Pallet Rack Testing

Pallet racks and the importance of it’s testing

Both the components of pallet racks and the materials from which they are made are tested; the first to determine their strength and elasticity capacities, while the second establishes their tensile strength and ductility, i.e., the ability to bend. These processes meet the international standard, which specifies the parameters that must be considered in terms of product quality and safety.

Rack safety is the moral responsibility of the employer and carries significant legal liabilities (civil and criminal). However, managers should be aware of the potential hidden costs of a rack collapse:

• Replacing materials and damaged goods
• Use of temporary storage facilities
• General disruption
• Workers’ compensation, general liability, and other insurance rate hikes following the loss
• Legal expenses from defending actions resulting from an accident
• Potential fines relating to violations of statutory safety requirements.

To test or not to test

Predicting the structural behaviour of racking is difficult due to the uniqueness of all of its components. They are made of highly resistant steel profiles with thicknesses ranging from 1.8 to 3.0 mm, and are prone to global, local, and distortional buckling, particularly on the uprights. To that end, the behaviour of all unions between beams and uprights, or between base plates and uprights, can be added.

As a result, modelling in this type of steel structure differs from that used in building structures. Racking design is based on specific trials to determine the mechanical properties of key components and their connections in order to ensure maximum product quality.

We have over ten years of experience investigating and designing new solutions to obtain more resistant profiles that meet the needs of its customers. To manufacture new profiles, a very efficient methodology is used, which consists of four phases:

1. Preliminary design of the profiles according to the collective experience and know-how of teams of professionals and engineers.
2. Use of design software and calculations of finite element software like ANSYS, which is capable of determining the behaviors of the distinct parts of the racks. This way the most appropriate model is analyzed on a theoretical level and prototypes are constructed from the extracted results.
3. Performing tests in its own laboratories, located in URS’s technological testing area, which are set up to gather empirical data for the purposes of understanding the behavior of the different elements and their connections.

According to the kind of test performed, some of the following results will be obtained:

• Load failure: buckling is a phenomenon in the elastic instability that occurs when the structure is submitted to the action of forces. With this result which loads produce the failure in structural elements is known, and which are permissible taking into account a particular safety factor.
• Stress-strain curve: the full structural body, when withstanding a force, buckles and the stress-strain diagram of the load process allows the relevant magnitudes of the process to be obtained.
• Characteristic value: this refers to the maximum value that, statically speaking, must not be exceeded in order to certify and guarantee the characteristics of the distinct materials and profiles.

It is obtained via two distinct values:

1. Correction by material, depending on the actual vs. nominal characteristics of the components.
2. Statistical correction, according to the number of tests performed.

Specific element, specific test

The characteristics and behaviors of the materials and elements that comprise the racking have a direct bearing on the safety and durability of structures. As such, each one of the components and its connections are submitted to specific tests, in order to establish quality and guarantee its strength. Several of these tests are described below, in order to better understand the process:

Material testing
It is indispensable to know the physical properties of the materials that are used in engineering projects, and thus it is necessary to carry out specific tests. The racking components are manufactured out of carbon steel.

Basically, there are two tests:

Tensile testing: verifies the internal force in which the profile is placed under in the application of two opposing forces, which tend to stretch it. It is applied with increased traction until breakage takes place.

Bend testing: verifies that the material is able to bend to a required angle. In this way, the form with which you can work and prevent breakage is known by it being submitted to bending without cracking.

 

Pallet racking uprights are open profiles manufactured from thin cold-formed steel sheet metal. They are perforated all along their length. Specific tests are fundamental to evaluate the global behavior of the racking elements and connections.

Compression testing:  This consists of compressing an axially cut section of an upright, i.e., along it longitudinal axis, to observe how it influences the perforations within localized buckling.

The results of this test allow the determination of:

a. The effective area of the section.

b. The application point of the load maximum, which will serve as a reference in other tests.

This test can be performed on short uprights and on 1,200 mm sections, which correspond to the separation of the diagonal frame joints. Moreover, this is the way to verify the influence of distortional buckling.

Testing the bending uprights: The behavior of the upright’s bending stress is analyzed, i.e., applying a force along the length of its axis.

This study determines the section modulus of an upright section with regards to its long and short axes. This permits the evaluation of the favorable impact of the diagonals that form the frame latticework.

Furthermore, other tests exist for other racking components, such as the upright unions via a splice or the connection of the upright to the floor. The objective is to demonstrate rigidity and strength in light of the load of the racks themselves and the pallets deposited therein.

In the compression of short uprights, the following results can be obtained:

• a) Application of the very displaced force towards the open portion of the section.
• b) Application of the moderately displaced force towards the open portion of the section.
• c) Application of the very displaced force towards the frontal facet (core) of the section.
• d) Application of the moderately displaced force towards the frontal facet (core) of the section.
• e) Application of the force at the point that provides the most profile resistance (maximum load failure).

Tests on frames

Frames are the vertical elements composed of two slotted uprights and are perforated along the length of the profile so that beams fit flush together.

They are set up on the floor via anchored feet (base plates) situated on the inferior ends. The width of the frame will depend on the dimensions of the pallets.

As with individual uprights, the frame compression tests determine the axil section load capacity, taking into account the effect of the diagonals.

In this case, shearing tests are also performed on frames, which consist of applying two parallel and opposing forces to different uprights to verify the behavior of the shearing strength.

Tests on the beams and beams connectors
Beams are the horizontal and strengthening elements of the racks upon which the loads rest. They require bend tests to analyze buckling when a force is applied from above.

They also need very specific studies to evaluate their characteristics and to extrapolate the load maximum that can be exerted upon them and what is the rigidity and strength of its materials.

The shearing test of the beam connectors is intended to demonstrate if the prongs are sufficiently effective to withstand the load. A reverse shearing test is also performed, which demonstrates that the safety pins are effective in the event that the inferior portion of beams suffers a blow. This could occur if the forklift miscalculates the removal of the pallets from the shelves and accidentally bumps the beams.

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