A Practical Approach For Fire Risitance Design Of Large Space Building Grid Structures

Large space building is widely used within public buildings. The fire safety of large space building structure must be researched by structural engineer. At first the temperature field which is attributed to energy dissipation must be determined, then analysis the behavior of large space structure imposed fire. However there is very limited research carried out. Researching temperature field used in large space structural design for fire safety, establishing utility temperature elevation empirical formula in large space fire, getting simply temperature calculation for protected or unprotected steel member based on utility temperature elevation empirical formula, considering local steel member elevated temperature by flame radiation are researched in this article. Because material properties may be changed with elevated temperature and internal strains may be induced by thermal expansion. As one of the large space structures regular pyramidic space structure behavior imposed design fire scenarios must be researched in order to get the utility method of fire resistance of regular pyramidic space structure. The specific works are outlined below.Based upon collected data of fire properties and recognized mechanics of elevated temperature in fire, estimated temperature field in building fire with arithmetic simulation can be gotten.The regularity of factor influencing elevated temperature of build fire must be obtained. Based upon the regularity of factor fire scenario can be designed. These scenarios may be simulated by computer programs "FDS" which use computational fluid dynamics researched by department of commerce of United States America in 2002.Simplified temperature variational field of large space fire through entire temperature elevation is established. Based on a great number of numerical experiments the mathematic model of temperature elevation in large space fire is presented . Finally, empirical formula of temperature elevation in large space fire is created, and the parameters of the empirical formula are fitted by regression analysis which fills up the space without the curve of temperature elevation in large space fire.The heat equilibrium equation based upon the lumped differential formulation usually be solved by iteration method. In order to simplify the iteration method The parameter of smoke temperature in heat equilibrium equation based upon the lumped differential formulation is substituted by the empirical formula of temperature elevation in large space fire, regression parameter, and analysis the parameters of heat equilibrium equation with regression method. Then the simplified analytical method to evaluate the temperatures of protected steel member and unprotected steel members can be obtained.The thermal properties parameters of flame (configuration factor,emissivity of the emitting surface,effective radiation area) are organized into heat equilibrium equation based upon the lumped differential formulation. The condition of neglected flame radiation in influencing elevated temperature of steel member can be gained by analyzed these thermal properties parameters of heat equilibrium equation based upon the lumped differential formulation.The geometrical nonlinearity and material nonlinearity behavior of regular pyramidic space structure under dead loading and elevated temperature is analyzed by the generic finite-element stress-analysis program "ANSYS". T₀ is the temperature at which member is buckling and T_cr is the temperature at which structure is failure . T₀ and T_cr can be gained by simulating the behavior of regular pyramidic space structures with diverse geometrical features under uniform and nouniform temperature field.The empirical value of T₀ and T_cr in varied condition can be gotten by analyzed the factors which influence the critical temperature (T₀ and T_cr) .If the empirical value of T₀ and T_cr are regarded as reference value, the T₀ and T_cr can be determined with interpolation method between these empirical values of T₀ and T_craccording to the geometrical feature of regular pyramidic space structure. If the time the structure load-bearing capacity lasting in the fire situation ruled by code and the smoke temperature in the same fire situation are presented, the T₀ and T_cr can be determined by the simplified analytical method to evaluate the temperatures of steel member. The T₀ and T_cr determined by the simplified analytical method to evaluate the temperatures of steel member is greater than the T₀ and T_cr determined with interpolation method between these empirical values of T₀ and T_cr according to the geometrical feature of regular pyramidic space structure, then structure is safety in fire,...