Section 13.3.1/Seismic Design for Nonstructural Components
ASCE 7-22 Section 13.3 provides the Fp seismic force equation for anchorage and bracing of MEP equipment, piping, and architectural components.
Nonstructural components (mechanical equipment, piping, ductwork, electrical panels, ceiling systems, partitions) must be designed for seismic forces using the equation: Fp = 0.4 SDS Ip Wp (ap/Rp) (1 + 2 z/h), where SDS is the design spectral acceleration, Ip is the component importance factor, Wp is the component weight, ap is the component amplification factor, Rp is the component response modification factor, z is the component height in the building, and h is the building height. The force increases linearly from ground level (z/h = 0) to the roof (z/h = 1). The 2022 edition introduced significant changes to this equation including new height amplification and short-period factors.
Why this section exists
Nonstructural damage typically accounts for 70-80% of earthquake losses in buildings. An HVAC unit that slides off its roof curb, a water heater that topples, or a suspended ceiling that collapses can cause injuries, disrupt building function, and trigger secondary hazards (water damage, gas leaks, fire). The seismic force equation ensures equipment is anchored and braced to resist the amplified accelerations within the building, which are highest at the roof.
What plan reviewers look for
Plan reviewers check the mechanical and electrical drawings for seismic anchorage and bracing details on all equipment. They verify the Fp calculation uses the correct SDS, importance factor, component factors (ap and Rp from Table 13.5-1 or 13.6-1), and height factor. They check that the anchorage design (anchor bolts, vibration isolator snubbers, pipe bracing) resists the calculated Fp force.