Flexural Test And Finite Element Simulation Of Steel-UHPC Composite Structure

The Orthotropic steel bridge deck and steel-concrete composite structure are widely used in bridge engineering.But there are two difficult problems in the orthotropic steel bridge deck,such as fatigue crack and pavement damage.The appearance of ultra-high performance concrete UHPC(Ultra high Performance Concrete)provides an opportunity for solving the two problems of orthotropic steel bridge deck.A new type of steel-UHPC composite deck slab formed by connecting the UHPC and Orthotropic steel bridge decks through short bolt-and-nail shear connection parts arises.In order to compare the flexural behavior of steel-UHPC composite beams and steel-UHPC composite deck slabs,the whole process tests of negative moment of composite beam and composite deck slab were carried out.The results showed that:the cracks of composite beam were produced on the UHPC surface above the transverse rib,with the increase of load,the number of cracks and the width increased,the measured structure crack load was 168.6kN,when the load reached 289kN,the transverse rib yielded and the structure unloaded.The cracking of the UHPC layer of the composite deck slab began at the outer side of the number 2 rib,and the measured structure crack load was 958kN,and when the load increased to 1240kN,the UHPC local crushing happened on the top of the number 1 rib which was at the loading point caused the structural damage.In order to compare the experimental results with the finite element results,ANSYS is used to establish the linear elastic finite element model of composite beam and composite deck slab,the UHPC nominal cracking stress of the two structures is 28.1 MPa and 53.1 MPa respectively according to the measured crack loads,and the allowable values of the UHPC nominal tensile stress of the two structures is 26.5MPa and 24.1 MPa respectively.The UHPC nominal cracking stress of composite beam is 6%higher than the allowable value of local standard and they are very close.While The UHPC nominal cracking stress of composite deck is 116.6%higher than the allowable value of local standard.The results show that the steel-UHPC composite bridge deck has strong ability of resisting overload.In order to explore the reason,the whole process nonlinear finite element(FE)simulation of composite beam and composite deck slab were carried out by using ABAQUS,focusing on the distribution of the tensile stress along the crack length on the UHPC top layer of the cracked section.The results showed that the tensile stress on the UHPC top layer of the composite beam was uniformly distributed along the crack length,and with the increase of the load,the tensile stress of the whole section UHPC was rapidly entering the strain-hardening stage.While the tensile stress on the UHPC top layer of the composite deck slab was at the peak of the loading center line,and it decreased along the two sides,and the structure showed obvious local stress characteristics.With the increase of load,the UHPC on the loading centered line firstly entered the strain hardening stage,then the stress spread to both sides,delaying the germination and development of the cracks,thus obviously improving the UHPC nominal cracking stress.It is shown that the steel-UHPC composite deck slab can withstand a larger local load without cracking and has excellent anti overload ability.To further study the transverse flexural performance of steel-UHPC composite slabs under both positive and negative bending moments,a series of static load tests were performed on eight steel-UHPC composite slab specimens.The whole damage processes of the specimens were recorded and analyzed.In the case of positive bending moment loading,the specimens experienced three distinct stages,i.e.,the linear elastic stage,the crack-developing stage,and the yield stage.The two turning points on the load-deflection curves represented the onset of interfacial slipping and the yielding of the steel plate,respectively.When the specimens approached failure,the UHPC was locally crushed near the loading point and the steel-UHPC interface was separated at both the shear-bending zone and the specimen end.While in the case of negative bending moment loading,a first decrease of the stiffness of the specimens was related to the initiation of transversal cracks in the UHPC layer.With the cracks developing,the internal forces redistributed in the specimens,leading the tensile stress in the steel bars to continuously increase until yielding.Then the crack width developed excessively and the stiffness of the specimens decreased severely;the specimens finally failed because of the fracture of the UHPC layer.To gain a deeper insight into the aforementioned observations,the load tests were simulated using a comprehensive nonlinear finite element(FE)analysis through the software ABAQUS.The FE models considered both the contact nonlinearity and material nonlinearity.The concrete damaged plasticity was taken into account for the UHPC to simulate its deterioration process.The analysis results were compared to the test results,and the factors that influence the flexural performance of the steel-UHPC composite slabs(e.g.,the ultimate capacity,the flexural stiffness,and the deflection)were discussed,including the interfacial adhesion mode,the longitudinal reinforcement ratio,and the number and arrangement of studs.The research results show that:1)No matter the positive moment or the negative moment mode,the simulation results of different interfacial bonding methods have obvious difference,and the calculation results of partial slip bonding are more consistent with the test curve;2)Increasing the longitudinal reinforcement ratio has no obvious gain effect on the flexural performance of the composite plate under the positive bending moment,but it can effectively delay and limit the germination and development of the UHPC crack in the negative bending moment mode,and improve the elastic ultimate load,rigidity,ultimate bearing capacity and ductility;3)Increasing the number of studs can effectively improve the combination effect between steel plate and UHPC,thereby the overall stiffness of the structure is improved.Pure curved segment studs have little effect on the flexural performance of the composite plate while the shear-bending studs are important to the flexural performance of the composite structure,which should be paid attention to in the design.