面向韧性的大跨度桥钢筋混凝土桥塔抗震性能设计与控制指标

Specific Performance Indices and Appropriate Performance Limits for Seismic Resilience Design of Reinforced Concrete Pylons of Long-span Bridges

摘要:

国内外大跨度桥钢筋混凝土桥塔在安全性设防地震下的性能目标基本一致，但具体的性能控制指标并不相同。系统分析了震后继续服役结构的承载能力极限状态和正常使用极限状态的性能要求，提出了面向韧性的结构抗震性能设计指标，包括残余承载力、残余位移、残余刚度和残余裂缝宽度等。基于巴拿马运河四桥，对比研究了首次屈服、等效屈服、有限延性q=1.5以及钢筋拉应变达到0.01或混凝土压应变达到0.004等4种钢筋混凝土桥塔性能控制指标。结果表明，4种性能控制指标所对应的地震动作用强度差异很大，已超过安全性设防地震和功能性设防地震的差异。基于建立的面向韧性的结构抗震性能设计指标，对4种性能控制指标进行评价。首次屈服、等效屈服和有限延性q=1.5等3种性能控制指标均可满足结构震后不需修复或经简单修复即可继续使用的性能目标；我国现行大跨度桥钢筋混凝土桥塔采用的等效屈服指标过于保守，至少可采用有限延性q=1.5；在充分考虑震后刚度折减对伸缩缝、支座、阻尼元件等变形需求的影响后，可采用钢筋拉应变达到0.01或混凝土压应变达到0.004的材料应变性能控制指标。

Abstract:

The performance objective of reinforced concrete pylons of long-span bridges under the safety evaluation earthquake （SEE） is consistent at home and abroad； however， the specified performance limits used for the seismic design of pylons are quite different. The performance requirements at the ultimate limit state and the operational limit state of post-earthquake structures are analyzed， and then the specific performance indices for the seismic resilience design of post-earthquake structures are presented， including residual capacity， residual displacement， residual stiffness， and residual crack width. Based on the fourth Panama Canal Bridge， the four widely used performance limits， such as the first yield moment， effective yield moment， limited ductility of q=1.5， and limits of material strains， i.e.， steel tensile strain less than 0.01 and concrete compressive strain less than 0.004， are compared. It is shown that the difference between seismic intensities corresponding to the four performance limits is very large， even larger than that between SEE and the functional evaluation earthquake （FEE）. The four performance limits are further evaluated with the specific performance indices presented for the seismic resilience design of post-earthquake structures. The first yield moment， effective yield moment， and limited ductility of q=1.5 can well satisfy the performance objective of sustaining to full functionality after the shock with none or only simple rehabilitation. The currently used performance limit of effective yield moments for the seismic design of pylons under SEE seems too conservative and at least the limited ductility of q=1.5 could be used instead. Moreover， considering the stiffness degradation due to the seismic damage and its effect on the increase of displacement responses of expansion joints， bearings， and damping units， the performance limit of material strains， i.e.， steel tensile strain less than 0.01 and concrete compressive strain less than 0.004， could be employed.