悬索桥平行钢丝主缆强度模型研究及承载力评估

Strength Model of PPWS Main Cable of Suspension Bridge and Load Bearing Capacity Evaluation

主缆是悬索桥的重要受力构件,美国国家公路合作研究项目报告(NCHRP Report 534)定义了脆性钢丝、有限延性和简化3种主缆强度模型。为准确计算及评估运营期悬索桥主缆的承载力,以某大跨度悬索桥为研究对象,进行开缆试验,采用3种强度模型对主缆承载力进行计算,对比分析各强度模型的适用性,并评估该桥主缆的安全性。结果表明:脆性钢丝模型综合考虑了各组钢丝的极限应力统计数据,具有较强的适用性;有限延性模型综合考虑了各组钢丝的应力~应变关系,宜在各组钢丝应力~应变曲线差异显著时使用;在未出现第五组腐蚀钢丝时,可采用简化模型初步评估主缆承载力;基于脆性钢丝模型、有限延性模型和简化模型得到的主缆下游跨中节段的承载力损失率分别为6.53%、10.65%、6.30%,安全系数分别为2.80、2.68、2.81;该桥最小安全系数大于设计值,主缆跨中节段在运营20余年后仍具有充足的安全储备。

Main cables are the vital load-bearing components of suspension bridges.In the Guidelines for Inspection of Suspension Bridge Parallel Wire Cables(NCHRP Report 534),three types of main cable strength models are defined,including the brittle steel wire model,limited ductility model and simplified model.A long-span suspension bridge is used as a prototype bridge in the study.The midspan sections of the main cables were opened to test and analyze the corrosion condition as well as mechanical property of the steel wires.The three types of main cable strength models were established to compute the load bearing capacity and assess the safety of the main cables.The results show that the brittle steel wire model is widely applicable,since it considers the ultimate stress statistics of the steel wires in each group.The limited ductility model takes account of the relationship between stress and strain of steel wires in each group,which is a better option when the differences among the stress-strain curves of steel wires in each group are significant.When there are no wires rated the fifth grade of corrosion,the simplified model can be used to preliminarily evaluate the load bearing capacity of the main cable.For the downstream midspan main cable section,the load bearing capacity ratios gained by the brittle steel wire model,limited ductility model and simplified model are 6.53%,10.65%and 6.30%,respectively,with corresponding safety factors being 2.80,2.68 and 2.81,respectively.The minimum safety factor is greater than the design value,proving that the midspan sections of the main cables still have sufficient safety margin after 20 years of service.