# Section Modulus per unit length of wall (per/ft or per/m)

This is the most important design criteria, as together with the allowable stress, it defines the carrying capacity (moment resistence M) of the section.

Allowable stress is a percentage of the yield point of the steel. Accepted engineering practice in the USA is to design to 65% of the yield point (F_{y}).

The calculation for the minimum required section modulus is:

S_{min} = M_{max} / .65 F_{y}

The calculation for the section modulus of the sheet piling section is:

S = I / c (per unit of wall)

## Note:

Aside from section modulus, the reason why many other properties are listed in specification sheets (moment of inertia, area, etc.) is to support other design calculations the engineer might require. These other properties should not be used as primary design criteria as section modulus is the critical design parameter.