摘要:疲劳损伤和大气腐蚀作用致使斜拉索性能退化,影响斜拉桥运营期的安全水平.为了分析拉索抗力退化对斜拉桥体系可靠度的影响, 建立了斜拉索抗力退化的串并联概率模型,提出基于机器学习的斜拉桥时变体系可靠度分析方法.以经典斜拉桥和某大跨度双塔混凝土斜拉桥为工程背景,研究了考虑拉索抗力退化的结构时变体系可靠度.研究结果表明:对于稀索体系的小跨度斜拉桥,随着斜拉索抗力的逐步退化,桥梁结构体系的主要的失效路径为由梁和塔的弯曲失效逐渐转变为由拉索腐蚀引起的拉索强度失效;当拉索抗力退化后的可靠度低于主梁关键截面可靠度时,结构体系可靠度将显著降低;对于密索体系的大跨度斜拉桥,在拉索疲劳和腐蚀共同作用下,该斜拉桥体系可靠指标将在29年降低到5.2.
关键词:斜拉桥;抗力退化;腐蚀;强度失效;风险评估;体系可靠度
中图分类号:U448.27文献标志码:A
System Reliability Assessment of Cablestayed
Bridges Considering Cable Resistance Degradation
LIU Yang1, WANG Qinyong1,2, LU Naiwei1
(1. School of Civil Engineering, Changsha University of Science and Technology, Changsha410114, China;
2. National Joint Engineering Research Laboratory for Longterm Performance Improvement Technology
for Bridges in Southern China, Changsha University of Science and Technology, Changsha410114, China)
Abstract:Fatigue damage and atmospheric corrosion lead to the degradation of cable performance, which affects the lifetime safety risk of the cablestayed bridge. In order to investigate the influence of cable resistance degradation on the system reliability of cablestayed bridges, a seriesparallel probability model of the cable resistance was established. A framework for timevariant system reliability evaluation of cablestayed bridges was presented based on machine learning. Both a typical bridge and a longspan cablestayed bridge were selected as prototypes to investigate the influence of the cable degradation on their structural system reliability indices. Numerical results show that the dominant failure sequence of the shortspan bridge with shortspacing cables changes from the bending failure of girders and pylons to the tensile failure of cables due to the cable corrosion. As a result, the structural system reliability significantly decreases in the period that the cable reliability is inferior to the one of the critical girder. For the longspan bridge with longspacing cables, the system reliability index decreases to the threshold value 5.2 in the 29year service period taking into account both fatigue and corrosion.
Key words:cablestayed bridge; resistance degradation; corrosion; strength failure; risk assessment; system reliability
斜拉橋结构体系的优点之一是斜拉索为主梁提供了弹性支撑[1].然而,拉索作为斜拉桥的主要承重构件,易受大气腐蚀及车载疲劳损伤致使强度降低[2].Mehrabi等[3]研究发现Hale Boggs桥的72根斜拉索中有39根在25年服役期后需修复或更换.拉索强度退化增加了拉索断裂的风险,同时可能导致其他拉索、主梁的破坏,甚至整个结构的倒塌,工程结构设计中需采用抗连续性倒塌的理念对此类结构进行设计.虽然斜拉桥的相关设计规范中提出了鲁棒性的建议,但仍需进一步研究随机因素与斜拉索抗力共同作用下既有斜拉桥的体系可靠度.