Working for client Galliard Homes on a design by architectural practice Rolfe Judd, Meinhardt UK is providing civil, structural and façade engineering consultancy services for Harbour Central – a mixed use, 907-home residential project that raised special challenges because of the height of its tallest tower and a basement that required record-breaking prop spans.
The design of the project, comprising seven buildings between eight and 42-storeys tall, was limited by how much the buildings would sway in the wind. Meinhardt engineered strict tolerances into the design, allowing for less than 300mm of movement in the strongest winds.
To refine and test the design, a physical model of the development was put through its paces in the BMT Fluid Mechanics wind laboratory. As the site is currently relatively exposed but with a growing number of tall towers, the team tested not only for the current environment but also for what might potentially be built there in future. Several wind mitigation measures, including optimising balcony heights, were introduced to provide a comfortable environment for residents and users of the space.
Meanwhile, the façade team advised on designing and specifying a cost-effective unitised curtain wall cladding solution to the complex articulated façade design that would achieve the design aspirations for the development and comply with sustainable construction rules on energy efficiency. The prefabricated façade units will arrive on site ready to be lifted into place to comply with a short installation program and limited space on site.
Building maintenance units on the roofs of the towers allow building access and maintenance to the 60,000m2 of façade.
By December 2016, the groundworks, basement and podium slab were completed. Slipforming of the cores for the four of the tallest towers – which are 25, 28, 36 and 42 storeys – has commenced and all four will be underway in early 2017. Cores will be slipped to around the 22-storey mark at a rate of three metres – almost an entire storey – a day.
Suspended between two of the blocks, an additional ‘link building’ will house a gym, leisure centre and lounge. The steel-framed structure will span the two buildings supported on two large fabricated steel girders.
The project’s 140m x 70m single-storey basement required a six-metre-deep excavation with some significantly deeper excavation to accommodate car park stacking machinery. The entire basement was propped during earthworks across its 70m width and diagonally with 17 props ranging from 610mm to 1220mm in diameter – making it one of the largest propped basements in Europe.
This record-breaking solution was driven by the project construction programme. Given the depth of some of the excavations, temporary raking props would have cluttered the basement and made access and construction difficult. The easiest way to provide access to the whole basement was meeting the challenge of the 70-metre span. Once the basement slab was in, the retaining wall was sufficiently stiff and contractors were able to remove the megaprops. It took approximately six months from the first prop going in to the last one being taken out.
As the usage of upper floors is primarily residential, the buildings have been designed so that columns come down around the perimeter and in the party walls between apartments. To create column-free zones in the lower levels of the tower, the team introduced a major 2mdeep transfer structure with nearly 400 tonnes of reinforcement.
It is undeniable that this is a project of spectacular design and scale, with engineering challenges to match. For its residents, the views from the penthouse balconies atop the tallest tower should be equally breath-taking.