A pallet rack system engineered to resist earthquake forces, typically with larger base plates, more or heavier anchors and stronger bracing, where the local building code requires seismic design.
Detailed Definition
Seismic rack is not a separate rack type. It is selective, drive-in, push-back or other racking designed to resist the sideways forces an earthquake puts on loaded frames. The design follows the locally adopted building code, which in the US generally points to ANSI MH16.1 for steel storage racks. An engineer uses the site's seismic design category, soil conditions, rack height and pallet weights to size the upright frames, beams, connectors, base plates and anchors. Permits and stamped calculations are often required.
What changes in a seismic design
During an earthquake, loaded rack sways and can rock on its base, so the critical points are the floor connection, the frame bracing and the beam-to-column joints. Seismic designs typically use larger base plates, more or larger anchor bolts, heavier or more closely spaced bracing, and beam connections checked for the expected forces. The concrete slab also has to be checked, because anchors are only as strong as the concrete they sit in. Some specialized systems use base isolation to reduce the shaking that reaches the rack.
How loading affects the design
Seismic calculations assume specific load weights at specific beam levels. Putting heavy pallets on upper levels raises the center of gravity and can exceed what the design allows, even if each beam pair is within its rated capacity. Load plaques should state the allowed weight per level, and operators should follow them. Some designs also call for row spacers, wire decking or load stops to help keep pallets in place.
Questions to ask before buying
- Were the calculations done for this address and its seismic design category?
- Does the package include a slab and anchor check?
- Who prepares drawings and handles the building permit?
- What review is needed if beam levels are moved later?
Related Glossary Terms
Frequently Asked Questions
Do I need seismic rack outside California?
Possibly. Seismic requirements come from the building code your jurisdiction has adopted and the seismic design category assigned to your specific site, not from the state name. Several regions outside the West Coast, including parts of the central and eastern US, can have seismic requirements that affect rack design. Ask the local building department what applies and have the rack supplier's engineer confirm the design criteria for your address.
Can I move beam levels on a seismic rack?
Changing beam heights changes how weight is spread up the rack and how it responds to shaking, so it can invalidate the original calculations. Before reconfiguring, ask the rack manufacturer or a qualified engineer to review the new layout, confirm the capacities, and issue updated load plaques. Some jurisdictions also expect a permit revision for permitted rack. Keep the revised drawings with your rack records.