The Relevance of Structural Fire Performance in Earthquake Damaged Structures

Abstract eng:
Earthquakes and fires are low probability, high consequence events. Although, traditionally careful consideration is given to the design of structures to separately withstand the occurrence of both of these events, little or none attention is given to the potential structural vulnerabilities arising from their combined occurrence. Fires following earthquakes or post-earthquake fires can result in severe threats to the structure of a building and its lifeline. Several studies have actually shown that this combined event state is not a rare situation. This papers examines the potential relevance of structural fire performance, and the design for it, in earthquake damaged structural systems. The mechanical degradation (e.g. reduced stiffness and load bearing capacity) of a structure after an earthquake can have a negative influence in the structural fire performance of the building. Prior studies on structural fire safety have concluded that thermally induced forces and deformations, and not mechanical degradation governs the structural fire performance. Furthermore, heating of structural elements may or may not be reduced by earthquake induced damage of the structural elements; e.g. cracking of concrete cover insulating reinforcement, effectiveness of steel intumescent coatings. Besides, damage generated by relatively large? deformations induced by earthquakes can result in fatal failure of non-structural components (e.g. fire-safe compartmentation, active fire protection systems); thus having a direct influence in the fire dynamics of a post-earthquake fire. The design philosophy of both engineering practices (earthquake and fire engineering) can differ in essence. Earthquake engineering lays under the premise that the structure should withstand the full duration of a “design earthquake,” and it does so by explicitly limiting the structural response in the spatial-domain (e.g. inter-floor drift, acceleration). Contrary, structural fire engineers assess fire performance on the basis of rating of elements in the time-domain, i.e. time resisted during a fire resistance test; this last is known as the Fire Rating; 30, 60, 90 min or more. Outcomes of this study evidenced the need for developing structural design guidelines explicitly considering the fire performance of structures after an earthquake. In addition, comprehensive analytical and numerical analysis tools need to be developed and validated against experimental data; the partial results of proposed studies are examined and discussed. Throughout the work presented herein, reinforced concrete structural systems are used as an exemplar to highlight the matter of analysis.

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