某三塔斜拉桥动力特性分析

1、城市道桥与防洪2009年5月第5期 收稿日期:2009-02-03作者简介:徐永胜(1974-,男,福建建瓯人,工程师,从事市政桥隧设计工作。摘要:某大桥是国内首座三塔斜拉桥,结构形式复杂。该文首先建立了大桥的三维有限元动力分析的三主梁模型,采用大型有限元通用分析程序ANSYS 对该桥的动力特性进行了分析,并给出了结构的自重效应对固有动力特性的影响。结果表明,这类斜拉桥结构的自重效应对整体固有频率影响很小。关键词:三塔斜拉桥;有限元通用分析程序;动力特性;有限元模型中图分类号:U448.27文献标识码:A文章编号:1009-7716(200905-0064-02某三塔斜拉桥动力特性分析徐永胜(

2、广州市市政工程设计研究院,广东广州5100601概述某大桥全长6km ,为公路特大型桥梁。大桥主桥为三塔双索面漂浮式混凝土斜拉桥,跨径布置为130m+2×310m+130m ,主梁采用开口混凝土截面,梁宽23.4m ,梁高为2.5m ,边塔高99.311m ,中塔高125.684m ,属塔梁悬浮体系,索距为8m ,两边跨各布置17对索,中跨布置23对索。主梁形式采用开口型断面,断面形式见图1。本文建立了该桥的三维有限元动力分析模型,采用大型有限元分析程序ANSYS 对该桥的动力特性进行了分析,并分析了结构自重效应对整体固有频率的影响。2大桥有限元模型在大跨度桥梁全桥的结构分析中,一般

3、都采用平面或空间有限元杆系结构进行描述。其中,墩、塔部分简化为若干通过其中心线的二节点梁单元,而主缆、吊杆、斜拉索简化为二节点杆单元,在平面分析时,一般都直接将主梁处理为二维梁单元。但在空间分析时,对主梁的处理有多种方式。由于主梁为一个实体,其横向尺寸较大,在其纵向的不同位置还有纵梁、拉索等构件连接,它的侧向和扭转方向的刚度构件的连接特性都使得仅用一个空间梁单元不能达到正确的描述。因而,必须对主梁的纵向和横向刚度进行分解。目前,应用较多的主梁计算模型主要有三种:鱼骨式、双梁式和三梁式,如图2。鱼骨式模型适用于扭转刚度较大的闭口箱型截面主梁,它把桥梁的刚度和质量都集中到中间节点上,节点和拉索之间

4、处理为刚臂连接或处理为主从关系。该模型的主梁的刚度和质量的模拟较准确,但横梁的刚度和主梁的翘曲刚度反映不桥梁结构642009年5月第5期城市道桥与防洪足。双梁式模型将主梁的刚度和质量平均分配给两个主梁,这样可以近似地考虑约束扭转的贡献,使用于开口和半闭口截面的主梁,该模型的缺点是对侧向刚度和约束扭转的刚度模拟不准确。三梁式模型由桥轴线上的中梁和位于索面处的两个边梁横向共同组成,通过适当的刚度和质量分配来满足等效条件。该模型力学性能好,但单元数多,计算梁大,主要用于具有开口断面的主梁。三主梁模型截面性质和质量分析见表1。表1中有关符号定义如下(其中i =1代表中主梁,i =2代表边主梁:A 为桥

5、截面面积,J x 为桥截面竖向惯性矩,J z 为桥截面侧向惯性矩,J d 为桥截面自由扭转惯性矩,J w 为桥截面约束扭转惯性矩,M 为桥截面单位跨长重量, I m 为桥面单位跨长转动惯量。考虑到大桥为开口型断面,为了正确地考虑约束扭转刚度的贡献,采用三梁式计算模式来模拟加劲梁。在建模时,采用三维梁单元来模拟桥面主梁和塔,采用杆单元模拟斜拉桥,压重单元采用质量单元来模拟,这样全桥共有1038个单元。桥面简化后的三主梁截面特性见表2,有限元模型图见图3。3整体动力特性分析对上述有限元模型采用大型有限元分析通用程序ANSYS 对大桥进行了整体动力特性分析。为研究成桥内力对结构动力特性的影响,本文计

6、算了考虑成桥内力状态和不考虑成桥内力状态两种情况下的振型和频率,计算结果见表3。从表3可以看出,拉索垂度和成桥内力状态对大桥的整体动力特性的影响很小。图4图6为该桥的振型图。 4结论大桥为国内首座三塔斜拉桥,结构形式复杂。本文根据大桥的结构形式,采用三主梁模型表1三主梁模型中的主梁截面性质和质量分布等效原则公式主梁截面性质和质量分布纵向刚度等效和侧向刚度等效A 1=A ,A 2=0,J z 1=J z ,J z 2=0A 1=A ,A 2=0,J z 1=J z ,J z 2=0竖向刚度等效和约束扭转刚度等效J x 1+2J x 2=J x ,2J x 2=J J z 1=J z -J b 2

