铝合金人行天桥设计分析要点

1、2012年3月第3期城市道桥与防洪0前言铝合金材料以其较高的弹性模量和良好的防腐性能在土木行业中得到越来越广泛的应用。1933年,美国第一次将铝合金应用在桥梁中。目前在欧美等发达国家铝合金桥梁已经发展得比较成熟,但是国内的铝合金桥梁研究还处于起步阶段,2006年建成的杭州市庆春路铝合金人行天桥是目前中国第一座全铝合金桥梁。铝合金材料与钢材有着较大的材料特性差异:首先是其材料的密度,铝合金因密度小而自重小;其次是材料的弹性模量与钢相比较小(虽然其极限强度和Q235相当。因此,铝合金桥在施工使用过程中存在诸多问题。例如,杭州市庆春路人行天桥是国内第一座铝合金桥梁,存在问题如下:在满人荷载作用下挠度

2、过大,自振频率和荷载作用下的频率相比变化较大。本文主要针对上述方面进行研究,分析出现这些现象的本质原因,以及提出解决问题的方案。本文依据杭州复兴路人行天桥建立模型,利用ANSYS 有限元软件辅助分析计算,以期能为将来我国设计建设更多的铝合金桥作参考和借鉴。1桥梁概况杭州市复兴路人行天桥为三跨铝合金梁,跨径布置为26.64m+19m+15.4m ,桥梁平面布置见图1。桥面宽度4.8m ,其中通行桥面宽4.5m (见图2。天桥桥跨采用中承式铝制主桁结构,桥面离主桁上弦杆1.265m 。主桁之间采用横向桁架连接,横向桁架上弦为桥面板的支承结构,桥面与上弦之间采用焊接互相连接。桥面为双层铝合金板结构,

3、在上下板之间用铝制竖向以及斜腹板联系。图3为桥面板结构图。计算分析的范围主要为上部结构,本次仅针对最大跨径26.64m 简支梁进行分析,其余同理。通过详细的计算分析,验算结构的挠度、自振频率。(1挠度验算:人群荷载作用下最大挠度不大于跨度的1/400。(2振动特性:计算结构的自振频率,保证桥梁在1kN/m 2活载下竖向振动频率大于3.0Hz 。2计算模型采用通用程序ANSYS 对结构进行弹塑性极限强度的验算,计算采用beam188单元模拟各上、下弦杆及竖斜腹杆,上下弦及斜竖腹杆按全截面取值,桥面采用等厚桥面板。26.64m 简支梁计算采用的有限元模型如图4所示。根据相关资料,极限承载力分析中采

4、用了图5所示的应力-应变关系。3分析计算3.1结构自振频率验算结果自振频率按是否考虑人群荷载分两种情况:(1恒载下的振动频率;(2恒载+1.0kN/m 2的人群荷载(桥面宽度按4.8m 计算。计算结果显示,在恒载下竖向振动自振频率为3.91Hz ,在恒载+1.0kN/m 2的人群荷载下自振频率为3.88Hz 。结果如表1所示,两种情形的振型图分别参见图6、图7。结果表明,两种状态下结构的竖向自振频率均超过了3.0Hz ,结构的自振频率能满足规范要求。3.2结构刚度验算在活载5kN/m 2作用下,跨中最大挠度为摘要:铝合金人行天桥在全国范围内已建成多座,但由于铝合金材料自身的特点,在设计过程中应

5、注重多方面的复核。依据杭州复兴路人行天桥建立模型,利用ANSYS 有限元软件辅助,就铝合金人行天桥的自振频率及稳定性进行重点分析计算,以期为以后的应用发展做出贡献。关键词:人行天桥;铝合金;自振频率;弹性模量;稳定性中图分类号:U448.11文献标识码:B文章编号:1009-7716(201203-0067-03收稿日期:2011-11-24作者简介:程子健(1980-,男,内蒙古人,工程师,从事路桥设计工作。程子健,杜晓燕(苏州市慧杰工程设计有限公司,江苏苏州215011铝合金人行天桥设计分析要点桥梁结构67城市道桥与防洪2012年3月第3期49.50mm ,桁架下弦的挠度为46.29mm

6、,为跨度的1/434和1/470,满足要求。活载作用下的结构变形见图8所示。4结论根据以上计算分析:(1铝合金人行天桥的震动频率变化幅度较钢图1杭州复兴路人行天桥桥型平面布置图图2主桥横断面图(单位:cm 图3桥面板结构图图5铝材的应力应变本构关系图4弹塑性极限强度的有限元模型表1自振频率结果振型序恒载恒载+1.0kN/m 2频率/Hz 振型频率/Hz 振型1 3.86一阶侧弯+扭转3.86一阶侧弯+扭转2 3.91一阶竖弯 3.88一阶竖弯振型参照图图6图7桥梁结构68桥梁结构69 2012年3月第3期城市道桥与防洪图6恒载作用下的结构振型图图7恒载+1.0kN/m2活载作用下的结构振型图(

