大跨度悬索桥抗震分析中几个问题的讨论
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摘要
为了使桥塔能够在强震下基本保持弹性,悬索桥通常采用全漂浮和半漂浮的隔震体系来减小地震反应。这两种体系将会导致相当大的梁端位移,梁端的过大位移可能会导致主梁与引桥的碰撞、落梁等事故,给大桥的整个安全性造成威胁。地震动空间变异性(场地效应、行波效应、相干效应)对于桥梁地震响应的影响是当今研究的一个热点。桩土相互作用在抗震计算中不可忽略,半无限空间地震动人工边界在桩土相互作用上的研究还比较少。
为了研究以下几点：粘弹性人工边界法在桩土相互作用上的实现,桩土相互作用对大桥自振特性和地震响应的影响；大桥主梁与引桥梁间碰撞和行波效应对桥梁地震响应的影响；最优非线性阻尼器的选择,及其对大桥地震响应的影响。
采用大型通用有限元软件Midas Civil建立有限元模型,土体采用实体单元模拟,地震动从实体单元边界节点输入。阻尼器、碰撞单元均采用软件自带的内力模型,对其进行参数敏感性分析。采用大质量法考虑行波效应,分析不同视波速下行波效应对大桥地震响应的影响。对于大跨度悬索桥,用于分析的结构响应主要包括：梁端位移、塔底剪力、塔底弯矩、阻尼力、碰撞力等。
研究分析结果显示：
(1)大跨度悬索桥主要以长周期振动为主,采用固结模型进行抗震设计偏于安全,采用粘弹性人工边界法时则相反,m法是一个比较好的选择。
(2)考虑引桥梁与主梁间的碰撞后,主梁与引桥梁间的相对位移、引桥墩内力明显减小。碰撞刚度和恢复系数对于碰撞响应有很大的影响,合理的恢复系数应通过实验确定,碰撞初始间隙是一个不确定的影响因素。
(3)桥址的地质情况良好,对大桥进行行波效应分析后发现可不用考虑行波效应对其影响。
(4)粘滞性阻尼器的减震效果主要体现在对梁端位移的控制和主塔内力的减小。最优阻尼器参数C=2000kN(sec/m)ξ,阻尼指数ξ=0.2-0.4,单个阻尼器的额定阻尼力可取为2250kN。
The seismic isolation system as all floating or half floating system is usually taken by the suspension bridge to keep the tower in elastic state. These two systems will bring out large displacement in earthquake, the large displacement at the end of main beam will cause the collision between main beam and the approach bridge, the safety performance of whole bridge will be in danger. The seismic response of the bridge influenced by the spatial variation of ground motions is studied by many scholars. The spatial variation of seismic ground motions is produced primarily by the three factors:geometric incoherency effect, wave-passage effect and local site effect. The pile-soil interaction cannot be ignored in the seismic computation and the application of viscoelastic artificial boundary is little researched.
In order to study the following points:how to realize the viscoelastic artificial boundary when considering the pile-soil interaction; the influence on seismic response of the pile-soil interaction, wave-passage effect and collision between the main beam and the approach bridge; optimal selection of nonlinear damper.
The finite element model was established by the software Midas Civil, the soil was simulated by the solid element and the ground motion was input on the boundary nodes. Damper and the collision units were simulated by the software's model. The large mass method was used to consider the wave passage effect and the seismic response under different apparent wave velocity was studied. For the long-span suspension bridge, structural response used to be analyzed includes the displacement at the end of main beam, shear force and bending moment at the bottom of tower, damping force and collision force.
The results showed that:
The main natural period of vibration was very long and influenced by the pile-soil interaction. It was safer but less economic when using the seismic response of fixed model to design. When using the viscoelastic artificial boundary model, it was more economic but safe. M method was a good way to consider the pile-soil interaction.
When considering the collision between the main beam and the approach bridge, the displacement between the main beam and approach bridge was decreasing and same for the internal force of pier of approach bridge. Collision stiffness and recovery coefficient had big influence on the collision reaction; the reasonable recovery coefficient should be confirmed by the test. The width of initial gap was an uncertain factor.
