Pallet Racks and Seismic Design

While pallet racks are not buildings, they are considered building-like, and therefore, just like a building, they need to be designed and engineered for safety in the event of seismic activity. California was the first state to require seismic engineering for pallet rack systems, but now many other regions of higher seismic activity, including northern New Jersey, South Carolina, Massachusetts, Memphis, St. Louis, Buffalo, and Atlanta, require seismic design of pallet racks. It is interesting to note, however, that about half of the major destructive earthquakes occur on previously unknown faults.

According to OSHA, all goods, materials, and equipment at work sites must be stacked, stored, and secured in such a way that they do not flow, move, roll, or collapse. Although rack collapses due to earthquakes are relatively rare, they can be devastating. In areas that are at known risk for seismic activity, your pallet rack must be stronger and able to withstand the forces of the earth’s movement without collapsing and damaging your inventory, or injuring (or killing) employees.

Pallet rack systems designed for seismic areas are constructed differently than conventional racking. They are typically more costly, as well, because they are designed, engineered, and constructed specifically to resist seismic events.

The Specification for the Design, Testing and Utilization of Industrial  Steel Storage Racks (ANSI MH16.1: 2012) states:

Where customer specifications require or local building codes dictate that provisions be made or earthquake effects and associated lateral forces, customers, or their representatives, shall bring such requirements to the attention of the rack manufacturer.

How do you know if your rack system design needs to account for seismic forces?

Seismic Categories

The old seismic zones (0-4), which are are no longer used, were based upon seismic ground motion that corresponded to the probability of occurrence within a zone. All structures within a zone were designed for the same requirements.

But, building codes today use what are now called Seismic Design Categories (SDC), which range from A to F. These categories are a function of the seismic hazard at the particular site, as well as the type of buildings and the soil data at the site. Areas in Seismic Design Category B and above face the potential of seismic activity to varying degrees. Each city block in a seismic area will have different codes, and you have to pass the inspection for that specific parcel of land you are located on.

Seismic Design & Calculations

Seismic design is quite site specific, and you should bring to the rack manufacturer ’s attention the specific local requirements, including building codes, the specific installation location, any knowledge of the supporting concrete slab, and any information about the below-slab soils and their properties.

Here are some general rules set forth by ANSI MH16.1: 2012 regarding storage racks and seismicity:

  • Storage racks that are more than 8 feet (2.44 m) in height to the top loaded shelf, and are not connected to buildings or other structures, must be be designed to resist seismic forces.
  • Adequate clearance shall be maintained between the storage rack and the building or other structures to avoid damaging contact during an earthquake
  • Soil classification will affect the design of your storage rack, so it’s important to know this.

Seismic design of storage racks can include calculations for these factors:

  • Minimum seismic forces at-grade elevation or above-grade elevation.
  • Redundancy factor
  • Seismic response coefficient
  • Design spectral response acceleration parameters
  • Site coefficients and adjusted maximum considered earthquake spectral response acceleration parameters
  • Connection rotational capacity
  • Seismic displacement
  • Seismic separation
  • Vertical distribution of seismic forces
  • Horizontal shear distribution
  • Overturning
  • Concurrent forces

Seismic specifications in many areas of our country are critical to the safe operation of storage racks and knowing the code in your location if you are in a riskier seismic zone is very important. If you have questions about seismic design and permitting your rack in seismic areas, contact us here or call 800-230-8846.

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