In November 2017, WSP joined forces with Stefanutti Stocks to respond to a bid for the construction of a new body shop for Mercedes-Benz South Africa as part of a major expansion to produce a new generation vehicle to be launched in 2021. This 45,000m2 building forms part of a R10 billion investment at the East London manufacturing plant where four new facilities, totalling 100,000m2, were constructed.
The body shop is typically the second stage of an automotive production line. After being formed in the press shop, the various body panels are assembled in the body shop before being treated against corrosion and then proceeding to the paint shop, powertrain assembly, and then general assembly.
The Architectural Brief
Daimler, the parent company of MBSA, appointed another consulting team to develop the technical specifications and high-level scheme for the overall facility, focusing on the various operational requirements from the client and equipment manufacturers.
These operational requirements for the body shop necessitated a double-storey building with a wide column spacing of 14.4m by 18m. The 22,000m2 suspended the first-floor is situated at 10.5m above the ground floor, offering 8.5m clear operational space underneath, and can withstand large storage loads of up to 4000kg per square meter. The first floor is covered by the lightweight steel roof, which also houses a 1800m2 plant area, above another 8.5m high operational zone. In addition to this, the façade consists primarily of a sheeted steel structure, with a steel-framed brick wall providing the necessary firebreak to the adjoining building.
The primary focus of WSP’s structural bid development was the buildability of the extremely heavy first-floor structure. In order to meet the programme requirements, construction had to take place concurrently on the ground-floor, first floor, and roof level. The erection of the steel structure had to slot in between the construction of the 2m deep inverted T-shaped primary concrete beams and the installation of the 30ton precast secondary beam system. The advancement of the steel erection was an integral part of the dovetailed construction programme in order to clear the space for the heavy lifting equipment for the precast concrete beams. The necessary speed and agility could only be achieved with material as light and nimble as structural steel.
The Structural Framing
The lightweight steel frame for the roof came with the following challenges:
The roof build-up mimics a European-style tanked flat roof, as opposed to the gravity-drained sheet metal roof types common in South Africa. The roof type consists of various layers of insulation and waterproofing, weighing five times more than the cladding for a conventional South African warehouse roof.
A portion of the roof houses the plant room for the building and is subjected to extremely high loads compared to typical warehouse roofs.
Due to the complexities of the hybrid first-floor structure, the roof structure had to be erected after placement of the primary first-floor beams, but before placement of the secondary beams and precast floor panels. This had to be a fast, reliable, and redundant process due to its critical role in the construction programme.
To support the unusually high roof loads, the 18m trusses make use of horizontally orientated channel chords in lieu of angles, which would typically be used for trusses of this length. The lattice structure consists of two sets of optimised angles welded to each side of the channel chords, reducing the requirement for heavier gussets while also lending a higher degree of lateral and torsional stiffness to the truss, ensuring easier handling on site. The girders follow the same rationale, but exchange the channel chords for universal beams, providing more compression capacity for their higher loads over the 14.4m spans.
The connection design and detailing, especially for the girder-to-column and truss-to-girder nodes, focused on a reduction of risk during the erection process. All major connections are first seated and secured, after which the main structural bolts or plates are fastened. This greatly reduced handling of heavy bolts and plates while girders or trusses were suspended from cranes.
Internally, the roof structure is supported by slender UB columns which were later partially encased by concrete to reduce the effective length of the steel section and protect it against accidental damage at floor level. The façades consist of intermediate UB columns spanning vertically to sets of CHS bracing, which directs the lateral forces to the primary reinforced concrete columns at roof level.
For the exposed, tunnel-like canopy on the eastern facade, simply supported castellated beams were utilised to limit the weight of the long-span beams while also providing a reticulation route for electrical and sprinkler services above the clear height required for delivery vehicles.
While Daimler’s technical specifications called for the internal and external layers of the building’s side cladding to be made from aluminium sheeting, there was a unique application of steel SAFLOK 700 sheeting as a load-bearing underlayer of the roof build-up. The SAFLOK sheeting was rolled from 0.8mm thick steel and installed inverted to offer a flat working surface. Load-bearing capacity and safety factors were determined via testing prior to installation. The bitumen-faced mineral wool panels were secured into the steel sheeting with self-tapping screws on large plastic washers.
The competitiveness of the project demanded that the steelwork be designed very economically, which always results in fabrication and transport being more challenging. The lattice elements for the trusses and girders were optimised to the smallest possible sizes without risking susceptibility to detrimental distortions during galvanizing. Furthermore, a detailed stacking method statement avoided damage during transport and lay-down on site. While the steel erection onto half-completed concrete beams 10.5m above ground posed a significant OHS challenge, WSP’s safety-focused connection design and a laterally stiff concrete column perimeter added valuable stability and reliability to the erection process.
What is most impressive about this project from a technical perspective?
If it was not for the inherent benefits of steel as a construction material, the impressive programming feat of this project would not have been possible. The safety and speed of the lightweight steel solution enabled the roof construction to slot in between two significant concrete construction phases of the first-floor structure.
How the project team worked together
Due to the complex nature of this factory, all the BIM models (engineering, architecture, fit-out) needed to have a very high level of detail to ensure that in-depth coordination and clash detection could be completed virtually before causing delays on site. WSP developed an LOD350 structural model with all steel elements modelled to a high degree of accuracy in 3D, instead of falling back to 2D drawing details for secondary steel items.
In addition to conventional drawings, WSP was able to issue 3D models of multiple assemblies to aid the workshop modelling process as well as the review thereof. Another major benefit of the collaboration between WSP and the workshop detailer was the agreement to model a typical roof bay and facade portion at a very early stage for in-depth review before proceeding with the bulk of the typical structure.
Project motivation editorials are provided by the project nominator. If any technical details, company names or product names are incorrect, please notify the SAISC so that the error can be corrected.
|Physical address of the project
|Cotton Road East
|Google Maps link||https://www.google.com/maps/place/33°01’37.6″S+27°53’46.9″E|
|Completion date of steelwork||June 2019|
|Completion date of full project||December 2019|
|Tonnage and steel profiles used||1,112 ton UB, UC, C, L, CHS, CFLC|
|CLADDING (If applicable)|
|Completion date of cladding||July 2019|
|Cladding profile/ type used||Safintra Saflok 700, Safintra Industrial 7|
|Cladding area coverage||42 742 m2|
|Cladding tonnage||218 ton|
|Project Team Role||Company|
|Project Lead Factory Planning, Client||Mercedes-Benz South Africa|
|Architect||Osmond Lange Architects + Planners|
|Project Manager||Arbuthnot Projects|
|Main Contractor||Stefanutti Stocks|
|Steelwork Contractor||Impact Engineering CC|
|Steel Erector||Impact Engineering CC|
|Cladding Manufacturer||SAFINTRA South Africa (Pty) Ltd|
|Cladding Supplier||Safal Steel|
|Cladding Contractor||Impact Engineering CC|
|Corrosion Protection||Phoenix Galvanizing|
|Photographer, Photo competition||WSP|
|Photographer, Other submitted images||WSP, Stefanutti Stocks|
If you were a part of this project, and your company details are incorrect or missing – please notify the SAISC so that the error can be corrected.