Research On The Flexural Performance Of UHPC-RC Box Composite Beam Structure

Ultra-high performance concrete(UHPC)material has high mechanical properties and durability,and has broad application prospects in bridge engineering.However,if the bridge structure is all UHPC materials,the project cost will be too high.In order to give full play to the excellent performance of UHPC materials and improve economic benefits,research on new UHPC-RC composite beams that can use both UHPC materials and ordinary reinforced concrete materials is to promote UHPC materials in one of the important methods practically applied in bridge engineering.This article takes a fully assembled UHPC-RC box-type composite beam used in a pedestrian overpass of an expressway in Anhui Province as the engineering background.Through theoretical analysis,scale model test,numerical simulation and other research methods,the bending performance of this type of UHPC-RC box composite beam is studied,and the sensitivity analysis of key design parameters is carried out to provide a basis for structural design optimization.The main work content and related conclusions of this paper are as follows:(1)The UHPC-RC box-type composite girder pedestrian bridge design scheme’s ultimate bearing capacity and serviceability limit state can meet the requirements of relevant regulations,and the bearing capacity is rich and safe.On this basis,a UHPC-RC box-type composite girder pedestrian bridge design scheme using unreinforced UHPC "U-shaped beams" is proposed.Through finite element analysis,it can be known that the flexural performance of the scheme meets the requirements of relevant codes.However,because there is no pre-stressed and ordinary steel bars,and the cross-sectional size of the UHPC "U-shaped beams" is light and thin,its cross-sectional bending stiffness is small,which will lead to greater deflection;(2)A scaled model of UHPC-RC box composite beams using unreinforced UHPC "U-shaped beams" was produced,and material performance tests and flexural performance tests were carried out to clarify the entire process of the test beam from elastic state to structural failure: linear elasticity stage,elastoplastic stage,crack development stage and failure stage.Although UHPC "U-shaped beams" are not equipped with steel bars,the ultimate failure state still has good ductility,and no brittle failure similar to plain concrete occurs.It fully shows that adding steel fiber can effectively improve the flexural bearing capacity and ductility of UHPC-RC box composite beams.(3)The main crack of the test beam appeared in the middle of the span,but some small diagonal cracks also appeared in the beam body.In the process of crack development and destruction,it can be observed that the steel fiber is continuously pulled out at the main crack,which further shows that the steel fiber at the crack has an effective connection and restricts the development of the crack.(4)Aiming at the structural and material characteristics of UHPC-RC box composite beams using unreinforced UHPC "U-shaped beams",referring to material performance tests,based on the ABAQUS software platform,a UHPC-RC box composite based on the concrete plastic damage model is established(Experimental)Beam nonlinear solid finite element model,and the whole process simulation of the anti-bending performance test was carried out.The results show that the finite element analysis results are in good agreement with the experimental data.On the one hand,it verifies the correctness of the modeling method.On the other hand,the force characteristics and failure mechanism of this type of UHPC-RC box composite beam are also verified.(5)Increasing the steel bar diameter or reinforcement ratio of the bridge deck and the tensile strength of UHPC materials can effectively improve the flexural load-bearing capacity of UHPC-RC box-type composite beams.Among them,the influence of steel bars is greater than the tensile strength.However,changing the compressive strength of UHPC material and the strength grade of ordinary concrete of bridge deck has little effect on the flexural bearing capacity of UHPC-RC box composite girder.