Column Supported on a Steel Ground Beam: Picture Frame Foundation

In standard domestic construction, a steel column bears onto a pad foundation at ground level. This works well when the foundation can be positioned directly below the column — but sometimes the column needs to sit close to or on the party wall boundary, where positioning a pad foundation would require excavation beneath the neighbouring property’s land.

The picture frame foundation is the solution for this situation.

What It Is

A concrete-encased steel ground beam cantilevers out from a pad foundation positioned fully within the homeowner’s property. The steel column then bears onto the end of this ground beam, rather than directly onto a pad beneath it.

The arrangement typically looks like:
– A pad foundation positioned centrally within the homeowner’s boundary
– A stub column rising vertically from the pad (usually same spec as the overhead column)
– A steel ground beam (typically the same section as the overhead beam) running horizontally from the stub column top to a point directly below the intended column position
– The main steel column bearing onto the end of the ground beam via a cap plate or direct bearing

Because the pad is offset from the column, the ground beam must carry a bending moment from the eccentricity — this is designed and specified by PorthouseDean.

When It Is Used

– Column position falls on or very close to the party wall boundary
– A direct pad would require excavation beyond the boundary (which typically requires the neighbour’s permission and a party wall agreement)
– Space constraints prevent the pad from being positioned directly below the column

Design Considerations

The ground beam must carry:
– The full vertical column load (as a cantilevered beam)
– The resulting fixed-end moment at the stub column connection
– The horizontal reaction at the pad, which becomes a shear at the stub column base

PorthouseDean sizes the ground beam, stub column, and pad for all these effects. Typically the ground beam is the same section as the overhead structural beam, concrete-encased and placed below finished floor level.

Concrete Encasement

The steel ground beam is fully encased in concrete. This provides:
– Structural composite action between the steel and concrete
– Fire protection
– Corrosion protection (the steel does not rely on a paint system below ground)

The concrete specification matches the pad foundation (typically C35/45, see foundation drawings).

Contact us if your project has a column that must sit at or near the boundary and you need a picture frame foundation.