Sheffield has embarked on an ambitious programme of regeneration that will transform the city centre into one of the region’s most desirable shopping areas.eading role.
Phase one of this programme centred around the completion of a new indoor Moor Market and nine retail units, while the current phase two – which kicked off in early 2015 – will deliver a three-level Primark store, a nine-screen cinema complex, restaurants and retail units all serviced by a large delivery yard.
Further phases are scheduled to begin later this year with more retail space in new and refurbished buildings.
Phase two is essentially split into two structurally independent steel-framed buildings, separated by a 70mm wide movement joint. One building is a standalone Primark store, while the other much larger structure accommodates the remainder of the scheme’s amenities.
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Main contractor Bowmer & Kirkland started phase two during March 2015 and, as the site had previously been cleared, the first task was to install foundations.
“Ground conditions have been more challenging than we initially anticipated, so we’ve had to reschedule the steel programme accordingly,” says Bowmer & Kirkland project manager Keith Birtwistle.
“It would have been easier, in terms of logistics and getting materials onto site, to erect the larger frame first and finish the steel erection with the Primark store,” he adds.
“However, as groundworks were ongoing, we had to do the reverse and erect the Primark store first.”
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Since the Primark store has been erected, site access for steelwork has been more challenging as the erected frame now blocks one of the previous entry points.
This means steelwork contractor Hambleton Steel has to make deliveries during early mornings and evenings, as these are the only times when the pedestrianised Moor shopping street can be closed. Meanwhile, larger steel elements are delivered via Debenhams’ adjacent temporary service yard, which overlooks the site.
Debenhams has a vested interest in the project as the site’s neighbour. Once the development is complete, it will be able to dispense with the temporary yard and once again use its main loading bays, which will be accessed via the new delivery yard.
The three level Primark store was constructed around a fairly typical retail-sized grid pattern of 8m by 8m.
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There are a few slight variations to this pattern, most notably around lift and stair cores, and in order to accommodate the ground floor access ramp to the development’s delivery yard.
“It’s a sway frame in two directions, as we wanted to avoid bracing,” explains Sanderson Watts Associates engineer Ryan McMullan.
“The building has glazed shop front elevations which aren’t suitable for bracing as the client didn’t want them in view, so we could only position supplementary cross bracings in discrete back-of-house locations.”
The building’s suspended floors and plant roof are designed to act compositely with the supporting steelwork beams, via shear studs welded to the beam flanges.
One of the most challenging parts of the steel programme was the initial phase of the large mixed-use structure. A total of eleven 26m-long by 2.5m-deep trusses had to be installed to form the large column-free space of the delivery yard.
To complete the yard’s roof, there are a further seven shorter trusses positioned at a 45˚ angle to the larger members.
The trusses vary in weight considerably, with the lightest only 7t and the heaviest coming in at 39t.
“Their weight depends on their position and the amount of column loadings they are going to absorb,” explains Hambleton Steel Site Manager Andrew Aykroyd.
Changing load patterns
The loadings differ as the steel complexity increases above the service yard trusses. This is because, as well as forming the roof over the yard, the trusses provide support to a host of columns forming the upper storey mall and the cinema.
The cinema steel frame superstructure (third floor and above) comprises two rows of mono-pitched portal frames, spanning over the screening rooms at approximately 4m centres.
In addition, a number of columns were off-set to allow for clear access to a sloping second floor pedestrian walkthrough mall. Therefore a series of transfer beams within the third floor structure has been utilised to support the cinema floor over the service yard.
Access to the cinema, restaurants and first floor shopping mall will be via an escalator link from the Moor.
Further trusses are located above the auditoriums, including a 17t 24m-long truss that will be installed at roof level. Also at this level are a series of 30m-long rafters forming the mono-pitch roof.
For ease of transportation, these long sections, each weighing 2.5t, will be brought to site in three pieces.
The service yard trusses, on the other hand, arrive on site in two pieces, which are then bolted together on the ground before being lifted into place using two mobile cranes.
The Moor phase two is due to be completed in October.
Project: Sheffield Moor
Main client: Aberdeen Property Trust
Architect: Leslie Jones Architecture
Main contractor: Bowmer & Kirkland
Structural engineer: Sanderson Watts Associates
Steel contractor: Hambleton Steel
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