| The light-gauge steel composite structure used in residential system is mainly composed of cold-formed steel frame and light building boards.It has the characteristics of beautiful appearance,green environmental protection,convenient construction and easy assembly.It is generally suitable for low-rise residence.With the rapid development of urbanization in China,the expansion of the residential system of light-gauge steel composite structure from low-rise into mid-rise can improve the land utilization rate and solve the problem of excess steel production.It is necessary to study the fire resistance of the light-gauge steel composite structure.The research group of Prof.Ye has completed series of fire tests of light-gauge steel composite assemblies with different configurations.In this paper,a two-dimensional finite element refined(original)model and a three-dimensional finite element refined(original)model are completed to simulate the tests.Moreover,a twodimensional equivalent simplified model and a three-dimensional equivalent simplified model are proposed.The main contents and conclusions are shown as follows:(1)With summarizing the falling-off law of each board in the fire tests,the shedding and failure criteria of gypsum board,potter board and rock wool are proposed.At same time,a two-dimensional finite element refined(original)model of the composite member,where the thermophysical parameters of the wall panels are measured by the research group and the thermal convection,heat radiation and heat conduction inside the cavity are considered,is built in COMSOL software.The comparisons between the experimental and simulated results show that the numerical simulation results are in good agreement with the experimental results.The validities of the numerical model and thermophysical parameters of the board at elevated temperatures measured by the research group are verified.The simulation results can be used to derive the equivalent simplified model.Moreover,the shedding and failure criteria of B1 gypsum board,rock wool and aluminum silicate wool can predict the shedding/failure time of the board accurately.If composite panels on fire side of different members have the same materials and forms,the heating laws of the composite panels on fire side are the same.(2)A new finite element model without studs is established on the basis of the two-dimensional finite element original model by COMSOL software.Then,the simulated results are compared by two finite element models.The contrasted results show that the heat conduction of the studs has small impact on the local and overall heat transfer of the composite members.On the basis of the finite element model without studs,the idea of using the equivalent heat conduction instead of cavity convection is proposed.The simulation results of the two-dimensional finite element original model are used to derive the calculation formula of the equivalent thermal conductivity.Then,a twodimensional equivalent simplified model is established to simulate heat transfer process of composite members.The compared results between equivalent simplified model and original model show that the temperature-rise curves of the two modes are in good agreement,where the validity of the equivalent simplified model is verified.Moreover,the derived equivalent calculation formula of thermal conductivity is applicable to the different members with the same composite panels on fire side.Taking the member G-3-1 as an example,the simulation time of the two-dimensional equivalent simplified model is 1 hour and 12 minutes,and the original model of the two-dimensional finite element is 6 hours and 33 minutes.The computational efficiency of the two-dimensional equivalent simplified model is significantly improved.(3)The three-dimensional finite element refined(original)model of the composite member is built by COMSOL software.The simulated results are compared with the experimental results and the two-dimensional finite element original model.The compared results show that the threedimensional simulation results are in good agreement with the experimental results that verify the validity of the three-dimensional finite element original model.In contrasted with the twodimensional finite element original model,the three-dimensional finite element original model considers the heat dissipation of the longitudinal side(mainly the longitudinal heat dissipation of the cavity).Therefore,the composite panels on fire side heat up faster than the two-dimensional model,and the composite panels on ambient side heat up slower than the two-dimensional model.The temperature on the middle of the longitudinal direction is high and the temperatures on the sides of the longitudinal direction are low.The longitudinal direction distance closer the cross-span is,the smaller the temperature change,and the longitudinal direction distance further the cross-span is,the greater the temperature change.The simplification method and equivalent formula of thermal conductivity used in the two-dimensional equivalent model are applied to the three-dimensional equivalent simplified model.The simulated results are compared with the experimental results.The comparison show that the results are consistent,indicating that the equivalent simplification method can be applied to three-dimensional.When the equivalent simplification method and the equivalent thermal conductivity formula are used for the other members with the same composite panels on fire side,the results have certain errors,but it is safe because the fire resistance time is less than the test result.Taking the member G-3-1 as an example,the simulation time of the three-dimensional equivalent simplified is 10 hours and 06 minutes,and the three-dimensional finite element original model is 38 hours and 20 minutes.The computational efficiency of the three-dimensional equivalent simplified model is significantly improved.The novelties of this paper:(1)Based on the fire test results of the light-gauge steel composite members,the shedding/failure criteria of the gypsum board,rock wool and aluminum silicate wool are proposed.(2)The idea of using the equivalent heat conduction instead of cavity convection is proposed.The equivalent calculated formula of thermal conductivity is derived.Based on the two-dimensional finite element refined model of the light-gauge steel composite members,the two-dimensional equivalent simplified model which can simulate the convection,radiation and heat transfer is built.Finally,such method is extended to the three-dimensional equivalent simplified model.(3)The longitudinal temperature distribution of light-gauge steel composite members is studied by three-dimensional finite element refined model and three-dimensional equivalent simplified model. |
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