely cracked steel bridge deck can constitute a lightweight composite bridge deck structure. By the proposed strengthening technique, the fatigue cracking of the deck plate will be well controlled.