Y Bridge Deck, Etiology And Strengthening Programs To Mechanical Performance

Y is a self-anchored, semi-supported concrete-filled steel tube (CFST) arch bridge with three-span of 76m+360m+76m. The bridge's floor system consists of concrete slab, little steel stringer and steel beam, and concrete slab combined with steel beam. Serious diseases have found in the connection between little steel stringer and steel beam, just after a decade's operations. With finite element method, floor system disease cause, plan of reinforcement and floor system's mechanical behaviors in the process of Strengthening were analyzed in this paper. The maioj tasks are summrized as follows:1. The space finite element model of the full bridge and three segments local finite element model of the floor system were established by using Midas. By studying original floor system's mechanical behaviors, comes to the reason of the disease:due to the very severe overloading in Yajisha bridge, the stress of connection angle which connect little steel stringer with steel beam, steel beam web which connected with little steel stringer is too large, leading to fatigue damage. Steel beams at the edge of some stiffening ribs have stress concentration, resulting in cracking.2. The two plans of reinforcement are studied. Through adding large steel stringer, strengthening steel beams and making little steel stringer and steel beam have another kind of connection, it raise floor system integrity and improve the safety factor of the bridge operation, and the stress of floor system is much more less than before, fatigue stress amplitude are within the allowable value even under overload. The results showed that the two plans of reinforcement are feasible in principle.3. The connection of little steel stringer and steel change to "Hanging, connecting steel beam web with steel stringer top flange by a hinged bolts, other parts are not connected" in reinforcement planⅠ, "connecting steel beam bottom flange with steel stringer bottom flange by a ordinary bolts, other parts are not connected" in reinforcement planⅡ. The connection's Maximum fatigue stress of plan I is 70.6MPa, planⅡis 29.4MPa. The plan II is more reasonable than plan I, so plan II being recommended at last.4. Floor system's mechanical behaviors in the process of Strengthening were analyzed. Steel beam will not be full section yield after drilling holes in it's web and bottom flange. The suggestion is that dealing with crack before drilling holes. In the process of change sling, floor system and adjacent cable's maximum stress is less than the yield strength. The sequence of large steel stringer installation has no great impact on deformation and stress state, so the sequence can be choose according to on-site construction conditions.The research results of this paper have applied to the reinforcement design and construction control of Yajisha bridge. Meanwhile, it can be as a reference for others same type bridges.