By nature of their application, trailers tend to spend more time away from the home base than in residence. For that reason, it becomes very important to mitigate the wear-and-tear damage related to cargo shifting, loading and unloading, all of which can have a direct impact on doors, lift gates and floors. You can do this by knowing what kind of flooring to spec.
Chris Lee, vice president of engineering at Great Dane Trailer, says that “at Great Dane, we take many factors into consideration when recommending a flooring option to our customers.” Some of the main considerations he mentions include:
- Forklift truck axle weight (load): The industry usually uses TTMA RP 37.
- Number of load cycles per day: For high cycle loading conditions, Lee recommends a higher floor rating.
- Fail safe design: The entire trailer deck system, including the floor, crossmember fastener connections and rails, must be designed and assembled to withstand both concentrated and fatigue load. Any one component failure can lead to entire floor system failure.
- Wood spices: In general, hardwood spices are used—oak, maple, apitong, etc. The spices play a major role in the durability of the floor.
- Moisture permutation for water tightness: Glue and sealant applied on floor planks is critical to preventing water leaks.
- Coating (both top and bottom) needs to resist damages from weather and road debris.
- Maintenance: The individual boards need to be designed and assembled for easy replacement and availability.
- Weight: This is an important factor since the floor takes up a big portion of trailer weight. Today, composite floors can provide significant weight savings.
- Floor thickness: This affects floor weight and load rating. The right floor thickness needs to be determined for particular options and weight.
“The primary things to consider when choosing the right trailer flooring are the overall weight of the payload, the type of product getting loaded and how the product is getting loaded,” says Steve Zaborowski, senior vice president with XTRA Lease. “Fleets should look at all of the items contributing to the usage of the trailer, including the forklift weight, pallet weight, freight weight and the number of cycles you’re operating to load the trailer. Some product applications require more durability and strength than others, such as beverage products, rolled paper and heavy industrial products.”
Traditionally, fleets spec trailer floor ratings in the 20,000-lb. range, with 1 3/8-in. floors that are built on 12-in. centers. At XTRA Lease, for example, trailers are built for a wide variety of uses, spec’ing trailers for added durability and strength. XTRA specs trailers with 1 3/8-in. oak floors rated up to 24,000 lbs. and built on 10-in. centers. Additionally, XTRA installs a 27-in. deep threshold plate at the entry point, along with two crossmembers in the last 4 ft. of the trailer to provide additional strength, Zaborowski says.
For heavier payloads, some fleets may take weight out of the trailer to accommodate the freight. They might choose a combination of wood and composite material to get the same strength and still reduce the tare weight. Fleets can also use aluminum floorboards to take weight out.
Choosing the right doors
“The majority of less than truckload [LTL] carriers use roll doors, whereas truckload [TL] carriers use swing doors,” he says. “Since LTL carriers make frequent stops and multiple door open-close operations, they need quick and less operationally laborious roll doors. At the warehouse dock, the roll door is also preferable since the drivers do not have to pre-open the door before backing into the dock. The TL carriers normally make long hauls and have fewer door opening and closing events, so the swing door better fits their operations. Here are the challenges:
- Thermal performance: The thermal efficiency of the door is important for temperature-controlled trailers. In general, swing doors are more thermally efficient than roll doors because swing doors provide better air tightness.
- Over-the-road and off-highway operations: In general, over-the-road trailers require fewer door hardware and structure reinforcements for the frame since there is less trailer movement (i.e. racking). However, off-highway trailers require more door hardware and frame reinforcements to prevent rear frame racking. Swing doors typically provide more structure reinforcements to the frame than roll doors, so the frame used with swing doors requires fewer structure members.
- Door opening dimensions: Swing doors provide more opening dimension than roll doors because of fewer frame structure requirements. Therefore, bulk carriers typically use swing doors.
- Impact resistant strength: Swing doors provide better impact resistance due to the door geometry and hardware reinforcement.
- Door hardware: The number of hinges, locking rods, fasteners and door blank thickness varies widely depending on the carriers’ operations.
- Corrosion resistance: Both the door panel and hardware should be properly coated to withstand road salts and chemicals that can cause corrosion.”
“We’ve gone standard with a 10-mm composite plate door material for all of our swing-door vans,” XTRA’s Zaborowski notes. “This type of product helps eliminate corrosion and damage. By taking the wood material out of the door, we’re able to provide a thinner and stronger door. On roll-door vans, we also use composite panels, and we install overhead door track protectors to avoid damage that can be caused by forklift trucks during loading or unloading.”
“The duty-cycle of the unit should be the main consideration,” said Gary Fenton, vice president of engineering with Stoughton Trailers. “Fleets need to understand the method of loading the cargo, the force applied to the floor through the forklift tires that results and the imposed load and footprint of the static cargo itself. The frequency of loads per period of time is also a consideration. It is also important to know the condition of the cargo as loaded [dry, wet, acidic, corrosive, etc.]. When considering doors, the following questions need to be asked:
- Are the units to be secured all the way to the docking of the trailer? If so, this would mandate a roll-up type door operation.
- Is the cargo subject to shifting or to be operated in rail service? (This can affect door stiffness and number lock rods and hinges to be included.)
- What door opening is specified? Is there a requirement for insulation?
- What level of security is desired?
- What color match or aesthetic covering is required? Is there a weight consideration?”
Lift gates and structure
When specifying lift gates, it’s all about the supplier and type of lift gate—tuck away, rail lift, etc. The interface and method of connection is dependent upon the lift gate brand. Dimensional and strength considerations must be matched to the specific type and brand of supplier. Thieman’s director of the engineering department, Terry Eyink, lists the following as tailgate spec’ing considerations for fleets:
- What’s the heaviest load that will be lifted?
- Will this be a typical load lifted frequently every week, or only on rare occasions a few times a year?
- Will the loads be lowered from bed height or raised from the ground typically? Each lift gate has an operating bed height range for which it is designed and deviating from that range can cause issues related to ground clearance, inability to reach the ground, etc.
- How many up/down cycles will the lift gate see on a typical day?
- How many of these cycles will be back to back or at one stop?
- How much drive time in a typical day will be involved?
- Do trucks have anti-idling feature? This can help determine if auxiliary battery kits are required and whether optional charging methods are needed.
- What is being loaded on the lift gate (carts, pallets, etc.) and how is the load transferred on and off the lift gate platform both at ground and at truck bed height?
- Will the lift gate be backed up to a dock?
- Will the truck or trailer be loaded with a forklift, when the truck is at a dock and the lift gate is not being used?
- Are cart stops or other options desired for the given task? And is a level ride lift gate desirable?
Structurally, the trailer frame on which the lift gate is installed must be structurally sound to meet the maximum load rating for the lift gate, according to Great Dane’s Lee. If the trailer frame needs to be modified to meet lift gate dimensional requirements, then the trailer OEM must be consulted for retrofit modification.
“It is preferable to have the trailer rear frames and under frames pre-designed to accept particular lift gates,” Lee says. “Additionally, electrical and hydraulic power line routing must be considered in the design of the trailer for proper installation.” Also consider that the rear underride guard needs to be compliant with NHTSA regulations. And the trailer floor should be flush (at the same level) with the lift gate extension plate.
Read more on trailers from Fleet Equipment‘s latest issue: from trailer tires to lighting to electrical systems.