Study On Mechanical Properties Of Fatigue-Failure Process Of Group Nailed Steel-Concrete Composite Beams

As a new structural form of steel-composite composite beam,compared with ordinary steel-hybrid composite beams.,group nail steel-hybrid composite beams have the characteristics of clear stress,light weight and perfect appearance,and their load-bearing capacity and shear resistance.The beams are all lifted.For the steel-concrete composite structure,the fatigue problem has always been the focus of attention,and most of the domestic and foreign research has focused on the fatigue of steel bridges,concrete slab fatigue,and fatigue problems of shear connectors.There are relatively few studies on the fatigue resistance of box girder and the degradation level of the bearing capacity under fatigue load.Firstly,combined with the current research situation at home and abroad,the overall stress performance of the steel-concrete composite beam is theoretically analyzed by the elastic-plastic calculation method,Refer to the fatigue design method of the existing steel bridge,and then perform fatigue-failure test to extract the data and results required by the test,and finally use the finite element numerical simulation to obtain the theoretical calculation results and summarize the data obtained from the solid test and the simulation test.Group nail steel-hybrid composite beam theory is optimized.In this paper,the fatigue-failure test uses a fatigue load amplitude of 10Kn-500 k N to load the group-nail steel-concrete composite test beam.After 70,000 loadings,it is then subjected to a static failure test to measure its residual bearing capacity and finite element Combined with the simulation analysis,the mechanical properties of the group nail steel-concrete composite beam during the entire fatigue-failure process are studied,and the conclusions are as follows:(1)During the loading of the fatigue test,the strain distribution of the group-nail steel-concrete composite beam conforms to the assumption of a flat section;after 70,000 times of loading with a fatigue amplitude of 10 k N-500 k N,no obvious damage is seen from the surface.However,there is a fine layering between the concrete and the steel plate,and the position of the neutralization axis has changed.(2)In the residual load capacity test,it is concluded that the failure process of the group-nail steel-concrete composite beam after fatigue has also experienced three processes in sequence: elastic stage,elastoplastic stage,and descent stage.The neutral axis of the composite composite beam continues to move up as the load increases,and the failure sign is that the deflection of the structure increases rapidly after the steel box yields;the failure mode of the group nail steel-concrete composite beam belongs to the concrete slab in three typical failure modes Crushed bending type damage.(3)The ultimate failure bearing capacity of the steel-concrete composite beam without fatigue load is 149 t,and the ultimate bearing capacity of the steel-concrete composite beam after 70,000 fatigue loads is 140 t,and the bearing capacity decreases by about 6%.In the numerical simulation,it is found that the static failure load of the group nail steel-concrete composite beam is 148 t,which is about 1% different from the ultimate failure load of 149 t obtained by the solid static load model test.