Sign Post Design

The lever arm is the height to the centroid of the sign, which can be calculated as the total sign post height minus half the sign height. The total height of the sign must include any parts of the post above the foundation which are buried.

Sign Post Design - Torsion

Torsion can be significant where part of the sign is shielded from wind or if a standard force of 0.5kN is applied at the extremity of the sign. Torsion from wind loading can be calculated as half the total wind load, applied at a distance of a quarter of the sign width. The torsion from a point load of 0.5kN is applied at a distance of half the sign width.

The combined bending and torsion moments will be considered when choosing a sign post section size. This is only applicable on single sign posts.

Sign Post Design - Shear Force

The shear force per sign post can be calculated simply as the wind force divided by the number of sign posts.

The shear force is unlikely to be critical except for very large signs mounted very close to the ground. It is included in the CivilWeb Sign Post Foundation Design Calculator as a design check anyway for completeness.

Sign Post Design - Temporary Deflection Check

The CivilWeb Sign Post Foundation Design Calculator also completes a design check on the temporary deflection of the sign post under wind loading. First the Wind Force must be altered from a 25 year return period to a 1 year return period, and taken at 75% of the reference wind velocity, which is the SLS criterion. This is done by multiplying the 25 Year Wind Force F_w,d by 0.75²/0.96².

This amended 1 year Wind Force (F_{w,d (1 Year)}) is then divided by the sign height to give the universally distributed load along the sign height.

The maximum deflection of the sign post at the top of the sign is given by the following equation where E = Elastic Modulus of Steel (typically taken as 205x10³N/mm²), I = Post moment of inertia, n = number of posts.