【作者】 白凤龙；

【导师】 李宏男； 郝洪；

【作者基本信息】 大连理工大学 ， 防灾减灾工程及防护工程， 2010， 博士

【摘要】 大跨度结构作为重要的公众设施,世界各国一直都十分重视其抗震性能的研究。大跨度结构在地震发生时其支承点受到的地震动激励均不相同,应深入研究地震动空间变化效应对大跨度结构地震反应的影响。针对目前空间变化地震动场合成技术的不够完善以及大跨度多支承结构多点地震激励反应分析的不够全面,本文在合理模拟空间变化地震动场的基础上,针对几种典型的大跨度结构,包括大跨度桥梁结构、输电塔-线体系和空间钢结构,进行了多点激励下的地震反应分析,分别考查了引起地震动空间变化的行波效应、部分相干效应、局部场地效应及其组合效应对结构反应的影响。本文的研究内容主要包括以下几个方面：(1)人工合成非平整非均匀场地的空间变化地震动时程曲线。在空间变化地震动传统三角级数合成方法的基础上进行了进一步的研究,基于经验相干函数模型和修正金井清功率谱密度函数模型模拟了非平整场地地震动的空间变化,基于波传播理论推导出的频响函数考虑局部场地效应的影响,其中对于非均匀多土层场地情况,地表面的空间地震动由包含面内波和面外波的基岩地震动通过土壤层模拟生成。综合采用三角级数法、波动理论和随机振动法提出了非平整均匀场地和非平整多土层场地的多点地震动合成方法,并人工合成了非平整场地的空间变化地震动时程曲线。利用该方法合成的空间地震动既考虑了地震动的空间相关性和非平稳特性,还考虑了局部场地效应的影响,可以应用于非平整场地上大跨度结构多点激励地震反应的研究。(2)进行了空间变化地震动激励下桥梁相邻结构的最大相对位移反应研究,该位移为避免结构碰撞所必需的模数式伸缩缝最小间距。基于相干函数和我国抗震设计规范定义的反应谱分别模拟了四类场地的空间变化地震动,数值计算了桥梁相邻结构在模拟的不同视波速和相干程度空间地震动激励下的相对位移反应,以此确定不同类型场地上为避免桥梁相邻结构碰撞所必需的伸缩缝最小间距,并分析了地震动空间变化、场地条件和结构振动特性对桥梁相邻结构最大相对位移反应的影响。分析结果表明：桥梁所在场地越软,相邻结构间的相对位移反应越大；地震动的空间变化对桥梁相邻结构相对位移反应有着重要影响,当桥梁相邻结构拥有相似的振动频率时影响最大。抗震设计标准推荐调整相邻结构基本频率相近而减小相邻结构间的相对位移,从而达到避免结构碰撞的建议仅在地震动空间变化效应可以忽略的前提下有效。(3)针对输电塔-线体系这种大跨度的高柔结构,分析了其在非平整场地空间变化地震动作用下的结构非线性反应并进行了详细的数值模拟。考虑导线的几何非线性,建立了输电塔-线体系的三维有限元模型。利用生成的非平整非均匀场地空间相关多点地震动时程,首先对非平整场地上的这种复杂大跨度结构进行了地震动一致激励、行波激励和全面考虑地震动空间变化的多点激励下的地震反应分析；然后分别研究了非平整多土层场地地震动多维激励和局部场地条件差异对大跨越输电塔-线体系地震反应的影响。分析结果表明了考虑地震动多维效应和空间变化对研究输电塔-线体系地震反应的重要性,为该类结构体系的抗震设计提供了有意义的参考。(4)分析了考虑场地效应的空间变化地震动水平向和竖向共同作用下大跨度拱桁架结构的反应,研究了拱桁架结构可不考虑地震动空间变化影响的界限跨度。空间变化地震动是根据抗震规范定义的特定场地2%阻尼比反应谱和经验相干函数模拟生成。分别分析了由行波传播、相干损失和不同局部场地条件引起的地震动空间变化对结构反应的影响,研究了空间地震动水平向作用和水平向与竖向共同作用下结构反应的差异。此外,对抗震规范定义的四种类型场地上不同跨度的拱桁架结构进行了多点激励分析和一致激励分析,比较了不同激励情况下结构杆件内力反应,给出了四种类型场地上拱桁架结构可不考虑地震动空间变化影响的最小跨度,所获得的结果可为拱桁架结构的实际抗震设计提供有益的信息和建议。最后,比较分析了大跨空间平板网架结构在地震动一致激励、行波激励和多点激励下的支承柱和上部杆件内力反应情况,分析结果表明忽略地震动的空间变化可能严重低估大跨度空间网架结构的地震反应。更多还原

