Fire Resistance And Thermal Properties Experiment Of Light Steel Composite Member And Numerical Simulation At Elevated Temperature

The light steel composite member consists of two parts:cold formed steel frame and wall boards.Compared with traditional residential structures,the light steel structure of this kind has a variety of advantages such as layout flexibility of building space,excellent seismic behavior.simple construction procedure.good economic performance.realization of construction industrialization.The mid-rise light steel housing construction is the most suitable choice in line with Chinese national situations.The light steel composite structure puts forward higher requirements of fire resistance to satisfy the development need from the low-rise building to the mid-rise structure.Therefore.in this paper the thermal conductivities of several kinds of commonly used boards were first measured to improve and supplement the thermal physical properties data.After that.a series of fire tests were carried out on various construction forms.On the basis of the tests.numcrical simulation of two-dimensional transient heat transfer was investigated.The main contents and conclusions are as follows:1.The thermal conductivity measurement of gypsum board,magnesium board and ALC board treated at different temperatures(room temperature up to 900?)and unequal time(10h to 1h)was completed in the electric furnace which provide the basic parameters for the heat transfer simulation.And then,the thennal conductivity was measured by Hot Disk thermal constant analyzer as soon as the specimen was cooled to room temperature.The comparison with the existing studies and theoretical data demonstrates that the Hot Disk method adopted in this study is available for the thennal conductivity measurement of gy psum board and glass magnesium board rather than ALC board.The reason lies in that ALC board possess numerous pores and rough surface,which results that the thermal conductivity of ALC board measured throughout high temperature stage is always small.Thus,it could draw a conclusion that Hot Disk method is not suitable for the specimen with high porosity and rough surface.2.18 test specimens with different construction forms were designed and were performed for fire tests of these light steel composite members,which took consideration of various factors including types of boards,the number of layers,two insulation materials which are rock wool and aluminum silicate wool,and two filling modes consisting of cavity insulation and external insulation.Among them.the types of boards are divided into magnesium board.gypsum board,Potter board,ALC board,OSB board,and so on.The refractory time,the interface time-temperature curve and the temperature-deflection curves of each specimen were obtained.The results showed that:the fire-resistant time of the specimen filled with aluminum silicate cotton was significantly longer than that with rock wool,the reason is probably that rock wool appeared different degrees of degeneration at high temperature which makes the structure more crisp;the thermal resistance effect of external insulation is better than that of cavity filling,and the effect of cavity filling depends on the height of the steel web.Moreover,the cold-formed steel skeleton composite members were durable for a short time due to premature brittle fracture of the Potter board,but the specimen with the simultaneous use of the Potter board and fire-resistant gypsum board withstood longer refractory time than that with pure gypsum board.The refractory lime of the test specimens with ALC board are above 2h.It shows that ALC board(thickness:5cm)has excellent fire insulation effect.However.OSB board is easy to be ignited in the test and cause open flame,which may increase the fire damage in practice engineering.3.The two-dimensional transient heat transfer model of light steel composite member was established by ABAQUS finite element software.A reasonable fell-off temperature of each board is first set according to the test results.And then,the thermal conductivity obtained from tests in this paper and other existed material properties of board and steel stud are inputted.Finally,The temperature field of composite components under different kinds of construction measures is computed,which consider heat convection and heat radiation on the border of the plate,the heat conduction of inner boards,the heat conduction of steel stud and the radiation of the internal cavity.The comparison denotes that the temperature field obtained using ABAQUS finite element software has a good agreement with the experimentally measured results.The rationality of the numerical model and the accuracy of the thermal conductivity test results are verified.