【作者】 黄信；

【导师】 李忠献；

【作者基本信息】 天津大学 ， 结构工程， 2012， 博士

【摘要】 对于跨江、跨海桥梁及西部库区的高墩深水桥梁,由于桥墩位于深水当中,地震作用下水—桥墩动力相互作用会对桥墩产生动水压力作用。然而,目前国内外对强震作用下深水桥梁的地震响应尚缺乏深入的研究。本文以深水桥梁为对象,对强震作用下深水桥梁地震响应进行系统的理论分析与振动台试验,从而为深水桥梁地震响应的精细化模拟及基于性能的抗震设计提供坚实的理论基础,具有重要的理论意义和工程价值。主要创新工作和研究成果如下:(1)基于辐射波浪理论,采用分离变量法,建立了深水桥墩地震动水压力考虑水体压缩性和自由表面波影响的计算公式,深入分析了自由表面波和水体压缩性对桥墩地震动水压力的影响。研究表明,自由表面波仅在荷载激励频率较低时影响水面附近的动水压力,对于实际桥墩结构而言自由表面波影响并不明显;水体压缩性仅在荷载激励频率较高时影响动水压力,而地震作用的主要频率小于使水体压缩性产生明显影响的荷载激励频率。因此,在深水桥墩地震动水压力计算中,可忽略自由表面波和水体压缩性的影响,可利用附加质量概念,分析深水桥墩在地震作用下的动力响应,且附加质量随着桥墩截面半径和水深的增加而增大。(2)深水桥墩地震动水压力分析中一般假定水底为完全刚性反射边界,而忽略水底柔性介质对动水压力波的吸收作用。通过引入水底反射系数建立了深水桥墩考虑水底柔性反射边界影响的地震动水压力计算公式,并分析了水底柔性反射边界对桥墩地震动水压力的影响。研究表明,当考虑水底柔性介质对动水压力波的吸收作用时,水底柔性反射边界会在特定的荷载激励频率范围内对桥墩动水压力产生影响,且动水压力随着水底反射系数的减小而变小;尽管考虑水底柔性边界条件后会降低动水压力作用,但水底柔性边界对动水压力的降低作用不明显。因此,在深水桥墩地震动水压力分析中可以忽略水底柔性反射边界的影响。(3)建立了地震作用下水—桥墩动力相互作用分析方法,并基于ABAQUS软件平台开发了动水压力计算程序,通过与数值方法的对比分析,验证了本文方法的正确性;同时分析了考虑不同频谱特性地震波输入、空心墩体内域水体和桥梁上部结构附加质量等因素时动水压力对深水桥墩地震响应的影响。研究表明,动水压力增大了桥墩结构的地震响应,其影响随着输入地震波的不同而有所差异;空心截面桥墩内域水体的动水压力对桥墩地震响应的影响明显,所以当桥墩存在内域水体时其内域水体的动水压力作用不容忽视;随着上部结构附加质量的减小,动水压力对桥墩地震响应的影响增大。(4)建立了考虑地震动空间效应的深水桥梁地震响应分析方法,对某深水连续刚构桥进行了非线性地震响应分析,同时考虑不同地震动输入机制,进行了一致激励、行波激励和多点激励,研究了动水压力对深水桥梁地震响应的影响。研究表明,动水压力对桥梁结构地震响应的影响主要是增大了桥梁结构的动力响应,其影响程度随着输入地震波、墩梁约束条件的不同而变化;考虑行波激励和多点激励时动水压力对桥梁动力响应的影响较一致激励而言有所差异;所以深水桥梁地震响应分析应考虑动水压力作用,同时应根据场地条件采用合适的地震动输入机制。(5)采用Morison方程和绕射波浪理论考虑不同尺度桥墩的波浪作用,建立了波浪作用下深水桥梁动力响应分析方法,对某深水桥梁进行了地震和波浪联合作用下的动力响应分析。研究表明,当波浪沿桥梁不同方向入射时,波浪作用对桥梁结构的动力响应影响有所差异;波浪作用对桥梁结构动力响应的影响较地震作用对桥梁结构动力响应的影响小;深水桥梁动力响应分析中考虑地震和波浪联合作用时,由于两者单独作用下的动力响应峰值并不出现在同一时刻,所以桥梁结构的动力响应幅值并不是地震和波浪分别作用下的动力响应幅值的叠加。(6)通过模型振动台试验,研究了水—桥墩的动力相互作用,并基于对模型试验的数值分析,验证了本文所建立水—桥墩动力相互作用分析方法的正确性。按动力相似原理进行模型设计并采用自制的加重橡胶作为模型材料,利用吸波材料模拟实际水域对动水压力波的耗散作用,在地震模拟振动台上对桥墩模型进行动力特性及正弦波和地震波作用下的动力响应试验,同时分析水底柔性反射边界的影响。研究表明,地震动水压力减小了桥墩结构的自振频率,同时地震动水压力作用增大了桥墩结构的动力响应;水底柔性介质对地震动水压力具有吸收作用,但其影响可以忽略;本文方法能够较好的模拟地震动水压力对深水桥墩地震响应的影响。更多还原