7、,J x 2=J 2b 2只有扭转刚度等效J d 1+2J d 2=J dJ d 1=J d ,J d 2=0质量系统等效M 1+2M 2=M ,2M 2b 2=I MM 1=M -I M b2,M 2=I M 2b2表2主梁截面几何特性梁A J z J xJ d 中主梁15.167 5.9001220.5500.218边主梁1.9600.03.413表3某大桥动力前15阶频率及振型特征序号不考虑自重考虑拉索垂度和成桥内力频率振型特性(主要频率振型特性(主要10.1374纵向漂移0.1394纵向漂移20.2354反对称竖弯0.2335反对称竖弯30.4373对称竖弯0.4336对称竖弯40.4

8、925反对称竖弯0.4865反对称竖弯50.5150反对称侧弯0.5150反对称侧弯60.6011对称侧弯0.6008对称侧弯70.6859对称竖弯0.6815对称竖弯80.8323反对称竖弯0.8243反对称竖弯90.8591桥面局部侧弯0.8566桥面局部侧弯100.8626桥面局部侧弯0.8570桥面局部侧弯110.8632对称竖弯0.8606对称竖弯120.9294对称扭转0.9287对称扭转130.9554反对称竖弯0.9463反对称竖弯140.9878对称竖弯0.9792对称竖弯150.9935反对称扭转0.9902反对称扭转桥梁结构65城市道桥与防洪2009年5月第5期 建立了某

9、大桥的有限元动力分析模型,对结构的动力特性进行了分析,结果表明:(1 斜拉索的垂度以及成桥状态的内力状态对该桥的整体动力特性影响很小;(2该桥的第一阶振型为纵漂振型,对该大桥的抗震有利;(3桥面的扭转频率跟竖弯频率比值高达4.22,说明大桥具有很好的气动稳定性。收稿日期:2008-12-02作者简介:马琳(1982-,女,吉林长春人,研究生,从事桥梁设计工作。摘要:该文通过有限元分析计算了两种不同计算模式下的盖梁内力。分析表明,当考虑立柱刚度影响时,盖梁内力将进行二次分配,致使跨中正弯矩减小、支点负弯矩增大,随着立柱与盖梁的线刚度比的增大,此种效应越显著。在工程实际应用中,由于工期紧张等因素,

10、当盖梁与立柱的线刚度比大于2时,可采用简化的双悬臂简支梁(连续梁图式,但在支点及跨中截面,应适当提高。关键词:盖梁;有限元分析;线刚度比中图分类号:U443.2文献标识码:A文章编号:1009-7716(200905-0066-03浅谈柱式墩盖梁的内力计算马琳,赵兴中(天津市政工程设计研究院,天津市30004570前言盖梁作为简支梁(板桥重要的承重构件,其承受着上部构造的恒载以及主梁传递给它的活载效应,并将这些荷载传递给桥墩。目前我国一级公路及高速公路四车道桥梁中常采用双柱式墩台或三柱式墩台,随着公路等级的提高、桥面宽度不断加大,盖梁的跨度也随之增大,常规的设计计算方法已经存在一定的局限性;加

11、之在设计过程中,设计者们往往也容易忽视盖梁构件的重要性,从而导致一些桥梁刚刚竣工便需要对盖梁进行加固后才能投入使用,造成一定的经济损失和不良社会反应。本文依托“塘承高速公路项目工程”对本工程项目中涉及到的部分盖梁进行计算分析及探讨,以供广大桥梁设计人员参考。1计算方法目前对盖梁计算图式的选取取主要有两种。(1双悬臂简支梁(连续梁计算图式下盖梁内力计算2双柱式桥墩,当盖梁刚度与柱的刚度比大于5时,为简化计算而忽略节点不均衡弯矩的分配及传递,一般可按双悬臂梁进行计算;对于多柱式的盖梁刚可按连续梁计算,这些计算图式可以快速解算出盖梁控制截面内力(见图1。(2悬臂刚构结构计算图式下盖梁内力计算在构造上

12、,柱的钢筋伸入到盖梁内,与盖梁钢筋绑扎在一起,因此盖梁与柱呈刚构结构状态,本文采用“桥博V3.01有限元软件”来进行盖梁的内力计算(见图2。盖梁的线刚度为:i 1=E 1I 1/l 1(1立柱的线刚度为:i 2=E 2I 2/l 2(2盖梁与立柱的线刚度比为:=i 1/i 2(32计算分析现行桥规1规定:墩台盖梁与柱应按刚构i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i桥梁结构66Keywords:lighting design,lighting standard

13、,energy saving,earthing typeBRIDGES&STRUCTURESeExample of Comprehensive Anchorage Waterproof Treatment Engineering of Suspension Bridg!Ying Ganzhou(50 Abstract:The anchorage structure is the key to guarantee the integral structural safety of suspension bridge.The anchorage waterproofing is the i

