Bridgewater Buildings

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Overview

Location: Leeds, UK

Client: · Bovis Lend Lease / P C Harrington Group

Scope: Design & Install Post-Tensioning

Bridgewater Place is a graceful yet awe inspiring 32 storey tower development in the business quarter of Leeds, one of the UK's principal northern cities. Located just minutes from the rail and motorway connections, it has already attracted a major firm of solicitors as main tenants. The nine lower storeys house 23,000m² of high quality office space in two buildings separated by the largest feature atrium in Leeds. 1,500m² of retail and leisure use are also contained in these lower levels. Rising majestically and offering superb panoramic views, the residential tower provides 200 luxury apartments within its additional 23 levels. The basement supplies 400 car parking spaces. It is estimated that Bridgewater Place will house 3000 people per day in its iconic 110m tall structure.

Consulting engineer Matt Macdonald selected post-tensioning for the slabs in order to maximise the floor space available within the building envelope, the thinner slabs allowing more storeys to be squeezed into a given height. A second significant benefit was the vast reduction in steel content that Post-Tensioning brings, with the project being started when world steel prices were very volatile.

The office levels comprise two floor plates which measure 120 by 17m and 76 by 17m. Both blocks contain two reinforced concrete cores and, in order to solve the restraint issue, Structural Systems introduced a temporary movement joint across both floor plates. This comprises sleeved dowels crossing the construction joint between two pours. Once sufficient slab shortening has occurred (28 days after stressing the second pour) the sleeves are grouted to lock the joint and restore structural integrity to the floor plates.

Typical loading for the offices is 4.0kN/m² (live) and 1.5kN/m² (superimposed dead) and this requires 225mm thick PT slabs to span the 9.0 by 7.5m grid, a span to depth ratio of 40. Plant loading (7.5 plus 2.0 kN/m²) necessitates slab depths of 270mm on levels 9 and 10. Tendon spacings vary between 800-1000mm for column strips and 1500-1700mm for middle strips, leading to a P/A of 1.7MPa in the longer span direction and 1.5MPa the other way.

The residential floors are 17m wide and range in length between 46 and 40m. Slab depth stayed at 225mm for the residential loading (1.5 plus 1.5kN/m²) in order to control deflections for the cladding. It was important to construct the building quickly and the reduced quantities used in PT construction helped PC Harrington, the concrete frame contractor, achieve floor to floor cycles of 3 days.