 # Reference Design Specification 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