14、mportant factor to guarantee the long-term safe use of the structure.The anchorage of the main bridge for Changjiang River No.2Bridge in Wanzhou is the compound anchorage structure.The most of anchorage chamber and the anchor block of this bridge are all placed below the normal water storage level o

15、f Three Gorges.The anchorage opening is limited from the waterside.The engineering geological condition is relatively worse.The waterproofing treatment is greatly difficult.Therefore,the comprehensive waterproofing treatment measure is taken.Keywords:suspension bridge,anchorage proofing,technical st

16、andard,integral scheme,engineering measureeCalculation Analysis and Design Discussion of25-m Continuous Plate Bridg!Li Chunxiao,Yang Junyi,Lin Tianqing,Li M inghong(54 Abstract:Taking the design of2-span3-span25-m post-tensioning continuous plate bridge as an example,the article analyzes the stress

17、characteristics of negative moment area at the top of continuous pier under the condition of a few piers,and contrasts and calculates this characteristic in detail.The relative contents can be referred for the design of the same bridges.Keywords:continuous plate bridge,analysis,designr Wang Hui(58 A

18、nalysis on M echanics Characteristic of Corrugated Steel Web PC Composite Box Girde!Abstract:Combined with the structural property of corrugated steel web composite box girder,the article systematically analyzes the axial deformation characteristic of corrugated steel web,the shear stress distribute

19、d characteristic of box girder and the torsion characteristic of the box girder.The result shows that the prestressed concrete box girder of corrugated steel web has the good stress feature and will be widely used in bridge engineering.Keywords:bridge engineering,PC composite box girder,corrugated s

20、teel web,mechanics characteristics Dai Pan,Hu Dalin(61 Analysis on Ultimate Bearing Capacity of Long Span Stone Arch Bridge!Abstract:Taking Danhe Bridge as an example,this paper determines the ultimate bearing capacity of masonry arch bridge by calculating ultimate bending moment of hinge point,and

21、considers the loading state of arch bridge and material characteristics comprehensively.It offers the new direction for researching the ultimate bearing capacity of masonry arch bridge,and the reference able for determining the ultimate bearing capacity of reinforced concrete arch bridge.Keywords:ar

22、ch bridge,ultimate bearing capacity,ultimate bending moment,limit eccentricitye Xu Yongsheng(64 Analysis of Dynamic Characteristic of a Three-pylon Cable-stayed Bridg!Abstract:A bridge is the first three-pylon cable-stayed bridge in China.Its structure is complicated.The article firstly sets up thre

23、e-main-beam model for the three-dimension finite element dynamic analysis,uses the large finite element general program ANSYS to analyze the dynamic characteristic of the bridge,and gives the influence of the deadweight effect of structure on the inherent dynamic characteristic.The result makes clea

24、r that the deadweight effect of this structure of cable-stayedbridge influences a little the integral inherent frequency.Keywords:three-pylon cable-stayed bridge,finite element general analysis program,dynamic charac-teristic,finite element modelmElementary Discussion on Internal Force Calculation o

25、f Column Pier Cover Bea!Ma Lin,Zhao Xingzhong(66 Abstract:The article calculates the internal forces of cover beams under two different calculation modes by the analysis of finite elements.The analysis makes clear that when considering the rigidity influence of upright column,the internal force of c

26、over beam will be secondarily distributed so as to make the positive moment in the span decrease and the negative moment support increase,and this kind of effect is more obvious with the increment of linear stiffness ratio of the upright column and cover beam.In the engineering practice and as the f

27、actors of the constructing period limit,it can be to use the simplified double-cantilever simple-support beam(continuous beampattern when the lin-ear stiffness ratio of the upright column and cover beam is larger than2,but it should be properly enhanced on the support and the section in the span.Key

28、words:cover beam,analysis of finite element,linear stiffness ratiotDesign of Bridge Structure of Kunming City Northeast Ring2Rebuilding Extension Projec!Liu Fang(69 Abstract:The article introduces the express system of Kunming M ain City Area Northeast Ring2 Rebuilding Extension Project including th

29、e structure type,anti-earthquake design,existing bridge re-building,durability design and engineering landscape design,which can be referred for the structural design of city elevated bridge projects.Keywords:bridge structure,rebuilding of existing bridges,anti-earthquake design,engineering land-sca

30、petDesign of Pile Foundation Underpinning Work of Expressway Elevated Bridge of Guangzhou Airpor!Liu Liying,Wei Lixin,Liu Fang(75 Abstract:Taking the foundation underpinning of an existing bridge pier in the expressway of Guangzhou Airport as an example,the article explains the key techniques in the design scheme,con-struction process and design construction of the pile foundation underpinning of the elevated bridge.The article combines