19. The traffic mix on a highway with flexible pavement is expected to have only
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19. The traffic mix on a highway with flexible pavement is expected to have only passenger cars and single- trailer trucks with three axles. The representative trailer truck is expected to have these axle loads: . Steering axle (single axle) load: 6,000 lb .Drive axle (tandem axle) load: 10,000 lb .Trailer axle (tandem axle) load: 10,000 lb What is the load equivalency factor for each axle? Assume a structural number of 4 and a terminal serviceability index of 2.5? (3 points) Trailer axle (tandem axle) 0.009 a. 10 009 steering axle (singe axle-.Do3 x0.006 0.0 O b. What is the ESAL factor for the truck? (2 points) What is the approximate total accumulated ESAL for the highway if the projected AADT is 10,000 veh/day, the growth factor is 20, the design lane factor is 1, and the truck traffic represents 5 percent of the AADT. (5 points) c.Explanation / Answer
Given data:
(a)
Steering axle=6000 lbs=6 kips (Single axle)
Drive axle=10000 lbs=10 kips (Tandem axle)
Trailer axle=10000 lbs=10 kips (Tande axle)
Load equivalency factors for structural number of 4 and servicability index of 2.5% is
Steering axle (Single axle)@ 6 kips=0.013
Drive axle (Tandexm axle)@10 kips=0.009
Trailer axle (Tandexm axle)@10 kips=0.009
(b)
Steering axle=6000 lbs=6 kips (Single axle)=0.013/1.0=0.013 ESAL
Drive axle=10000 lbs=10 kips (Tandem axle)=0.009/0.092=0.097 ESAL
Trailer axle=10000 lbs=10 kips (Tande axle)=0.009/0.092=0.097 ESAL
Total=0.20 ESAL
This can be also solved by using 4th power law
Steering axle=(6/18)4=0.123
Drive axle=(10/18)4=0.095
Trailer axle=(10/18)4=0.095
Total=0.20 ESAL (Which gives approximately the same answer)
(c)
AADT=10000
G=20
Fd=1
Truck traffic=5% of AADT
FEI=load equivalency factors
ESAL=fdxGxAADTX365XNXFEI
ESAL=1x20x10000x365x3x0.05x0.013
ESAL=1x20x10000x365x3x0.05x0.009
ESAL=1x20x10000x365x3x0.05x0.009
The contribution of the passenger cars is negligible for ESAL and is neglected
Total ESAL=(0.14235+0.09855+0.09855)x106
Total ESAL=0.33945x106
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