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Fire damage can weaken structural steel members of buildings
Structural steel is very frequently used in taller buildings, sports arenas, exhibit/convention centers and industrial facilities. Code allowances provide for unprotected noncombustible construction for particular occupancies and within specified heights and areas. For larger and taller buildings, fire resistive steel construction is required which usually necessitates use of fire protection materials.
The effects of a severe uncontrolled fire in a building or facility can be enormous in terms of casualties, injuries, and property damage. The fire-induced property consequences may not be limited to only destruction of the building contents, finish and fire protection materials, but they may also weaken its basic structural skeleton through various forms of member damage (cracking, spalling, buckling, charring, yielding, fractures, large deformations) and connection failures. JENSEN HUGHES has conducted many engineering studies and reviews of major fire events in landmark high-rise buildings, most of which had structural steel framing, as well as numerous post-fire investigations of more common low-rise construction of masonry, concrete, steel and wood materials. The latter investigations have covered both fire resistive and unrated construction.
The common forensic tasks in this type of post-fire investigator have included detailed documentation of the event, survey of the site, analytical simulation of the fire development, prediction of its heating effects on the structure, identification of the resulting structural vulnerabilities, assessment of the structural performance and evaluation of suitability for future service. An examination of the fire-exposed steel condition and its deformations can help to approximate the maximum intensity and duration of the severe fire. If remediation of the surviving construction is considered feasible, a more thorough examination and testing of the structural and/or fire protection materials may be conducted.
At high temperatures during a fire exposure, steel can sag, buckle, and potentially fracture. Structural steel construction is often subjected to post-event reviews after it has experienced a major fire exposure. Any localized member or connection distortions and failures are identified for potential repairs or replacement, together with replacement of all damaged fire protection materials. If the building/facility is to be re-instated, tests of samples extracted from the fire-exposed steel may also be conducted to verify that the residual mechanical properties have not been adversely affected. Sometimes, if the fire damage is deemed too prevalent and widespread, the preferred decision is to demolish and rebuild.
At high temperatures, concrete is susceptible to cracking, spalling, and fractures which can result in reduction of section size and/or loss of concrete cover to steel reinforcement.