The geological condition was good and the wave-passage effect could need not to be considered.
The seismic reduction effect was good for the suspension bridge with viscous dampers, and the reduction effect was mainly reflected on the displacement at the end of main beam and the internal force of main tower. The optimal damper parameters were C=2000kN(sec/m)ζ, ζ=0.2～0.4, rated damping force of one single damper could be2250kN.
为了研究以下几点：粘弹性人工边界法在桩土相互作用上的实现,桩土相互作用对大桥自振特性和地震响应的影响；大桥主梁与引桥梁间碰撞和行波效应对桥梁地震响应的影响；最优非线性阻尼器的选择,及其对大桥地震响应的影响。
采用大型通用有限元软件Midas Civil建立有限元模型,土体采用实体单元模拟,地震动从实体单元边界节点输入。阻尼器、碰撞单元均采用软件自带的内力模型,对其进行参数敏感性分析。采用大质量法考虑行波效应,分析不同视波速下行波效应对大桥地震响应的影响。对于大跨度悬索桥,用于分析的结构响应主要包括：梁端位移、塔底剪力、塔底弯矩、阻尼力、碰撞力等。
研究分析结果显示：
(1)大跨度悬索桥主要以长周期振动为主,采用固结模型进行抗震设计偏于安全,采用粘弹性人工边界法时则相反,m法是一个比较好的选择。
(2)考虑引桥梁与主梁间的碰撞后,主梁与引桥梁间的相对位移、引桥墩内力明显减小。碰撞刚度和恢复系数对于碰撞响应有很大的影响,合理的恢复系数应通过实验确定,碰撞初始间隙是一个不确定的影响因素。
(3)桥址的地质情况良好,对大桥进行行波效应分析后发现可不用考虑行波效应对其影响。
(4)粘滞性阻尼器的减震效果主要体现在对梁端位移的控制和主塔内力的减小。最优阻尼器参数C=2000kN(sec/m)ξ,阻尼指数ξ=0.2-0.4,单个阻尼器的额定阻尼力可取为2250kN。
The seismic isolation system as all floating or half floating system is usually taken by the suspension bridge to keep the tower in elastic state. These two systems will bring out large displacement in earthquake, the large displacement at the end of main beam will cause the collision between main beam and the approach bridge, the safety performance of whole bridge will be in danger. The seismic response of the bridge influenced by the spatial variation of ground motions is studied by many scholars. The spatial variation of seismic ground motions is produced primarily by the three factors:geometric incoherency effect, wave-passage effect and local site effect. The pile-soil interaction cannot be ignored in the seismic computation and the application of viscoelastic artificial boundary is little researched.
In order to study the following points:how to realize the viscoelastic artificial boundary when considering the pile-soil interaction; the influence on seismic response of the pile-soil interaction, wave-passage effect and collision between the main beam and the approach bridge; optimal selection of nonlinear damper.
The finite element model was established by the software Midas Civil, the soil was simulated by the solid element and the ground motion was input on the boundary nodes. Damper and the collision units were simulated by the software's model. The large mass method was used to consider the wave passage effect and the seismic response under different apparent wave velocity was studied. For the long-span suspension bridge, structural response used to be analyzed includes the displacement at the end of main beam, shear force and bending moment at the bottom of tower, damping force and collision force.
The results showed that:
The main natural period of vibration was very long and influenced by the pile-soil interaction. It was safer but less economic when using the seismic response of fixed model to design. When using the viscoelastic artificial boundary model, it was more economic but safe. M method was a good way to consider the pile-soil interaction.
When considering the collision between the main beam and the approach bridge, the displacement between the main beam and approach bridge was decreasing and same for the internal force of pier of approach bridge. Collision stiffness and recovery coefficient had big influence on the collision reaction; the reasonable recovery coefficient should be confirmed by the test. The width of initial gap was an uncertain factor.
The geological condition was good and the wave-passage effect could need not to be considered.
The seismic reduction effect was good for the suspension bridge with viscous dampers, and the reduction effect was mainly reflected on the displacement at the end of main beam and the internal force of main tower. The optimal damper parameters were C=2000kN(sec/m)ζ, ζ=0.2～0.4, rated damping force of one single damper could be2250kN.
