【作者】 江辉；

【导师】 朱晞；

【作者基本信息】 北京交通大学 ， 防灾减灾工程与防护工程， 2007， 博士

【摘要】 近断层区的严重震害给抗震界提出了新的课题,靠近活动断层区域的地震动以其长持时速度脉冲的巨大破坏能力而对现行抗震设计方法提出了新的考验,迫切需要在搞清近断层地震动主要特性的基础上改进现有的抗震设计方法。随着近年来仪器技术的进步,已经记录到相当数量高质量的近场强震记录,使这项研究具备了地震输入的必要基础。由于结构对地震作用的抵御在本质上是地震输入能量的消耗过程,本文以脉冲型近场地震动为对象,发展了桥梁结构基于能量的性能评估方法,建立了能够同时考虑累积耗能和最大变形需求的基于预期性能目标的桥梁结构抗震设计方法,主要工作如下:1.挑选具有速度脉冲的典型近震记录为输入,以隔震连续梁桥为对象提取了决定速度脉冲破坏能力的控制参数I_p,建议了一种采用三角函数叠加高频分量的速度脉冲模拟模型,并利用所收集到的世界范围内的近断层强震记录对脉冲控制参数进行了回归分析。引入累积能量和瞬时能量概念,能量谱分析表明在近断层地震动诸参数中,脉冲周期和脉冲强度是影响结构峰值响应的决定性因素,累积输入能量受高频地震分量影响明显,而瞬时输入能量则主要取决于速度脉冲。等效单墩的算例分析表明,瞬时输入能量是表征地震破坏能力的有效指标,从累积耗能比和瞬时耗能比的分布特征可得出,LRB双线性隔震支座耗能效率在0.3～0.6的范围内,表明近场脉冲下被动隔震装置的耗能能力有待提高,需要发展合理可靠的减震、耗能方式。2.在总结既有的输入能量简化计算方法不足之处的基础上,建议了一种基于谱速度的改进模型,用近场记录验证了本文方法的准确性。基于地震动记录分组,进行了输入能量均值谱、84%包络曲线的分布特征分析,采用半经验、半统计方法建议了适用于0～15km断层范围内的输入能量设计谱(EIDS),并用实际记录进行了验证。与日本建筑抗震规范(1985、2001)及Akiyama、Climent等模型的对比表明,本文建议的设计能量谱能较好的反映近断层区潜在的能量需求,而其他规范则存在取值偏低等明显不足。从所建议的输入能量简化计算模型出发,推导了与当前中、美主要抗震设计规范(GB50011-2001、UBC97)加速度谱相容的输入能量等效速度谱,和本文所建议设计谱对比表明我国GB50011-2001规范除在Ⅲ、Ⅳ类场地下的9度罕遇烈度设防地震下能一定程度上体现近场地震的能量放大效应外,在其他设计加速度和场地条件下均明显低于断层距在0～15km范围内的能量输入需求,近场地震中速度脉冲效应(Fling or Pulse Effect)对结构破坏的影响在GB50011-2001规范的反应谱曲线中未能反映出来,其谱参数需要进行调整;而与美国UBC97规范相容的能量谱对比表明除了在基岩场地(S_A)上UBC97规范参数取值偏低外,在其他场地条件和断层距范围内均和本文所建议的0～15km断层距的输入能量谱较好地吻合,表明该规范采用近场因子N_A、N_v考虑近场效应是必要的,也从另一角度印证了本文建议谱的合理性。3.在对记录分组进行大量工况分析的基础上得出影响输入能量分配的决定性因素为结构阻尼和变形延性,提出了引入长周期下降段的全面考虑结构阻尼和延性需求的滞回耗能与输入能量比,对比表明本文模型取值更符合近场地震动的能量分配特征。采用考虑刚度退化的滞回模型,讨论了地震动输入能量和SDOF体系非弹性最大变形之间关系,采用分段线性化方法建议了考虑场地分类的函数表达式,并用多自由度实体桥墩为算例进行了验证。在给出多自由度结构的地震输入总能量和滞回耗能需求、结构耗能能力以及总能量分配计算方法的基础上,提出了基于能量的桥梁结构损伤评估方法,并以3座加拿大的实际桥墩为对象进行了验证。4.采用改进的Park-Ang双参数损伤评估模型,对三类不同场地下基于等延性的强度折减因子设计的刚度退化单自由度体系的地震损伤分析表明,考虑单一变形延性的设计方法不能有效考虑地震动累积损伤效应,由于刚度退化导致的累积损伤会使得传统的设计方法偏于不安全。定义了基于确定性能目标的强度折减因子,自编程序计算了三类场地下刚度退化体系等性能目标强度折减因子的分布特征,构造了5%阻尼条件下的回归模型。以此为基础,推导了与UBC97抗震设计规范相容的等性能目标非弹性位移谱,发展了基于性能的桥梁墩柱抗震设计方法,并用算例验证了本文方法的可行性。最后,讨论了长细比取值较大的高柔桥墩和不等高MDOF全桥结构的多阶模态效应,引入多自由度振型分解反应谱理论提出了全桥结构基于性能的简化设计方法。更多还原

