Page 213 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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BUILDING CODES, LOADS, AND FIRE PROTECTION*

BUILDING CODES, LOADS, AND FIRE PROTECTION 4.41

concept. In a fire, the circulating water in a tubular column is expected to limit the temperature rise
in the steel. Generally, corrosion inhibitors should be added to the water, and in cold climates,
antifreeze solution should be used for exterior columns.
(Fire Protection through Modern Building Codes, American Iron and Steel Institute,
Washington, D.C.)
In still another approach, sheet-steel covers are applied on the outside of a building to insulated
flanges of steel spandrel girders to act as flame shields, as illustrated in Fig. 4.14. These sheet-steel
covers not only serve to deflect flames away from the exposed, exterior web of a girder but also pro-
vide weather protection for the insulated flanges. As shown, a flame-shielded spandrel girder is pro-
tected in the interior of the building in a conventional manner.
As illustrated by full-scale fire tests on flame-shielded spandrel girders, the standard fire test is
not representative of the exposure that will be experienced by exterior columns and girders. Research
on fire exposure conditions for exterior structural elements has led to development of a comprehen-
sive design method for fire-safe exterior structural steel which has been adopted by some building
codes. Likewise, fire engineering principles can be used to determine if less or no protection may be
justified for conditions that are beyond the prescriptive code limits, or as an alternative to them. Use
of more realistic natural fires, heat-transfer relationships, and structural analyses for these cases can
provide the needed rational solutions.
(Design Guide for Fire-Safe Structural Steel, American Iron and Steel Institute, Washington, D.C.)

4.12.7 Restrained and Unrestrained Construction
One of the major sources of confusion with respect to design of fire-resistant buildings is the con-
cept of restrained and unrestrained ratings. This concept is peculiar to ASTM E119 and U.S. codes,
and is not used in other countries. Fire-resistant design is based on the use of tested assemblies and

FIGURE 4.13 Tubular steel columns filled with water for fire resistance. (a) Temperature
variation during exposure to fire. (b) Schematic arrangement of fire-protection system.

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