Experimental And Theoretical Researches Of Double Curve Arch Bridge Strengthen With Steel Truss In Unfavorable Geological Condition

In China, most of the double curve arch bridge was built in last century60s and70s, because of the design load standard and the level of construction was lower, thedamage of bridge is increasing.The double curve arch bridge is sensitive to unfavorable geological conditions,ground foundation subsidence and slippage and other diseases cause serious damageon foot section of arch. In northeast region of China, the temperature stressaggravated this damage, it leads to the actual mechanical behavior of double curvearch bridge changed. As the growth of the bridge service time, the traffic flow andvehicle load increase gradually, and the risk of bridge security increase rapidly. Archbridge repair and reinforcement becoming a important problem to be solved. Thispaper analyzed the actual mechanical behavior of double curve arch bridge, detectedthat the arch foot has tiny rotation, forming half-consolidation. Base on this fact, Thispaper proposed a method that using steel truss to reinforce arch ribs, thereinforcement principle and calculation theory was analyzed in this paper, arch ribmodel test, numerical simulation analysis and actual engineering test was carried on.The main research work of this paper includes the following content:(1) The author refered to a large number of relevant documents, introduced thehistory of the double curve arch bridge and summarized reinforcement method. Thispaper analyzed the damage mechanism of double curve arch bridge under unfavorablegeological conditions and the feasibility of reinforcement method. (2)Through the study on mechanical properties of the two-hinged arch, this paperpointed that poor resistance of live load moment is the main reason that leading tobearing capacity reduce. Based on the research，it analyzed mechanics principle oftwo-hinged double curve arch bridge reinforced with steel truss.(3) This paper suggested that sets the arch rib as rigid member and steel truss as abear axial force components. Then set up the simplified mechanics model. Throughthe analysis of the geometry parameters of steel truss, reasonable suggestions of steeltruss geometry design were put forward. On the basis of the simplified mechanicalmodel, put forward the calculation method of arch rib reinforced by steel truss.(4) Using the general finite element program ABAQUS to establish two finiteelement model, The results showed that the moment of arch rib reduced. Its stressstate was more reasonable, and the carrying capacity increased by2.4times.(5) According to the damage characteristics of the double curve arch bridge underunfavorable geological conditions, two arch rib test model were made. From theexperimental results, Unreinforced arch rib cracks in the middle of span verticalupward developed, when close to the limit load, near the1/8span, the top of the archrib crack. Cracks in the middle of arch rib reinforced by steel truss decrease obviously,and does not appear cracks on the top.(6) In the process of test, the deflection at the1/8span of unreinforced arch ribdown first, then up gradually. At1/4,3/8span and the middle span of unreinforcedarch rib, deflection increases downwards.All the deflection of arch rib reinforced by steel truss developed downwards.Two specimens deflection distribution was same, Mid-span deflection was the largestone, then decreasing along the arch rib. By data analysis showed that the lineargrowth condition of reinforced arch rib’s deflection is better than unreinforced arch rib, it shows that after strengthened with steel truss, the overall stiffness of thespecimen is more symmetrical, component integration degree increased significantly.(7) Through the analysis, after strengthening, the bend moment of arch rib in1/8,1/4span greatly reduced, section keep compression state.3/8span and mid-span the ttensile strain of bottom longitudinal rebar was greatly reduced. It shows that arch rib’sforce bearing status is more reasonable after strengthened with steel truss. Thecracking load, yield load and ultimate load increased by2.94times,2.94times and2.94times respectively, greatly improve the bearing capacity of the specimen.(8)We strengthened chang ’an bridge by using this method,and load test was carriedout. Experimental data shows that the overall mechanical performance is improvedsignificantly after reinforcement, the bearing capacity of bridge structure and theoverall stiffness significantly promoted, the strengthening desired effect is achieved. Itproves that steel truss reinforcement method is feasible.