Sway Bracing Layout
Earthquake Resistant Fire Protection System

Over the past few months the havoc that earthquakes can wreak has been abundantly clear. While the devastation in Haiti wrought by substandard building codes is not likely to be repeated soon, fire protection systems can be vulnerable to earthquakes, even in buildings that are built to more stringent safety codes.

Earthquake related strains are imparted to a fire protection system through the building or the ground to which it is attached, or through the inertial movement within the system itself.

In a Property Loss Prevention Data Sheet entitled “Earthquake Protection for Water-based Fire Protection Systems,” FM Global says that uncontrolled differential movement can cause damage when fire protection systems are not provided with the necessary features that incorporate sway bracing, flexibility, clearances and anchorage where needed.

Significant impairments to fire protection systems may expose a facility to a severe fire loss following an earthquake.

The most common type of damage is water damage due to water leakage from broken overhead sprinkler piping or sprinklers, primarily due to lack of sway bracing where needed.

Common sources of water damage were broken or separated overhead sprinkler piping, broken sprinklers due to impact with nearby structural members or other equipment, broken sprinklers or pipe drops due to excessive differential movement between unbraced suspended ceilings and the pipe drops, and broken inrack sprinkler system piping or sprinklers due to excessive rack movement.

In addition to damage from water leakage, fire protection systems are often impaired due to direct damage to the systems, or due to damage to public water supplies or utilities needed for fire protection.

In evaluating the many incidents of damage, FM Global says two conclusions are very apparent:

1. Only by providing in a systematic manner the necessary features, which incorporate sway bracing, flexibility, clearances and anchorage where needed, can a fire protection system be adequately protected to mitigate potential damage from earthquakes; and

2. Omission of only a few of the critical components necessary for adequate earthquake protection may create conditions where significant earthquake damage may result in substantial water damage. The necessary shutdown of the system to stop further damage also creates a fire protection system impairment.

To improve the likelihood that the fire protection systems will remain in working condition after an earthquake, and to minimize potential water damage from fire protection system leakage, FM Global recommends the following:

1. Brace piping or equipment to minimize uncontrolled differential movement between piping or equipment and the structure to which it is attached;

2. Provide flexibility on piping systems and on other equipment where differential movement between portions of those piping systems or equipment is expected;

3. Provide clearance between piping or equipment and structural members, walls, floors, or other objects so that potential damage from impact is minimized;

4. Provide anchorage to minimize potential sliding and/or overturning;

5. Use appropriate types of pipe hangers and sway bracing, properly locate them, and properly attach them to the structure to minimize the potential for pullout;

6. Use appropriate types of piping and pipe joining methods to minimize potential pipe breaks; and

7. Provide fire protection system plans and calculations with proper verification of design, and proper verification that the completed installation is in accordance with the design as well as good installation practices.

Sway Bracing

Sway bracing for sprinkler systems, when provided in conjunction with the recommended flexibility will minimize differential movement between the piping system and the structure to which it is attached. Flexible couplings allow sufficient flexibility between portions of systems where needed.

Actual design of sway bracing is based on horizontal seismic load. For risers and overhead sprinkler piping, there are two sway bracing designs: two-way and fourway. Two-way braces are either longitudinal or lateral, depending on their orientation with the axis of the horizontal pipe. Lateral and longitudinal braces resist differential movement perpendicular and parallel, respectively, to the axis of the pipe, and are typically used on feed mains, cross mains and system branch lines that are 2.5 in. (63 mm) and larger in diameter.

Four-way sway bracing resists differential movement in all horizontal directions, and is typically provided on risers. Where lateral and longitudinal sway bracing locations coincide, four-way bracing may be used to satisfy design requirements for both.

Sway Brace Design

There are four steps to properly design sway bracing: Step 1: Lay out sway bracing locations with respect to the sprinkler piping and to the structural members to which the bracing will be attached.

Step 2: Calculate the seismic design load requirements for each sway bracing location.

Step 3: Select the proper sway bracing shape, angle of attachment, size and maximum length based on the horizontal design load requirement.

Step 4: Select the proper method to attach the sway bracing to the structure and to the piping.

A four-way sway brace should be provided on all sprinkler risers (whether single or manifolded type) within 24 in. (0.6 m) of the top of the riser. The use of manifolded sway bracing at the top of multiple adjacent risers requires careful design work and should be avoided. If used, no more than two risers should be used in a manifolded arrangement, and bracing should be designed to carry the total loads for both risers.

Intermediate four-way sway bracing should be provided at an interval not to exceed 40 ft. (12.2 m). Where flexible couplings are used, four-way sway bracing should be provided within 2 ft. (0.6 m) of every other flexible coupling (with no more than two flexible couplings between sway brace locations).

A two-way lateral sway brace should be provided within 2 ft. (0.6 m) of the end of any horizontal manifold piping longer than 6 ft. (1.8 m), or when there is one or more flexible coupling(s) on either the horizontal manifold piping or on the riser stub between the floor and the connection to the horizontal manifold piping.

Vertical cross main or feed main piping: Four-way sway bracing should be provided at both the top and bottom of the vertical pipe run of 6 ft. (1.8 m) or more. Each brace should be located within 24 in. (0.6 m) of the respective piping turn. Intermediate four-way sway bracing should be provided similar to risers as recommended above.

For vertical pipe runs of less than 6 ft. (1.8 m) without bracing provided, flexible couplings should not be present within the vertical pipe run (including the piping turns). If flexible couplings are provided at one or both turns for vertical pipe runs of less than 6 ft. (1.8 m), then four-way bracing should be provided within 24 in. (0.6 m) of each turn equipped with flexible coupling(s).

Horizontal changes of direction: Cross main or feed main piping that has pipe runs of 6 ft. (1.8 m) or more adjacent to the change in direction should be provided with both lateral and longitudinal sway bracing at the change of direction.

Ends of feed mains and cross mains: Provide lateral bracing within 6ft. (1.8 m) of the end, and provide longitudinal bracing within 40ft. (12.2 m) of the end. When structural member locations for lateral sway bracing attachment are such that this 6ft (1.8 m) distance cannot be met, the cross main or feed main should be extended to allow proper location of the lateral sway bracing.

Seismic separation assemblies in feed mains and cross mains shall be considered as the end of the piping on both sides of the assembly.

For branch lines 2.5 in. (64 mm) or larger that need sway bracing, the first lateral sway bracing location should be no closer than 20 ft. (6.1 m) nor greater than 40 ft. (12.2 m) from the branch line connection to the cross main. FSM For more on this topic or other Property loss prevention methods, go to www.fmglobal. com/fmglobalregistration/default.asp x?action=newcut for art as well.