Project Profile: Pretoria Porsche Dealership

The new Pretoria Porsche dealership is the fourth facility built in South Africa in the last ten years. This showroom will be their first dealership in Pretoria with the objective to increase Porsche’s footprint in South Africa. The 13 000m² dealership contains a large showroom for new and pre-owned car sales, administrative offices on the ground and mezzanine levels; a new workshop for servicing and maintenance of the vehicles; a parts store; bodyshop for the repair of damaged vehicles; valet wash bays; and stores for general purpose storage. There is also a 4 500m² basement parking area for the staff and new car storage.

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The showroom curved facade, with glass curtain walls is an architectural feature prominent in all Porsche centres. A lot of the exposed steel on the project is driven by Porsche’s corporate identity especially the showroom’s columns and exposed bottom chord to the trusses. The facade support structure is made out of hot rolled vertical members bracketed off the exposed steel circular columns and cold rolled girts of matching depth were used to allow flush faces internally and externally which were clad with aluminium panels.

The steel over the workshop and bodyshop was chosen for its long span ability over the required areas. In order to satisfy deflection limits on relatively long roof spans over workshop and bodyshop areas, options to use plate girders or conventional parallel boomed trusses were considered. The plate girders option was found to be unjustifiably heavy and prompted for the truss option. In the past raised monitor sections were placed on top of the roof structure to provide natural light and ventilation. But, owing to long roof span and slope, the truss and monitor arrangement would have led to unacceptably high roof profiles.

The roof girder and monitors were then innovatively combined into a single Vierendeel truss. Unlike a conventional truss, with triangle-shaped voids and pin-joints, the Vierendeel utilises rectangular openings and rigid connections, designed to resist bending forces. This kind of truss is rarely used by engineers since it is usually less economical. However, after careful optimisation, though slightly heavier compared to the conventional system, with a very industrial appearance, the Vierendeel truss could serve both aesthetics and functionality. The straight lines and symmetrical square openings of the truss gave a clean and elegant look to the space and maximized natural lighting.

The truss was pre-cambered to eliminate all dead load deflections leaving a very straight roof line.The upper and lower purlins were aligned with the top and bottom chords of the Vierendeel, providing a very neat, uncluttered appearance. This was achieved by ensuring that each structural component was accurately detailed.

The metal sheeting to the exterior and interior is attached to the steel framed structure.
The front cladding externally and internally is Hulabond aluminium panels fastened to an aluminium subframe that is in turn attached to the steel frame.

The black horizontal cladding around the workshop and bodyshop, a signature element to the Porsche ‘look’, posed a challenge in the Pretoria climate, and called for heavy insulation. Internal walls were also to be clad. Taking that into consideration, vertical girts were then designed to serve as fixing supports for both internal and external sheets, with insulation layers in between.

The general concept of the building was to construct a concrete core with slab-column configuration and then landing steel roofs on top. One of the challenges faced during the project was integration of concrete and steel structures, due to discrepancy in structural tolerances between concrete and steel constructions.

The program was tight, rain delays for the first month of the programme and industrial action in the middle of the construction process put the programme on the back foot from the get go. This was a challenge in its own right and required all parties to put in the extra work to complete the project.