【作者】 刘艳辉；

【导师】 强士中；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2008， 博士

【摘要】 基于对现代地震经验和教训的深刻反思,美国学者于20世纪90年代初提出了基于性能的抗震设计理论,这是工程抗震发展史上的一个重要里程碑。基于性能的抗震设计的目的是将所设计的结构在受到不同水平地震作用下的性能达到一组预期的性能目标;它使抗震设计目标由传统的以生命安全为单一设防目标转为考虑生命安全与财产损失两方面的具体要求,强调了“个性”设计。高架桥是现代化大城市的立体交通网络中关键的基础设施,随着城市现代化的发展,在城市生命线工程中占有越来越重要的地位。本文在对城市高架桥的抗震设防水准、性能水准和基于性能抗震设计理论弹性设计等方面的简单探讨基础上,以桥墩顶点位移延性系数为设计参数,建立了一套完整的基于性能抗震设计理论的抗震设计方法,并着重研究了几个相关的关键性问题。1.提出了城市高架桥的抗震设防水准的建议值和高架桥重要性分类标准,并采纳改变设计基准期的方法来体现重要性的差别;提出了城市高架桥的5级性能水准和4个性能目标,确定采用桥墩顶点的位移延性系数作为性能指标;对常规城市高架桥推导了桥墩位移延性系数、破损指标与性能水准的对应关系。2.根据各个重要性等级下各级抗震设防水准下的超越概率,推导了地震影响系数最大值α_max的具体数值,并制作成表格,可用于基于性能的结构弹性阶段的设计,为设计人员提供了更广泛更灵活的选择。3.选取了434条地震波,按《双层城市高架桥抗震设计指南》关于场地类别和地震动特征周期分区的要求分为12组,对大量具有不同屈服强度系数的单自由度体系在进行了弹塑性时程分析,求得了延性需求谱和基于A_y-D_y格式的地震需求谱,并探讨了阻尼比对延性需求谱的影响。研究表明:两种需求谱与结构的强度水平、自振周期有关;阻尼比影响系数与结构的阻尼比、自振周期有关;以上两种需求谱和阻尼比影响系数都受场地类别和地震动特征周期分区等因素的显著影响。通过非线性回归分析,建立了考虑场地类别和地震动特征周期分区等因素的两种需求谱和阻尼比影响系数的数学表达式,其成果可供基于《双层高架桥抗震设计指南》和《城市桥梁抗震设计规范》的高架桥弹塑性阶段设计和相关研究直接使用。特别是A_y-D_y格式的地震需求谱,具有如下性质:过原点的射线与屈服强度系数的需求谱曲线相交,各交点对应的周期都相同,这为实现考虑多级性能目标的基于位移的结构抗震设计提供了便利。4.从5个独立桥墩和6个全桥结构在十几条地震记录作用下的弹塑性时程分析入手,对桥梁结构Push-over分析采用的水平加载模式进行了研究。分析结果表明:对于规则（长细比大于2.5小于10）独立桥墩,采用基于位移的水平加载模式对桥墩进行Push-over分析比基于水平力模式更加合理;桥墩的位移模式由第1模态振型确定,并可简化为桥墩顶部重心处施加一个位移的方式。对于全桥结构,通过对桥梁上部结构位移、桥墩顶点位移和桥墩底部剪力等指标分布规律的分析,得到全桥结构Push-over分析的水平加载模式可采纳在上部结构（各桥墩对应点处）重心处施加水平位移的方式,全桥结构的位移模式由上部结构的模态振型（组合）确定。5.结合求得的延性需求谱和A_y-D_y格式的地震需求谱的数学表达式,提出了结构非线性位移反应的简化求解方法——弹塑性需求谱法。在阐述了弹塑性需求谱法的理论依据基础上,提出用该方法计算桥梁结构弹塑性位移的具体步骤:首先借助模态Push-over分析,将非线性多自由度体系分解为多个独立的非线性单自由度体系及确定有关参数;运用基于A_y-D_y格式的地震需求谱的特点,确定结构在不同模态各级地震作用下的屈服强度系数;根据延性需求谱,确定位移延性系数并得到等效单自由度体系的位移,最后将结果转化为多自由度体系,并进行组合。6.从Mander等人给出的约束应力——应变的本构关系出发,通过一系列的假定,得出了矩形、圆形截面桥墩力学配箍率ω_w、轴压比η_k和曲率延性系数μ_φ之间的关系表达式——桥墩的变形能力公式;将之与25组试验数据进行对比,本文公式与试验结果在平均意义上吻合较好。7.阐述了城市高架桥基于性能的抗震设计的两个阶段和具体的设计步骤:一是弹性设计阶段,这一阶段的设计过程为大家所熟悉,主要是采用反应谱法进行设计;二是弹塑性设计阶段,主要的步骤为:（1）采用弹塑性需求谱法求解结构在指定地震作用下的弹塑性位移;（2）在指定性能目标下,对桥墩的变形能力进行设计。以某城市高架桥的一联作为算例,进行了基于性能的抗震设计,并将计算结果与弹塑性时程分析结果进行比较,证明了本文方法的正确有效。更多还原

