Static Behavior Of Circular Tubed Reinforced Concrete Stub Columns Under Axial Compressive Loading After Exposure To Fire

The circular tubed reinforced concrete (CTRC) column is a kind of compositestructural member with outer steel tube terminated at the beam-column joint.Compared to concrete-filled steel tubular (CFST) columns, the axial load transferredby outer steel tube is very small for CTRC columns. Therefore the steel tube mainlyworks as hoop reinforcement and the confinement effects of the steel tube to thecore concrete can be maximized. CTRC column possesses high load bearingcapacity and high ductility. It’s possible to reduce cross sectional dimensions ofcolumns (increase usage space) and aviod shear failure of stub columns. Thus,CTRC columns are often used in lower levels and equipment levels of high risebuildings.Static behavior of CTRC columns after exposure to ISO-834standard fire wasinvestigated experimentally and numerically in this research. The main workincludes:1. Fifteen CTRC columns after exposure to ISO-834standard fire and sixCTRC columns at ambient temperatrue were tested under axial compression loading.Considered parameters include fire exposure time, diameter of cross section andcompressive strength of concrete. Firstly, those specimens were subjected toISO-834standard fire in an unstressed condition. The temperatures of furnace andspecimens during the heating and cooling processes were measured. After cooling toambient temperature, the axial compression test was conducted. The load-aixaldisplacement curves, longitudinal and transverse strains of steel tube were recorded.It can be found that the residul capacity decreases slightly with increasing ofexposure time, whereas the stiffness and ductility decrease significantly.2. After determinating the thermal and mechanical properties of materials,element types, interaction definition and mesh densities, a finite element (FE) modelwas developed with the program ABAQUS. The FE model was verified with testedspecimens in this research and good agreenment can be attained.3. Parametric studies were conducted with the FE model. Fire exposure time,diameter of cross section, compressive strength of concrete, yield strength of steeltube, yield strength of bar, steel ratio and reinforcement ratio were considered. It canbe found that the heating time and diameter have noticeable influences on residulcapacity, while steel ratio and reinforcement ratio have slight influences. Otherparameters have very small influence. Based the parametric studies, a simplifieddesign method was proposed for predicting residual capacity of CTRC columns afterfire.