| Cold-formed steel composite structures have been widely used at home and abroad due to their advantages of lightweight,high strength,and environmental protection.The fire resistance performance of cold-formed steel composite structures has become a key problem to be solved in its application.When using numerical simulation to study the fire resistance of cold-formed steel composite structures,the high-temperature thermophysical properties(including specific heat capacity,thermal conductivity,and density)of the constituent materials are important factors that affect the simulation accuracy of structural and thermal responses.At present,high-temperature thermophysical properties need to be obtained through tests.However,the test parameters used in high-temperature thermophysical tests have not been given accurate and comprehensive standard values in the existing specifications,making it difficult to guarantee the accuracy of test results.Therefore,this study focuses on six commonly used building materials of cold-formed steel composite components,i.e.gypsum board,calcium silicate board,autoclaved lightweight concrete board(i.e.ALC board),rock wool,aluminum silicate wool and extruded polystyrene foam board(i.e.XPS board).The standardized values of the high-temperature thermophysical test parameters of each material are put forward based on test results and finite element numerical results.The effectiveness of these values is verified.The main content and conclusions are as follows:Based on the uniform design method,a series of tests are designed and carried out to determine the specific heat capacity of six commonly used building materials.The influence of test parameters such as heating rate,sample quality,and sample size on the specific heat capacity curves of these materials is considered.At the same time,the influencing mechanism of test parameters is analyzed and their influence is quantified.The results show that the increase of heating rate and sample quality cause the dehydration reaction of gypsum board,calcium silicate board,and ALC board to lag,which increase the dehydration peak temperature of the specific heat capacity curve.There is no obvious chemical reaction of rock wool,aluminum silicate wool and XPS board in their heating range,and the specific heat capacity curve can be simplified to a constant(i.e.the basic specific heat value).Only the sample quality has a significant impact on its basic specific heat value.The sample particle size affects the proportion of each component in each sample of gypsum board,calcium silicate board,and ALC board,and also affects the dehydration and dehydration heat absorption of the specific heat capacity.The uniform design method was used to design and conduct high-temperature thermal conductivity tests for six commonly used building materials.At the same time,the influencing mechanism of each test parameter(i.e.heating temperature,sample size,average temperature of cold and hot plate,temperature difference between cold and hot plates)on its thermal conductivity is analyzed.The mathematical model between thermal conductivity and its test parameters is obtained.The results show that the increase of heating temperature causes the dehydration reaction of gypsum board,calcium silicate board and ALC board,which causes the decrease of their thermal conductivity.The reduction of sample size aggravates the heat dissipation on side surface of the gypsum board,calcium silicate board,ALC board,rock wool and aluminum silicate wool,leading to more heat loss and thereby increment in its thermal conductivity.The change in the average temperature of the hot and cold plates and the temperature difference between the hot and cold plates aggravate or reduce the heat conduction of air in the pores and the radiation between the pores of gypsum board,rock wool,aluminum silicate wool,and XPS board,and thereby affect its thermal conductivity.Two-dimensional models of cold-formed steel composite components are established and a numerical simulation of heat transfer is conducted using the finite element software COMSOL.The sensitivity of the simulated time-temperature curve to the high-temperature thermophysical properties of six commonly used building materials and the relationship between them are analyzed.Standardized high-temperature thermophysical test parameters of six commonly used building materials are proposed based on mathematical model between high-temperature thermophysical properties and experimental parameters.The results show that the temperature at the end of the dehydration platform in the time-temperature curves of gypsum board,calcium silicate board,and ALC board is significantly sensitive to the peak temperature of its specific heat capacity curve.These two temperatures are deemed to be consistent.The standardized values of heating rate and sample quality of specific heat capacity of gypsum board,calcium silicate board and ALC board are thus proposed.It is found that when the particle size of gypsum board sample is no more than 40μm and that of calcium silicate board and ALC board is no more than25μm,the proportion of each component of the sample will not be in accordance with reality.In order to ensure the authenticity of the sample composition and the accuracy of the test results,the standardized value of the particle size of the specific heat capacity samples of gypsum board,calcium silicate board,and ALC board are given.Based on the specific heat capacity test samples and the heat capacity balance equation of the reference materials,the standardized values of the specific heat capacity test parameters of rock wool,aluminum silicate wool and XPS board are given.The thermal conductivity of gypsum board and calcium silicate board affects the falling-off time of the board and the time to produce through cracks.Based on the actual time for the middle plate to fall off and produce through cracks obtained from the fire resistance test data,the standardized values of the thermal conductivity test parameters of gypsum board and calcium silicate board are given.The simulated time-temperature curves of the ALC board,rock wool,aluminum silicate wool,and XPS board is not significant sensitivity to their thermal conductivity.According to the degree of agreement between the simulation results and the test results,the standardized values of the thermal conductivity test parameters of the four materials are obtained.The high-temperature thermophysical tests of six building materials are carried out using their standardized test parameters.Then,the test results are used as the high-temperature thermophysical properties of each material to perform two-dimensional transient heat transfer simulations on a variety of cold-formed steel composite components.Finally,the simulation results are compared with the test results.The results show that the high-temperature thermophysical curve measured using the standardized test parameters has a good accuracy,which verifies the effectiveness of the standardized test parameters proposed in this paper,and improves the completeness and accuracy of the high-temperature thermophysical test data of six materials.At the same time,the standardization method for determining test parameter proposed in this paper can also be extended to the specific heat capacity test of other building materials.As a result,the high-temperature thermophysical test can follow a basic standard. |
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