7、下转第78页城市道桥与防洪2012年3月第3期材略大,但是人行荷载作用下可满足安全要求;(2铝合金材料的弹性模量小,挠度大,但是在跨径不大的情况下,由于铝合金材料自重小,挠度反而在安全范围内,可满足使用要求。参考文献:1姚常华,杨建国,吴利权.铝合金结构桥梁的应用现状、前景及发展建议J.钢结构,2009(7:1-5.2陈宝春,杨亚林,孙潮.铝桥的应用与发展J.世界桥梁,2004(2:68-70.3徐业飞.铝合金人行天桥结构分析D.杭州:浙江大学,2007.4张铮.铝合金结构压弯构件稳定承载力研究D.上海:同济大学,2006.5王春生,袁卓亚,高珊,叶礼锋.铝合金在民用与军用桥梁中的应用J.世界

8、桥梁,2007(3:9-12.6陈海滨.桁式钢管混凝土拱桥极限承载能力研究D.杭州:浙江大学,2006.7靳欣华,陆逵,鲁宏.上海某铝合金人行天桥荷载试验分析J.城市道桥与防洪,2009(2:33-35.8竺豪立,程晓东.铝合金人行天桥的特性及设计对策J.建筑,2007(24:44-45.9黄勇,许雷挺,李海沙.运营中铝合金人行天桥的监测J.建筑施工,2010(12:1250-1252.图826.64m 简支梁满载作用下的结构变形图(单位:mm宽0.5m ,为使横梁施工方便,索力传递均匀,以锚点为中心,每侧分布0.25m 宽度。(5桥头灯柱设计由于空间及地形限制,单独设立基础修建灯柱比较困难。

9、因此桥头灯柱设置在桥台背墙上面,分列护栏外侧。灯柱为钢筋混凝土结构,柱高3.5m ,柱截面为圆形,直径0.3m ,柱体主筋深入背墙里面,以背墙为基础。背墙宽度0.4m ,灯柱侧边距背墙外缘均为5cm 。这样做,既保证了灯柱有坚实的基础,又节省了空间。(6结构计算本次结构计算按城市专用人行桥计算,人群荷载取4.23kN/m 2设计。计算荷载包括恒载:结构自重、人行道铺装、护栏、灯饰、灯柱等;活载:温度力、风力、流水压力、混凝土收缩徐变等。a.箱梁设计按A 类预应力混凝土构件控制;b.主塔及下部结构按照普通钢筋混凝土构件控制;c.混凝土及预应力钢束、拉索结构按公路钢筋混凝土及预应力混凝土桥涵设计规

10、范(JTGD62-2004检算各项指标;d.钢结构部件按公路桥涵钢结构及木结构设计规范(JTJ 025-86检算各项指标。4结论综合以上过程,该项目具备了下面4个特征:(1统一和谐多样统一是形式美的一种高级形态,也是创造形式美的最高要求。从该项目来讲,桥梁周围环境复杂多样,既有姿态万千的建筑,又有形态各异的桥梁。该项目的加入,不仅与岸上莲花灯柱相呼应,也增加了桥梁组成的多样性,为周围环境增添了新的风景。总体来看,桥梁建筑自身及周边环境成为有机的整体,而不是杂乱无章,支离破碎。(2均衡稳定中国美学家朱光潜先生曾说:“美的形体无论如何复杂,大概含有一个基本原则,就是平衡和匀称。”该项目对称均衡,通

11、过它的外在形象所展示的体量就有一种均衡稳定感。整体结构具有稳重、庄严之美,而搭配的灯饰和护栏又有灵活、翔动的美。(3比例协调比例在建筑艺术上是非常重要的。该桥塔高、柱径、灯饰大小经过多次比较筛选,在众多方案中选出合适比例的配合,再通过不同颜色之间的搭配,收到了良好的效果。(4特征鲜明该桥建筑风格时代感强烈,配饰融入了民族地域风格。桥型简洁明快、轻巧纤细、连续流畅、融入自然。参考文献:1范立础.桥梁工程(上册M.北京:人民交通出版社,2001.2和丕壮.桥梁美学M.北京:人民交通出版社,1999.3许秀平,彭卫.桥梁建筑美学特征与结构设计J.金华职业技术学院学报,2004(3:29-32.(上接

12、第69页!桥梁结构78theoretical calculation mode,and the deck vibration frequency satisfies the rule of simplified calculation formula.The dynamical characteristic of this bridge is excellent.Keywords:flying-swallow concrete filled steel tube arch bridge,finite element,natural vibration characteristic,modal

