【作者】 岳福青；

【导师】 李忠献；

【作者基本信息】 天津大学 ， 结构工程， 2007， 博士

【摘要】 桥梁作为城市重要交通基础设施之一,其抗震防灾问题日益受到学术界和工程界的高度重视。强震作用下桥梁易发生碰撞,导致主梁梁端开裂、伸缩缝挤压、支座失效等破坏现象,甚至引发落梁等严重灾害。然而,目前国内外对强震作用下桥梁碰撞的机理、模拟方法以及预防措施等尚缺乏深入的研究。本文以城市高架桥梁为对象,对强震作用下隔震高架桥梁的碰撞反应进行系统的理论分析与振动台试验,从而为城市高架桥梁的地震碰撞危险性分析以及防碰撞设计提供可靠的理论依据,具有重要的理论意义和工程价值。主要创新工作与成果有:(1)建立了桥梁碰撞分析的等效Kelvin碰撞模型及其参数确定方法。基于Hertz接触理论,考虑波动效应,推导了Kelvin碰撞模型的碰撞刚度和阻尼的解析表达式;仿真分析了Kelvin碰撞模型碰撞刚度和阻尼的变化规律,并确定了其在实际工程中的合理取值范围。结果表明,Kelvin碰撞模型的碰撞刚度随Hertz接触刚度、撞击速度及邻梁长度比的增大而增大,且波动效应对碰撞刚度的影响明显、不能忽略;Kelvin碰撞模型阻尼的恢复系数随撞击速度增大而减小,且随邻梁长度比的增大而增大。(2)系统分析了强震作用下隔震高架桥梁的碰撞反应。基于所提出的等效Kelvin碰撞模型,考虑桥墩非线性和土-基础相互作用,建立了隔震简支梁桥和隔震连续梁桥的非线性有限元模型;生成了拟合规范反应谱、且考虑地震动空间差动效应的人工地震波;仿真分析了强地震动的一致激励及仅考虑行波效应、仅考虑部分相干效应或同时考虑行波效应与部分相干效应的非一致激励下隔震梁桥的非线性碰撞反应。结果表明:地震动空间差动效应对隔震梁桥碰撞反应的影响大,且对连续梁桥的影响更大;考虑地震动空间差动效应,碰撞过程中撞击力明显增大,且同时考虑行波效应和部分相干效应时撞击力的增幅最大;随着视波速的增大,其影响逐渐减弱。(3)建立了隔震梁桥地震碰撞临界间隙的计算方法。考虑隔震支座恢复力的非线性特性,建立了周期不等的邻梁(联)碰撞分析的2个双自由度简化系统;基于随机振动理论,建立了系统的非线性运动方程及等效线性化方程,推导了碰撞临界间隙的计算表达式;仿真分析了隔震梁桥考虑地震动空间差动效应和土-基础相互作用的碰撞临界间隙。结果表明:碰撞临界间隙随邻梁(联)周期比、上、下部结构质量比及隔震支座屈服变形的增大而增大,但随隔震支座屈服力与上部结构重量的比值增大而减小,而隔震支座屈服后与屈服前的刚度比的影响很小;地震动空间差动效应对碰撞临界间隙的影响大,其中部分相干效应的影响更大,且部分相干效应越大,碰撞临界间隙越大;当地基土的剪切波速小于200m/s时,考虑土-基础相互作用对碰撞临界间隙有一定的影响。(4)应用粘弹阻尼器对隔震梁桥地震碰撞反应实施了被动控制。基于随机振动理论,考虑隔震支座恢复力的非线性特性,建立了在邻梁(联)间或在主梁与桥墩间安装粘弹阻尼器的隔震桥梁碰撞分析方法;提出了防碰撞非线性粘滞阻尼器的参数设计方法;仿真分析了邻梁的周期比和质量比、阻尼器的性能参数以及场地特征频率等对隔震桥梁碰撞反应控制效果的影响。结果表明,在邻梁间安装粘滞阻尼器,能显著减小邻梁的相对位移,从而能有效抑制碰撞的发生;邻梁周期比越大,控制效果越好。(5)应用磁流变(MR)阻尼器对隔震桥梁地震碰撞反应实施了半主动控制。建立了在邻梁(联)间或在主梁与桥墩间安装MR阻尼器的隔震桥梁碰撞分析的4自由度简化体系;应用模糊控制论,以邻梁相对位移的极小化为目标函数,建立了基于MR阻尼器的模糊控制器,并对其隶属函数、量化因子和比例因子进行了离线遗传优化和在线自调整;仿真分析了不同控制方案下多跨隔震连续梁桥碰撞反应的控制效果。结果表明,基于MR阻尼器的半主动控制,能有效控制邻梁的相对位移和隔震支座的横向变形,且在主梁与桥墩之间安装阻尼器的控制效果更佳;与传统模糊控制和仅遗传优化的模糊控制相比,经离线遗传优化且在线自调整的模糊控制的控制效果和鲁棒性更好。(6)对隔震梁桥的碰撞反应进行了振动台试验。设计制作了一两跨隔震简支梁桥模型;通过振动台输入不同的地震波激励,测试了具有不同结构参数的模型梁桥的碰撞反应,以及应用MR阻尼器对模型梁桥邻梁相对位移的控制效果,并与计算结果进行了对比分析。结果表明,所建立的等效Kelvin碰撞模型能较准确地模拟强震作用下隔震梁桥的碰撞反应,包括邻梁间的撞击力和主梁的水平位移;邻梁间隙和周期比以及隔震支座特性等对隔震梁桥的碰撞反应的影响大,增大邻梁间隙或减小邻梁周期比,能显著地减小邻梁碰撞反应;在邻梁之间安装MR阻尼器,可显著地减小邻梁相对位移,且对墩顶位移影响不大。更多还原

【Abstract】 Bridges are one of the important transportation infrastructures in urbans, and its earthquake resistance and hazrad mitigation have been paid more attention by researchers and engineers. The bridges excited by strong earthquake occur pounding easily, which may cause some damages such as crashing at ends of girders, collision at expansion joints, and failure of bearing, even serious hazard as unseating of girders. Until now, a few studies have been carried out on the mechanism, simulation and prevention of pounding of bridges under strong earthquake action. In this dissertation, taking the urban elevated bridges as objects, a systematic theoretical analysis and shaking-table test on the pounding responses of isolated elevated bridges are performed under strong earthquake action. This provides a reliable theoretical basis for risk prediction and prevention design on seismic pounding of the urban elevated bridges. The following innovative work and achievements are included:(1) An equivalent Kelvin impact model and determination method on parameters of the model is proposed for seismic pounding analysis of bridges. Based on the Hertz contact theory and considering the wave-motion effect, the analytical expression on impact stiffness and damping of the equivalent Kelvin impact model is derived. The changing law of the impact stiffness and damping of the Kelvin impact model are simulated, and its rational value ranges are obtained for the practical engineering. The results show that the impact stiffness of the equivalent Kelvin impact model increases with the increment of the Hertz contact stiffness, the impact velocity, and the length ratio of the short to long girders. The wave-motion effect has remarkable influence on the impact stiffness and can not be neglected. The restitution coefficient of the damping of the equivalent Kelvin impact model decreases with the increment of the impact velocity, but with the decrement of the length ratio of the short to long girders.