WESTGATE SHOPPING CENTRE, OXFORD
Hayward explains. “To create something as simple as this roof is very intensive. We used parametric modelling – in terms of geometry and making it work there’s quite a lot involved.”
South Arcade
The 110 metre long South Arcade presented BDP with a different set of challenges. With Leiden Square and Middle Square, ventilation – in order to allow any smoke to billow out in the event of a fire – was more or less taken care of by the spaces’ open form. South Arcade however, which connects the two, presented a much “tighter space” explains Downey. “We couldn’t float the roof like we did on Leiden Square because it started to get too high for the height restriction,” he says. The roof was therefore broken up into three sections running down the space – a main section that runs down the middle with two raised elements either side, allowing them to halve the required gap for ventilation. The design for the main glazed roof section that runs down the centre of the arcade progressed from utilising cold bent glass to a more cost-effective sawtooth design, which minimised its height and allowed for the run off of rainwater. Each piece of single-glazed glass – laminated with a PVB interlayer – is at a three-degree fall and rises up 150 mm, supported by struts placed underneath and fixing to a main beam at either end. BDP built the gutters into these beams, which “minimised the detail by using elements for multiple things,” says Hayward.
The two raised elements on either side were initially going to be glass as well. However Allies & Morrison’s design for the louvre elements that run up above the shop fronts progressed, so instead of stopping at the roof they continue and extend partially across it. “These were value engineered and because you can’t really see them the decision was made that they could be ETFE,” Downey explains. Rather than the usual ‘pillows’, this is a single layer kept tight by cables running through it.
Middle Square
The smallest of the three spaces, BDP’s work on Middle Square consisted of covering the square itself plus two lanes either side. “It started off as a continuous glazed element, but that was further broken down as a design development,” explains Hayward. “We worked with Dixon Jones to redefine it and it became a very simple,
ADF MAY 2018 strong parallelogram.”
The parallelogram aspect is fixed to the two buildings either side and pitches up slightly at two points. The two roofs over the lanes sit at a lower level and “there are overlaps of 45 degrees to prevent rain ingress.” The glass is supported by “strong, deep steel beams which define the parallelogram, then secondary steel beams to split up the glass,” Hayward explains.
A collaborative development An extensive project involving so many contractors and architects naturally required a substantial amount of collaboration. “When you’re integrating the common elements into the individual buildings it’s critical that there’s a level of understanding of what each other is doing,” says Hayward. Supporting this aim, BIM proved key to the success of Westgate, allowing updated drawings to constantly be shared.
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© Gareth Gardner
To create something as simple as this roof is very intensive – we used parametric modelling
Neil Hayward, BDP
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