DS 2-8 Earthquake Protection for Water-Based Fire ... - FM Global

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2-8 Earthquake Protection Page 10 FM Global Property Loss Prevention Data Sheets 2. For crossmains, the zone of influence includes the tributary length of crossmain being braced plus the length of all branch lines attached to that section of crossmain that are not distributed to branch line longitudinal sway bracing. 3. For branch lines that require sway bracing, the zone of influence typically includes the length of the branch line to the left and right of the sway brace that is tributary to that sway brace. The tributary length of pipe between the first lateral sway bracing location and the crossmain connection may either be based on an equal distribution to the crossmain longitudinal bracing and the first lateral sway bracing location (see Section 2.2.1.2.3[C][2]), or may be totally distributed to the first lateral sway bracing location. C. Longitudinal two-way sway bracing: 1. For feedmains, the zone of influence includes the length of the feedmain to the left and right of the sway brace that is tributary to that brace. 2. For crossmains, the zone of influence includes the tributary length of crossmain being braced; do not include loads from branch lines, except when a portion of branch line lateral sway bracing is being included as described in Section 2.2.1.2.3(B)(3). 3. For branch lines that require sway bracing, the zone of influence typically includes the length of the branch line to the left and right of the sway brace that is tributary to that sway brace. The tributary length for the piping between the crossmain and the first sway bracing location should be based on an equal distribution between that bracing location and the crossmain lateral sway bracing as described in Section 2.2.1.2.3(B)(2). D. For sway bracing at horizontal changes in direction that is located within 2 ft (0.6 m) of the end of a feedmain or crossmain connection to a perpendicular main of the same or smaller diameter, and which will be used as a lateral sway brace for one pipe and a longitudinal sway brace for the perpendicular pipe, the zone of influence includes the total tributary lateral and longitudinal weights of mains and branch lines as described above. 2.2.1.3 Configuration and Design of Sway Bracing 2.2.1.3.1 Provide sway bracing to resist horizontal seismic loads. Sway brace(s) at each location should be capable of resisting the horizontal design load (H) as determined per Section 2.2.1.2. In addition, provide additional members to resist any net vertical force component that occurs as a result of sway brace placement (see Section 2.2.1.3.5[D]). 2.2.1.3.2 A properly sized and attached U-bolt that fastens the pipe directly to, and holds the pipe tightly against, a structural supporting member may be used as a lateral sway brace when located on horizontal piping, or as a four-way sway brace when located on vertical piping. Consideration of a vertical resultant force is unnecessary for this configuration. 2.2.1.3.3 Do not use U-hangers, including wraparound types, as lateral sway bracing for feedmains and crossmains. 2.2.1.3.4 Wraparound U-hangers may be used as lateral sway bracing for branch lines that need sway bracing if they meet the following criteria: • They have both legs bent out at least 30 degrees from the vertical, • They are the proper diameter and length per Tables 2 through 7 for the seismic loads involved, • They are properly attached to the building structure per Section 2.2.1.3.6, and • There is no more than 1 ⁄ 2 in. (13 mm) of space between the top of the branch line piping and the wraparound portion of the U-hanger. ©2010 Factory Mutual Insurance Company. All rights reserved.
Earthquake Protection 2-8 FM Global Property Loss Prevention Data Sheets Page 11 NOTES FOR TABLES 2 THROUGH 7: NOTE 1: The following are tangent values for various angles: Angle Tangent Angle Tangent 30 0.58 60 1.73 35 0.70 65 2.14 40 0.84 70 2.74 45 1.00 75 3.73 50 1.19 80 5.67 55 1.43 85 11.43 Note 2: The slenderness ratio, l/r, is defined as a brace length/least radius of gyration. The least radius of gyration, r, can be determine for various brace shapes as follows: 2 Pipe: r =[√(r - r 2 ) ]/2 o i where r o = radius of outside pipe wall r i = radius of inside pipe Rods: r = (radius of rod/2) Flats: r = 0.29h where h = smaller dimension of two sides. (Angles require a much more detailed calculation.) Note 3: The steel yield stress (F y) value used to generate the tables was taken as the yield stress for commonly used steel. ©2010 Factory Mutual Insurance Company. All rights reserved.
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DS 2-8 Earthquake Protection for Water-Based Fire ... - FM Global

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