n the case of the width of the backside beam is 20 cm., the calculation of the length of the Dconcorrugated planks will use the distance between the center of the beam and the center of the beam subtract 5 cm. On the other hand, in case of the width of the backside beam is 15 cm., the calculation will use the distance between the center of the beam and the center of the beam subtract 3 cm. or use the distance from the center of the beam to the center subtract the distance of backside beam plus span across the beam not less than 5-7.5 cm. (Including adding not less than 10-15 cm.) will be the correct size in use.
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