Manchester has become an oasis of steel construction by the catalyst of the 2002 Commonwealth Games. Developer Crosby Homes' confidence in the booming market for residential buildings is evidenced by the 19 storey, mixed residential and commercial project.

Conceived as a steel-composite structure, No 1 Deansgate is the largest residential building since London's Barbican in the 1970s, and the tallest in steel in the UK. A podium level allows for pedestrian circulation below the residential block. It links with the Shambles area, re-built since the 1996 bomb devastation.

Ian Simpson Architects worked closely with structural engineers, Martin Stockley Associates(MSA), to develop an innovative and exciting design concept within the client's cost schedule. MSA had previously worked with Crosby Homeson another multi-storey steel residential buildingat the opposite end of Deansgate.

 The chosen structure is more readily associated with multi-storey steel framed commercial buildings, but is given a unique feature by a storey-high steel transfer truss which supports the upper 14 floors, and is itself supported by inclined tubular steel columns. Although structurally complex, the building retains an apparent simplicity and lightness.

The 84 apartments including eight penthouses were provided with a fully-glazed façade and a ‘buffer zone' externally for regulation of internal temperatures. The inner skin is double glazed and the outer skin comprises fully openable single glazed louvres.

The grid size of the residential block is based on a 4.1 m x 6.8 m column spacing, and secondary beams are eliminated by use of a long spanning composite slab. The shallowest sensible structure was achieved by the use of Universal Column (UC) sections as beams. The steel structure had to be constructed within accurate tolerances to facilitate installation of the glazing.

The building is also innovative in that it has been ‘fire engineered' to evaluate the fire risk and structural behaviour in fire, leading to considerable savings in fire protection costs.

Despite its 60 m height, the building is relatively lightweight and uses existing foundations, where possible. Construction of the concrete sub-structure started in mid-2000 and the building was opened in mid-2002. Importantly, 80% of the apartments were pre-sold, a reflection of the perceived value of the property.

This project highlights the design opportunities using steel in the medium and high-rise residential sectors especially in urban locations, where there is a premium for speed of construction, and reduced disruption due to construction process.

The upper 14 floors, typically of 60 m x 17 m external plan, comprise a regular steel structure in which a 4.1 m span composite slab is supported by 6.8 m span composite beams using 203 mm UC sections that are perforated for ducts serving the internal kitchens and bathrooms. The 165 mm thick composite slab uses Ribdek 80 decking and has a 40 mm screed. A suspended ceiling, comprising two layers of 15 mm fire resisting decking and has a 40 mm screed. A suspended ceiling, comprising two layers of 15 mm fire resisting plasterboard, enhances the inherent fire resistance of the UC sections to provide the required fire resistance and to economise on fire protection costs.

At 16 m above ground level, the upper residential block is supported by a storey-high steel transfer structure to reduce the wider grid of the retail area below to the sensible residential grid. This is achieved by two directional trusses supported by inclined tubular legs, which were designed to be architecturally interesting at the podium level as well as structurally functional. The longitudinal transfer structure was erected as large braced sections fabricated from UC sections and cruciforms from 40 mm steel plate.

Construction Manager, MACE, and the steel fabricator developed an innovative temporary platform from which the floor beams could be erected rapidly, and safely. The platform was raised as the work progressed. Decking followed on the floors beneath and stabilised the structure. The UC sections were propped to reduce deflections.

The erection of the 800 tonne steel structure took only 30 weeks, representing an average of one floor every two weeks, including the complex transfer structure. The columns are UC sections located within the separating walls. The smallest possible circular hollow sections are used where the columns are exposed adjacent to the glazed façade.

The outer skin of glazing is suspended fromthe floor above and the structure was designed to tight tolerances and minimum movement.

Separating walls used double layer lightsteel sections with two layers of 15 mmfire resisting boards on each side with insulating quilt between to provide a highlevel of acoustic insulation. The mass of thefloor and its fire protection achieve the required acoustic insulation for this highquality building.

Key information

Number of storeys	19
Apartments	84
New-build home

Britains Tallest Residential Development