Structural analysis for performance-based design of steel and composite framed structures in fire

Abstract

The implementation of the performance-based design for fire safety called for the development of design methods that can reasonably reflect the structural fire behaviour. In a simplified manner, the behaviour of structural members like beams and columns can be considered studied separately with the restraint from the rest of the building represented by a few restraint sprints. Based on these simplified models, this thesis studied the behaviour of steel beams, steel columns, and composite beams in fire when they are subjected to linear-elastic axial and rotational restraints. From the behaviour study, new fire limit states were defined for these members and methods were proposed to calculate the limiting temperatures of these members. The methods for the design of single members were then put into the analysis of 3D frames. One steel frame and one composite frame were analyzed and fire protections were designed. The analysis results were compared to advanced finite element analysis results and were found that they give a reasonable prediction of the real structural behaviour in the frame in terms of the member forces and displacements. The proposed design methods were also compared to the Eurocode design methods. The proposed methods were general able to significantly reduce the fire protections to the beams and be cost-saving. With respect to the threats from terrorist attacks, the fire resistance of blast damaged structures was studied. Methods for blast load prediction and blast effect estimation were discussed. Effect of blast loading to the fire resistance of single columns was studied. An analysis was performed to a 3D multi-storey building subjected to blast and fire using advanced finite element analysis. Techniques for integrated blast and fire analysis were illustrated and importance for integrated blast and fire analysis were highlighted.