【作者】 张勇；

【导师】 蒲黔辉；

【作者基本信息】 西南交通大学 ， 建筑与土木工程（专业学位）， 2019， 硕士

【摘要】 钢桁梁拱桥兼备拱桥优美的外观、强大的跨越能力和钢桁梁桥超高的承载能力,在各种形式的桥梁结构中占据着重要地位,并受到当代铁路桥梁设计师的青睐。近些年国内外修建了一批大跨度的钢桁梁柔性拱桥,在其跨越能力大大增加的同时宽跨比也在减小,尤其是在铁路中桥梁的宽跨比可能小于1/20,因此也带来了结构横桥向的稳定性问题。本文结合广州南沙港铁路洪奇沥水道特大桥主桥工程,对钢桁梁柔性拱桥的稳定进行系统的研究,研究内容如下:(1)介绍钢桁梁拱桥受力特点,同时概述了国内外该类型桥梁的发展状况,并列举了近几年国内修建的著名桥例;在综述关于桥梁稳定问题研究现状的基础上,指出了现在研究中存在的问题,彰显了研究大跨度钢桁梁柔性拱桥稳定性的必要性。(2)根据世界上最大跨度的钢桁梁柔性拱桥洪奇沥水道特大桥的工程概况,建立了钢桁梁柔性拱桥的ANSYS和MIDAS CIVIL有限元模型,并结合桥梁的施工工艺和运营阶段的不同荷载组合确定了不同阶段桥梁所承受的荷载情况,通过理论分析指出了桥梁在钢梁合龙前阶段、拱肋拼装阶段、拱肋合龙前、后阶段等关键施工阶段有较大可能发生失稳现象。(3)基于桥梁的稳定理论,介绍了在有限元中求解桥梁稳定问题的线弹性分析方法、几何非线性分析方法以及材料和几何双重非线性分析方法,并简要介绍了三种分析方法在有限元软件中的实现步骤。采用线弹性分析方法,探究了在不同施工阶段和运营阶段多种荷载组合下洪奇沥水道特大桥的第一类稳定问题,研究表明:随着桥梁建造过程的发展,结构的稳定性发生非常明显的变化,不同阶段桥梁的稳定安全系数和失稳形式具有明显的差异;在桥梁建设初期钢桁梁合龙前阶段结构的稳定系数最低,而钢桁梁合龙后稳定系数最高,表明临时支撑对结构的稳定性提供明显的辅助作用;钢桁梁柔性拱桥在运营阶段的不同荷载组合形式下稳定安全系数差异很大,但是结构都能较好地保证稳定性;横桥向不对称施加的列车制动力和顺桥向不对称分布的列车荷载对桥梁的第一类稳定影响较大,而横向风荷载和系统温度荷载对结构的弹性稳定影响不明显。(4)通过在钢桁梁拱桥的有限元模型中引入几何和材料非线性的方法,研究了桥梁的第二类稳定问题,在获取结构极限承载力的基础上,对比分析了不同非线性因素对桥梁第二类稳定产生的影响,利用荷载递增过程中结构的荷载-位移曲线和典型杆件的截面内力变化,探究了钢桁梁柔性拱桥的失效路径和失效机理,研究表明:线弹性方法和几何非线性计算结果差异较小,而利用双重非线性方法计算的结构安全系数明显小于前两者,并且荷载-位移曲线表现出较强的非线性关系,因此可知钢桁梁拱桥中几何非线性对结构的稳定性影响较小,材料非线性在计算结构承载力时不能忽略。考虑了初始缺陷后桥梁的安全系数降低了5.82%,施加缺陷后结构的竖向刚度变化不明显,而横向刚度具有一定程度的降低,且钢桁梁拱桥在横桥向的荷载-位移曲线更具非线性,结构失效时横向位移更大;在极限荷载作用下,通过几何非线性和线弹性方法计算拱肋和桁梁的关键位置结果差异较小,而两者都与双重非线性具有明显的不同,跨中到3/4跨区间内计算结果差异最为明显,其他位置的结果偏差较小,考虑结构的双重非线性后结构的位移和轴力有增大的趋势;钢桁梁拱桥在荷载加载初期所有杆件都处在弹性阶段,随着荷载的增大到一定值时,边跨上弦杆件弯矩减小,轴力增长缓慢,当弯矩减为0时,杆件进入塑性状态,结构的刚度减小,内力重新分配,继而主跨跨中的下弦杆进入塑性,塑性杆的弯矩转移到其他杆件,直至结构刚度下降到不能承担荷载。(5)基于已建立的ANSYS有限元模型,研究了活载分布形式、初始缺陷、横向荷载以及温度变化等关键参数对钢桁梁柔性拱桥第二类稳定问题的影响,量化分析了这些外界因素变化对桥梁承载力的影响趋势和影响机制,研究表明:不同的列车荷载形式对结构承载力影响存在明显差异,在列车荷载不对称作用下桥梁的极限承载能力最低;缺陷的施加方式以及量值都会对结构承载能力产生比较显著的影响,通过失稳模态添加的初始缺陷对结构的承载力影响较大,而施加偏心的方式对结构的承载能力影响较小;横向风荷载和系统温度的变化对钢桁梁柔性拱桥极限承载力的影响较小,在极限条件下才有产生一定的影响,极限风荷载相比运营风荷载的安全系数降低0.291,考虑全年最大温差时,结构的安全系数降低了2.3%。更多还原