【Abstract】 Based on the profound reconsidering to modern earthquake experience and lesson, the American scholars proposed performance-based seismic design theory in the beginning of 1990s, this is an important milestone in the engineering seismic development history. The core content of the performance -based seismic design theory is to make the structure achieves a group of anticipated performance objectives under different design earthquake levels; It causes the seismic design objective changed from the traditional objective which taking the safety as the single defended goal to consider safety and the property damage two aspects requirement, emphasizing the individual design. The viaduct is the essential infrastructure in transport networks of modern cities, along with the development of urbanization process, it holds the more and more important status in the city lifeline project. Based on the simple discussion on urban viaduct earthquake design levels, performance levels and structural performance-based seismic elastic design, in this dissertation , a set of performance-based seismic design method for urban viaduct is established completely by taking the bridge pier top displacement ductility coefficient as design parameter, and several related key problems are emphatically studied.1. Proposed the purposed value of the urban viaduct earthquake design levels and importance classification levels, and by changing the design reference period method to represent the important difference; Proposed the urban viaduct 5 performance levels and 4 performance objectives; Selected the displacement ductility coefficient of bridge pier top as the performance parameter; It is deductived in this dissertation about the corresponding relations of displacement ductility coefficient of bridge pier top, the damage index and the performance levels to conventional urban viaduct.2. According to the exceeding probability under all of design earthquake levels in certain important level, the earthquake affecting coefficient maximum α_max is deductived and manufactured to table form, this is available to performance-based seismic design in elastic stage, and provided a more widespread more flexible choice to design personnel.3. In this dissertation, 434 earthquake ground motion records are selected, and be classified into 12 groups according to the soil conditions and the earthquake ground motion characteristic periods grouping in "Double-decked Urban viaduct Earthquake resistance Design Guide", The elasto-plastic time history analysis is carried on to a great deal of SDOF system with various yield strength coefficient, and obtained the ductility demand spectrum,the A_y-D_y form earthquake demand spectrum and the damping ratio influence coefficient. The research indicated that, the two kinds of demand spectra are related to yield strength coefficient and periods,and the the damping ratio influence coefficient are related to damping ratio, the above three items depend on soil conditons and earthquake ground motion characteristic period groupings strongly. Through the non-linear regression analysis, the mathematical expressions of above two kinds of demand spectra and the damping ratio influence coefficient are established that considering soil conditions and earthquake motion characteristic periods grouping, it might supply in viaduct design in plastic randge and correlative research based on "Double-decked Viaduct Earthquake resistance Design Guide" and "City Bridge Earthquake resistance Design Standard" .Specially the A_y-D_y form demand spectrum, that has the following characteristic of that structural periods represented by radial lines which crossing zero point intersecting demand spectra with different ductility factors are all the same. This has provided the convenience for the realization multiple performance objectives in displacement-based seismic design.4. In this dissertation, the lateral load pattern for bridge Push-over analysis is studied by means of elasto-plastic time history analysis to 5 single piers and 6 whole bridge structures under tens of earthquake ground motion records. The analysis result indicated that: to regular single pier （slenderness ratio is bigger than 2.5 and smaller than 10） , it is more reasonable that by using displacement-pattern-based lateral load pattern in bridge Push-over analysis than lateral force-pattern-based; The bridge pier displacement pattern is determined by the 1st vibrate mode, and may be simplified to a single displacement that loading on the center of gravity of bridge superstructure. As for the whole bridge structure, by analyzing the distributation of the displacement of superstructure, the displacement of pier top and the pier base shearing force, the Push-over analysis displacement pattern is determined by the vibrate mode and it’s combination of superstructure.5. Based on the ductility demand spectrum and the A_y-D_y form demand spectrum, Elasto-plastic demand spectral method is proposed to calculate the non-linear displacement responded. The basic solving process of elasto-plastic demand spectral method is put forward. Firstly , the MDOF system is decomposed into several inelastic SDOF systems using modal Push-over analysis, and to determined related parameter; Secondly, the yield strength coefficient under difference vibrate mode and difference design earthquake levels are determined using A_y-D_y form demand spectrum; Thirdly, according to the ductility demand spectrum, the displacement ductility coefficient and the equivalent SDOF system displacement are obtained; Finally, the displacement of equivalent SDOF system is transformed to MDOF system, and be combined.6. Starting with the stress-strain constetutive relationship of confined concrete which from Mander et al., through a series of hypotheses, the deformation capacity formulas of rectangular, circular section bridge pier are proposed , which shows the relationship among mechanical stirrup reinforment ratioω_w, the axial compression ratioη_k and the curvature ductility coefficientμ_φ. At the same time , the formula is evaluated with 25 group of tentative data, and the result showsμ_φcalculated by the formula approaches to test data in the average significance.7. The urban viaduct design procedure based on performance seismic design theory is proposed: Firstly, the response spectrum method is used in the elastical design range, that is familiar with for everybody; Secondly, in elasto-plastic design stage, the main step is: （1） Calculating the elasto-plastic displacement under a certain design earthquake level by using the elasto-plastic demand spectral method; （2） Designing the deformation capacity of bridge pier under a certain performance objective. The completed design procedure is illustrated with a urban viaduct, and the elasto-plastic time history analysis is used to validate this method. It shows that the elasto-plastic demand spectrum method is effective and correct to calculate the nonlinear displacement.更多还原