Seismic Bracing Design

Two objectives, every time

Non-structural components need seismic protection of their own, separate from the structural design of the building. Every bracing design we produce works to two objectives:

• Keep movement within limits. Displacement during an earthquake stays inside what the system and its connections can safely absorb.
• Carry the load into the structure. Every brace generates a force, and every design accounts for where that force goes and what the structure needs to receive it.

Controlled movement plus a clear load path is what separates seismic restraint from hardware that is simply bolted on and hoped for the best.

We won’t brace what doesn’t need it

Not every component needs bracing. Services on short hangers, smaller pipe and duct sizes, and some trapeze-mounted items often fall within the exemptions of the applicable code. We check this before we design anything, so you do not pay for hardware, drawings and installation labour your project does not need.

01Bracing for building services

Cable or rigid

Where the geometry allows it, cable bracing is often the more efficient choice: cables work in tension only and absorb movement without the stiffness, and the cost, of rigid braces. Rigid braces carry compression too, so they must be checked for buckling, which adds calculation, hardware and installation work. We choose case by case, by span, load and load path, not by what is easiest to specify.

Fire sprinkler systems

Sprinkler and standpipe piping carries its own seismic bracing requirements under NFPA 13. We handle that scope inside the same design package, not as a separate job. For fire protection work beyond bracing, see our fire safety engineering service.

What you receive

• Bracing calculations for pipework, ductwork, cable trays and sprinkler piping
• Assessment of where bracing is, and is not, required
• Layout drawings showing restraint locations across the services scope
• Installation details for site use

02Bracing for suspended equipment

Equipment hung from the slab — fan coil units, air handling units, fans, tanks — behaves differently from a pipe run. Its mass is concentrated, so the seismic force is concentrated too, and it has to be restrained in every horizontal direction, not only across a run.

Hanger rods take the uplift

Under seismic load a braced unit pulls on some hanger rods and pushes on others. A rod in compression can buckle, so we check every rod and specify rod stiffeners where the length and load require them.

Play video: ARS-C Rod Stiffener (opens YouTube)

Isolated equipment: restrained, not fixed

Plant on spring hangers is resiliently mounted yet seismically restrained. The bracing must not short-circuit the isolation. Cable restraints are installed with a small, controlled slack: in normal operation the unit floats on its springs, and in an earthquake the cables take up the movement before it becomes damaging.

How a bracing project runs

1. 01
   Scope review

   Drawings and equipment schedule in; what needs bracing, and what is exempt, out.

2. 02
   Calculations

   Seismic forces, brace spacing, connection and anchor checks to the applicable code.

3. 03
   Layout drawings

   Restraint locations across the full services and equipment scope.

4. 04
   Installation details

   Brace, hanger and anchor details for the site team.

5. 05
   Site verification On request

   Inspection of the installed bracing against the design. Part of the package when the project needs it; the design stands on its own without it.

What seismic bracing does — and doesn’t — do

Bracing keeps a component in place and carries the seismic loads it generates into the structure. It does not, by itself, prove the component’s internal integrity, or that it still works after the event. Those questions are answered by analysis or testing, and they apply mostly to floor-mounted and freestanding equipment.