Ground-Breaking Use of Precast Concrete Anchors New Motor Museum
In what is undoubtedly a unique application of precast concrete in South Africa, 12 U-shaped precast concrete columns, manufactured by Concrete Manufacturers Association member, Cape Concrete, have been used as the primary anchor material for the construction of a motor museum at Lourensford Wine Estate in Somerset West.
Limited by town planning to a maximum 900m² footprint, architect Anton Heyn designed the building to resemble a barn and to accommodate as many cars as possible, 42 in all, as well as motorbikes and other memorabilia. A pair of timber barn doors at each gable end provides vehicle access and cars are displayed in four bays, each flanked by four of the precast columns.
“To a large extent the exhibition space determined the shape of the concrete columns,” said Heyn. “ In order to optimise our limited space allowance, we angled the two lateral faces of each column at XXº angles instead of at right angles. This created an additional 20% of exhibition space which not only allowed 10 cars to be parked in two opposing fanned crescents in each display bay, but made for better spectator visibility.”
A 3m wide central section, which runs the full length of the barn, forms the viewing area and another two cars can be displayed in the reception area situated in the middle of the building.
The precast columns were used to secure the building’s lighter construction elements such as the timber-framed walling. It was clad with Zinacalume aluminium roof sheeting which was also used for the roofing above each of the four exhibition bay sections and the central reception area.
The roofing also comprised four 15m x 2.6m in-situ slabs which were cast between the Zincalume roof sections, and were supported at each end by the columns. The slabs were tapered from 350mm to 250mm to provide a slope for stormwater which drains into the hollow sections of the U-shaped columns. Similarly, the five discrete mono-pitch Zincalume roofs, slope in the same direction, draining into gutters mounted on the building’s western elevation.
In addition, eight 15m x Xm (height) in-situ beams were cast on either side of the four concrete roof slabs to support four wooden truss assemblies for the Zincalume roofing and it ceilings.
The columns are founded in 120mm (depth)x 200mm (width) U-shaped channels which were cast into the footings.
“We had to increase the depth of the footings to ensure we didn’t compromise their structural integrity,” said structural engineer, Gawie Combrinck, managing director of GFC Consulting Engineers. “The original design had a 50mm cover above the reinforcing steel but it wasn’t sufficient for the founding channel. So we increased the cover to 150mm to give us a 120mm groove. Once a column was lowered into a groove it was shimmed level and grouted with a flowable non-shrink grout.
“When I first arrived on site I thought to myself this is beautiful concrete. I realised then that it heralded a spectacular concrete display because with tolerances of less than 4mm on each, the columns were as perfect as you can get them. There is not a single crack on any of the units thanks to some heavy reinforcing.
Cape Concrete director, Walter Botes, commented that because an off-shutter finish was required on all sides, the columns were cast vertically.
“This entailed pumping self-compacting concrete from the bottom of the mould, a process which eradicated air bubbles without the need for external vibration and gave a much smoother finish. The columns were cast with rebar extensions at the top to tie into the cast in-situ roof beams.
“The four corner columns were cast with an additional concrete wing to which the timber barn doors have been attached. These columns are all identical, except that two were cast with door openings for staff access. A single mould was used for casting all 12 columns but the mould required some slight modification for casting the four corner units.
“Transporting the columns to site required careful planning. Weighing 13 tonnes apiece, they were lowered onto their side and delivered two at a time. Using lifting anchors cast into the top of the columns, they were tilted into the upright position before installation. We used a four-legged chain running over two rollers, belt slings and a spreader beam to lower the columns into position,” said Botes.
“This project is quite unique,” added Heyn, “and was completed in what was a very tight budget. Precast concrete is a very flexible and malleable building product and I can’t think of any better material which we could have used, especially as we needed to opt for shapes which offered better space utilisation.
“I’m very happy with the excellent finishes achieved by Cape Concrete. As an architect one couldn’t have expected better than this. It’s what we visualised and it’s turned out perfectly,” concluded Heyn.
The motor museum follows the contours of the site and the flooring in each bay section is stepped down 200mm. The floor has a very smooth finish which was protected during construction with plastic sheeting and a layer of sand.
As direct sunlight dulls paint work over time, the museum’s lighting is generated artificially and naturally; diffused natural light is supplied by four corner windows in each display bay and by windows above the reception area. And an air pressure system has been installed to keep the museum as dust-free as possible.
The museum is linked by a path to the Lourensford market area where, in a second phase of the project, additional cars will be displayed in cut-off containers. The path and the immediate area surrounding the museum has been paved with grey interlocking pavers supplied by concrete Manufacturers Association member, C.E.L. Paving Products.
Architect: Anton Heyn
Structural Engineers: GFC Consulting Engineers
Quantity surveyors: Piet Bentum
Main contractor: Build A Way
Precast concrete columns: Cape Concrete