(2) The pounding responses of the isolated elevated bridges under strong earthquake action are systematically investigated. Based on the proposed equivalent Kelvin impact model, and considering non-linearity of piers and soil-structure interaction, nonlinear finite element models for isolated simply-supported and continuous bridges are built up. An artificial seismic wave is generated to fit the normalized response spectrum and consider spatial variation of earthquake motion. The nonlinear pounding responses of the isolated bridge under the uniform excitation and the non-uniform excitations considering the traveling wave effect only, the partial coherence effect only,or both of the traveling effect and the partial coherence effect, of the strong earthquake motion is simulated. The results indicate that the influence of the spatial variation of earthquake motion on the pounding responses of the isolated bridges is significant, especially for the isolated continuous bridge. Taking the spatial variation of erathquake motion into account, the impact forces during the pounding is clearly increased, especially when the traveling wave effect and the partial coherence effect are considered simultaneously. This influence may be attenuated gradually with the increasing of the apparent velocity.(3) A calculation algorithm for the critical gap length of the isolated bridges is proposed. Considering nonlinear property of restoring force of the isolation bearings, a simplified system with two 2-DOFs is built for pounding analysis of the adjacent girders (or segments) with different natural periods. Based on random vibration theory, nonlinear equations of motion of the system and its equivalently linearized equations of motion are set up, and a calculation expression of the critical gap length of pounding is derived. The critical gap length of pounding of the isolated bridges considering the spatial variation of earthquake motion and the soil-foundation interaction is simulated. The results indicate that the critical gap length of pounding increases with increments of the ratio of the natural periods of the adjacent girders (or segments), the ratio of masses of superstructure to substructure, and the yield deformation of the isolation bearing, but decreases with increment of the ratio of the yield force of the isolation bearing to the weight of the superstructure. However, the ratio of post-yield to pre-yield stiffness of the isolation bearing has little influence on critical gap length. The influence of the spatial variation of earthquake motion on the critical gap length of pounding is significant, especially of the partial coherence effect in which the the partial coherence effect stronger, the critical gap length of pounding larger. When the velocity of shear wave of soil is smaller than 200m/s, there is a certain influence on the critical gap length of pounding by considering the soil-foundation interaction.