The tallest tower in Toon
The 83m Hadrian’s Tower occupies a very tight site in the centre of Newcastle
Newcastle’s tallest tower is currently under construction. On a logistically challenging site, main contractor Tolent is using offsite technology widely, including a unitised facade manufactured in eastern Europe. Will Mann reports.
Standing 83m, Hadrian’s Tower is set to become the tallest building in Newcastle when construction finishes next year.
Situated between St James’ Park and the main railway station, main contractor Tolent is constructing the tower for developer High Street Residential on an incredibly tight site, where neighbouring buildings are just 75mm from the new structure.
This has led the contractor, headquartered in Gateshead, to prefabricate many components, most notably the unitised facade which is being manufactured and assembled at various locations across Europe.
Client: High Street Residential
Main contractor: Tolent
Structural engineer: Alan Johnston
M&E consultant: Desco
Concrete frame: 4D Structures
Facade: EVB/GA Installations
H&V: H Malone & Sons
Ceilings and partitions: Kenmor
Programme: 118 weeks
Scheduled completion: August 2020
Project manager Paul Consterdine, also from Gateshead, recently returned to the north east after five years in the capital, and says that “logistically, this is like working on a central London site”.
The 27-storey tower is an irregular trapezium on plan with a total floorspace of around 12,500 sq m. The building footprint is 62 sq m. Tolent’s site office is in a neighbouring building. What little spare space there is at ground level is being used by the concrete frame contractor to assemble column and slab reinforcement.
“Otherwise materials are unloaded from the lorry on arrival and go straight onto the tower,” explains Consterdine. “Floorplates are small so we can’t preload with materials.
“We have just one tower crane and one hoist so our just-in-time delivery system has to be spot on – and on busy days we have up to 30 deliveries. “Fortunately, we had a long lead in which allowed us to plan the construction methodology.”
Tolent was awarded the negotiated contract from High Street Residential and started on site in August 2017, managing the demolition and enabling works. Given the area’s mining history, six boreholes were drilled to the core seams below, which were unworked. There were also no discoveries from the archaeological investigations – the site is next to the old city wall – allowing the foundations construction to get under way in May 2018, with the piling mat installed as part of the enabling phase.
Some 245 CFA piles, 600mm in diameter, were driven to depths of 22m to 25m. Of these, 153 are load bearing. Because of the close proximity to the neighbouring buildings, Tolent had to install a contiguous retaining wall of 76 piles. A further 16 piles support the tower crane base.
The structural frame, which uses 6,000 cu m of concrete and 1,000 tonnes of reinforcement, is mostly conventional apart from the bottom nine levels. The four lowest levels flare outwards at one corner, then twist inwards for the next two storeys, and again for the next three, before becoming uniform from floor 9 up to the roof. On plan, the trapezium changes into a parallelogram.
The tapered design creates steps at floors 4, 6 and 9, where triangular green sedum roofs will be installed.
The tower will have 162 PRS apartments, with 30 different layouts in total, most of the variations in the unusual shape of the lower levels. From 9 to 23, each floor comprises six apartments with identical layouts, and the top four storeys contain penthouses.
Above: How the 27-storey tower’s unitised facade will look. Below: The lower levels flare out at one corner, then twist inwards before becoming uniform from floor 9
There were a few significant changes from the original structural design. The first was the incorporation of an extra storey. “This meant increasing the overall height of the tower by an extra metre, the maximum level allowed by the planning permission, and then shaving 50mm off the height of each storey – to 2,925mm,” explains David Thompson, Tolent’s regional director for the north east.
“We also reduced the thickness of the floor slabs and the height of the ceiling voids – this has meant the ventilation ductwork now takes up the full depth of the ceiling void, so we’ve had to plan the services coordination carefully.”
The other main change from the original design was the inclusion of a third lift shaft to allow direct access to the planned lounge area at roof level.
“This meant rationalising the structural design, reducing column numbers but beefing up their thickness by about 30% to 40%,” adds Thompson.
The columns are typically 300mm x 800mm thick. Internally, these are set out at 5m centres, with reinforced concrete piers at 1.3m centres around the perimeter. Shear walls have been used as well as columns, to achieve lateral stiffness, up to level 6 on the west side and all the way up to the top floor on the east side.
