This project has transformed the site of a former tyre manufacturing warehouse in Birmingham into a modern office and hotel complex. Constructed in 1925, the vast site had lain derelict for 25 years. Curtins were commissioned by Urban Splash to appraise the building’s condition, and develop a cost effective scheme that would allow the 100m x 52m structure to be flexible to allow for single and multiple occupancy of each of the 7 upper floors.

Concept Design

Our approach on this project has continued from concept design through to construction and has given our client greater flexibility for the use of his building. After an initial inspection of the building and an assessment of the ground conditions , we determined the key items that affected the structural design. Using “in house” developed spreadsheets we considered the options for several different types of floor uses that included retail, leisure, commercial and some residential. This design model allowed a flexible approach, enabling the developer to try varying options for the use of the floors and obtain an almost instant answer on the need for expensive strengthening of the structure. As well as subdivision of floors, the effect of introducing additional floors was considered on columns, foundations and shear wall construction.

Following early planning meetings it became apparent that the residential element would be dropped completely and the multi-storey hotel would be formed inline with the centre of the offices. It had been decided that the existing roof would be removed and replaced with a modern long span structure thus creating the largest green roof in the country. A new timber deck “promenade” in the style of a seaside pier was introduced above the roof level of both the offices and hotel, giving views of Birmingham beyond. A full length plant room was hidden behind this promenade.

Final Design

The chosen layouts required major alterations to the concrete encased steel framed building. Having minimal beam to column connections, this unbraced structure created many engineering challenges. A 3D computer model was “built” to extend the concept design spreadsheet and more accurately assess the effect on the critical elements which were found to be the upper columns and the pad foundations. The effects of removing one of only two walls that could brace the whole structure was considered and then adapted to provide the strengthening structure.

The building relied on floors to act as diaphragms to transfer the wind loading into the shear structure however the new layout required these slabs to be punctured with large penetrations to form service risers, lift and staircase shafts through the centre of the building. These effects were modeled on the computer and the design developed to provide the necessary strengthening.

The external walls presented further challenges. The Fort’s basement structure extends beyond the external wall line, creating a platform effect to the perimeter. The supporting beams rely on slender mass concrete panels to support the walls. Most had shear cracking which required repair. The windows to external walls at all levels were removed and full length fenestration set back creating a balcony and a method of distributing the mechanical services. Structure, services and architecture achieved in one detail.

Transfer structure was introduced to support both the glazed wall at the hotel junction and for the large openings which were formed on the main entrance line allowing columns to be removed. Schedules were prepared in a manner that allowed the masonry and concrete repairs to be quantified and prioritised.