【Abstract】 Steel truss arch bridge has the advantages of beautiful appearance,strong spanning capacity and super high bearing capacity of the arch bridge.It occupies an important position in various forms of bridge structure and is favored by contemporary railway bridge designers.In recent years,a number of large-span steel truss flexible arch bridges have been constructed at home and abroad.The span-width ratio of such bridges is also decreasing,especially in railways where the width-span ratio of bridges may be less than 1/20,which also brings about the stability of the structure in the transverse direction.In this paper,the stability and stability of flexible arch bridges with steel truss girders are systematical y studied in conjunction with the main bridge project of Hongqili steam Bridge in Guangzhou.The research contents are as follows:(1)This thesis introduces the mechanical characteristics of steel truss arch bridge,summarizes the development of this type of bridge at home and abroad,and lists some famous bridges built in China in recent years.On the basis of summarizing the current research status of bridge stability,it points out the existing problems in the research,and puts forward the necessity of studying the stability of long-span steel truss flexible arch bridge.(2)According to the engineering situation of the Hongqili steam Bridge,the world’s largest steel truss flexible arch bridge,ANSYS and MIDAS CIVIL finite element models of the steel truss flexible arch bridge are established,and the load conditions of the bridge in different stages are determined according to the different load combinations in the construction process and operation stage of the bridge.Through theoretical analysis,the bridge in the preclosure stage of the steel beam and the arch are pointed out.Instability may occur in key construction stages,such as rib horizontal assembly stage,before and after closure of main steel arch.(3)Based on the stability theory of bridges,the linear elastic analysis method,geometric nonlinearity analysis method and material and geometric double nonlinearity analysis method for solving bridge stability problems in finite element method are introduced,and the implementation steps of the three analysis methods in finite element software are briefly introduced.The linear elastic analysis method is used to study the first kind of stability of Hongqili steam Bridge under various load combinations in different construction and operation stages.The results show that with the development of bridge construction process,the stability of the structure has changed significantly,and the stability safety factor and instability form of bridges in different stages have obvious differences.The stability factor of steel truss bridge is the lowest in the pre-closure stage,while that of steel truss is the highest after closure,which indicates that temporary support has an obvious assistant effect on the stability of the structure;the stability safety factor of steel truss flexible arch bridge varies greatly under different load combinations in the operation stage,but the structure can better guarantee the stability;the train braking applied to the asymmetric transverse bridge The force and train load asymmetrical y distributed along the bridge direction have great influence on the first kind of stability of the bridge,while the transverse wind load and system temperature load have little effect on the elastic stability of the structure.(4)By introducing geometric and material nonlinearity into the finite element model of steel truss flexible arch bridge,the second stability problem of bridge is studied.On the basis of obtaining the ultimate bearing capacity of structure,the influence of different non-linear factors on the second stability of bridge is compared and analyzed.The load-displacement curve of structure and the variation of cross-section internal force of typical members are used in the process of increasing load.The failure path and failure mechanism of steel truss flexible arch bridge are studied.The results show that the difference between linear elastic method and geometric non-linear method is smal,while the structural safety factor calculated by double non-linear method is obviously smal er than the former two,and the load-displacement curve shows a strong non-linear relationship.Therefore,the geometric non-linearity of steel truss arch bridge has a strong non-linear effect on the structural stability.The material nonlinearity can not be neglected when calculating the bearing capacity of structures.Considering the initial defect,the safety factor of the bridge decreases by 5.82%.The vertical stiffness of the structure does not change obviously after applying the defect,but the transverse stiffness decreases to a certain extent.Moreover,the load-displacement curve of the flexible arch bridge with steel truss girder is more non-linear in the transverse direction,and the transverse displacement is larger when the structure fails.Under the ultimate load,the arch is calculated by geometric nonlinearity and linear elasticity methods.The results of the key positions of ribs and trusses are slightly different,but both of them are obviously different from the double nonlinearity.The difference between the middle span and the 3/4 span is the most obvious.The deviation of the results from other positions is smal.The displacement and axial force of the structure tend to increase after considering the double nonlinearity of the structure.All members of the steel truss arch bridge are in the elastic stage at the initial stage of loading,with the load increasing.When the load increases to a certain value,the bending moment of the upper chord member in the side span decreases and the axial force increases slowly.When the bending moment decreases to zero,the member enters the plastic state,the stiffness of the structure decreases,and the internal force redistributes.Then the lower chord member in the main span enters the plastic state,and the bending moment of the plastic member transfers to other members until the structural stiffness decreases to the point where the load cannot be borne.(5)Based on the established ANSYS finite element model,the influence of key parameters,such as live load distribution,initial defects,transverse load and temperature change,on the second kind of stability of steel truss flexible arch bridge is studied.The influence trend and mechanism of these external factors on the bearing capacity of bridge are quantitatively analyzed.The results show that different train load forms have influence on the structural bearing capacity.The ultimate bearing capacity of the bridge is the lowest under the double-track action of train spanning;the mode and magnitude of the defects will have a significant impact on the bearing capacity of the structure.The initial defects added through the instability mode have a greater impact on the bearing capacity of the structure,while the eccentricity mode has a smal er impact on the bearing capacity of the structure;the transverse wind load and the change of system temperature.The ultimate bearing capacity of flexible arch bridges with steel truss girders is less affected by the change of temperature.Only under the ultimate conditions can the safety factor of the structure be reduced by 0.291% under the ultimate wind load compared with the operation wind load.Considering the maximum temperature difference in the whole year,the safety factor of the structure is reduced by 2.3%.更多还原