Wiley Metal has fabricated parts and accessories for the truck trailer industry for decades. We are proud to count some of the largest and most world-renowned truck trailer manufacturing companies among our clients.
These companies have high expectations and they challenge us to produce world-class truck trailer parts and accessories. Door track protectors, rub rails, trailer scuffs, thresholds, and crossmembers are just some of the products we fabricate. Some of these are structural while others protect truck trailers from damage. All are engineered to help truck trailers work harder and last longer. Here’s a closer look at one part that seldom gets the respect and attention it deserves: the crossmember.
A Critical Component
A lighter dry van or flatbed trailer can carry a heavier payload. That’s why strength-to-weight ratios are part of semi-trailer engineering. The best way of maximizing this ratio is by using beams with an “I” profile.
An I-beam resists bending through simultaneous compression and elongation of the upper and lower webs. These are joined by a flange, and the depth of this flange is the primary factor in determining the bending resistance of the beam: the deeper the flange the stronger the beam. However, when it comes to resisting lateral loads, it’s the width of the webs that matters most, with wider being stronger.
Where I-beams don’t perform so well is in resisting twisting or torsional loads. Neither the webs nor the flange can do much against these forces, but fortunately, in semi-trailers, they’re usually low.
Wear, Tear, and Damage
Look under any large trailer and you’ll see the floor is supported by massive I-beams running from front to back, and a ladder-like structure of crossmembers, also with the same “I” profile. These crossmembers support the decking and bear the weight of the payload.
Like other components of a truck trailer, semi-trailer crossmembers are subject to weather, wear, and aging. They can also be damaged from both above and below.
Damage from above happens when the load is concentrated over too small of an area or sharp objects are dropped on or dragged across the decking. It’s also possible for chemicals to leak and cause corrosion. Damage from below can result from accidents or again, from corrosion. When a semi-trailer crossmember is damaged, it needs addressing quickly to avoid sudden and catastrophic failure.
Load Bearing Capabilities
Crossmembers in semi-trailers are designed to achieve a target “beam rating”. This is the maximum weight that can be supported by a 4′ section of decking. In a dry van, where the greatest loads come from a fork truck driving into place or unloading pallets, the beam rating is typically around 52,000 lbs. A flatbed trailer intended for transporting coil could require much higher strength, so the beam rating might be as much as 80,000 lbs.
When Damage Occurs
Minor scrapes on the floor of a trailer are rarely a problem. If, however, gouges exceed ½ inch in depth there may be damage to the crossmembers beneath. Such situations warrant close visual inspection.
If one or more crossmembers have become bent, either vertically or laterally, it may be possible to straighten them, so long as they are not pulled away from the trailer’s floor. However, a cross member should be replaced if it is bowed downward more than 1/4″.
In a new trailer, each crossmember is designed to meet the requirements and fabricated to the drawing specifications. This generally means each crossmember is the same, although there may be situations where deeper or less deep flanges and wider or narrower webs are needed in different parts of the trailer. More often, though, local load handling requirements can be met by either changing crossmember spacing or, outboard of the longitudinal I-beams, adding bracing.
When replacing crossmembers in an existing trailer, the new part should match the old, both in dimensions and in material specifications. Deviating from what was used before risks either creating an area of local weakness or adding more strength, and weight, than is required.
When it comes to crossmember materials, there are two choices: aluminum and steel. Generally, trailers are designed with one or the other. Aluminum doesn’t have the ultimate strength of steel, but it does have a higher specific strength. This means that while an aluminum trailer will need larger crossmembers to meet a specific beam rating target, it will likely be lighter than one of the same strength fabricated from steel. A secondary benefit of aluminum is the corrosion resistance it provides, eliminating the need for painting or coating and extending trailer life.
Durability Starts with a Great Part
The team at Wiley Metal are experts in designing and fabricating semi-trailer crossmembers. These structural, load-bearing components not only need to support the floor of a semi-trailer and its contents but do so efficiently. This means engineering crossmembers with high strength but low weight. Our efficient designs maximize the weight that can be hauled, creating more fuel-efficient trailers. In addition, our semi-trailer crossmembers are designed to provide years of service and value.
If you are a semi-trailer manufacturer in search of American-made truck trailer metal fabrications, contact us. We will be happy to provide our resume of industry experience and explain how that experience can work for you. If you are in the market for replacement semi-trailer crossmembers contact us as well. At Wiley Metal, we take pride in fabricating products that provide value year after year. We would welcome the opportunity to assist you.