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

More documents

Recommendations

Info

2-8 Earthquake Protection Page 20 FM Global Property Loss Prevention Data Sheets 2.2.1.3.5 For sway bracing that consists of individual diagonal element(s) or diagonal plus vertical elements, configure and size these elements per the following guidelines. Braces can be steel pipe, steel angle, steel rods, or steel flats. Figs. 3 and 4 show bracing options for lateral sway bracing. Figs. 5 and 6 show bracing options for longitudinal sway bracing. A. Position diagonal element(s) at an angle of at least 30 degrees from the vertical. B. For braces used to resist both tension and compression, choose the shape, size, and length of the braces so the slenderness ratio, l/r (length/least radius of gyration), does not exceed 200, in order to provide adequate resistance to buckling. Base the slenderness ratio on the actual length of the brace between attachment points to the structure and the pipe being braced. C. For braces used in tension only, choose the shape, size, and length of the braces to result in a slenderness ratio, l/r (length/least radius of gyration), that does not exceed 300. Base the slenderness ratio on the actual length of the brace between attachment points to the structure and the pipe being braced. D. Select each brace so the maximum length between attachment points to the structure and the pipe being braced does not exceed the length calculated based on the slenderness ratio, l/r, limitations in Sections 2.2.1.3.5(B) and 2.2.1.3.5(C); and so the brace can resist the percentage of the total horizontal design load, H, that is assigned to it. These values may be calculated or taken from Tables 2 through 7. These tables indicate maximum allowable lengths for different brace shapes and sizes and maximum horizontal design load (either H or a fraction of H not less than H/2, depending on sway bracing configuration) for each brace for three different ranges of angles for the brace as measured from the vertical. Maximum horizontal design loads are included for l/r = 100, for l/r = 200, and for l/r = 300 (tension only). The following guidelines apply: 1. For Figs. 3 or 5 using one vertical and one diagonal brace: a) The angle from the vertical for Brace A must be at least 30 degrees. b) Size and arrange Brace A to carry in both tension and compression (l/r = 200 or less) the full horizontal design load H, determined in Section 2.2.1.2. c) Calculate the net vertical uplift force derived from the horizontal design load H, as: V F = (H/tan Θ) - 1/2 W P Where V F = Net vertical uplift force. H = Horizontal design load from Section 2.2.1.2. Θ = Angle of Brace A from vertical. W P = Weight of the water-filled pipe within the zone of influence. If V F is less than or equal to 0 (zero), Brace B is not needed. d) Brace B, when needed, can either be of the same shape and size as Brace A, and connected to the pipe at the same point as Brace A, without any further calculation, or can be selected on the basis of the actual calculated net vertical uplift force. Although less desirable, Brace B may be a hanger that is located no more than 6 in. (150 mm) from the point of attachment on the pipe for Brace A and meets the following criteria: • The hanger has been determined to be able to resist the net vertical resultant load uplift force V F (this may necessitate the use of a rod stiffener or other means, but in any case the l/r should not exceed 200), • The hanger is capable of transferring vertical upward loads and is fastened to the structure by a positive means of mechanical attachment, such as through bolts, lag screws, or concrete anchors that are properly sized for the load, and • The hanger attachment to the fire protection system piping is snug and concentric, with no more than 1 ⁄ 2 in. (13 mm) between the top of the piping and the hanger so that excessive movement cannot occur. ©2010 Factory Mutual Insurance Company. All rights reserved.
Earthquake Protection 2-8 FM Global Property Loss Prevention Data Sheets Page 21 2. For Figs. 4 or 6 using two opposing diagonal braces, each capable of resisting tension and compression (l/r = 200 or less): a) The angle from vertical for Braces A 1 and A 2 must be at least 30 degrees. b) Size and arrange both Braces A 1 and A 2 in Figures 4 or 6 to carry the larger of one-half the horizontal design load H determined in Section 2.2.1.2 or the load determined by proportional distribution of design load H to the two braces. Considering Fig. 4, if the distributed portion of the horizontal seismic load reacted by Brace A 1 is H 1 and the distributed load reacted by Brace A 2 is H 2, the load distribution can be expressed as: H 1 = (H)((tan Θ 1)/(tan Θ 1 + tan Θ 2)) H 2 = (H)((tan Θ 2)/(tan Θ 1 + tan Θ 2)) The distribution of loads will be similar for the arrangement shown in Fig. 6. c) These sway bracing arrangements will provide adequate resistance to vertical force and no additional procedures are needed in that regard. 3. For tension-only sway bracing (l/r = 300 or less), which may be used when it is necessary to have longer brace members due to physical or dimensional constraints, treat as a special condition of Figs. 3 or 5 by providing opposing diagonal braces (i.e., two Braces A) similar to item 1 above: a) The angle from vertical for Braces A must be at least 30 degrees. b) Size and arrange Braces A in Figs. 3 or 5 to carry, in tension, the full horizontal design load H determined in Section 2.2.1.2 since neither brace is being considered as capable of resisting compression. c) Brace B, when needed, may vary in shape and size from Braces A. Evaluate Brace B based on the net vertical uplift force (V F) per item 1 above. 2.2.1.3.6 Select the proper method to attach the sway bracing to the structure and to the piping per the following guidelines: A. Arrange all parts and fittings in a straight line to avoid eccentric loading on any of the sway bracing components. B. Connections to the structure or the piping that are not FM Approved should provide a positive mechanical attachment. These connections should also be able to be visually verified as to correct installation (see Fig. 7). Fig. 7. Special threaded pipe fitting for attachment of sway brace to structure. C. Make attachments to the structure in accordance with the following guidelines. 1. Determine the shear and tension loads on the fasteners based on the fastener and sway bracing configurations illustrated in Figures 8 to 13. When using these figures, note the following: ©2010 Factory Mutual Insurance Company. All rights reserved.
Page 1 and 2: FM Global Property Loss Prevention
Page 3 and 4: Earthquake Protection 2-8 FM Global
Page 19: Earthquake Protection 2-8 FM Global
Page 65: Earthquake Protection 2-8 FM Global

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

Create successful ePaper yourself

Delete template?

Save as template?