Effect of fire on composite long span truss floor systems

Much research has been and is currently being done to try and accurately recreate the effects of fire on structures including the effects of redistribution within the structure and the associated changes in load carrying mechanisms. This work has mostly focussed upon the most common and simplest structural forms currently used. As such most of the research to date tends to involve Universal Beam and Universal Column sections in a grid formation with spans of 6–9 m. This paper reports on an investigation of the effects of heating on a long span truss floor system. The ABAQUS finite element package is used to model the structure including fully non-linear behaviour and thermal expansion effects. Different boundary conditions and heating regimes are investigated to understand the response of the truss members to fire. The effects of heating on the lateral restraint available from the slender floor systems to a column have also been studied. The results and analysis indicate that composite truss flooring systems may not fail suddenly. Individual member buckling seems to be a much more gradual occurrence linked to material failure and expansion based geometry change rather than sudden “failure”.