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The design trend of dry van trailers in North America includes technologies to reduce weight and improve the longevity of trailers. It is no surprise that the next generation of trailers is currently built with glass fibre reinforced oak flooring, a perfect combination of durable oak and high strength composite.
(Published on October - November 2007 – JEC Magazine #36)
GOPAL PADMANABHAN, VP - PRODUCT ENGINEERING,
BRUCE BADER, PRESIDENT, HAVCOWOOD PRODUCTS LLC
A durable, versatile trailer floor
The lifetime of van trailers is normally estimated to be about seven years. In recent times, the transportation industry has been making efforts to engineer trailers so that their lifetime can be extended to ten years or more. Moreover, weight reduction has become necessary due to the high cost of fuel. The transportation industry is also aiming to reduce maintenance costs by specifying more durable parts. Large transportation companies need to operate standard trailers in varied applications such as general freight and specialized transport of heavy and weightsensitive loads like paper rolls and beverage, or tough use in the automotive industry. A durable and versatile trailer is a flexible and productive asset. However, fleets do not like to add weight to trailers by using a heavier conventional floor system to obtain the needed higher load ratings for the versatile trailers. These demands are being solved by incorporating high strength composite materials. Many fleets are willing to bear a higher upfront cost for durable, lighter and versatile trailers since they provide tangible benefits during road service and have a higher trade-in value.
Laminated oak flooring has been successfully used in dry-van trailers for more than four decades in North America. Due to its natural properties like high strength, resistance to decay, nailability, wear resistance and plentiful availability, oak is the preferred hardwood for making van trailer flooring in North America. Even though conventional wood floors can be strengthened by adding additional cross-members, there is a significant weight penalty. Stronger, lighter and fatigue-resistant composite flooring has been developed by Havco to address this issue. Composite flooring is made of laminated oak boards and glass fibre reinforced epoxy panel. This product has been field tested and road-service proven in trailers for more than ten years. It has been commercially produced since 2000. Composite flooring offers higher strength, resistance to fatigue, moisture protection, longer life, and weight savings compared to conventional wood flooring. Composite flooring has a thin layer of glass/epoxy panel adhesively bonded to the bottom side of each laminated oak floorboard. Typically, eight floorboards make up a trailer floor. A polyurethane hotmelt adhesive is used for bonding the composite panel to oak. The top side of each composite floor board is composed of laminated oak as in conventional wood flooring (Figure 1). Surface characteristics of wood, appearance, nailability, installation method, etc., are preserved while the high strength, environmental resistance and fatigue resistance of glass/epoxy panel are additionally incorporated into the flooring. The mechanical strength properties of the composite flooring (Figure 2) are significantly higher than those of the conventional wood flooring. This aspect allows the use of thinner composite boards leading to weight savings of about 103 kg per trailer.
The glass/epoxy panel of the composite flooring is produced by a continuous lamination process. Continuous roving of E-glass fibres is used along with woven glass as the reinforcement. Continuous roving provides longitudinal strength and stiffness to the floor boards while the woven glass roving provides transverse strength properties and resistance to board splitting. The glass reinforced panel has a tensile strength of about 900 MPa and a tensile modulus of 40 GPa. The nominal thickness of the panel is about 1.3 mm. The same thickness of composite panel is used on all composite floors irrespective of their overall thickness. By varying the thickness of the wood layer in the composite floor, higher structural properties are obtained at the lowest additional cost. At the same thickness, a composite floorboard is about 90% stronger than an oak floorboard (figure 3).
The overall thickness of the composite floor is determined by the desired floor rating (7,257 to 10,886 kg). Typical thicknesses of composite flooring are 26.9, 28.5, and 30.2 mm. The most common thicknesses of conventional wood flooring are 33.3 and 35 mm. Reduction in thickness compared to conventional wood flooring is made possible due to the higher strength of composite flooring. Typically, composite flooring saves about 6.3 mm of wood thickness while providing comparable or better performance than conventional wood flooring.
Lifetime economic benefits and ROI
The total cost of composite flooring includes the cost of the wood board, the composite panel, hotmelt adhesive and labour for the composite bonding operation. Savings are achieved through the use of thinner layers of wood since thinner composite flooring is structurally equivalent to thicker conventional oak flooring. However, the net cost of composite flooring is higher than the cost of equivalent oak flooring and accordingly, the initial purchase price of composite flooring is also higher. The economic benefits of the composite flooring are derived as follows:
Future of trailer flooring
In the last few years, large transportation companies such as Contract Freighters Inc., Dart Transit, Transport America, Paschall Truck Lines and others have tested the road-service performance of composite flooring in their trailers. The results of these tests have proven the advantages of composite flooring. They have confirmed the benefits of a versatile trailer that can haul a wide variety of cargo including general freight and specialized loads of paper rolls, beverage, and automotive parts. As we learn more about the roadperformance of composite flooring in these versatile trailers, its acceptance in dedicated heavy-haul transport applications remains firm. It is clear from the varied applications of composite flooring that the future of trailer flooring is closely tied to the incorporation of high strength and light weight composite materials.