关于改进我国大跨缆索支承桥抗震设计的意见
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摘要
结合我国公路大跨缆索承重桥抗震设计规范的编制和修订 ,讨论“中震不坏 ,大震可修”的两阶段抗震设计原则 ,用重现期表示两个地震动水准 ,分析模型应包含伸缩缝的摩擦和撞击并考虑非经典阻尼。弹性设计使用反应谱振型分解法 ,设计反应谱应针对不同阻尼比 ,其周期范围应达到桥的基本周期 ,当一座桥不同桥墩地基有不同场地类型时建立包络谱或加权平均谱的方法 ,反应谱振型分解法中用有效振型参与质量比确定参与组合的振型数 ,并可用横桥向加速度反应谱与剪切行波引起的结构水平最大转角间的关系以及用压缩行波引起的地基相对位移的简化计算法近似确定非一致地震动的影响 ,分析对地震地面运动三方向分量的反应的必要性及组合方法。非弹性设计使用时程分析法 ,此时恒载与地震地面运动三方向分量时程应当同时作用到结构上 ,使用高质量一致或非一致地震地面运动时程 (包括近场强震特有的大速度脉冲 )的必要性和产生方法 ,用Pushover分析验算非弹性时程分析的结果 ,能力设计的必要性和超强系数的确定 ,以及延性设计的特殊构造要求。
Seismic design of long-span cable-stayed b ridge is based on two-level earthquake ground motions represented by the return period, one for elastic design against modest earthquake, and the other for inel astic design against strong earthquake. Requirements of analytical models of suc h bridge for the two levels are discussed including an emphasis on details of ex pansion joints. For the elastic design, the mode number for mode combination sho uld be determined from the effective mode participation mass. The response spect ra should be extended to the first eigen period of bridges. The non-classical d amping should be considered because unevenly distributed damping in the bridge s ystem and can be solved by using modal superposition procedures. Seismic respons e spectral components in three directions for different damping ratios should be used and responses to the three components of seismic motions should be combine d. Modification of response spectra is discussed when sites at foundations of di fferent pylons and piers are different. The elastic effects of asynchronous seis mic ground motion is important and can be solved in simple ways. The elastic hor izontal rotation induced by traveling waves of transverse seismic acceleration c an be determined by acceleration response spectra in the transverse direction. T he pseudo-static effects induced by compressive waves of longitudinal seismic ac celerations can be solved from maximum seismic ground velocity impulses.For inel astic design, bridge analytical model should represent friction and impact at ex pansion joints. Issues on generating synchronous and asynchronous three-compone nt seismic ground motion time histories satisfying responses spectra, with ″fli ng″ caused by earthquakes with near by seismic center are discussed. The pushov er analysis should be used to give deformation and ductility capacity of bridges and to compare with analytical inelastic deformations for checking if damage in bridge under intensive earthquakes is repairable. Finally the necessity of capa bility design of concrete pylons and piers is discussed. For the part of concret e pylons and piers which neither binding yielding nor shear failure is permitted . Expression on over strength factors is discussed on the basis of statistic dat a taken in China. Requirements on longitudinal reinforcements and stirrups in pl astic hinge areas are also discussed in the paper.
Seismic design of long-span cable-stayed b ridge is based on two-level earthquake ground motions represented by the return period, one for elastic design against modest earthquake, and the other for inel astic design against strong earthquake. Requirements of analytical models of suc h bridge for the two levels are discussed including an emphasis on details of ex pansion joints. For the elastic design, the mode number for mode combination sho uld be determined from the effective mode participation mass. The response spect ra should be extended to the first eigen period of bridges. The non-classical d amping should be considered because unevenly distributed damping in the bridge s ystem and can be solved by using modal superposition procedures. Seismic respons e spectral components in three directions for different damping ratios should be used and responses to the three components of seismic motions should be combine d. Modification of response spectra is discussed when sites at foundations of di fferent pylons and piers are different. The elastic effects of asynchronous seis mic ground motion is important and can be solved in simple ways. The elastic hor izontal rotation induced by traveling waves of transverse seismic acceleration c an be determined by acceleration response spectra in the transverse direction. T he pseudo-static effects induced by compressive waves of longitudinal seismic ac celerations can be solved from maximum seismic ground velocity impulses.For inel astic design, bridge analytical model should represent friction and impact at ex pansion joints. Issues on generating synchronous and asynchronous three-compone nt seismic ground motion time histories satisfying responses spectra, with ″fli ng″ caused by earthquakes with near by seismic center are discussed. The pushov er analysis should be used to give deformation and ductility capacity of bridges and to compare with analytical inelastic deformations for checking if damage in bridge under intensive earthquakes is repairable. Finally the necessity of capa bility design of concrete pylons and piers is discussed. For the part of concret e pylons and piers which neither binding yielding nor shear failure is permitted . Expression on over strength factors is discussed on the basis of statistic dat a taken in China. Requirements on longitudinal reinforcements and stirrups in pl astic hinge areas are also discussed in the paper.
引文
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[2] TYLinInternational.SanFranciscoOaklandBayBridge,EastSpanSeismicSafetyProject,DesignCriteria,Draft71699,Revi sion7[S].SanFrancisco,USA ,1999.
[3] TYLinInternational.GoldenGateBridgeSeismicEvaluation[S].SanFrancisco,USA ,1990.
[4] 日本道路协会.道路桥示方书[M].耐震设计篇.1996.
[5] CENEUROCODE 8.DesignProvisionsforEarthquakeResistanceofStructuresPart2:Bridges[S].1994.
[6] 交通部.公路工程抗震设计规范JTJ 00489[S].北京:人民交通出版社,1990.
[7] RWClough,JPenzien.DynamicsofStructures[M].McGrawHill,NewYork,1993.
[8] SEAOC .RecommendedLateralForceRequirementsandCommentary,16thEd.[S].USA ,1997.
[9] 本四联络桥公团.耐震设计基准[S].1977.
[10] Caltrans.GuidelinesforGenerationofResponseSpectrumCompatibleRockMotionTimeHistoriesforApplicationtoCaltransTollBridgeSeismicRetrofitProject[S].California,USA ,1996.
[11] KTamura,etal.GroundMotionCharacteristicsforSeismicDesignofHighwayBridges[C].2ndItalyJapanWorkshoponSeismicDe signandRetrofitofBridges.Rome,Italy,1997.
[12] 郭修武,贡金鑫.工程结构可靠性[M].西安:地震出版社,1995.
[13] MNPriestley,GCalvi.SeismicDesignandRetrofitofBridges[M].JohnWiley&Sons,NewYork,1996.
[14] 秦 权,楼 磊.非经典阻尼对悬索桥地震反应的影响[J].土木工程学报,1999,32(3):17—22.
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