Fire-resistance Redundancy in Steel Framing

摘要

The assessment of framing redundancy dur-ing a fire differs from room-temperature as-sessments, and thus it is necessary to exam-ine the external forces at work during a fire and the changes in strength characteristics of the structural members that these forces cause. The first factor to be taken into account in an examination of the working external forc-es is that a fire breaks out in one part of a building. Fig. 1 shows the differences in the external forces dealt with in fire-resistant design and seismic design. The Earth's gravi-tational load works vertically throughout an entire building structure; and, during an earthquake, the ground vibrates and the resultant seismic energy also works not only on the foundation but on the entire building structure as well. On the other hand, because a fire generally breaks out in only part of a building and is extinguished before spreading through the entire building structure, temperature loads caused by fires work on only part of a building. Accordingly, the temperature of structural members located in the space where a fire breaks out will rise, but members located in sections untouched by the fire will not be affected.