BAM

Heart of the City II will be the new Sheffield headquarters of HSBC, and with the bank due to move into its new premises in mid-2019, programme was “absolutely key”, according to Nick Howdle, construction manager for Bam on the £70.5m project.  Bam was appointed by Sheffield City Council to a preconstruction agreement in August 2016, before the design-and-build contract started on site in April 2017. Working with Leonard Design Architects, the contractor quickly decided to modularise key work packages, including the structural cores.  The scheme’s 30,000 sq m main building sits on a sloping site, roughly triangular on plan, with a capacious basement and five above-ground levels. In situ concrete was originally planned for the three cores of the superstructure, but Bam was a little nervous about the programme. “The cores had to be finished absolutely on schedule, so we could move straight on to the steel frame,” says Howdle. “So we decided to switch to precast – just 16 weeks before the units would have to be delivered.”The contractor visited Creagh to explain the challenge. “We wanted to look at the factory and check the materials were right as this was such a programme-critical item,” says Howdle.

Creagh’s BIM manager at Sheffield, Connor McMahon, says the scheme was “was an opportunity for Creagh use our digital capability to deliver high-quality cores while meeting a fast-track programme”.   The cores are 34.5m-tall and each one has 17 precast sections, consisting of flat walls, ‘C-shape’ units, boxes, stairs, landings and capping slabs. The largest sections were 8m by 4.6m across and 2m high, weighing around 27 tonnes.  “We modelled the precast cores in Revit to a level of detail of 5, which allowed Creagh to produce production drawings straight from the model,” McMahon explains.  The cores sections also included cast in steel plates for the connections to the steelwork structure.  “We liaised closely with steel supplier Severfield to guarantee that their steel plates were delivered in advance of our cast date,” explains McMahon.

McMahon says the use of BIM meant a reduction in design and engineering costs, and an “improved service to our customer” through creating 3D visualisations of the project.“The model becomes an interactive tool, so we can visualise the product on the project virtually, before the prefabricated component is cast in the factory and arrives on site,” he says. “Creagh uploaded data drops to the common data environment (CDE) used on the project, so this provided Bam with evidence of how the precast cores had been developed.”  

Of course, the site assembly of the core sections needed to be accurate and the product quality was checked in Creagh’s yard prior to despatch, McMahon adds.  Creagh also liaised with architect Leonard before applying a high-quality Type B finish on all the core elements, with some units having a mist coat applied.  Logistical challenges on the tight, city centre site included coordinating the high volume of large loads that had to be scheduled within a short time scale. “As a couple of cores were being fitted in tandem, it was vital the correct loads were delivered on time and off loaded efficiently to maximise installation time,” adds McMahon.

 The first of the cores was installed on site in just eight days.  “Credit to Creagh, they delivered,” says Howdle. “It was a big help on such a tight programme.”

 Bam completed its contract at Sheffield in January and the building is now undergoing fit-out ahead of HSBC moving in.