针对这种现象，以位于埃塞俄比亚奥莫河上一座128 m的钢桁梁桥为研究对象，拟采用增设斜拉索法进行提载加固。考虑到钢桁梁桥的跨径，拟选取16 m的矮塔和26、30 m的常规塔高，采用分析桥梁受力时常用的有限元方法建立大跨度钢桁梁桥模型。在三种荷载工况下，分别从刚度、承载能力以及稳定性三个方面来分析对比不同的索塔高度对加固效果的影响。在工况1（活载作用）下，分析钢桁梁桥加固前和不同塔高加固后的挠度变化；在工况2（正常使用极限状态标准荷载组合1.0恒载+1.0活载）下，分析三种塔高下斜拉索加固后桥梁的整体稳定性，即进行屈曲分析；在工况3（承载能力极限状态基本组合1.25恒载+1.75活载）下，分析加固前后上弦杆应力分布、下弦杆应力分布以及斜杆的应力分布。节点板是钢桁梁中的关键部位，其构造复杂，并且受力时存在应力分布不均匀的现象。针对这种情况，同样采用有限元方法，对钢桁梁桥受力复杂的节点建立实体模型，根据节点各构件力的传递主要通过焊接连接和摩擦型高强螺栓提供的摩擦力的特点，选择加固前、后内力最大的节点板进行模拟，将各杆件的轴力和面内、外弯矩加到相应的杆件上，对加固前、后的内外侧节点板应力、内外侧斜杆螺栓应力以及内外侧连接板螺栓应力进行分析，了解其应力分布特点。
综合考虑以上分析得出结论：单独考虑加固效果时，26 m塔高斜拉索加固后的加固效果最好；16 m塔高斜拉索加固后效果较26 m塔高斜拉索加固效果稍次之；30 m塔高斜拉索加固效果最差。结合工程经济效益考虑后，建议将16 m塔高斜拉索加固作为奥莫河大桥的加固方案。
With the rapid development of the world economy, the traffic volume and load levels continue to increase. The bearing capacity of some large-span steel truss girder bridges can not meet the current needs and have experienced excessive deflection and stress under the effect of the existing load levels due to the low load level of the original design. To improve the bearing capacity and extend the service life, the structure need to be strengthened. After knowing about it, steel truss girder bridges can be strengthened by adding stay cable method, adding suspension cable method and external prestressing reinforcement method. Above those three methods, the stay cable method is the most effective.
Focusing this phenomenon, in this paper, a 128m steel truss bridge on the OMO River in Ethiopia is proposed to be reinforced by adding stay cable method. After looking up relevant information and considering the span of the steel truss bridge, plan to choose a 16m short tower and a 26m and a 30m conventional tower height. And establish the long-span steel truss bridge model by using the finite element method often used in bridge analysis and analyzes the influence of different tower heights on the reinforcement effect of the bridge under three load conditions from three aspects of stiffness, bearing capacity and stability respectively. Under the action of the first working condition, i.e. under the action of live road, analyze the deflection changes of steel truss bridge before and after the reinforcement of different tower heights; Under the second working condition, that is, under the standard load combination 1.0 constant load+1.0 live load in normal use limit state, the overall stability of the bridge after the reinforcement of the three towers with high stayed cables is analyzed, that is, the buckling analysis is conducted. Under the third working conditions, that is, the stress distribution of the upper chord, the lower chord and the inclined chord before and after the reinforcement is analyzed under the basis combination of 1.25 constant load and 1.75 live load in the ultimate bearing capacity state. The nodal plate is a key part of the steel truss girder with complex structure and uneven distribution of stress. In view of this situation, a solid model is established for the complex joints of steel truss bridge also by the finite element method. Components according to the node force transfer mainly through welding and friction type high strength bolt connection with the characteristics of the friction of the choice before and after reinforcement, to simulate the internal forc-e of the largest node plate axial force of each bar and internal and external bending moment on the corresponding bar, inside and outside nodes before and after the reinforcement plate stress, inside and outside helical rod bolt stress and inside and outside connection plate bolt stress analysis, understand the stress distribution characteristics.
After comprehen-sive consideration of the above analysis, the conclusion is drawn:when considering the reinforcement effect alone, the reinforcement effect brought by the 26 m tower high stay cable is the best, the reinforcement effect of the 16m tower high stay cable is slightly inferior to that of the 26m tower high stay cable, and the reinforcement effect of the 30m tower high stay cable is the worst. Considering the economic benefit of the project, it is suggested that the 16m tower stay cable should be used as the reinforcement scheme of the Omo River Bridge.