A highway culvert is a drainage facility that allows water to flow under the road without causing any traffic disruption. Corrugated and spiral steel pipe are popular for culverts because they can be installed quickly, have long life, are low in cost, and require little maintenance. With corrugated steel pipe, the seam strength must be adequate to withstand the ring-compression thrust from the total load supported by the pipe. This thrust C, lb/ft (N/m), of structure is

C=(LL+DL)S/2

where
LL= live-load pressure, lb/ft2 (N/m2)
DL= dead-load pressure, lb/ft2 (N/m2)
S= span (or diameter), ft (m)

The pipe should have sufficient handling and installation strength so as to withstand stresses due to shipping and placing of the pipe in the desired position. The handling strength is measured by a flexibility factor which is:

FF=D²/EI

where
D =pipe diameter or maximum span, in (mm)

E= modulus of elasticity of the pipe material, lb/in2
(MPa)

I =moment of inertia per unit length of cross section of the pipe wall, in4/in (mm4/mm)