The envelope design is also different at the lower levels. SFS and brickwork are used on levels 0 to 5, while from level 6 up it is all unitised glass spandrel panels with anodised aluminium.
The unitised sections, 1,968 in total, are supplied by Pilkington and assembled at its various locations around the continent. The glass is manufactured in Germany, the double-glazing units assembled in Poland, then shipped to Ukraine – where the anodised aluminium is manufactured – and there they are structurally bonded into the unitised facade units. From Ukraine, they are delivered straight to the Hadrian’s Tower site.
“The decision was partly due to speed – and obviously the cost had to work – but also safety and logistics,” says Thompson. “We didn’t want to use mast-climbing work platforms, because it would have meant having the mast-climbing structures on two elevations.”
The tower crane is so close to the structure that Tolent had to put in a tie to stop the mast deflecting in high winds
The units arrive on stillages, are unloaded from the lorry by mini telehandlers and lifted onto the hoist, then taken up to the floor plates. A spider crane on the floor above raises the units from the stillages individually, then lifts them up and out of the building, and on to the brackets attached to the concrete structure, where they are secured in place internally.
“This requires considerable preparation,” says Consterdine. “The tolerances are just +/– 10mm for each unit. The brackets have to be accurately set out and torqued. The frame’s concrete mix is 15N – unusually high for a concrete slab – but the tolerances are so tight we have to avoid any deflection.”
One other significant design issue on the facade installation was the fire-stopping.
The concept design for Hadrian’s Tower pre-dated Grenfell, explains Thompson. “Typically, on this type of project, there would be a spandrel panel around 500mm deep which effectively conceals the fire-stopping,” he says. “Here, the architect wanted a clean line between each storey, to create a transparent effect up the whole facade, with each floor clearly visible. This meant creating a bespoke design for the fire stopping between each floor.”
“Logistics has been the biggest issue, particularly planning crane hook time and hoist time. We would have liked more than one hoist but there wasn’t room”
Paul Consterdine, Tolent
With this design, the Siderise fire stop product sits below the horizontal transom, sealing the gap between the floors and the external unitised facade panels, maintaining continuity of fire resistance. This achieved the minimalist, transparent effect the architect intended.
“However, there was no prior test data for this design,” says Thompson. “Initially, we carried out a desktop study, but when we went to Tyne & Wear fire brigade, they asked for a physical test. So we had to build up a sample panel to get tested first, which was done in Warrington by Exova.”
“The design also had to be signed off by building control,” adds Consterdine. “Creating and finalising this part of the design took six months and involved three fire consultants.”
The other significant offsite package is the bathroom pods. All 175 of them are being supplied by modular outfit Offsite Solutions.
“The bathroom pods are lifted by tower crane onto cantilevered decks, which come off the floorplates, and we wheel them onto the floors,” explains Consterdine.
The pods also present a challenge with the services integration, with no central risers on the tower. “The services have to be installed before the pods are fixed into their final positions,” says Consterdine. “So before we install them, we have to test all the pipes, fire stops, ventilation ductwork and seals above the pods, because we can’t do it afterwards.”
The close proximity of neighbours has been a big consideration throughout the works. For safety reasons, Tolent is using a full perimeter protection screen during the concrete frame construction. The screen, supplied by RMD preassembled, comprises a lightweight steel frame with robust plastic sheeting. On the upper floors, the wind gusts are barely detectable behind the screen. The screen covers four floors, moving up the tower as floor slabs are cast.
A full perimeter protection screen is used for safety
“When working so close to neighbouring buildings, these are necessary for safety,” says Consterdine. “They are more common in London, but I think this is the first time one has been used in Newcastle.”
Meanwhile, the tower crane is so close to the structure that Tolent has had to put in an intermediate tie at level 18 to stop the mast deflecting in high winds and hitting the top of the building. “The worst case scenario is 2m in either direction,” says Consterdine.
Tolent is required to maintain access to the car park of Nexus, which occupies the building next door, 24 hours a day.
“We came to an arrangement where we split the road in half on Rutherford Street [the only access road], took access of one half for our site compound, and left the other half to provide access for Nexus,” explains Consterdine.
“Logistics has been the biggest issue on the project, particularly planning crane hook time and hoist time,” he reflects. “We would have liked to have had more than one hoist but there wasn’t room.”
Hadrian’s Tower is due to complete in August 2020 and is on schedule, says Consterdine.