Research On Flexural Behavior Of Steel-UHPC Lightweight Composite Deck Structures

The steel-UHPC lightweight composite deck structure is a composite structure consisting of the Ultra-High Performance Concrete(UHPC)layer with internal longitudinal and transverse reinforcement mesh connected to the steel plate by short studs,it can effectively solve two difficult problems of fatigue cracking of traditional orthotropic steel bridge deck and damage of asphalt pavement.Based on finite element software(ABAQUS),the effects of key design parameters(e.g.thickness of UHPC layer,thickness of U rib,Stud spacing and reinforcement ratio)on the longitudinal and transverse flexural behavior of steel-UHPC composite structures are studied in this paper.In addition,the formulas for calculating the cracking load and ultimate bearing capacity of steel-UHPC composite beam are proposed.The main research contents and conclusions are as follows:(1)The nonlinear finite element model of steel-UHPC composite plate was established,the influence of 4 key design parameters(such as thickness of UHPC layer,stud spacing,longitudinal reinforcement ratio and cover thickness)on the transverse flexural behavior of steel-UHPC lightweight composite bridge deck was studied.The results show that increasing the thickness of UHPC layer can significantly increase the stiffness and ultimate bearing capacity of the members from elastic stage to crack propagation stage,but has no effect on the cracking stress,and the ductility of composite plates tend to decrease.The combination effect between the UHPC layer and the steel plate can be improved by reducing the stud spacing,and the slip between two components can be reduced effectively,the effect of shear-bend stud is much greater than that of pure-bend Stud.Reinforcement bar has no effect on the initial elastic stage of composite plate,while increasing the longitudinal reinforcement ratio and decreasing the cover thickness can increase the cracking stress and ultimate bearing capacity of members.(2)Based on the orthogonal test method,16 nonlinear finite element models of steel-UHPC composite plates were established to analyze the comprehensive influence on bending performance,and the sensitivity ordering of 4 key design parameters(such as thickness of UHPC layer,stud spacing,number of longitudinal reinforcement bars and cover thickness)to the critical slip load of composite plates is obtained:thickness of UHPC layer>stud spacing>number of longitudinal reinforcement bars>cover thickness.The sensitivity ordering of the difference between yield load and elastic limit load(crack propagation stage)is:thickness of UHPC layer>number of longitudinal reinforcement bars>cover thickness>stud spacing.The sensitivity ordering to ultimate bearing capacity is:thickness of UHPC layer>number of longitudinal reinforcement bars≈cover thickness>stud spacing.(3)The nonlinear finite element model of steel-UHPC composite beam was established,the influence of 5 key design parameters(such as thickness of U rib,thickness of UHPC layer,thickness of steel plate,longitudinal reinforcement ratio and cover thickness)on the longitudinal flexural behavior of steel-UHPC lightweight composite bridge deck was studied.The results show that the stiffness,ultimate bearing capacity and ductility of the composite beam can be improved by increasing the thickness of U rib.Increasing the thickness of UHPC layer has a certain effect on improving the mechanical properties of composite beams.When the thickness of U rib is small(6mm to 10mm in this paper)and the member is damaged by the yield of U rib,increasing the thickness of steel panel has no effect on the ultimate bearing capacity,but only increases the stiffness of the member in the crack extension stage in a small range.The effect of reinforcement bars on the composite beam is very small,so the change of longitudinal reinforcement ratio and cover thickness has little influence on the behavior of composite beams.(4)The calculation formularies of cracking load and ultimate bearing capacity of the steel-UHPC composite beam are proposed.The results show that the theoretical calculation values are in good agreement with the experimental and finite element results,the relative errors are basically within 10%,so it can provide reference for the engineering design of steel-UHPC lightweight composite deck structure.