引文
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[2]叶爱君,管仲国,范立础.桥梁抗震[M].北京：人民交通出版社,2011：3-7.
[3]李国豪.桥梁结构稳定与振动[M].北京：中国铁道出版社,1996.
[4]范立础.桥梁抗震[M].上海：同济大学出版社,1997.
[5]范立础,卓卫东.桥梁延性抗震设计[M].北京：人民交通出版社,2001.
[6]范立础,胡世德,叶爱君.大跨度桥梁抗震设计[M].北京：人民交通出版社,2001.
[7]Priestly M J N, Serible F, Calvi G M. Seismic design and retrofit of bridges [M]. New York:John Wiley & Sons,1996.
[8]中华人民共和国交通部.汶川地震公路震害图集[M].北京：人民交通出版社,2009.
[9]Philip James Meymand. Shaking table scale model tests of nonlinear soil-pile-superstructure interaction in soft clay[M]. University of California, Berkeley,1988.
[10]同济大学土木工程防灾国家重点实验室.汶川地震震害[M].上海：同济大学出版社,2008.
[11]刘晶波,杜修力,欧进萍.结构动力学[M].北京：机械工业出版社,2011.
[12]A.K.Chopra. Dynamics of Structures[M]. Prentice Hall,2000.
[13]R.克拉夫,J.彭津.结构动力学[M].王光远等译校.北京：高等教育出版社,2006.
[14]中华人民共和国行业标准.JTJ00489公路工程抗震设计细则[M].北京：人民交通出版社,1990.
[15]Seismic Design Criteria Version1.1 [M]. California:California Department of Transportation (CALTRANS). Division of Structure,1999.
[16]AASHTO. Specification for LRFD seismic bridge design[M]. Washington DC: American Association of State Highway and Transportation Officials,2007.
[17]中华人民共和国行业标准JTG/T B02-01—2008.公路桥梁抗震细则[M].北京：人民交通出版社,2008.
[18]Eurocode 8. Design provision for earthquake resistance of structure[M]. London: European Committee for Standardization,1994.
[19]雷坚.大跨度三塔斜拉桥几何非线性分析[D].硕士毕业论文,2009.
[20]刘晶波,王振宇,杜修力,杜义欣.波动问题中的三维时域粘弹性人工边界[J].工程力学,2005,22(6)：46-51.
[21]杨常生.公路桥梁板式橡胶支座应用与分析[D].硕士毕业论文,2007.
[22]吴彬.铅芯橡胶支座力学性能及其在桥梁工程中隔震应用的研究[D].博士毕业论文,2003.
[23]中华人民共和国交通行业标准JT/T 4-2004.公路桥梁板式橡胶支座技术标准[M].北京：人民交通出版社,2004.
[24]李俊,强士中,李小珍.地基系数的比例系数m的确定[J].铁道标准设计,2004(11)：83-85.
[25]中华人民共和国行业标准JTG D63--2007.公路桥涵地基与基础设计规范[M].北京：人民交通出版社,2007.
[26]林在贯.岩土工程手册[M].北京：中国建筑工业出版社,1994.
[27]孙利民,张晨南,潘龙,范立础.桥梁桩土相互集中质量模型及参数确定[J].同济大学学报,2002,30(4)：409-415.
[28]LYSMER J, KULEMEYER R L. Finite dynamic model for infinite media[J]. Journal of the Engineering Mechanics, ASCE,1969,95(EM4):859-877.
[29]CLAYTON R, ENGQUIST B. Absorbing boundary conditions for acoustic and elastic wave equations[J]. Bulletin of Seismic Society in America,1977,67(6):1529—1540.
[30]LYSMER J, WASS G. Shear waves in plane infinite structures[J]. Journal of the Engineering Mechanics, ASCE,1972,98(EMI):85—105.
[31]张国民,汪素云,李丽,张晓东,马宏生.中国大陆地震震源深度及其构造含义[J].科学通报,2002,47(9)：663-668.
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