Study On Fire Performance Of Recycled Aggregate Concrete-Filled Steel Tubular Columns

Effective use of recycled aggregate concrete (RAC) can solve the problem in waste concrete processing and conserve the natural resources, but the properties of RAC are generally worse than those of the corresponding normal concrete with natural aggregates, considering that the water absorption and porosity of recycled aggregates are higher than those of natural aggregates and the recycled aggregates contain a certain number of old cement mortar particles. The concept of RAC-filled steel tube (RACFST) is proposed to make a more extensive application of RAC in engineering. RACFST is produced by filling RAC into steel tube and the advantages of steel tube and core RAC can be fully used owing to the interaction between them. However, RACFST members might be apt to failure under fire attack because of the poor fire performance of steel, which may affect the safety of entire structure. Therefore, it is necessary to investigate the fire performance of RACFST members to provide the basis for fire resistance design of RACFST structure in real projects.Based on experimentally and theoretically, this paper investigates the fire performance of RACFST columns. The main works are summarized as follows:(1) Summary of the related studies, including the performance of RAC under high temperatures, the behavior RCAFST members at ambient temperature and the fire performance of concrete filled steel tubular columns, is clarified.(2) Nine square specimens are tested under fire to investigate the effect of recycled coarse aggregate replacement ratio, axial compression ratio and fire protection thickness on the fire performance of RCAFST columns.(3) Based on the determination of constitutive model of core RAC and steel under high temperatures, a finite element analysis (FEA) model is developed for the simulation of RACFST columns under fire, and the simulated responses generally agree well with the experimental results.(4) The influence of fire exposure time, cross-sectional dimension, slenderness ratio, recycled coarse aggregate replacement ratio, steel ratio, yield strength of steel, concrete strength and load eccentricity ratio on bearing capacity index of RACFST members under standard fire curve is investigated by using the FEA model.