UNI EN 16681: Anti-Seismic Design of Pallet Racking

Industrial anti-seismic shelving must be designed and manufactured in full compliance with specific national and European regulations, particularly in high seismic risk areas. The main reference for safety in Europe is UNI EN 16681, a standard that sets out the criteria for the anti-seismic design of steel pallet racking. Its goal is to ensure the stability and resistance of the structure during an earthquake.

It is important to highlight that UNI EN 16681 applies exclusively to this type of storage system and does not cover mobile racking, drive-in or drive-through systems, cantilever, or static shelving systems in steel. Moreover, it integrates with other key standards, including:

• EN 1998-1 (Eurocode 8), which regulates the design in seismic areas.
• UNI EN 15512, which concerns the general calculation principles for steel shelving.
• UNI EN 15635, which defines the requirements for the use and maintenance of the shelving.

According to the regulation, pallet racking must be designed to meet the following requirements:

• Resist seismic events without collapsing, while maintaining residual load-bearing capacity, strength, and ductility.
• Ensure structural integrity, minimising permanent damage after an earthquake.
• Account for pallet movement. During a seismic event, pallets may slip or overturn, especially at higher levels. The standard therefore requires preventive measures: in seismic-prone areas, accessories or solutions must be adopted to prevent pallets from falling within the racking system.

Seismic action: factors to consider

When assessing seismic action on racking and similar structures, it is fundamental to take into account a number of factors, some of which at the same time as the seismic action itself.

Actions to be considered simultaneously with seismic action:

– Permanent static loads: weights of materials, structures, or equipment fixed permanently.
– Variable load units: pallets, goods, and packages of different sizes.
– Snow (variable action).
– Loads from walkways and floors (variable action).
– Handling equipment (if supported by the racking): when mechanical handling systems (forklifts, stacker cranes, or others) are supported by the racking, this must be considered in the design phase. The supplier of the handling equipment must provide the necessary data to the racking supplier.

Actions not to be considered simultaneously with seismic action:

– Wind: assessed separately, not combined with seismic action.
– Horizontally or vertically positioned loads: occasional forces applied to the racking (e.g. load tests).
– Functional loads caused by equipment guided by the racking (if not supported by it).
– Handrail pressures
– Thermal loads: variable loads caused by temperature variations.
– Global imperfections
– Impact and other accidental loads, such as collision with a forklift
– Maintenance loads: weights related to maintenance activities.

Another aspect addressed by UNI EN 16681, directly related to seismic action, concerns the design working life of shelving, already defined in detail by NTC 2018.

Specifically, UNI EN 16681 establishes the following design working lives:

• 50 years for self-supporting warehouses.
• 30 years for shelving installed in seismic areas.
• 10 years for static shelving projects.

Based on the design life, the seismic analysis is carried out using the modal response spectrum method, considering both the horizontal and vertical components of seismic action. The seismic mass must include all permanent and variable loads supported by the racking, providing a complete overview of the forces involved.

Design approaches: dissipative vs. non-dissipative structures

To ensure seismic resistance of the shelving, UNI EN 16681 defines two distinct design approaches, based on the behaviour factor “q”, which represents the ductility of the structure:

1. Non-dissipative structure (factor q ≤ 2): predominantly elastic behaviour, mainly based on material strength. In this case, seismic effects are assessed using a global elastic analysis, without considering significant material non-linearities.
2. Dissipative structure (factor q > 2): allows certain parts of the racking to undergo controlled plastic deformation during a seismic event. Combined with the elastic response of the remaining elements, this enables the structure to dissipate energy and withstand seismic stresses more effectively.

The choice between the two methods directly affects material selection, joint design, and calculation criteria.

Structural regularity and anchoring

Another fundamental principle of UNI EN 16681 is structural regularity, which is crucial for improving racking performance during an earthquake. Uniformity in load distribution, beam levels, and bracing systems is therefore required, in line with the regularity criteria of the standard.
Anchoring is equally crucial: it must comply with and be certified under ETAG 001, especially for non-dissipative structures. Designers must carefully assess concrete conditions, including possible cracking, which could compromise anchor safety even in low-seismicity areas.

UNI EN 16681 is a fundamental standard to ensure the safety and reliability of pallet racking in seismic risk areas. Choosing solutions designed in full compliance with the regulation is therefore essential for any company wishing to manage its warehouse safely and responsibly.

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