Despite the advance of the research in the field, the fire design of steel structures is mostly accomplished by verifications of single members exposed to a standard fire. These verifications don’t account for the effects of the rest of the structure on the elements, nor ensure the stability of the structure beyond the nominal required resistance time. Nevertheless, restrained thermal expansion is known to significantly affect the behavior of steel structures in fire, and has been referred as possible cause of collapses in some building fires, such for example the WTC collapse in 2001.
Several tests and studies carried out after the WTC collapse have highlighted the possibility of relying on the catenary and membrane effect of the horizontal members and limit the fire insulation of steel structures to vertical structural elements; however, these measures affect the relative stiffness of the steel elements during a fire and may increase the effect of the hindered thermal expansion provided by the insulated columns on the horizontal uninsulated members. It is therefore of interest to investigate the effect of thermal expansion and the response of the overall steel system to fire with respect to two different structural typologies in particular: single-story buildings and multi-story buildings.
Single story buildings, such as car parks and industrial halls, are often characterized by stiff beams and flexible columns. As a consequence, they may experience an outward (sway) collapse during a fire, endangering people and properties outside the building. It is therefore a current interest of the research to investigate the collapse behavior of single-story steel frames and identify relevant structural characteristics that influence the collapse mode.
Multi-story buildings are characterized by stiff columns at the bottom floors, where the stability of beams may be endangered by the effect of restrained thermal expansion already at very low temperatures. Even if rare, the failure of horizontal elements in a high-rise building may have very severe consequence, as it can trigger the vertical propagation of both the damages and the fire.
A final problem related to the insulation of steel elements concerns the limited knowledge on the real behaviour in a fire of intumescent coatings, which represent nowadays the preferable fire insulation for steel structures and the main viable solution in case exposed steel elements are used as architectonical design features. Recent improvements in the formulation of intumescent coatings have also eliminated the need of high pressure application and increased up to 120 min the nominal fire resistance they can provide to usual steel members, thus spreading their use to high-rise steel buildings too.
Nevertheless, current verification and design of steel elements insulated by intumescent coatings presents several shortcomings, mostly due to the complexity of the intumescent process and the difficulties in describing the heat transfer process through the coating. It is therefore of interest to further investigate the behavior of intumescent coatings in fire and outline a simple but more realistic model for integrating their effects into the current design methods of insulated steel elements.
Research Project
Thermal resistance of intumescent coatings, research project funded by COWI
Publication
Giuliani L., Budny I.:
Different design approaches to structural fire safety
Int. J. of Lifecycle Performance Engineering (IJLCPE), vol.1, (2), pg.135-158, 2013
Gentili F., Giuliani L., Bontempi F.:
Structural response of steel high rise buildings to fire
Journal of Structural Fire Engineering, vol: 4, issue: 1, pg. 9-26, 2013
Dondera A., Giuliani L.:
Fire-induced collapses of steel structures
Proceedings of Applications of Structural Fire Engineering (ASFE 2013), Prague, Czech Republic, 2013 - link to Orbit
Contact
Luisa Giuliani
Grunde Jomaas