ASD/LRFD Manual - American Wood Council

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ASD/LRFD MANUAL FOR ENGINEERED Wood Construction 139 Figure M16.1-22 Cross Sections of Possible One-Hour Area Separations M16: FIRE DESIGN 16 American Forest & paper association
140 M16: FIRE DESIGN Area Separation Assemblies It is of great concern when fire-rated assemblies are designed and specified without consideration of sound structural principles. Should a fire develop, these structural inadequacies could cause the assemblies to fail unexpectedly, increasing the risk of loss of life. There are a number of ways to provide sound structural and fire endurance details that maintain 1-hour rated area separation assemblies. Figure M16.1-22 shows several possible assemblies that can be used to make up the 1-hour rated system for separation between occupancies for a) floor trusses parallel to the wall assembly; and b) perpendicular to the wall assembly. A 2x4 firestop is used between the walls next to the wall top plates. This effectively prevents the spread of fire inside the wall cavity. A minimum 1/2-inch gypsum wallboard attached to one side of the floor truss system, and located between the floor trusses, also provides a draftstop and fire protection barrier between occupancy spaces if a fire starts in the floor truss concealed space, which is a rare occurrence. The tenant separation in the roof is maintained through the use of a 1/2-inch gypsum wallboard draftstop attached to the ends of one side of the monopitch trusses and provided for the full truss height. Figure M16.1-22 effectively provides 1-hour compartmentation for all the occupied spaces using listed 1-hour rated assemblies and the appropriate draftstops for the concealed spaces as prescribed by the model building codes. If a fire-resistive assembly, rather than draftstopping, is required within concealed attic spaces, the details shown to the right (UL U338, U339, and U377) provide approved 1-hour and 2-hour rated assemblies that may be used within the roof cavity and that may be constructed with gable end frames. The critical aspects for fire endurance assemblies include: • Ensuring that the wall and ceiling assemblies of the room use 1-hour rated assemblies. These are independent assemblies. The wall assembly does not have to be continuous from the floor to the roof to meet the intent of the code or the fire endurance performance of the structure. The intent of the code is that the building be broken into compartments to contain a fire to a given area. Fire resistance assemblies are tested to provide code-complying fire endurance to meet the intent of the code. The foregoing details meet the intent of the code. • Properly fastening the gypsum wallboard to the wall studs and trusses. This is critical for achieving the desired fire performance from a UL or GA assembly. • Ensuring that the detail being used is structurally sound, particularly the bearing details. All connection details are critical to assembly performance. When a fire begins, if the structural detail is poor, the system will fail at the poor connection detail earlier than expected. • Accommodating both sound structural details with appropriate fire endurance details. Since all conceivable field conditions have not been and cannot be tested, rational engineering judgment needs to be used. The foregoing principles could also be applied to structures requiring 2-hour rated area separation assemblies. In this case, acceptable 2-hour wall assemblies would be used in conjunction with the 2-hour floor-ceiling and roof-ceiling fire endurance assemblies. Through-Penetration Fire Stops Because walls and floors are penetrated for a variety of plumbing, ventilation, electrical, and communication purposes, ASTM E814 Standard Method of Fire Tests of Through-Penetration Fire Stops uses fire-resistive assemblies (rated per ASTM E119) and penetrates them with cables, pipes, and ducts, etc., before subjecting the assembly to ASTM E119’s fire endurance tests. Despite the penetrations, firestop assemblies tested according to ASTM E814 must not significantly lose their fire containment properties in order to be considered acceptable. Properties are measured according to the passage of any heat, flame, hot gases, or combustion through the firestop to the test assembly’s unexposed surface. Upon successful completion of fire endurance tests, firestop systems are given F&T ratings. These ratings are expressed in hourly terms, in much the same fashion as fire-resistive barriers. To obtain an F-Rating, a firestop must remain in the opening during the fire and hose stream test, withstanding the fire test for a prescribed rating period without permitting the passage of flame on any element of its unexposed side. During the hose stream test, a firestop must not develop any opening that would permit a projection of water from the stream beyond the unexposed side. To obtain a T-Rating, a firestop must meet the requirements of the F-Rating. In addition, the firestop must prevent the transmission of heat during the prescribed rating period which would increase the temperature of any thermocouple on its unexposed surface, or any penetrating items, by more than 325°F. The UL Fire Resistance Directory lists literally thousands of tested systems. They have organized the systems with an alpha-alpha-numeric identification number. The first alpha is either a F, W, or C. These letters signify the American Wood Council
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2005 EDITION ASD/LRFD MANUAL MANUAL
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Updates and Errata While every prec
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ASD/LRFD MANUAL FOR ENGINEERED Wood
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M1: general requirements for struct
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38 M7: PREFABRICATED WOOD I-JOISTS
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Page 175: American Forest & Paper Association
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