What is Cantilever Beam Deflection?
Cantilever beam deflection is the gradual downward bending of cantilever arms under heavy loads. A small amount of deflection is average for cantilever arms, but too much threatens the rack system and its structural viability.
Before we begin, let’s clear up the term “cantilever beam deflection.” Typical pallet racking consists of upright frames and horizontal “beams” that connect one frame to the next. Cantilever racking has arms that protrude out of the system rather than beams.
Although they are officially called arms, many people refer to cantilever arms as beams since they perform the same function – supporting the load.
When Does Cantilever Beam Deflection Occur?
Cantilever arms deflect under loads too heavy for the arm’s capacity rating. Improper loading techniques can also cause arms to deflect or other damage to occur. Improper loading includes point loads and overloading.
Point loads (also called tip loads and end loads) are placed at the end of the cantilever arm, not centered or near the upright. Point loading causes unnecessary stress concentration on cantilever arms and may result in cantilever beam deflection where the ends of the arms bend downward.
Overloading is storing more weight on a cantilever arm than intended. Some arms have higher storage capacities to handle heavier loads. Low-capacity arms must be properly loaded with the right amount of product to avoid overloading and deflection.
5 Tips to Avoid Cantilever Beam Deflection:
Brace set length
Each arm should carry equal weight. Cantilever beams must be equally spaced for the product to achieve equal distribution across arms. Cantilever brace sets determine arm spacing, so choosing the right brace set length is vital to prevent cantilever arm or load deflection.
Choose the right arms
There are three factors to choosing the right cantilever arms: Arm length, arm capacity, and arm pitch.
The arm length should match the size of the load. If the load overhangs the end of the arms, it is incorrectly stored and may lead to deflection.
The arm capacity should meet or exceed the capacity being stored. When choosing cantilever arms, always refer back to the heaviest load and possibly slightly heavier to be safe.
Choose between straight and inclined arms depending on the product stored. If the product is cylindrical and at risk of rolling forward, inclined arms will work best.
Properly load the arms
Proper loading is a crucial factor in avoiding cantilever beam deflection. Shock loads occur when the load is dropped suddenly onto the arms and can cause arm damage and deflection. Load slowly to avoid shock loads.
Avoid point loads with uniform distributed loads (UDLs). Achieve UDLs by centering the product on the arm or as close to the upright as possible. Evenly distributing loads is standard practice and the best strategy to extend arm life.
Leave overhang
Although overhang off the ends of the arms is improper practice, there is a type of overhang that is good and allows equal weight distribution between arms. It is essential to enable overhang off the first and last arms to the left and right. This allows each arm to support the same weight without putting more strain on any one arm (particularly the first and last).
The proper amount of overhang is determined by the distance between arms. It is recommended to distribute the load so that 25% of the load overhangs each side. Another factor that determines overhang is how rigid the load is.
Implement forklift training
Good lift truck drivers will follow responsible forklift principles. Ensure every certified lift truck driver is extensively trained and screened with ongoing quality checks. Forklifts are the primary cause of pallet rack damage and cantilever arm damage.
Leaving at least 6” of vertical lift clearance between the top of the product and the next arm, allows forklift drivers to safely load and unload the racking.
Allowable Deflection for Cantilever Beams
Both pallet racking and cantilever racking have some percentage of allowable deflection. It is usual for deflection to occur under heavy loads – it’s the natural effect of gravity.
All cantilever arms are manufactured with at least a 2-degree pitch – this is to compensate for deflection. When fully loaded, the arm should never bend lower than parallel to the floor.
It is essential to be aware of your storage system’s limit by calculating allowable deflection.
How to Calculate Cantilever Beam Deflection
Typical pallet rack beams have a formula to calculate acceptable deflection. For cantilever racks, you really can’t apply a formula in the same manner.
A cantilever arm’s pitch determines if the arm is over-deflected. The arm, fully loaded, should never be less than parallel to the base – or less than 90 degrees. If an arm is less than parallel, the load could slide off onto the ground. A level put on the load (if it is a level surface) should never be less than plumb.
Cantilever Arm Replacement
Have your cantilever arms been damaged or deflected past the allowable limit? In the image to the right, the cantilever arm has sustained damage from deflection including a warped end connector, arm damage, and bent arm lip. Cantilever Rack Now offers replacement cantilever arms for scenarios like this.
For help choosing replacement arms, call CRN at 888-680-2256. We happily answer any questions and help bolster storage systems with new parts.
