Study On Mechanical Properties Of T-shaped Section Concrete-filled Steel Tubular Columns Under High Temperature (Fire)

Recent years,China's economic has came into a new normal state.In the face of reducing capacity and cost,environmental protection and the people's urgent need for a better living environment,goverment vigorously develop steel structure,promote the structure of green,industrialization,information,and promote the transformation and upgrading of traditional construction industry.As a new type of structural member,T-section concrete-filled steel tubular column with good economic,environmental and social benefits,can replace traditional reinforced concrete column well.Besides,it has been applied in some construction projects currently,such as Guangzhou new China Building and Wuhan International Securities Building.T-section concrete-filled steel tubular column is a new type of Steel-concrete composite structure,which formed by pouring concrete in T-shaped steel column.it has some advantages,such as remarkably improving the bearing capacity of the structure,improveing the plasticity,toughness,fire resistance and the convenience of construction.In addition,it also can effectively increase the use of residential area,avoid appearing angle in the interior,beautify the interior space of the building.With the city land's price becoming more and more expensive,the house price level unceasingly climbs,People pay more attention to the structure of the house and the layout of the living room,and it demand for high housing space utilization rate.The structure design method of using T shaped cross section columns will become the future development trend.At the same time,the frequency of fire in China is high,the harm of fire to society is more and more great.The society is becoming more and more concerned about fire-resisting ability of building structure,and the demand for fire-resistant research of building structure is more and more urgent.therefore,the following research is carried out on the fire resistance of T-section concrete-filled steel tubular columns under fire.(1)The structure characteristics of T-section concrete filled steel tube columns and the main ways of setting stiffeners are summed up by consulting relevant documents,besides the main methods of various stiffening forms are analyzed.(2)The basic theory of the design of steel tube concrete structure is expounded,including the unified theory,the superposition theory,the quasi steel theory and the quasi concrete theory,and the theory and method of the design of the bearing capacity of the concrete filled steel tube columns in the main countries are summarized.(3)The main methods of calculating the bearing capacity of T shaped concrete filled steel tube columns under high temperature fire are summarized,including cross section equivalent method,cross section superposition method,and continuous multiplication,and on this basis,the calculation of axial compression bearing capacity of T shaped concrete filled steel tube columns under high temperature fire environment is deduced.The formula for calculating axial compression capacity of T section concrete-filled steel tubular columns with longitudinal reinforcement under high temperature fire is derived.(4)The axial compression bearing capacity of three structures of T-section concrete filled steel tube column,reinforced T-Section concrete-filled steel tube column and reinforced concrete T column in high temperature fire environment are compared and analyzed by a numerical example.The study shows that the anti-Fire bearing of T-shaped concrete filled steel tube column can significantly improve the fire resistance of the column.Therefore,the cement mortar and fireproof paint should be applied to the concrete filled steel tube column of the T shaped section.Fire prevention measures;(5)The finite element model of reinforced and unreinforced T-section concrete filled steel tubular columns is established by Ansys software,and obtaining the temperature field of concrete-filled steel tube column by thermal analysis under the ISO-834 standard heating curve.By comparing the results of finite element analysis and theoretical calculation,we come to the main conclusions as follow: The distribution of longitudinal bars has little influence on the temperature field of T-shaped concrete-filled steel tubular columns;The theoretical derivation formula can be used for reference for engineering fire resistance design.After 90 min,the error is relatively large,and further test verification is needed.The reinforced concrete filled steel tube column with T shaped section is 45 before the fire.The finite element simulation results of the axial compression bearing capacity of min are in good agreement with the calculation results of the theoretical formula.The theoretical derivation formula can be used for reference for the design of fire resistance in engineering.The error of the 45 min is relatively large,and it needs further test and verification.