Experimental Study On Flexural Performance Of Steel Plate-UHPC-NC Composite Beam Bridge

In China,small and medium span bridges are an important part of the transport network.However,bridge diseases of the main girder cracking,excessive deflection and the damage of bridge deck pavement are common in traditional medium and small span bridges.Meanwhile,it is also difficult to control the value of the pre-camber.In addition,the assembling rate of medium and small span bridges is low,as the result of the size and weight of bridge fabricated with normal strength concrete,which restricts the further development of medium and small span bridges.Based on the superior mechanical properties and durability of Ultra-high Performance Concrete(UHPC),a novel Steel Plate-Ultra-high Performance ConcreteNormal Concrete(Steel Plate-UHPC-NC)composite girder is proposed that satisfies the requirements for cost of construction as well as accelerated bridge construction.This study investigated the behavior of flexural and shrinkage and creep effect.The main work contents and conclusions of this study are as follows:(1)According to the requirement of the object,a design plan of steel plate-UHPC-NC composite girder with a span of 30 m is proposed.To investigate the crack development,bending behavior of the composite girder and failure model,a 1:2 scale specimen was tested.According to the test results,the layout of steel bars of the composite girder is optimized,which meets the requirements of the bending design of the composite girder.(2)The strain and temperature of the Steel Plate-UHPC composite structure were measured during the fabrication of the test girder,and the shrinkage law of the UHPC under the restraint of steel plate was obtained.The residual stresses in the prefabrication of UHPC due to the restraint of steel plate are calculated and analyzed.The internal force distribution model of shrinkage and creep of Steel Plate-UHPC-NC composite girder is established by the internal force distribution method.The results indicate that shrinkage and creep of UHPC can cause non-negligible tensile stress(6.24 MPa)at the bottom edge of the UHPC girder,and the tensile stress decreases with the increase of creep coefficient and loading age.(3)Based on the bending test results of the test girder,the finite element model of the test beam is established,and the finite element analysis results are in good agreement with the test results,which can further simulate the bending behavior of the Steel Plate-UHPC-NC composite beam.The parameter analysis of the flexural behavior of the structure is carried out and the results show that: Increasing the thickness of steel plate and the yield strength of steel plate can greatly increase the ultimate bearing capacity of composite girder;Increasing the tensile strength of UHPC can only slightly increase the ultimate bearing capacity of the composite girders,while NC compressive strength has no effect on the ultimate bearing capacity of the composite girders;The thickness of steel plate and the tensile strength of UHPC have a great influence on the stiffness of composite beams after cracking,while the yield strength and NC compressive strength of steel plate has little influence on the stiffness after cracking.(4)The bending bearing capacity of Steel Plate-UHPC-NC composite girders is calculated and analyzed,and the simplified formula of the bending bearing capacity considering the tensile effect of UHPC is derived by using the method of the equivalent rectangular stress Diagram,the calculated results are in good agreement with the experimental and finite element analysis results.At the same time,the bearing capacity without accounting UHPC tensile strength is calculated,the results show that the moment bearing capacity decreases by 7% ～ 15.5%.