Experimental Study On Fatigue Performance Of The Prestressed Concrete Beams With Corrugated Steel Webs Under Combined Bending And Torsion

The corrugated steel web composite beam is a lightweight,economical,and practical new steel-concrete composite structure that has been widely used in bridge engineering.However,in the long-term service process,the corrugated steel web beam bridge is prone to bending-torsion fatigue problems caused by the eccentric load of vehicles.Based on the technology demonstration project of the Ministry of Transport for the safe and intelligent construction of the Fengjian expressway in the Three Gorges Reservoir area,this thesis carried out fatigue performance tests on prestressed corrugated steel web composite beams under bending-torsion combined action,revealing the fatigue damage mechanism of the composite beam structure.Furthermore,the fatigue life of prestressed corrugated steel web composite beams under bending-torsion combined action was studied,and the main work and conclusions obtained in this thesis are as follows.Firstly,Through static loading tests on prestressed corrugated steel web composite beams under bending-torsion combined action,the static performance of the composite beam under bending-torsion combined action was studied.The stress,deformation law,and failure mode of the steel web,concrete,and prestressing strands were revealed.The cracking bending moment/torsion moment and ultimate bearing capacity of the corrugated steel web under bending-torsion combined action were obtained.It was found that the failure mode of the corrugated steel web composite beam under static bending moment was characterized by the oblique crack of the bottom plate concrete at 50° and the twisting deformation of the steel web until failure.The cracking bending moment/torsion moment of concrete was 4.04 k N·m/2.01 k N·m,and when the bending moment/torsion moment reached 17.765 k N·m/6.47 k N·m,the model beam reached the ultimate bearing capacity state.Secondly,Through fatigue loading tests on prestressed corrugated steel web composite beams under bending-torsion combined action,the fatigue performance of the composite beam under bending-torsion combined action was studied.The stress,deformation law,fatigue failure mode,and strain distribution law along the height of the beam’s center section of the steel web,concrete,and prestressing strands were revealed.It was found that the development of bottom plate concrete cracks in corrugated steel web composite beams under constant amplitude fatigue load spectra can be divided into four stages: nucleation,stable expansion,penetration,and fracture.When the bottom plate concrete developed a penetrating crack,the steel web at the fold angle position near the mid-span of the beam cracked and failed due to stress concentration.Furthermore,measures were proposed to increase the structural fatigue life by adding stiffeners at the junction of the steel web and flange plate.Thirdly,Through ABAQUS finite element simulation,the static and fatigue performance of the corrugated steel web composite beam under bending-torsion composite action was analyzed and compared with experimental results for validation.Furthermore,the most unfavorable load points of the corrugated steel web composite beam under different load spectra were analyzed.It was found that the cracking load and ultimate load in the finite element model differed from the experimental values by a maximum of 7.11%,and the failure mode was the same as that of the experiment.The most unfavorable load points with a safety factor less than 1 were found at the junction of the corrugated steel web and the lower flange,as well as at the 1/4 position of the beam and the junction of the upper flange.Fourthly,Through Fe-safe fatigue analysis,the influence of steel web plate thickness,prestressed tendon tension,concrete compressive strength,and steel reinforcement tensile strength on the fatigue life and safety factor have been revealed.The study found that the larger the concrete strength,the longer the structural fatigue life.When the thickness of the corrugated steel web plate is above 5mm,it contributes significantly to the fatigue life.The fatigue life increases rapidly when the yield strength of ordinary steel bars reaches400 MPa.When the prestressed tendon tension reaches 700 MPa,the fatigue life is highest and the safety factor is greater than 1.Based on the sensitivity analysis of the above structural parameters,an optimized design scheme for the corrugated steel web composite beam has been proposed,which provides a basis for the design of corrugated steel web composite beam bridges.