The project is the refurbishment of BT's Stadium House and its location ensured the results would be something special. The 17-storey building stands adjacent to the city's Millennium Stadium and the designers Parsons Brinckerhoff wanted the building to reflect this futuristic mood.
The catalyst for the project occurred around three years ago when the existing concrete cladding on the building began to fail and an emergency scheme was carried out to remove the projecting nibs of the concrete panels. "This," explains Amec project manager Stuart Price, "left an unattractive building." Thus, the challenge was set to breathe new life into the tower.
Various options were considered, including the construction of a steel skeleton around the building, before opting for an overcladding scheme. But this solved only part of the problem. "They would still have had a rectangle," explains Price, "which, standing against the stadium on the approach road to Cardiff, was not desirable." This, and the wish to create a clean skyline, led Parsons Brinckerhoff to look to the building roof.
The building houses numerous BT services, including Internet and call centres; consequently the roof is littered with communications equipment. The plan to add a rooftop structure to create interest and incorporate some of this equipment was well received by town planners. "The idea was to have something that related to the masts of the stadium, and trying to a degree to replicate that," explains Price. The result is a cake-like carousel topped by a 35 m-high mast.
Amec was appointed for the construction management of the refurbishment project under a framework agreement with BT. Its role has included the installation of the blue, white and silver vertical striped cladding, which is due to be complete by the end of August, and of the mast and 80 tonne steel carousel, which are already in place. As well as concealing the rooftop equipment, the carousel has increased the overall height of the building to 120 m. This installation involved major pre-planning and close coordination between all project team members, including the m&e contractor, Hills Electrical & Mechanical.
Hills won the competitive tender for the building's lighting scheme having already completed the contract to fit temporary power and lighting and an auxiliary alarm system onto the generator rooftop exhaust flues. The installation of temporary services began on site in June 2001 and was completed before the refurbishment could begin in earnest to satisfy the site constraints. Much of the refurbishment had to be completed out of office hours due to the high levels of background noise drilling into the concrete slabs created.
Raising a giant
How do you raise a 28 m diameter carousel onto the roof of an 85 m-high building?
The possibility of total rooftop assembly was rejected as the project team wanted to minimise working at heights; raising it in one piece was also deemed impossible due to its weight and worries over glass breaking during the process. The decision was taken to pre-assemble and raise large sections, while minimising the fixings to be completed on the roof.
"The last thing that we needed was to have steel erectors struggling to put things together at a great height," stresses Price, "so we did a trial erection of the carousel at Newport." Originally a replicable segment was to be pre-assembled, but Amec opted for a full trial and the entire structure was completed and cable tray for the lighting and BT equipment installed by Hills. The carousel was then disconnected at the radial nodes for transporting to site.
The trial was carried out at a height of around one metre by the same staff that completed the final erection – a deliberate tactic so that lessons learned would be remembered and could be built upon. "The trial helped with a lot of the logistics of fitting it together that are not easy to see on drawings," explains Chris Ogden, electrical contracts manager at Hills. "When we came to put it together we knew exactly what we were doing."
Space restrictions and wind speeds around the building deemed a tower crane the best option for raising the segments. In areas the stadium is under 10 m away and Price reports: "Windspeeds have regularly reached 70-75 mph." The maximum windspeed at which a mobile crane could be used was 11 mph; the tower crane could work at windspeeds of up to 38 mph, but up to eight weeks have still been lost on the project purely due to the wind.
Prior to the rooftop work precise safety induction material and method statements were prepared. "All risks at height were considered," assures Price. However these risks are lower than they may at first seem as the carousel does not overhang the roof, there being a 3 m gap at the closest point.
The positioning on the roof was vital. The team had to make sure that supports feed into solid concrete walls running the height of the building around its central core, and that any drilling into the rooftop didn't affect BT's operations. The latter point was particularly important as an Internet server farm is on the building's top floor and one of the main electrical risers sits directly below the roof.
Lighting up
No modern design can be complete without lighting and Stadium House is no exception – the new floodlighting scheme involves specialist lamps from top to bottom, and an entire new electrical distribution system.
While structural work was being carried out on the roof, Hills was inside the building installing cabling for the lighting system. Two feeds were taken directly from the existing mains incoming panel and from these, two new sub-mains distribution have been run – one at roof level for the carousel floodlighting and one at basement level for ground level lamps. Existing services routes were followed as much as possible.
"It was quite a complex task to achieve the required lighting levels from low level floodlighting," Ogden states, "and technically more of a challenge than the roof lighting." An even 70 lux light level was wanted for the full height, so very powerful lamps were needed at ground level.
Hills selected specialist 1000 W compact source iodised floodlights from Thorn Lighting. These give the throw needed, and 15° filters will be fitted so that narrow bands of light will wash up the building. The control gear for each of these floodlights weighs 20 kg – too large and heavy to be wired to the lamp in position. Special panels were built on site to hold this equipment, with the control gear for each lamp positioned on individual skids to ease maintenance.
At rooftop level 65 lamps fitted around the top of the carousel wash the sides of the structure, which is formed from alternating strips of PTFE fabric and glass. As well as creating a neat edging to the carousel this will hide BT's equipment, which is being raised onto it after installation work is complete.
The fittings are a combination of 70 and 400 W white lamps, with eight blue lamps being used to reflect the striped colouring of the cladding across the carousel. Blue fluorescent tubes fitted behind the glass on the carousel's outer edge continue the striped colour scheme.
Four 400 W beacon lamps form a cross of light over the building roof and a further four uplighters create a spire effect with the mast, which is topped by two red aircraft warning lights. The choice of aircraft warning lights and wiring to them needed careful thought as they are 120 m above ground level. LEDs were chosen for their long life and the lamps fitted from a crane basket.
Two multi-core cables feed the lights from below. The top two sections of the hollow mast were joined on the ground and the cable fed through these before it was raised.The cable was then fed through the lower section of the mast when it was completed.
At each mast section, brackets support the cable. Ogden explains: "These take the weight of the cable and prevent pulling on the top glands. The fittings have a 20 year lifetime so we had to make sure that there was a similar life on the cable; there will be some movement of the mast and if there were no brackets the cable would have swung around and worn down."
All lamps used on the roof are capable of withstanding extreme weather conditions: a necessity due to the close proximity of Cardiff Bay. Cable was also chosen for its durability and the steelwork was double-dip galvanised.
Attempts to minimise installation times on the roof were also applied to the cabling. Hills chose to use multi-core armoured cable, so instead of 50-60 cable lengths across the carousel from the roof centre distribution room there are only eight – one to each section. These feed into junction boxes mounted onto the sections, where they are split to feed the system as required. "It was a more expensive way to do it but a far safer and better installation," explains Ogden.
Emergency and walkway lighting have been installed on a separate circuit with three-hour battery back-up.
The refurbishment is due to complete in September, with the switch-on ceremony planned for October – an event that is sure to get Cardiff residents looking skywards.
Source
Electrical and Mechanical Contractor
Credits
Project BT Stadium house floodlighting Client BT Project manager Amec Architect Parsons Brinckerhoff (Cardiff) M&E consulting engineer Parsons Brinckerhoff (Cardiff) Lighting designer Parsons Brinckerhoff (Cardiff), Thorn Lighting Main contractor Amec M&E contractor Hills Electrical & Mechanical Cable Cleaveland Cables Cable management Operational Resources, a division of Hills Electrical & Mechanical Electrical distribution Merlin Gerin LV switchgear Merlin Gerin Lighting Thorn Lighting Lightning protection EES Bristol
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