The Granger Bay Demountable Parking (GBDP) project arose out of the V&A Waterfront’s urgent need for additional parking. The site consisted of an open area on approximately 12 to 15m of fill material with a gravel surface approximately level with the roads around its perimeter. It was selected for this project due to its close proximity to the Victoria Wharf Mall; however, it had been earmarked for a substantial development at some stage in the future, possibly five years’ time. For this reason, the V&A Waterfront Development Team decided to consider a temporary parking solution such that the land could be used for parking in the medium term and then developed as planned in the future.
Initially, the V&A investigated importing a proprietary system. When considering the full project cost, the proprietary system would have cost more than a traditional concrete parking garage of the same size, although it would have had residual value after five years since it could be re-used elsewhere. The V&A Waterfront then approached LH Consulting Engineers to develop an alternative scheme using local technology. Together with the Quantity Surveyor, Union Steel, NMC Construction and Portland Concrete, this scheme was developed to suit the following requirements:
– The structure had to be easily demountable and able to be re-installed elsewhere
– It had to be modular such that the structure – or parts of the structure – could be reinstalled in different configurations
– It had to be sufficiently lightweight such that shallow foundations would be adequate (the fill material was not sufficiently consolidated to support conventional loading on shallow foundations)
– The structure was to provide two levels of structured parking and be designed to receive a third level
– The project had to be designed, developed and completed within a six month period, including obtaining the necessary Council approvals
The cost for the local alternative came in at approximately 60% of the cost of the proprietary system. This option was therefore given the go-ahead from the V&A.
The structure was set out on a 7.5m x 8.5m grid and consisted of a structural steel frame and precast hollow-core floor slabs bolted to the frame. Primary beams consisted of plate girders with a parallel flange channel section for the top flange. The precast floor slabs were designed to span the 7.5m between the primary beams. Curved plate sleeves were inserted into the ends of the hollow-core slabs to enable an angle section to be bolted to the underside of the slab at each end in the factory. Once the panels had been dropped into position on the structural frame, the factory- fitted angles were then bolted to the sides of the channel section top flange. The joints between the precast panels were then grouted to ensure load-sharing between panels and diaphragm action for stability purposes. No topping was required.
The perimeter barriers spanned between columns and provided a threefold function of balustrade, parking barrier and support to the cladding system.
As part of the development process, two full bays were constructed. After inspection by the Design Team, the mock-up was then completely disassembled and reconstructed. This prototype served to demonstrate that the structure could be taken apart and re-installed without difficulty and without damage to the components.
The choice of materials allowed for off-site fabrication, which got underway while the Principal Contractor prepared the platform and constructed the reinforced concrete column bases. The modular design resulted in a high degree of standardisation of components, which enabled a fast- track detailing and fabrication process. With careful planning of the installation sequence, the two levels of structure were fully installed over the 90m x 50m footprint in 49 working days.
To comply with building regulations, the structure was required to provide 30 minutes fire stability. The precast floor slabs inherently met this requirement, but the structural steel required additional protection. This was addressed by means of intumescent paint, which was applied in the factory to save costs and time.
Although this was intended to be a temporary structure, corrosion protection was a concern since the site is approximately 100m from the sea. A high specification paint application with a five-year warranty was chosen over hot-dip galvanising as this was more economical, met the design requirements and saved time. Drilling and fixing to the steelwork by follow-on trades was restricted and closely monitored to ensure that any damage to the paint system was carefully repaired.
The cladding system had not been developed by the time the installation of the structure had commenced on site, so the support system had to be retrofitted. In light of the abovementioned restriction on drilling into the steelwork, it was decided that the cladding system had to be clamped around the paring barriers rather than relying on conventionally bolted brackets.
Despite delays caused by external factors, the structure was completed in time for the end-of-year tourist season and provided a much needed additional 350 parking bays to the V&A Waterfront. When the time comes for re-development of this land, it is intended that the structure will be relocated elsewhere within V&A Waterfront.
The potential for re-use of the structure is exciting from a sustainability point of view. The modular construction and component detailing allows for flexibility in re-use. The structure can be re-used elsewhere in its entirety, in part, in different formats and even for different occupancy classes if a topping and shear connectors are introduced.
|Project Team Role||Company|
|Client/ Developer||V & A Waterfront|
|Structural Engineer||LH Consulting Engineers (PTY) LTD|
|Quantity Surveyor||BTKM Quantity Surveyors|
|Project Manager||NMC (PTY) LTD|
|Main Contractor||NMC (PTY) LTD|
|Steelwork Contractor||UNION STEEL|
|Structural Steel Detailer||UNION STEEL|
|Steel Erector||L&A Steel Erectors|
|Corrosion Protection Paintwork Contractor||Nu Nation Protective Coating|