(4) Passive control on the seismic pounding responses of the isolated bridges s performed using visco-elastic damper. Based on the random vibration theory and considering the nonlinear property of restoring force of isolation bearing, a method for analyzing the seismic pounding responses of the adjacent girders (or segments) with installation of the visco-elastic dampers between girders or between girder and pier are established. The parametric design method for the nonlinear viscous damper to pounding prevention is proposed. The influences of the ratios of natural period and mass of the adjacent girders, the performance parameters of the damper, and characteristic frequency of the ground on the control effect of pounding responses of the isolated bridges are investigated. The results show that the relative displacement between the adjacent girders can be reduced significantly by installing the viscous damper between the adjacent girders, so to prevent the occourence of pounding effectively. The control effect increases with the increment of the ratio of natural periods of the adjacent girders.(5) Semi-active control on the seismic pounding responses of the isolated bridges is performed using magneto-rheological (MR) damper. A simplified 4-DOFs system for pounding response analysis of the isolated bridges is built by installing the MR damper between adjacent girders or between girder and pier. Employing the fuzzy control theory, and taking the minimization of relative displacement between adjacent girders as the objective function, a MR damper based fuzzy logic controller (FLC) is established. The offline genetic optimization and online self-tuning are proceded for the membership function, the quantification factor and the scaling factor of the FLC. The control effect on the seismic pounding responses of an isolated multi-span continuous girder bridge is simulated under different control strategies. The results indicate that the relative displacement between the adjacent girders and the lateral deformation of the isolation bearing may be effectively suppressed by employing the MR damper based semi-active control strategy, and the control effect is better by installing the MR dampers between the superstructure and the pier. Comparing with the conventional FLC and the FLC optimized by GA only, the control effect and robustness of the FLC with the offline genetic optimization and the online self-tuning are better.(6) Shaking-table test on seismic pounding responses of the isolated bridge is performed. A model of two-span isolated simply-supported bridge is made. Through different seismic wave inputs by the shaking-table, the seismic pounding responses of the model bridge with different structural parameters and the control effect on the relative displacement between adjacent girders by employing MR damper are tested and compared with the calculated results. The results show that the proposed equivalent Kelvin impact model may make a relatively accurate simulation on the pounding responses, including the impact force between the adjacent girders and the longitudinal displacement of the girders, of the isolated bridges under strong earthquake action. The influence of the gap length between the adjacent girders, the ratio of the natural periods of the adjacent girders, and the properties of the isolation bearing on the pounding responses of the isolated bridge is significant. The pounding responses between the adjacent girders may be reduced remarkably by increasing the gap length or decreasing the ration of the natural period of the adjacent girders. Installing the MR damper between the adjacent girders may decrease the relative displacement between the adjacent girders, while has little influence on the drift at the top of the pier.更多还原