Research Of Static And Fatigue Properties In Negative Moment Regions Of Steel-concrete Composite Beams

Due to the existence of unfavorable factors such as tension in concrete slab and compression in steel beam,the negative moment region of steel-concrete continuous composite beam presents complex nonlinear behavior even under a low static load level.The service performance and durability of the structure are often further affected,under the long-term action of fatigue loads such as moving vehicles,winds and waves.The mechanical properties,the development rules of cracks and the calculation methods of structural deformation and crack width in the negative moment region of composite beams under static and fatigue loads were intensively studied with scaled model test,theoretical analysis and numerical simulation.Details of this study are summarized as follows:(1)The corresponding test beams equipped with studs and PBLs connectors(stud specimen and PBL specimen)were designed and fabricated under the same degree of shear connection.The static behavior of the composite beam under negative moment was simulated by statically loading on an inverted test beam.A series of test results including the bearing performance,failure shape,load-deformation curve,concrete strain,steel bar strain,steel beam strain,shear connector strain,relative slip and crack development law were analyzed.(2)Based on the static test results of ultimate bearing capacity and the law of crack development,the fatigue load level was determined,and the fatigue performance test of the composite beam under negative moment was further carried out.Through the observation of the fatigue loading process and the analysis of the test results,the failure shape,fatigue life,fatigue deformation of each member,and crack development law in negative moment regions of steel-concrete composite beams were discussed.(3)The calculation model of residual deflection related to pre-cracked loading in the negative moment region of composite beams was presented,based on the research results of partial prestressed concrete beams.The calculation formula of the residual deflection related to fatigue loading of composite beam under negative moment was derived,based on the differential equation of the residual interface slip and the computing method of the residual slip in push-out specimens of studs.The tension-stiffening effect of cracked concrete and interface slip effect were considered,when calculating the instantaneous deflection in the negative moment region under fatigue loading.The calculation method of the total mid-span deflection in the negative moment region was further given.(4)Through the introduction of transverse reinforcement spacing in the existed calculation model and the regression analysis of a series of test data,a modified formula of average crack spacing in the negative moment region of composite beams was given.By considering the bond-slip relationship between reinforcement and concrete,the slip effect between steel beam and concrete slab,concrete shrinkage strain and tension-stiffening effect,the numerical calculation model of the crack width in the negative moment region under static loading was established based on the bond-slip theory.On the basis of the static analysis model of crack width,the calculation model of crack width in the negative moment region of composite beam under fatigue loading was established by selecting appropriate fatigue constitutive relation and fatigue stress calculation method of reinforcement at cracked section.(5)The static properties of composite beams with/without CFRP laminates in the negative moment region were modeled and analyzed by ANSYS,and the influence of related parameters was studied.