Listings of fire resistance ratings for tested

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struction assemblies that meet specific building code requirements. Listings of fire resistance ratings for tested construction assemblies are available from the following sources: Fire-Resistance Directory , Underwriters Laboratories (UL), Northbrook, Illinois. Fire-Resistance Ratings , American Insurance Services Group, New York, New York. Fire-Resistance Design Manual , Gypsum Association, Washington, D.C. The term "fireproof" is often used to describe fire-resistant buildings. Some manufacturers use this term to describe fire protection materials. The use of "fireproof" and "fireproofing" is improper because it connotes absolute pro- tection; experience has clearly shown that large-loss fires can occur in fire-resistant buildings. No building is truly fireproof. OCCUPANCY DESIGNATION OCCUPANCY FIRE LOAD (psf) EQUIVALENT FIRE SEVERITY (hours) Assembly 5 to 10 0 to 1 Business 5 to 10 0 to 1 Educational 5 to 10 0 to 1 Hazardous Variable Variable Industrial Low Hazard 0 to 10 0 to 1 Moderate Hazard 10 to 25 1 to 2½ Institutional 5 to 10 0 to 1 Mercantile 10 to 20 1 to 2 Residential 5 to 10 0 to 1 Storage Low Hazard 1 to 10 0 to 1 Moderate Hazard 10 to 30 1 to 3 Table 5 Typical Occupancy Fire Loads and Fire Severity
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SYSTEMS PAGE 60 Effect of Temperature on Steel The elevated temperatures developed during standard fire tests adversely affect the properties of virtually all materials, even noncombustible ones such as steel. In general, structural steel retains 60 percent of its ambient temperature yield strength at 1,000° Fahrenheit. During most building fires, temperatures in excess of 1,000° Fahrenheit are developed for relatively brief periods of time. Additionally, the structural elements are generally not loaded to their full design strength. Consequently, even bare steel may have sufficient load carrying capaci- ty to withstand the effects of fire. The "standard" ASTM fire test is conducted so that temperatures continuously increase, assuming an inexhaustible fire load, and the members are loaded to full design load. Figure 28 shows the time/temperature curves for fires under the standard ASTM test compared with "real" fires with different fire loads. As a result of the "standard" fire tests, when building codes specify fire-resistant construction, fire protection materials are required to "insulate" structural steel elements. Fire casualty statistics indicate that occupant safety is threatened much more by toxic smoke than structural col- lapse. Temperatures of Fire Exposed Structural Steel Elements Basic heat transfer principles indicate that the rate of temperature change of a steel beam or column will vary inversely with mass and directly with the surface area through which heat is transferred to the member. Thus, the weight-to-heated-perimeter ratio ( W/D ) of a structural steel member significantly influences the temperature that Figure 28. Time/temperature curves for various fire exposures
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PAGE 61 SYSTEMS the member will experience when exposed to fire. As used in this expression, W is the weight per unit length of the member (lbs/ft) and D is the inside perimeter of the fire protection material (inches). Expressions for calcu-
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  • Fall '19
  • Structural steel

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