基于数值仿真的悬索桥锚碇温度敏感性及开裂成因分析

Analysis on Temperature Sensitivity and Cracking Causes of Suspension Bridge Anchorage Based on Numerical Simulation

为了解决悬索桥锚碇在运营期间的开裂问题,针对一座运营10余年、大跨径悬索桥混凝土锚碇逐年增长的裂缝,从索力、环境、材料、施工等多方面因素全面开展了分析。采用大型空间有限元软件建立了锚碇精细化数值模型,模型能够模拟主缆索股力传递给锚体混凝土的真实受力状态。充分考虑桥址环境特点,考虑6种温度工况对锚碇进行了温度敏感性仿真分析,分析了不同温度工况下锚碇结构的应力分布。结果表明:锚碇开裂与锚杆力作用相关性不大;在工况2下整体升温20℃,锚碇侧墙主拉应力达到容许应力1.5倍;工况6下锚碇表面混凝土由40℃骤降为20℃,锚碇侧墙主拉应力达到容许应力的2.4倍;在内外约束双重作用下,冷击效应导致锚碇混凝土表面温度骤降产生“内约束裂缝”,整体升温导致锚碇混凝土膨胀产生“外约束裂缝”,这两种类型裂缝一般为深层裂缝和增长裂缝,该锚碇侧墙竖向裂缝最大深度达到6 cm;环境和施工因素是造成横向施工开裂的主要原因。最终采用外包带防裂钢筋网的高性能混凝土对锚碇进行了加固,后续观测效果良好。

In order to solve the cracking problem of anchorage of suspension bridge during operation,in view of the cracks growing year by year in the concrete anchorage of a long-span suspension bridge in operation for more than 10 years,the factors such as cable force,environment,materials and construction are comprehensively analyzed.The fine numerical model of the anchorage is established by using large space finite element software,which can simulate the real stress state of the main cable force transmitted to the anchor concrete.Taking full account of the environmental characteristics of the bridge site and considering 6 temperature conditions,the temperature sensitivity of the anchorage is simulated and analyzed,and the stress distributions on the anchorage at different temperatures are analyzed.The result shows that(1) there is little correlation between anchor cracking and anchor force;(2) when the overall temperature rise is 20 ℃ in working condition 2,the main tensile stress of the side wall of the anchorage reaches 1.5 times of the allowable stress;(3) when the concrete on the surface of the anchorage suddenly drops from 40 ℃ to 20 ℃ in working condition 6,the principal tensile stress of the side wall of the anchorage reaches 2.4 times of the allowable stress;(4) under the dual effects of internal and external constraints,the cold shock effect causes the sudden drop of the surface temperature of the anchor concrete to produce “internal constraint cracks”,and the overall temperature rise causes the expansion of the anchor concrete to produce “external constraint cracks”,the 2 crack types are commonly deep cracks and growing cracks,the maximum vertical crack depth of the side wall of the anchorage reaches 6 cm;(5) environment and construction factors are the main causes of transverse construction cracks.At last,the anchorage is reinforced with high-performance concrete with anti-crack reinforcement mesh,and the follow-up observation result is good.