【Abstract】 As for most of the cross-sea and cross-river bridges or the reservoir area bridges in West China, the bridge piers are usually located in deep water. Therefore, with a consideration of the water–bridge pier dynamic interaction, the earthquake induced hydrodynamic pressure on bridge piers is significant. However, there is still a lack of further research about the seismic responses of bridges in deep water both at home and abroad. Theoretical study and shaking table test are developed for earthquake response analysis of bridges in deep water under earthquake excitation, which has great theoretical significance and engineering value to improve theoretical basis for the earthquake hazard refined simulation and performance based seismic design of bridges in deep water. The following innovative work and achievements are include:(1) earthquake induced hydrodynamic pressure formulary of bridge piers in deep water is established based on radiation wave theory and variables separation method, which can consider free surface wave and water compressibility. Meanwhile, the influence of free surface wave and water compressibility on earthquake induced hydrodynamic pressure on bridge piers is studied. The results indicate that: free surface wave will only influence hydrodynamic pressure about the vicinity of water surface under low-frequency load excitation, and this influence can be ignored in seismic analysis of bridge piers. Water compressibility only takes effect on hydrodynamic pressure under high frequency load excitation, and it is found that the primary frequency of earthquake action is smaller than the frequency threshold that water compressibility starts to have obvious effect on hydrodynamic pressure on bridge pier in deep water. In conclusion, the influence of free surface wave and water compressibility can be ignored in the calculation of earthquake induced hydrodynamic pressure on bridge piers in deep water. Added mass concept can be used to analyze seismic responses of bridge piers in deep water, and hydrodynamic added mass will increase with the increase of bridge pier radius and the relative water depth.(2) Earthquake induced hydrodynamic pressure on bridge piers in deep water is usually established based on rigid bottom reflection boundary, and the absorption action of bottom flexible medium on hydrodynamic pressure wave is ignored. Earthquake induced hydrodynamic pressure formulary of bridge piers in deep water is established by introducing bottom reflection coefficient, which can consider the influence of bottom flexible reflection boundary Furthermore, the influence of flexible reflection boundary on hydrodynamic pressure on bridge piers is analyzed. The results indicate that: earthquake induced hydrodynamic pressure on bridge piers will be changed in special load excitation frequency range when bottom flexible reflection boundary is considered, and hydrodynamic pressure on bridge piers will be decreased with the reduction of reflection coefficient. Although earthquake induced hydrodynamic pressure on bridge piers in deep water will be decreased, and this decrease effect on hydrodynamic pressure is not obvious. Therefore, the influence of bottom flexible reflection boundary on earthquake induced hydrodynamic pressure on bridge piers in deep water can be ignored.(3) Water-bridge pier dynamic interaction analysis method is established, and program of applied hydrodynamic pressure on bridge piers is complied based on ABAQUS software platform, which is verified by comparisone with numerical method. Also, the influence of earthquake induced hydrodynamic pressure on seismic responses of bridge pier is analyzed when different earthquake excitations and internal water within the bridge pier with hollow section are considered. The results indicate that: dynamic responses of bridge pier are augmented because of earthquake induced hydrodynamic pressure action, which changes with different earthquake excitations. The effect of hydrodynamic pressure induced by internal water on bridge pier with hollow section seismic responses can’t be ignored. Influence of hydrodynamic pressure on dynamic responses of bridge piers in deep water increases with the decrease of the upper structure added mass.(4) Seismic response analysis method of bridges in deep water is established, which can consider spatial variation of ground motion. Nonlinear seismic response analysis of continuous rigid-framed bridge is made by considering the earthquake induced hydrodynamic pressure; meanwhile, earthquake inputs including uniform excitation、traveling wave effect and multi-support excitation are respectively adopted. The results indicate that: dynamic responses of bridge are augmented because of earthquake induced hydrodynamic pressure action, and the influence of hydrodynamic pressure on seismic responses of bridge changes with different earthquake wave excitations and constraint condition about pier-box girder. The effect of hydrodynamic pressure on earthquake responses analysis of bridge is different under traveling waves or multi-support excitation relative to uniform excitation. In conclusion, hydrodynamic pressure action should be necessarily considered in seismic responses analysis of bridges in deep water, and earthquake excitation should employ reasonable earthquake input.(5) Morison equation and radiation wave theory are used to consider wave load for different size of bridge pier, analysis method of bridges in deep water under wave action is established. Dynamic responses analysis of bridges in deep water under wave and earthquake combined action is made. The results indicate that: the effect of wave action on bridge changes with different wave incident directions, meanwhile, the influence about wave action on bridge is smaller than earthquake action. Wave and earthquake action on bridge can’t be simplified into a simple linear superimposition when wave and earthquake action are considered at the meantime.(6) Water-bridge pier dynamic interaction is studied with a scaled bridge pier model shaking table test, and the analysis method of water-bridge pier dynamic interaction established is verified. Shaking table test of water-large diameter bridge pier dynamic interaction is carried out. Dynamic similarity ratio design is made using self-made rubber material, and absorbing material is adopted to simulate water area dissipative action on hydrodynamic pressure wave. Experiments for dynamic characteristic and dynamic response of bridge pier in deep water is are performed under the shaking table simulated earthquake excitation. Meanwhile, influence of flexible reflection boundary of bottom on hydrodynamic pressure is analyzed. The results indicate that: natural frequency of bridge pier is decreased and dynamic responses of bridge pier are also augmented because of hydrodynamic pressure effect. Nevertheless, the influence of flexible reflection boundary on earthquake induced hydrodynamic pressure on bridge pier can be ignored. The earthquake induced hydrodynamic pressure action on bridge piers can be well simulated using the analysis method established in this dissertation.更多还原