Scale Ticket, Steel Coils, and a Sliding Fifth Wheel
At a Colorado port of entry, your 5-axle tractor-semitrailer with a 48-foot flatbed scales as follows: steer axle 12,400 lb (limit 12,000), drive axles 33,200 lb (limit 34,000), trailer tandems 33,000 lb (limit 34,000), gross 78,600 lb (limit 80,000). The load is six steel coils totaling 42,000 lb, arranged in a single row. You have two grade-70 chains with working load limits of 8,000 lb each; a third strap is damaged and has been removed. The coils are not blocked or chocked. The fifth wheel is in its forward position and can slide rearward up to 12 inches; the trailer tandems can also slide. Your route crosses a 6 percent mountain grade in 30 miles. The scale officer has not yet placed you out of service, but you must correct the problems before leaving.
1. Calculate whether the current tiedowns meet the minimum aggregate WLL for the 42,000-lb load. Show the calculation.
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The minimum aggregate WLL is 50 percent of the cargo weight: 0.50 x 42,000 = 21,000 lb. Two chains at 8,000 lb each give 16,000 lb, which is 5,000 lb short. Add at least one more grade-70 chain rated 8,000 lb, for 24,000 lb aggregate, and place it so the coils cannot roll or slide. Because the coils are not blocked, also chock or block them; tiedowns alone may not prevent rolling. Recheck each chain for damage and load binders for tightness.
2. Which axle is over limit, and which adjustment should you try first? Explain the weight transfer.
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The steer axle is over by 400 lb (12,400 vs 12,000). The drive axles are 800 lb under (33,200 vs 34,000), so there is room to move weight rearward. Sliding the fifth wheel rearward shifts part of the kingpin load from the steer axle to the drive axles. Move it in small increments, then re-scale; do not move it all 12 inches at once, because that could put the drive axles over. The trailer tandems do not need to move first, since the trailer axle is under limit and the problem is the steer axle.
3. What is the correct order of securement and weight adjustment before leaving the port?
Read the worked answer
First, correct the securement: add the third chain and block or chock the coils so the load cannot move when the tractor is adjusted. Then slide the fifth wheel rearward in small steps and re-scale the steer and drive axles. After the scale shows the steer at or below 12,000 and the drives at or below 34,000, recheck the chains, binders, and blocks because the adjustment may change chain tension. Confirm gross weight and trailer tandem weight, then complete the walk-around before leaving. If a re-scale cannot get all axles legal, do not leave; shift or reconfigure the load.