Research On The Key Technologies Of Heavy-haul Railway Bridges Strenghened By External Prestressing

Increasing the axle load of freight car can effectively improve the transport efficiency of heavy haul railway in China, but will make bearing capacity of the existing bridges relative insufficiency. Externally prestressed strengthening method is one of the most effective methods to solve the problem of bridge structure with insufficient bearing capacity under heavy haul railway truck when axle load greatly improved, but inadequate research and rare application in china’s railway bridge reinforcement. Therefore it is important to start the research on strengthening the heavy haul railway bridge with external prestressed reinforcement method for promoting the application of externally prestressed technology in the field of heavy haul railway bridge’s strengthening and the development of China’s heavy haul railway transport capacity.It is the key technological problem to successfully strengthen railway bridges for externally prestressed strengthening system composed of external cable, anchorage, deviator etc. Theoretical calculation of external cable force, system structure design, anchoring bearing capacity, overall system performance test, reliability etc are the key technologies around the external prestressing system to strengthen the railway bridges. Based on State863Projects 《Cheking and strengthening technologies of heavy haul railway bridges and roadbed》, the main research contents are as follows::(1) Based on the allowable stress method of the china raiway standard, the external cable force calculation method is researched; The calculation methods of bridge’s maximum stress, arch deflection and deflection etc are also discussed, then staged calculation method was established taking into account the concrete cracks’ closure, and the calculated results are experimentally verified.(2) The existing externally prestressed strengthening systems have the disadvantages of slow construction speed, installation quality being difficult to control, anchorage and external cable connection point being easy to cause the bending fatigue damage etc, so a rotating anchorage and cable type externally prestressed system is proposed according to the basic strengthening requirements of heavy haul railway bridge. The new system is significant to promote the application of external prestressing technology in heavy haul railway bridge strengthening field, and to improve the transportation efficiency of China heavy haul railway. At the same time, craftsmanship, external force tension and fatigue performance of the whole system are installed on the reinforced concrete beam and tested. (3) In view of the lack of theoretical and experimental study on the anchoring bearing capacity of externally prestressed system bonded to the bridge beam at home and abroad, detailed studies were carried out on the anchoring bearing capacity by experimental method and theoretical analysis. Firstly, the contrast test research of two different anchoring ways shows that the best anchoring method for strengthening the heavy haul railway bridge is bonding friction anchorage; Then based on the mechanical analysis of the bonding friction anchoring method, the experience formula of anchoring bearing capacity was established through the method of regression analysis of experimental data.(4) To solve the problem of insufficient space at direct use of jack to tension external cable when the external prestressed anchoring points are set in the concrete beam end of heavy haul railway bridges, a front-put tensioning device suitable for fork-ear anchor was proposed, and was proved feasibility and applicability in strenthening heavy haul railway bridge with numerical analysis and experimental study.(5) The reliability of the heavy haul railway bridge strengthened by the rotating anchorage and cable type externally prestressed system was also studied. Based on the analysis of the random variable of live load, dead load, durability factors, fatigue factors etc, and comprehensively considering the tnteraction of fatigue and durability factors on bridge structure reliability, the time invariant reliability calculation model and the time variant reliability calculation model considering the fatigue and durability factor were established.