1 Onslow Street is a substantial, six storey (including Lower Ground Floor), 1960’s reinforced concrete framed building with stability provided by reinforced concrete cores/shear walls.
To the North was an original three-storey extension occupying an approximate footprint of 9m x 10m.
This project was to add a further three storeys to this original extension – increasing its height to that of the main building.
As the existing three storeys of 1 Onslow Street were fully occupied during the project, we were unable to strengthen the existing foundations and r.c. columns in any way and, even with using new, lightweight construction, the increase in loading on the existing columns/foundations, due to an additional three storeys, was substantially more than the normally acceptable increase of 10%.
We were, however, able to obtain a full set of the original archive drawings (including reinforcement drawings) which give the pile layouts and their allowable loads, the ground beams and their reinforcement, and the existing r.c. column sizes and reinforcement, etc.
This information was also confirmed by and supplemented with targeted opening up works.
By adopting lightweight construction (e.g. timber floors and roof on steel beams, new perimeter walls formed using brick slips on top SFS studwork, etc.) and by locating the new (steel) columns directly over the existing reinforced concrete columns, we were able to justify the increase in loading onto the existing columns and their piled foundations.
Stability was provided by the reinforced concrete core of the adjoining main building.
Structural Works: Included the following:-
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New, full height, Steel Frame with timber floors and roof.
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New, full height, Perimeter Walls formed using brick slips on top SFS studwork.
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New connections to the existing reinforced concrete core of the adjoining main building.