13、analysisAnalysis on Unconstrained Length of Externally Prestressed Cable!Wang Shousheng(54 Abstract:The externally prestressed cable among the turning blocks(anchoring endmay produce the vibration independently from the girder.If its frequency is closing to the inherent frequency of the girder, the

14、sympathetic vibration will cause.It is not the good solving method to change the section characteristic of girder or the normal using stress of external cable when the frequencies are closing.The ideal method can yet be regarded in the aspects of economy,effect and feasibility to change the restrict

15、ed length of the external cable so as to change its inherent frequency.The unconstrained length of non-lateral support for external cable should not be over long.Based on the common bridge frequency and the using condition of steel strand in China,the external cable can be controlled within12m.In th

16、is way,the natural vibration frequencies of bridge and external cable will stagger,and also avoid the sympathetic vibration.Keywords:external prestressing,sympathetic vibration,frequency,unconstrained lengthThree-dimension Finite Element Simulation Analysis on Full-pile Foundation of Bridge Based on

17、 ANSYS!Chen Hui(58 Abstract:The bridge foundation is an important composed part of bridge structural engineering.It bears the weight of the upper structure and the external force,and conveys them to the subgrade.Based on the finite element software ANSYS,the article carries out the three-dimension s

18、imulation analysis on the full-pile foundation of bridge,including the constitution design,modeling and network division of the full-pile foundation of bridge,and the stress analysis under the dead weight and vehicle live load.Keywords:bridge structure,full-pile foundation,finite element analysis,AN

19、SYSDesign Method of Long-span Continuous Steel Box Beam!Dai Shaoxiong,Xie Bin(61 Abstract:The article introduces the design and construction methods of long-span continuous steel box beam for the overpass bridge in the west longitudinal contact line of expressway,systematically describes the design

20、process,analyzes the key nodes in detail,and puts forward the feasible design method,which can be referred for the construction of the similar bridges.Keywords:long-span continuous steel box beam,steel deck slab,shear lag,pivot structureCrossbeam Design of Variable Section Pre-stressed Concrete Cont

21、inuous Box Beam Bridge Zhou Haixia(64 Abstract:The article analyzes the crossbeam constitution,calculation model and reinforcement design of variable section pre-stressed concrete continuous box beam bridge by the engineering cases.Keywords:variable section pre-stressed concrete continuous box beam,

22、crossbeam,constitution,model, reinforcementDesign and Analysis Gist of Aluminium Alloy Pedestrian Overpass!Cheng Zijian,Du Xiaoyan(67 Abstract:Many aluminium alloy pedestrian overpasses have been built in China.However,the recheck has to been focused in many aspects in the course of design because o

23、f the characteristics of aluminium alloy material.Based on the model built for Fuxing Road Pedestrian Overpass of Hangzhou,the natural vibration frequency and the stability of aluminium alloy pedestrian overpasses are focused on analysis and calculation by utilizing the ANSYS finite element software

24、 so to make the contribution for the application and development of its future.Keywords: pedestrian overpass, aluminium alloy, natural vibration frequency, elastic modulus, stability Design of 64-m Curve Steel Truss Beam ! Peng Min (70 Abstract: The article introduces the design of railway steel tru

25、ss bridge, and focuses on analysis of whether or not the deck concrete is concerned with the stress of structure system and the influence of curvature on the stress of the inner and outer lateral rods, which can be referred for the design of the same bridge. Keywords: curve steel truss beam, railway

26、 bridge, structural calculation, design Analysis on Design and Calculation of Overall Structure for Datong Beidou Bridge ! ! Chen Hefeng, Wu Yongxian, Wang Shuo (73 Abstract: The article introduces the structure design and construction schemes of Beidu Bridge, which is an important landscape bridge

27、connecting the old and new city areas in Datong City of Shanxi province. Its main bridge is a 140-m single-span through steel truss arch bridge with the design of unilateral double booms. Through the static and stability calculation analysis, and the three-dimensional analysis of partial arch foot,

28、the rationality and security of this design scheme are verified, which can be referred for the design of this kind of bridges. Keywords: steel truss arch bridge, structure design, structural calculation analysis, Datong City Design of Single-pylon Single-plane Pedestrian Landscape Cable-stayed Bridg

29、e in Baoting County of Hainan ! Liu Yaozong (76 Abstract: The article introduces the design of a single-pylon single-plane pedestrian landscape cable-stayed bridge on Baocheng East River in Baoting County of Hainan, and discusses how to deal with the harmonious unification of the structure and the l

30、andscape. Keywords: single pylon, landscape, cable-stayed bridge, design Discussion on Design of River Landscape Bridge ! Liu Xiangyang, Li Baoyuan (79 Abstract: With the advancement of the society and the enhancement of the people living level, the s river taken as an important carrier of urban landscape is more and more concerned by the people. Many cities, such as Beijing, Shanghai, Hangzhou and etc. all actively se