【Abstract】 Serious earthquake disaster close to the active fault brings forward bran-new challenge. Records with velocity pulse of long duration near fault region result in a new test for modern structure seismic design theory. There is an urgent need to understand the major characteristics of near-fault earthquake and improve existing seismic design methods. Along with technological advances in digital equipment, a number of near-fault earthquake records have been obtained. Necessary scientific foundation of this study is accessed. Based on the understanding that the mechanism of structure resisting earthquake impact is essentially a process of seismic energy consumption, energy-based performance evaluation method for bridge structure under near-fault earthquake was proposed, and seismic design method with exact performance goal to consider both cumulative energy and maximum deformation demand was developed in this paper. The main contents are as follows:1. Relied on selection of typical earthquake records with velocity pulse of long duration, the control parameter I_p was extracted as index of velocity pulse destructive capacity from dynamical computation results of an isolated continuous bridge, and a pulse simulation model using trigonometric function was introduced and regressed based on the collection of horizontal earthquake records all around the world. By introduction the concept of cumulative energy and instantaneous energy, energy spectrum analysis shows that pulse period and intensity are key factors for structure peak response during various parameters of near-fault earthquake. Cumulative input energy is affected significantly by high-frequency component, and instantaneous energy depends mainly on pulse velocity. Example analysis of isolated piers indicates that instantaneous input energy is an effective indicator to characterize the earthquake damage capacity. From the distribution characteristic of cumulative energy dissipation ratio and ratio of instantaneous dissipation energy, it can be drawn that energy dissipation efficiency of dual-linear isolation bearings can not exceed 0.6, and is about 0.4 under normal conditions, which means the energy dissipation capacity of LRB isolated structure excited by near-fault pulse needs to be strengthened, and reliable energy absorbing approach is requisite.2. In summing up simplified models for evaluation of input energy, a computation method based on response spectrum velocity was advised according to the demerit of each existing model, and the accuracy of this method was verified by near-field records. Based on record division, mean-value spectrum and 84% envelope curve of input energy was calculated, as a result the energy input design spectrum (EIDS) was recommended applicable to 0-15km fault zone, and was verified by actual records. Compared to Japan Seismic Codes(1985、2001) and Akiyama、Climent models, it can be concluded that the proposed design energy spectrum can reflect betterly the potential energy demand of near-fault earthquake. From the proposed simplified calculation model of input energy, input energy spectrum compatible to major China and USA seismic codes (GB50011-2001、UBC97) was derived. Contrast results shows that GB50011-2001 Code can reflect the amplification effect of near-fault only for HK IV soil types. On the contrary, UBC97 Code can match the recommended input energy spectra in most conditions except for soil S_A , which means the necessity of N_A、N_V and the rationality of the proposed EIDS in this paper from another aspect.3. The decisive factors for distribution of input energy among damping and deformation dissipation energy was discussed, on the basis the energy ratio taking into account structural damping and displacement ductility was introduced considering a decline in long period region. Based on hysteretic model considering stiffness degradation, the relationship between seismic input energy and inelastic seismic deformation of structure was studied. A function expression considering soil classification was proposed by piecewise linear method and was verified by example of MDOF bridge structure. In making certain the total input energy and hysteretic energy demand of earthquake, as well as energy dissipation and distribution ability of MDOF structure, an energy-based damage assessment method for bridge was developed and a validation computation was conducted by 3 piers of Canada.4. An improved dual-parameter Park-Ang damage model was developed to assess the exact damage of stiffness degradation SDOF system designed by constant ductile strength reduction factor, and it can be drawn that such method can not effectively consider the effect of cumulative damage from stiffness degradation, maybe being somewhat on the unsafe side. Based on the definition of strength reduction factor of constant performance goal, large numbers of cases of stiffness degradation SDOF system were accounted by self-writing computation program and a regression model under 5% damping was extracted. On the basis, constant performance goal non-elastic displacement spectrum compatible with UBC97 Seismic Design Code was educed, a performance-based seismic design method for bridge pier was proposed and its feasibility was checked by example. Finally, multi-phase modes effect of flexible bridge pier with high slenderness and MDOF full-bridge structure was discussed, and decomposition theory of multi-degree of freedom response spectrum was introduced to develop a performance-based seismic design method for full-bridge structure.更多还原