【Abstract】 The seismic properties of large-span structures, used as important public facilities, are always the focus research to be paid more attention all over the world. Due to the seismic excitations on supporting points of large-span structures are not uniform when earthquake occurrence, the effect of ground motion spatial variation on seismic response of large-span structures should be studied thoroughly. Considering the generation technique of spatially varying ground motion field still not perfect and the seismic response analysis of large-span multi-supported structures subjected to spatial ground motions are not comprehensive at present, seismic responses of several typical large-span structures, including large-span bridge structure, electrical transmission tower-line system and spatial steel structure, are analyzed under multi-support excitations based on the reasonable simulation of spatially varying ground motion field in this study. The influence of ground motion spatial variation induced by wave passage effect, coherency loss effect and local site effect on structure response are studied respectively, and the combined three effects are also studied. The main aspects of research work in this thesis are listed as follows:(1) Generation of spatially varying ground motion time histories corresponding to an uneven heterogeneous site. Based on traditional trigonometric series method, further research on generation technique of spatially varying ground motion is conducted. The ground motion spatial variations of the uneven site are simulated randomly based on an empirical coherency loss function and a filtered Kanai-Tajimi power spectral density function. The local site effect is considered by a transfer function derived from wave propagation theory. In view of heterogeneous site with multiple soil layers, the spatial ground motions of ground surface are simulated by the base rock motions propagating into the soil site, including out-of-plane wave and in-plane waves. With the trigonometric series method, the wave propagation theory and the random vibration method, the methods of simulating spatially varying ground motions corresponding to uneven homogeneous site and uneven site with multiple soil layers are performed, and the spatial ground motion time histories of the uneven site are generated. The generated spatial ground motions by this method considering ground motion spatial correlation, non-stationary property and local site effect, which can be used to analyze seismic response of large-span structures on an uneven site subjected to spatially varying ground motions. (2) The maximum relative displacement response between two adjacent bridge segments subjected to spatially varying ground motions is investigated, the relative displacement is the minimum gap that a modular expansion joint system must have to avoid pounding between bridge segments. The simulated spatially varying ground motions corresponding to four soil types are individually compatible with response spectrum defined in Chinese seismic design code, and are compatible with an empirical coherency loss function between each other. Numerical calculations of the relative displacement response between two adjacent bridge segments to spatial ground motions with different wave velocities and coherency losses are conducted, which can be used to determine the minimum gap that a expansion joint must have to avoid pounding between bridge segments on different site conditions. Moreover, the influences on maximum relative displacement response between two adjacent bridge segments induced by ground motion spatial variation, site condition and structural vibration characteristics are investigated. Numerical results indicate that the softer is the site, the larger is the relative displacement response between two adjacent structures. The effect of ground motion spatial variation on the relative displacement response is significant, especially when the vibration frequencies of two adjacent bridge segments are similar. To reduce the relative displacement and preclude pounding between adjacent structures, the design recommendation of adjusting the adjacent structures to have similar fundamental frequencies is valid only when the effect of ground motion spatial variation can be neglected.(3) Due to the large-span and high-rise flexible characteristics of a transmission tower-line system, the nonlinear responses of the structural system on an uneven site are analyzed subjected to spatially varying ground motions and comprehensive numerical simulations are carried out. A three-dimensional finite element model of the transmission tower-line system is established considering the geometric nonlinearity of transmission lines. Using the generated spatially varying ground motion time histories of the uneven heterogeneous site, seismic responses of the complex large-span structures on the uneven site under uniform excitation, wave-passage excitations and the multi-support excitations comprehensively considering ground motion spatial variation are analyzed. Discussions on the effects of the multi-component ground motions and the different local site conditions on responses of the example transmission tower-line system on uneven site with multiple soil layers are made. These investigations demonstrate the importance of considering the simultaneous multiple earthquake ground motion components and ground motion spatial variations on seismic responses of transmission tower-line system, which provide useful reference for practical seismic design of the structural system. (4) Seismic response of a large dimension steel trussed arch structure subjected to the combined spatially varying horizontal and vertical ground motions including site effect are analyzed, and the limitation span of trussed arch structure which is not required to consider the effect of ground motion spatial variation is investigated. The simulated spatial ground motions are individually compatible with the design response spectrum with 2% damping for specific site conditions defined in the Chinese seismic design code, and are compatible with an empirical coherency loss function between each other. The effects of ground motion spatial variations induced by wave propagation, coherency loss and changing site conditions on structural responses are discussed, respectively. The differences between structural responses subjected to horizontal ground motions and simultaneous vertical and horizontal ground motions are studied. Moreover, the responses of different span trussed arch structure on four site conditions defined in the design code are investigated under uniform excitation and multi-support excitations, and the internal forces of the structure induced by different excitation cases are compared. The minimum spans of trussed arch structure on four site conditions which are not required to consider the effect of ground motion spatial variation are given. The results obtained provide useful information and suggestion for practical design of steel trussed arch structure. Finally, the internal force responses of the supporting columns and upper bars in a large-span plate type truss structure induced by uniform excitation, wave-passage excitations and multi-support excitations are studied and some differences are reached. The analyzed results show that neglecting ground motion spatial variation may lead to a substantially under-estimated seismic response of large-span spatial truss structure.更多还原