Seismic Restraint and Expansion Joint in a Parkade Main
A 100 mm Schedule 40 steel main runs 58 m through an unheated concrete parkade. It is suspended from the slab by 12 mm threaded rods and clevis hangers at 4.5 m centres. The main turns 90 degrees 20 m from the riser and crosses a 150 mm building expansion joint at 34 m. The building is in a region with a design spectral acceleration that requires seismic restraint. The contractor has installed lateral sway bracing only at each end of the run and has clamped the pipe rigidly on both sides of the expansion joint. The sprinkler layout is otherwise complete. The AHJ has flagged the support and seismic details before the hydrostatic test. The parkade slab has no finished ceiling and the pipe is exposed.
1. Evaluate the hanger spacing and seismic bracing layout. What is required?
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Check two separate limits: hanger spacing/load and seismic restraint.
For 100 mm Schedule 40 steel, NFPA 13 permits hanger spacing up to about 4.6 m for this size. The 4.5 m spacing is therefore within the prescriptive limit, provided the hanger and 12 mm rod are listed and the concrete anchor is rated for the load. A water-filled 100 mm main weighs roughly 18 kg/m, so a 4.5 m bay imposes about 81 kg plus valve and brace loads. Verify the anchors and rods for that load.
The seismic layout is not acceptable. Lateral sway bracing is required at each end and at intervals not exceeding 12 m. A 58 m run needs intermediate lateral braces so no spacing exceeds 12 m - for example at 0, 12, 24, 36, 48, and 58 m. The contractor has only the two end braces. Longitudinal bracing is required at intervals not exceeding 24 m, typically at 0, 24, 48, and the end, with the end brace counting.
The expansion joint cannot be clamped rigidly. The pipe must be free to move: use a sleeve or flexible coupling with clearance, and place sway braces on each side so each side is independently restrained.
2. What should be changed before hydrostatic testing, and what documentation should be provided?
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Before testing, direct the contractor to remove the rigid clamps at the expansion joint and install a proper clearance sleeve or listed flexible coupling. Add the missing lateral and longitudinal sway braces per an engineered layout. Verify that brace attachments are made to the structure, not to other pipes, and that hanger rods, clevis hangers, and concrete anchors are rated for the calculated loads.
Documentation should include revised support and seismic drawings, manufacturer listings for braces and flexible couplings, anchor submittals, and an inspection record. After corrections, perform the hydrostatic test at the required pressure and duration, and observe the expansion joint for movement. If the joint remains restrained, thermal movement can crack pipe, pull anchors, or damage the sprinkler system.