| Hollow-core slab bridge is widely used in the construction of medium and small span bridges in China.However,with the increasing volume and load of traffic in China,the hollow-core slab bridge is prone to damage,especially the hinge joint damage.To ensure the integrity and durability of hollow-core slab bridge,it is necessary to reinforce it.At present,many reinforcement methods have been proposed for the hinge joints of hollow-core slab bridges in China,but the research on the total failure process of hollow-core slab bridges under different reinforcement methods is insufficient.In addition,in practical engineering,the bridge is under the repeated load of vehicles,but in the retrieved public documents,most tests or finite element analysis are conducted under the static load.Based on this,our research group put forward the reinforcement methods of pinned rebar,prestressed tendon,passive carbon fiber cloth and active carbon fiber cloth,and carried out static load test and fatigue test on beams with hinged joints respectively to explore the deterioration process and force transmission mechanism of hinged joints under different reinforcement methods.At the same time,based on the static load test results,the corresponding finite element model is established and analyzed.In addition,according to the parameters obtained from the finite element model,a three-beam and two-hinged hollow-core slab bridge with a span of 10 m is numerically simulated to explore the total failure process and reinforcement effect of the hollow-core slab bridge.The specific research contents of this paper are as follows:(1)The cracking load and ultimate load of hinge joints can be improved by the methods of pinned rebar,prestressed tendon and passive carbon fiber cloth.Compared with traditional hinge joints,the cracking load of hinge joints reinforced by pinned rebar,prestressed tendon and passive carbon fiber cloth are increased by 28.6%,85.7% and 200.0% respectively.The ultimate load increased by 88.2%,155.9% and 47.1% respectively.(2)The fatigue life of traditional hinge joint,hinge joint reinforced by pinned rebar,hinge joint reinforced by prestressed tendon and hinge joint reinforced by active carbon fiber cloth is 13,000,19,000,70,000 and 2.049 million,respectively.Under the action of fatigue load,the stress level of U-bar and the relative deflection of hinge joints can be reduced by pinned rebar,prestressed tendon and active carbon fiber cloth.When 10,000 times of fatigue loading,under the load of 120 k N,the stress of unloaded segment rebar reinforced by pinned rebar and prestressed tendon is 53.0% and 23.9% of that of traditional hinge joints,and the relative deflection is 9.1% and 38.6% of that of traditional hinge joints,respectively.The stress of rebar in the loaded and unloaded segment of the hinge joints strengthened with carbon fiber sheets is 7.7% and 0.4% of that of the traditional hinge joints respectively,and the relative deflection is 42.0% of that of the traditional hinge joints.(3)Interface unit method simulates the new-to-old concrete interface better.The analysis results show that the interface stiffness and tensile strength have great influence on the through-joint load.For beams with hinged joints with different reinforcement methods,the reasonable range of interface stiffness is 12000MPa-20000 MPa,and the reasonable range of tensile strength is 0.6MPa-1.8MPa.Compared with the static load test results,the error of each finite element model is within 15%.(4)The results of finite element analysis show that,the total failure process of hollow-core slab bridge with a span of 10 m under load is that the mid-span part cracks first,and with the increase of load,the width and height of cracks in the mid-span part increase.At the same time,with the increase of load,the mid-span cracks gradually extend to both sides along the longitudinal direction,and the width and height of cracks in the newly cracked parts gradually increase.Under the ultimate load,the longitudinal crack span of the traditional hollow-core slab bridge is 0.22L-0.7L,and the longitudinal crack span of the hollow-core slab bridge reinforced by pinned rebar,prestressed tendon and passive carbon fiber cloth is0.36L-0.61 L,0.3L-0.7L and 0.29L-0.71 L respectively.(5)Compared with the traditional hollow slab bridge,the cracking load of hollow slab bridge reinforced with pinned rebar and prestressed tendon increased by 233.3% and 50.0%respectively.The through-joint load increased by 116.7% and 91.7% respectively.The ultimate load increased by 50.0% and 66.7% respectively.In addition,the through-joint load and ultimate load of hollow-core slab bridge reinforced with passive carbon fiber cloth increased by 8.3% and 94.4%.Under the same load,the rebar stress,relative deflection and crack width of the reinforced hollow-core slab bridge are smaller than those of the traditional hollow-core slab bridge,and all three reinforcement methods can restrain the damage and deterioration speed of the hollow-core slab bridge.(6)Under the static load,the damage of hinge joints with different reinforcement methods can be divided into three stages: uncracked stage,working stage with cracks and failure stage.In the uncracked stage,the load of each hinged joint beam is mainly transmitted by the adhesive force at the interface between new and old concrete.In the working stage with cracks,the traditional hinge joints transmit loads together with U-bar by interfacial bonding force,while the hinge joints reinforced with pinned rebar,prestressed tendon and passive carbon fiber cloth transmit loads together with three layers of U-bar,prestressed tendon and carbon fiber cloth by interfacial bonding force.In the failure stage,the traditional hinge joints are only supported by U-bar,and the hinge joints reinforced by pinned rebar,prestressed tendon and passive carbon fiber cloth are supported by three layers of U-bar,U-bar and prestressed tendon,and U-bar and carbon fiber cloth.(7)Under fatigue load,the damage of hinge joints with different reinforcement methods can be divided into three stages: rapid damage stage,slow development stage and failure stage.In the rapid damage stage.In the stage of rapid development,the traditional hinge joints mainly transfer the load by the interfacial bonding force and U-bar.Pinned rebar reinforce hinge joints mainly by interfacial adhesive force and three-layer U-bar to transfer load.Prestressed tendons reinforce hinge joints mainly by prestressing tendons,interfacial adhesion and U-bar to transfer loads.The active carbon fiber cloth is mainly used to reinforcement the hinge joint by carbon fiber cloth,interfacial adhesive force and U-bar to transfer the load.Only the active carbon fiber cloth reinforced hinge joints experienced a slow development stage and a failure stage.In the slow development stage,the interfacial adhesion of new-to-old gradually withdrew from work.In the failure stage,the U-bar quit working,and only the carbon fiber cloth transfers the load.(8)The fatigue test results show that the hinge joint reinforced with active carbon fiber cloth shows the best durability,and its fatigue life reaches 157.6 times that of the traditional hinge joint.The results of finite element analysis show that the ultimate bearing capacity of hollow-core slab bridge reinforced with passive carbon fiber cloth is the highest,and its ultimate load is 1.9 times that of traditional hollow-core slab bridge.Therefore,the method of carbon fiber cloth reinforcement has the best reinforcement effect. |
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