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                                          BUILDING CODES, LOADS, AND FIRE PROTECTION*


                   4.46  CHAPTER FOUR








































                                   FIGURE 4.16  Variation in fire resistance of structural steel column with weight-to-heated perimeter
                                   ratios and gypsum wallboard thickness.

                               This interrelationship is clearly illustrated in Fig. 4.16, which gives the fire resistance of steel
                               columns protected with different thickness of gypsum wallboard as a function of W/D. The curves
                               show that in determination of fire resistance, W/D is significant, as is the thickness of the fire-
                               protection material.
                                 In recognition of this basic principle, several semiempirical design equations have been devel-
                               oped for determining the thicknesses of fire protection for structural steel elements as a function of
                               W/D for specific fire-resistance ratings. Some of these equations have been incorporated into the
                               Underwriters Laboratories Fire-Resistance Directory and are also described in the following publi-
                               cations. ASCE, “Standard Calculation Methods for Structural Fire Protection,” ASCE/SFPE 29-99,
                               1999; International Building Code, 2003; and AISC, “Fire Resistance of Structural Steel Framing,”
                               Design Guide 19, 2003. These calculation methods also have been recognized by model building
                               codes and are widely used in design of cost-effective, fire-resistant steel buildings.

                   4.12.9 Rational Fire Design
                               Building code requirements for structural fire protection are generally prescriptive and based on stan-
                               dard (ASTM E119) fire tests. This approach suffers from the following significant limitations:

                               • The standard fire exposure is arbitrary and does not necessarily represent real building fires. In
                                many cases, real fires result in high temperatures of short duration.



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