Load Bearing Capacity Study On Tubed Reinforced-concrete Intermediate Columns At Elevated Temperature

The tubed reinforced-concrete intermediate column,a now structural type,has received lots of popularity in recent years.Which has been applied to high-rise buildings,large span structures and bridges due to its small cross-section,high load-carrying capacity and excellent deflection performance.Researches on the tubed reinforced-concrete intermediate columns have been richly studied,while there are less researches on which at elevated temperatures.In this paper,in order to investigate the temperature distributions and mechanical behaviors of the tubed reinforced-concrete intermediate columns,works were carried out as follows:(1)Six tubed reinforced-concrete intermediate columns and six tubed steel reinforced-concrete intermediate columns were tested to failure,under the ISO-834 standard fire condition.There were two axially loaded columns and four eccentrically loaded columns in each group.The influences of key parameters on the temperature distributions and mechanical behaviors at elevated temperatures including load ratio and cross-section diameter to steel tube thickness ratio were also investigated.In the fire tests,the cross-section temperature distributions,axial loads,axial displacements and lateral displacements at the mid-height of columns were recorded and discussed.(2)By means of the program ABAQUS,the thermal analysis model and structural analysis model of the tubed reinforced-concrete intermediate columns under the ISO-834 standard fire condition were developed and validated against the tests.Then the parametric studies on the temperature distributions and fire resistance ratings were carried out.In the thermal analysis,the influences of cross-section diameter and steel tube to concrete area ratio on the temperature distributions were studied.With a result that there was almost no effect of the steel tube to concrete area ratio.In the structural analysis,a series of key parameters including load ratio,cross-section diameter,material strength,steel tube to concrete area ratio,reinforcement ratio were considered to investigate the influences on the fire resistance ratings of the columns.According to the parametric studies,it can be concluded that all the studied parameters had influences on the fire resistance ratings as the load ratio was small,while as the load ratio was high,parameters had few effects on the fire resistance ratings except the load ratio and cross-section diameter.(3)Depending on the analysis above,simplified methods were proposed and validated against the numerical analysis to predict the fire resistance ratings of the tubed reinforced-concrete intermediate columns and tubed steel reinforced-concrete intermediate columns under the ISO-834 standard fire condition.(4)Innovations in this paper: tubed reinforced-concrete intermediate columns and tubed steel reinforced-concrete intermediate columns were tested under the ISO-834 standard fire condition.Both the specimens axially loaded and the ones eccentrically loaded were tested.Simplified methods predicting the fire resistance ratings of the tubed reinforced-concrete intermediate columns and tubed steel reinforced-concrete intermediate columns under the ISO-834 standard fire condition were proposed.