Slabstress – Great Marlborough Street, Manchester

Bonded tendonsClient
Student Castle

Principal Contractor
Shepherd Construction

Structural Engineer

Frame Contractor

Post-tensioning Contractor
Freyssinet Ltd

Contract Duration
11 months

Works Completed
November 2011

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Student Castle in Manchester offers high quality student accommodation in a great city centre location, just a few minutes walk from the main University of Manchester and Manchester Metropolitan University.

The structure consists of 35 levels, all formed from post-tensioned concrete. The thinness of the slabs allows extra storeys to be squeezed in for a set building height, which can really make a difference to the financial viability of tall buildings.

The 11,000m2 job comprised mainly 200mm deep slabs with one corner of each floor plate increasing to 250mm to cater for the 3.2m cantilever. Elsewhere the spans were 6.8 by 6.4m.

Numerous penetrations had been accommodated in the design – from temporary openings for hoists, 4.6m long slots for risers and edge fixings for climbing edge-protection screens.

Freyssinet used the 3B13 and 5B13 anchorage for the bonded tendons. This anchorage system fully complied with the requirements of ETAG 013 “Post-tensioning kit for prestressing of structures.”

The bonded tendons comprised a flattened galvanised steel sheath which is 43mm wide for the 3-strand tendon and 70mm wide for the 5-strand version. After the tendons have been stressed, cement grout is injected under pressure into every sheath to completely fill the void. This provides corrosion protection to the strands as well as establishing bond between the structure and the tendons.