EQUIVALENT SINGLE WHEEL LOAD (ESWL)

EQUIVALENT SINGLE WHEEL LOAD (ESWL)

  • EQUIVALENT SINGLE WHEEL LOAD (ESWL) is considered for the Fixed traffic approach (Airport Pavement design- where a number of repetitions not considered) as one single load movement is sufficient to cause damage to pavements.
  • ESWL is the single wheel load that produces the same value of maximum stresses at the depth Z as the dual wheel assembly
  • The effect on the pavement through a dual wheel assembly is not equal to two times the load on any one wheel
  • Let d is the clear gap between the two wheels and S be the spacing between the center of the wheels and a be the radius of the circular contact area of each wheel then S=d+2a
EQUIVALENT SINGLE WHEEL LOAD (ESWL)
  • Up to d/2 wheel load P acts independently after that over lapping takes place.
  • At depth equal or greater than equal to 2S magnitude of 2P acts
  • For intermediate location linear logarithm relation exist

COMMERCIAL VEHICLES – As per IRC, vehicles having gross load greater than 3 ton called Commercial Vehicles.

EALF (Equivalent axle load factor)- It is defined as damage caused to the pavement by one application of the axle load relative to the damage caused by a single application of std axle load. The axle that is not equal to a Single axle load is converted to EALF

 EALF=(\frac{Axle\: Load}{Std.Axle\: Load})^4

No. of repetition of equivalent std. axle load=  \displaystyle\sum\limits_{i=1}^m (EALF)_in_i

Where m is the number of axle load group, ni is the number of repetition of the ith group during the design period

VEHICLE DAMAGE FACTOR (D) – It is defined as the equivalent number of standard axles repetition per commercial vehicle. It is used to convert the commercial vehicle to the number of standard axle load repetitions.

 N=\frac{365A[1+r]^n-1}{r}

Where A is initial design traffic in the vehicle per day in the year of completion of construction calculated as A=P(1+r) t

where
t is construction period in the year,
r is the rate of increase normally taken as 7.5% per year,
P is No. of the commercial vehicle per day at last count

No. of Std. axle in design life to be adopted for design

 N_A=\frac{365A.D.F[1+r]^n-1}{r}

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