基于Ferry Borges理论的地震与重卡车作用下桥梁内力的组合问题
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摘要
目前的AASHTO LRFD桥梁规范主要考虑重力荷载和卡车等活荷载的组合情况,而没有在概率基础上考虑地震等极端荷载的组合问题。包括LRFD在内的很多桥梁抗震规范都是主要考虑地震的作用,甚至设计时不考虑其他荷载的作用,LRFD设计指导手册中在考虑地震等极端荷载时,也只是提到在特殊情况和桥梁比较长的情况下再考虑卡车的作用,而且,也比较模糊。文中在考虑地震荷载与卡车荷载时将其视为2种随机过程函数,并分析其各自的荷载特点。结合最近一些年USGS收集的极端荷载数据,文中认为桥梁设计(考虑地震和重卡车设计)时应该综合考虑地震和重卡车的影响,对它们进行荷载组合。接着,文中简单回顾了几种荷载组合方法,对比之后,认为FerryBorges(也称Ferry Borges-Castanheta模型)模型考虑了荷载的持时因素与荷载发生概率,虽然也对荷载做了极大的简化,但很好地解释了随机过程转化成随机变量以及与其他随机变量组合的复杂问题。最后,本文以美国西雅图地区的一桥梁为研究对象进行了算例分析。
The current AASHTO LRFD Bridge Design Specifications are mainly calibrated against gravity load and live load.However,they do not cover extreme load effects in a consistent probability-based fashion.Many seismic design specifications including LRFD mainly focus on seismic load,even not consider any other loads.And the time and method for identifying the factors of truck load in LRFD guide specification are not detailed.In this paper,earthquake load and truck load are time variable processes with their load characteristics.Based on some extreme loads data from USGS,it is very necessary to combine earthquake load and heavy truck load in seismic bridge design.Some methods for loads combination are compared and the Ferry Borges-Castanheta model is proposed,which considers loads lasting duration and happening probability and well describes how the random process converts to random variable and how it combines with other random variables.Finally,a simple example of bridge in Seattle is given for heavy truck load and earthquake load combination.
The current AASHTO LRFD Bridge Design Specifications are mainly calibrated against gravity load and live load.However,they do not cover extreme load effects in a consistent probability-based fashion.Many seismic design specifications including LRFD mainly focus on seismic load,even not consider any other loads.And the time and method for identifying the factors of truck load in LRFD guide specification are not detailed.In this paper,earthquake load and truck load are time variable processes with their load characteristics.Based on some extreme loads data from USGS,it is very necessary to combine earthquake load and heavy truck load in seismic bridge design.Some methods for loads combination are compared and the Ferry Borges-Castanheta model is proposed,which considers loads lasting duration and happening probability and well describes how the random process converts to random variable and how it combines with other random variables.Finally,a simple example of bridge in Seattle is given for heavy truck load and earthquake load combination.
引文
[1]AASHTO LRFD Bridge Design specifications[S].4th ed.,Washington,D.C.,2007.
[2]AASHTO Guide specification for LRFD seismic bridge design[S].1st ed.,Washington,DC.,2009.
[3]Susan E Hida.Statistical significance of less common load combinations[J].Journal of Bridge Engineering,2007,12(3):389-392.
[4]Novak A S.NCHRP Reporta.368:Calibration of LRFD bridge design code[R].Transportation Research Board of the National Academies,Wash-ington,D.C.,1999.
[5]Lee C.G.,Liang Z.,et al.A framework for development of muti-hazard load and resistance factor design[R].MCEER Technical Report,2012.(in press)
[6]Melchers R E.Structural reliability:analysis and prediction[M].John Wiley&Sons,New York,NY,1999.
[7]Armen Der Kiureghian.Non-ergodicity and PEER’s framework equation[J].Earthquake Engineering and Structural Dynamics,2005,34(13):1643-1652.
[8]Soong T T.Fundamentals of probability and statistics for engineers[M].State University of New York at Buffalo,Buffalo,New York,USA,2004.
[9]Moses F.Calibration of load factors for LRFD bridge evaluations[R].NCHRP Rep.454,Transportation Research Board of the National Acade-mies,Washington,D.C.,2001.
[2]AASHTO Guide specification for LRFD seismic bridge design[S].1st ed.,Washington,DC.,2009.
[3]Susan E Hida.Statistical significance of less common load combinations[J].Journal of Bridge Engineering,2007,12(3):389-392.
[4]Novak A S.NCHRP Reporta.368:Calibration of LRFD bridge design code[R].Transportation Research Board of the National Academies,Wash-ington,D.C.,1999.
[5]Lee C.G.,Liang Z.,et al.A framework for development of muti-hazard load and resistance factor design[R].MCEER Technical Report,2012.(in press)
[6]Melchers R E.Structural reliability:analysis and prediction[M].John Wiley&Sons,New York,NY,1999.
[7]Armen Der Kiureghian.Non-ergodicity and PEER’s framework equation[J].Earthquake Engineering and Structural Dynamics,2005,34(13):1643-1652.
[8]Soong T T.Fundamentals of probability and statistics for engineers[M].State University of New York at Buffalo,Buffalo,New York,USA,2004.
[9]Moses F.Calibration of load factors for LRFD bridge evaluations[R].NCHRP Rep.454,Transportation Research Board of the National Acade-mies,Washington,D.C.,2001.
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