39 – 49 Wigmore Street
The addition of a new floor to this office building, designed by Seifert in 1972, posed many structural challenges. The existing structure is a strong concrete frame supported on under-reamed piles. Even so the additional structure for a new floor and partial infilling of a light well required serious structural gymnastics to bring the loads down to appropriate points.
We started by identifying where the loads could go – this came down to an asymmetrically positioned corridor – and devising a structure to bring them there. The new edge wall between offices and light well has a deep girder on each storey and notional dado area at the lower part of the wall. As the girder cantilevers from two columns, this strategy required careful sequencing.
First we installed the girder, as this takes dead load it deflected; we then jacked up the columns to level the floors. This new structure increases the lettable area of the building entirely within the building’s existing footprint.
Structural analysis of a Seifert office block to incorporate an extra storey
£ 14 million