三桁钢桁梁桥横桥向内力调整方法及影响参数

Internal force adjustment of three main trusses and the parameters that influence it in steel truss bridge with three main trusses and double decks

针对多主桁钢桥结构成桥状态中边桁受力不均衡的情况,结合三桁刚性悬索加劲钢桁梁桥─—东江大桥,介绍了通过预设横向预拱度来横向调整三片主桁构件内力这一新技术,并分析了其调整原理。为了验证此技术的有效性,应用有限元程序,建立实桥三维有限元模型,对比了内力调整前后中边桁控制弦杆与加劲弦的轴力与不均衡系数,分析了横梁竖向抗弯刚度(EI)、横梁与主桁连接节点刚度(K)对中边桁构件内力分布的均衡性及横向内力调整效果的影响。研究结果表明,利用预设横向预拱度方法,使中桁支座沉降37 mm,可以有效地将中桁内力分担至两边桁,成桥后使中边桁对应弦杆与加劲弦不均衡系数ηi控制在±5%以内;横梁EI对三桁内力分布的均衡性有较大影响,随EI的增大,ηi逐渐减小;节点刚度K对三桁内力分布的均衡性影响显著,铰接模型不均衡系数较刚接模型高出50%左右,是决定内力调整效果的关键。最后,针对实桥横梁与主桁连接并非完全刚接的情况,提出了位移与支反力双控的施工措施。

Aiming at that internal forces of middle truss were larger than those of side truss in multi-truss steel bridges after construction,based on a steel bridge with three main trusses stiffened with rigid cables—Dongjiang Bridge,a new technique which could balance internal forces of three trusses by setting camber of lateral direction was introduced and the principle of internal force adjustment was analyzed in detail.In order to prove the validity of this method,a 3D finite element model of Dongjiang Bridge was established by FEM software,axial forces and unbalance factors for main chords and stiffened rigid cables of middle truss and side truss before and after internal force adjustment were compared,and the influences of the vertical flexible stiffness（EI） of floor beam and connection stiffness（K） between floor beam and primary truss on internal force distribution of middle truss and side truss and efficiency of internal force adjustment were studied.The results show that the method distributes the redundant internal forces from middle trusses to side trusses through floor beams by forcing supports of middle truss to settle down 37 mm,and the unbalance factor ηi between middle truss and side truss is controlled within the range of ±5%.The flexible stiffness（EI） of floor beam has great influence on internal force adjustment of three trusses,and ηi becomes smaller with the increase of EI.The connection stiffness（K） between floor beam and main truss has significant influence on internal force adjustment of three trusses and is the key to determine internal force adjustment effect.Being aware that connection between floor beam and primary truss is not completely rigid in practice,both displacement and reaction monitoring of supports is suggested in construction.