Hangers, Supports, Sway Bracing, and Seismic Protection
Support the pipe, restrain the system
Hangers carry gravity loads; sway bracing resists lateral and longitudinal movement during an earthquake or a major flow change. Hangers must be listed, attached to building structure, and sized so the rod and attachment carry the wet or dry weight of the pipe plus fittings and water. Never hang sprinkler pipe from another pipe, duct, or ceiling grid. The first hanger near a pipe end is limited to a short distance (3 ft is the familiar figure), and hanger spacing follows the code table for pipe size - smaller pipe is supported more closely than large mains. Verify the table in your code edition rather than reciting it from memory.
Seismic restraint basics
Lateral braces act perpendicular to the pipe; longitudinal braces act along the pipe axis. Typical maximum spacing is 40 ft for lateral and 80 ft for longitudinal bracing, with braces placed near the ends of runs and at changes of direction. Braces work best installed between about 30° and 60° from horizontal; a brace laid nearly flat or nearly vertical is ineffective. Flexible couplings and clearance from structure allow controlled movement instead of breakage.
Traps
- Assuming braces can attach to anything; load path to structure matters.
- Forgetting that seismic bracing generally applies only to pipe of a certain size and larger (commonly 2 in. and above) - smaller line is still restrained per code.
- Confusing lateral and longitudinal spacing limits.
Worked example
A 120 ft main needs lateral bracing at intervals not exceeding 40 ft, so at minimum braces near each end and one near mid-run; longitudinal bracing at 80 ft means at least two along the run. Each brace must land on structural members capable of taking the load.