2702 Chapter 22 



ber. With log-run raw material resources, manufacturers resell the upper grades, 

 using the #1 common and lower material for flooring. Steps in the manufactur- 

 ing process are: 



1 . Rough plane 4/4 or 5/4 lumber. 



2. Rip lumber to desired thickness of deck, i.e., l-Vs inches. 



3. Plane ripped strips to 0.880 or 1 inch. 



4. Cut out defects. 



5. End match strips with hook joint. 



6. Turn rippings on edge and face laminate with a melamine fortified urea 

 adhesive in a continuous lay-up operation. 



7. Cure laminated flooring in a hot press. 



8. Crosscut continuous ribbon to the desired length of the trailer. 



9. Rip the large panels into 12-y8-inch-wide floor boards. 



10. Apply surface and edge detail with planer-matcher or molder. Usually 

 a shiplap or tongue and groove joint is machined on the board for edge 

 matching. A 1/16-inch crusher bead is also machined on one edge to 

 insure spacing between planks adequate to prevent buckling on 

 wetting. 



11. Finish cross cut as necessary. 



The five most important material characteristics considered in the design of 

 trailer flooring are strength, durability, nailability, coefficient of friction, and 

 weight to strength ratio. 



Strength. — Van trailer flooring is normally supported on, and fastened with 

 self tapping machine screws to steel junior I-beams, 12 to 16 inches on center 

 and must be capable of supporting concentrated, moving fork lift loads of up to 

 18,000 pounds over these spans. Engineering requirements dictate that in actual 

 service the flooring product should weigh less than 5.0 pounds per square foot 

 and support a concentrated load of at least 9,000 pounds (the load on one of two 

 forklift wheels) over 12-inch spans without excessive deflection or failure. As an 

 example, using a simple span beam analog for analysis and based on practical 

 deflection limitations for fork life operations, a 0. 1-inch deflection is the maxi- 

 mum allowable over a 12-inch span. Under these assumptions, a wood-base 

 material would need a minimum stiffness (EI) property of 346,000 pound inches 

 squared per inch and an ultimate bending strength of greater than 8,650 psi to 

 support the load. In general, a thin flooring material with a high modulus of 

 elasticity value is desired, because thinner floor materials provide more volume 

 in the van trailer for pay loads. 



Durability. — The strength and durability of the glue line for laminated wood 

 flooring is normally established by means of wet and dry block shear tests and 

 cyclic delamination tests. ASTM, AITC, or other teting standards are used to 

 evaluate these properties, although no one particular standard is used by all 

 concerns. Most corporate standards are modified by experience with delamina- 

 tion and glue-bond failure in actual service. Average shear value of a sample 

 tested according to ASTM Test D905-49 should probably be at least 800 psi and 

 delamination should represent less than 15 percent of the total glue line area in 

 AITC Test 110. 



