Full Structural Behaviour
The analysis of a full structure in fire conditions would be extremely complex and costly, therefore it is rarely conducted unless fully required. Typically single member analysis or simplified structural analysis is sufficient as conservative design factors should be in place to account for shortcomings in knowledge. Thornsteinsson showed the importance of assessing the structure beyond the model in relation to the restraint in the slab, as this proved to have an effect on the stresses carried on the underside of the slab and also in the column. However the slab will not be free or fully restrained as the structure will allow some movement, this is figuratively shown in the diagram below.
There will also be moment redistribution, as a slab-column connection is heated and consequently loses strength, some of the load that was being carried will be distributed to adjacent columns away from the high temperatures above the fire. Choi & Kim found that the moment redistribution limit is directly affected by the ratio of the nominal punching shear strength to the nominal flexural shear strength of the slab, additionally they noted that the assignment of safety factors in EC2 methods may give conservative moment redistribution of up to 30% (Choi, J.W. & Kim, J.H.J "Experimental investigations on moment redistribution and punching shear of flat plates" 2012).
There will also be moment redistribution, as a slab-column connection is heated and consequently loses strength, some of the load that was being carried will be distributed to adjacent columns away from the high temperatures above the fire. Choi & Kim found that the moment redistribution limit is directly affected by the ratio of the nominal punching shear strength to the nominal flexural shear strength of the slab, additionally they noted that the assignment of safety factors in EC2 methods may give conservative moment redistribution of up to 30% (Choi, J.W. & Kim, J.H.J "Experimental investigations on moment redistribution and punching shear of flat plates" 2012).