Abstract: 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.