Flexural Behaviour And Fire Resistance Of Composite Beams With Ushaped Steel Girder And Angle Connectors

Composite beam with U-shaped steel girder has high load capacity,large flexural stiffness,good seismic behavior,small sectional dimension and fast construction speed due to the composite action.Furthermore,it also has higher flexural capacity,better fire resistance and architectural effect compared with traditional composite beams,therefore,it has been applied in construction in various countries.However,headed studs is the most used shear connector in such composite beam currently,which would bring some obstacles in construction,such as extra requirement of construction equipment,high construction cost and unstable U-shaped steel section in construction.Besides,such composite beam with exposed steel girder require fire resistance design as same as steel beam although its fire resistance is better.However,no design methods for composite beams with U-shaped steel girder are available in the existing design provisions and researches.The abovementioned limitations have hindered the wide application of such composite beam and to solve these problems,this thesis intends to find a suitable type of shear connector for composite beam with U-shaped steel girder and to study the flexural behavior and fire resistance of such composite beams,eventually,to propose the design methods of composite beams with U-shaped steel girder and new shear connectors.The main contents are as follows:(1)Push-out tests of 5 different types of shear connectors were performed to compare their shear resistance,such as failure modes,load capacities,slip capacities,ductility,stiffness and load-slip curves.The studied shear connectors include steel angle welded to webs of U-shaped steel section,steel angle welded to flanges of Ushaped steel section,headed studs welded to flanges of U-shaped steel section,two steel plates welded to webs of U-shaped steel section and steel angle welded to webs of U-shaped steel section work together with headed studs welded to flanges of Ushaped steel section.Then another 6 push-out test specimens were performed to study the load transfer mechanism of steel angle welded to the webs of U-shaped steel section.(2)Finite element models were created using ABAQUS to simulate the push-out tests of angle connectors welded to webs of U-shaped steel section,in which ductile damage and shear damage of steel,tension and compression damage of concrete were considered.After validation by test results,FE(finite element)models were used to analyze the influence of material strength and steel angle dimensions on the shear resistance of such angle connector.Based on the parametric analysis,simplified formulae were proposed for load capacities,slip capacities,slips at load capacity and load-slip curves of angle connector welded to webs of U-shaped steel girder.(3)Four full-scale composite beams with U-shaped steel girder and angle connectors were tested to investigate their failure modes,flexural capacities,slip deformations and strain developments.The influence of different types and numbers of shear connectors on flexural behavior of such composite beams were compared through the test.The design provisions for flexural capacity of composite beams with full and partial shear connection in existing design standards were validated with the test results of composite beams with U-shaped steel girder.Besides,simplified calculation methods were proposed for determining the full-stage moment-curvature curves of full shear connected composite beams with U-shaped steel girder.(4)Four full-scale composite beams with U-shaped steel girder and angle connectors were tested to failure under ISO 834 standard fire condition.The developments of temperatures,deformations of specified positions,the fire resistance and failure modes of different specimens were recorded during the test,then the influence of load ratio,fire proof and longitudinal reinforcements on the fire resistance of such composite beams were compared.(5)FE models were created using ABAQUS to analyze the temperature field and fire resistance of composite beams with U-shaped steel girder and angle connectors under ISO 834 standard fire condition.After validated by the tested results,FE analysis were performed to compare the fire resistance of composite beams with Ushaped steel girder and box girder.The influence of sectional dimensions and fire proof thickness on temperature field of such composite beams,the influence of load ratio,sectional dimensions,material properties,fire proof thickness and arrangements of longitudinal reinforcements on fire resistance of composite beams with U-shaped steel girder were investigated.Based on the parametric analysis,simplified formulae were proposed to calculate the temperatures of U-shaped steel girder,longitudinal reinforcements and concrete components.Considering the influence of temperature on the material properties,simplified formulae were proposed for predicting the flexural capacity of composite beams with U-shaped steel girder under ISO 834 standard fire condition.