It is important to remember that the building causes the strains on sprinkler piping during earthquakes. If sprinkler piping could be isolated from the building, earthquake strains could only enter the sprinkler system through the riser. The various movements of the building cause the strains onto the piping. Increasing the flexibility of the major components of the sprinkler system can lessen these strains. One section of piping should never be rigidly attached to another, more flexible section. Providing flexible couplings and allowing greater clearance through floor and wall openings will allow the sprinkler system to move independently of the building. However, if allowed to vibrate excessively, damage may occur. Excessive movement can be reduced or dampened by use of braces and hangers. Any system used for earthquake protection should incorporate both flexibility and dampening.
Sprinkler control valves should preferably be located outdoors where movements between the building and the valves are reduced and also allows for closing the valve in event of partial building collapse.
Flexible couplings should be provided near the top and bottom of each riser on each story of a building to accommodate the maximum expected story drift. These couplings must be placed with 12 inches of the floor and 24 inches of the ceiling. Flexible couplings are also needed on both sides of major walls that sprinkler piping passes through. Piping 3 inches in diameter normally moves freely enough not to need flexible couplings.
Whenever sprinkler piping passes through floors or walls, adequate clearance should be provided. This will allow the piping to move freely during the vibrations. Clearances of one inch or more should be allotted for all piping smaller than 4 inches in diameter. A two-inch clearance is needed for all piping 4 inches and greater. The openings around the pipe should be sealed with an approved barrier. This barrier should consist of mineral wool or a weak, easily broken mortar.
During an earthquake, the larger and heavier mains will pull on the lighter branch lines. If the branch lines are held firm to the building, fittings can break due to increased stresses. Sway bracing will allow piping to move in a controlled manner. Risers need to be held in place with four-way braces. Four-way braces provide longitudinal and lateral bracing for the riser and adjacent mains. These keep the risers and larger mains aligned and minimize shifting. Two-way bracing provides either longitudinal or lateral bracing. These would be placed on cross-mains or branch lines.
All components are necessary to reduce vibration. The proper design will keep your systems intact and operational long after the quake has subsided.
