Reference Design Specification

A.Consider load

Description

HS 20-44 represents the total weight of 36 tons of tri-axial trailer due to its weight is distributed on three axis, so the loading level is the same as the bi-axis HS 20-44 truck (total weight of 20 tons) belonging to the same loading level T20.
HS 15-44 represents the total weight of 25 tons of tri-axial trailer. As above, the loading level is the same as the bi-axis of HS 15-44 truck (total weight of 14 tons) belonging to the same loading level T-14.
Load instructions can be found on the highway bridge design specifications.

B.Consideration of vehicle forwarding direction

B. Even with the same loading, the different direction of the main lever (I-beam) and the moving vehicle results in different distribution of forces. So it should be considered the vehicle and the main lever (I-beam) to be parallel or perpendicular.

C.Strength Calculation

1.General side trench cover

  • Standard Type : I50*400*995
  • Rear Loading : P=8000kg(T-20)
  • Ground Area : a 20cm* b 50cm
  • Impact Factor : i=0
  • Spacing : L=30cm(span)
  • Allowable Stress : σ b=18kgf / m㎡
  • Moving Direction: Parallel with the main lever (crossing trench )
  • Main Lever Spacing : 35.3cm
  • Loading Distribution of the Numbers of Main :
    n=(a 20cm / 3.53cm)+1piece=6piece
  • Section Modulus of the Main Lever : Z=2.57cm³
  • Type : I-50
  • Stress:
    σ=P*(L / b)*L/ 8*n*Z=8000*(30/50)*30/8*6*2.57
    =1,167=11.7kgf/mm²<σ b

2.Fixed trench cover

  • Standard Type : I50*400*995
  • Rear Loading : P=5600kg(T-14)
  • Ground Area : a 20cm* b 50cm
  • Impact Factor : i=0.4
  • Spacing e: L=35cm(span+5cm)
  • Allowable Stress : σ b=18kgf / m㎡
  • Moving Direction: Parallel with the main lever (crossing trench )
  • Main Lever Spacing : 35.3cm
  • Loading Distribution of the Numbers of Main :
    n=(b 50cm / 3.53cm)+1piece=15piece
  • Section Modulus of the Main Lever : Z=2.57cm³
  • Type : I-50
  • Stress :
    σ=P*(1+i)*(2L-a)/ 8*n*Z=5600*(1+0.4)*(2*35-20)/8*6*2.57
    =1,271=12.7kgf/mm²<σ b