Fire And Post-fire Behaviours Of Reinforced Concrete-filled Stainless Steel Tubular Columns

As one of the common natural disasters in daily life,building fire can damage the daily necessities,production equipment and the appearance of the building.In some serious cases,it can also damage the load-bearing components of the building structure,such as beams and columns,and cause the collapse of the building.In the past 20 years,the design and construction technology of tall buildings in China have developed rapidly,and the number and scale of tall buildings in China have become larger and larger.By the end of 2009,there were about 19000 high-rise buildings in the mainland of China,and about 1700 buildings with a height of more than 100 meters.At the same time,fire on high-rise and super-high-rise buildings is more frequent.According to the statistics,more than 9000 fires occurred in 1998-2007 in China,resulting in more than 400 deaths,a direct economic loss of 1 billion,and showed an annual growth rate of nearly 30%.Concrete filled steel tubular(CFST)structures have been widely used in high-rise buildings because of their high bearing capacity,high lateral stiffness and small section size.Compared with the ordinary concrete filled steel tubular columns,the stainless steel tubular concrete columns composed of stainless steel instead of ordinary steel have higher bearing capacity and ductility,better fire resistance,corrosion resistance and other advantages.Domestic and foreign scholars have studied the bearing capacity at room temperature,mechanical properties at high temperatures and after high temperatures,but the high cost of building limit its use in actual projects.On the premise of unchanged steel ratio of column section,the steel section of stainless steel tube reinforced concrete column is composed of steel section in stainless steel tube reinforced concrete column,which is helpful to reduce the cost of column.The main contents and achievements of this paper are as follows:(1)The fire resistance tests of two SCRFFST tube concrete columns under ISO834 standard fire were carried out,and a model was also established to analyze the fire resistance of the steel tube concrete columns.Combining with the simulation results of axial displacement-time relationship curve,failure mode,redistribution of cross-section internal force and stress,the working mechanism of SCRFFST column under fire is analyzed.(2)The mechanical properties of four SCRFFST tube reinforced concrete columns after fire were tested,and the influence of section size and the addition of steel section on the residual bearing capacity of the columns after fire were analyzed.(3)The temperature analysis model of the SCRFFST column in the whole fire process was established,and its reliability through the test data was verified.Referring to the calculation method of ultimate bearing capacity under high temperature in European code,the residual bearing capacity of steel tubular concrete columns after fire is simplified by using the temperature analysis model to calculate the region below 500?.The historic maximum temperature of the column section in the whole process of fire is extracted,which was used as the predefined temperature field of the mechanical model to simplify the calculation of its residual bearing capacity and stiffness after fire.