Study On Fire Resistance Of Circular Tubed Steel Reinforced Concrete Stub Columns

Material properties of steel and concrete was fully utilized by circular tubed steel reinforced concrete columns,it has been applied to large span structures and high-rise buildings,due to its high load bearing capacity,little self-respect and fast construction speed.The temperature of the structural components without fire protection increases rapidly in fire,and it will result in significant decline in the strength of steel and concrete.However,no study has been reported on the fire behaviours of circular tubed steel reinforced concrete columns.The code about reinforced concrete structure was not appropriate for the circular tubed steel reinforced concrete columns.This thesis intends to investigate the temperature and the fire resistance of circular tubed steel reinforced concrete columns.The main contents are as follows:(1)Eight full-scale axial circular tubed steel reinforced concrete columns and eight full-scale eccentric circular tubed steel reinforced concrete columns were tested to failure,under the ISO834 standard fire condition.The cross-sectional temperature,axial displacements,fire resistance and failure modes were recorded and discussed.The influence of key parameters on the deformation and fire resistance of circular tubed steel reinforced concrete columns were also investigated,including load ratio,wall thickness of steel tube,eccentricity.(2)Choosing the right thermal parameters of concrete and steel,a sequentially coupled thermal-stress finite element model was developed using the program ABAQUS,featuring heat transfer and stress analysis.The accuracy of the proposed model was evaluated using the available test results for benchmarking purpose.Extensive parametric analysis was then carried out with the FE model to investigate influences of key parameters on the thermal distributions and fire resistance.The considered parameters included the cross-section dimensions,thickness of steel tube and the types of concrete for thermal analysis,and the load ratio,the cross-section dimensions,thickness of steel tube,the strength of concrete and steel,the eccentricity for fire resistance analysis.(3)Simplified methods were proposed to predict temperature of steel of circular tubed steel reinforced concrete columns subjected to fire.The existing methods for temperature of steel tube and concrete were be verified.The effect of temperature on material properties and the asymmetry of temperature were analyzed and the Simplified method of bearing capacity of axial loading columns and N-M curve of eccentric columns in fire were proposed.(4)Innovation points of this paper:axial circular tubed steel reinforced concrete columns and eccentric circular tubed steel reinforced concrete columns were tested to failure,under the ISO834 standard fire condition.Simplified methods were proposed to predict temperature of steel of circular tubed steel reinforced concrete columns subjected to fire.Simplified method of bearing capacity of axial loading columns and N-M curve of eccentric columns in fire were proposed.