Method for proving the safety against collapse of load-bearing systems under fire load

Abstract

The present invention relates to a method for proving the safety against collapse of load-bearing systems under fire load by calculating the changes of the material properties during the fire and the residual strength after the fire on the basis of data obtained by means of bar statics which were already obtained from the construction of the building component and which relate to the design of the building component for standard load cases such as dead load, loading in consequence of groundwater and of earth pressure, and living load.

What is claimed is:  
     
         1 . A method for proving the safety against collapse of load-bearing systems under fire load by calculating the changes of the material properties during the fire and the residual strength after the fire on the basis of data obtained by means of linear bar statics which were already obtained from the construction of the building component and which relate to the design of the building component for standard load cases such as dead load, loading in consequence of groundwater and of earth pressure, and living load, wherein input values for the calculation of the component under temperature influence are determined as follows: 
 by definition of the fire load;    by definition of a time t and the calculation of the thermal load over the entire cross section at said time t, and    by determining the material properties under temperature influence and after the fire influence; with    load curves for this cross section at this time, i.e. the determination of the load-bearing capacity of the cross section by the determination of the interaction between bending moment and normal force by means of load curves,    the conversion of the internal forces resulting from the temperature load into equivalent outer temperature loads, and    the determination of the system stiffnesses applicable for the respectively viewed cross section, i.e. flexural strength and coefficient of elasticity,    being determined with said determined data over the cross-sectional height of the component for each of said time steps under consideration of the different non-linear material properties at each place of the cross section by integration within determined state at limit strains and the internal forces as obtained by using frame analysis are delimited against the then applicable load curves by taking into account the altered stiffnesses and applied substitute temperature load.    
     
     
         2 . A method according to  claim 1 , wherein in the case of a negative analysis of the safety against collapse of the respective load-bearing system, the method steps as mentioned in  claim 1  are repeated with changed material properties to be determined until the desired safety against collapse has been achieved.  
     
     
         3 . A method according to  claim 2 , wherein the material properties are altered by increasing the armoring and/or increasing the share of concrete and/or by including a plastic hinge in the calculation.  
     
     
         4 . Application of a method according to  claim 1 , wherein after the preparation of the construction sheets for erecting a statically loaded building structure the safety against collapse of said building structure in the case of a possible fire are determined on the basis of data obtained by means of bar statics, which data have already been obtained from the construction of the building component and which relate to the standard load cases such as dead load, loading in consequence of groundwater and of earth pressure, and living load and optionally the constructional features are altered to such an extent that the safety against collapse during a fire load or the required residual strength after the fire is given.