What is the purpose of the structure/project?
At 15 stories above the ground, the building consists of two basement parking levels, a ground floor or public/retail level, five parkade levels, and nine stories of offices from a podium level. It will allow everyday pedestrians to traverse without barriers from the Gautrain through to the adjacent malls.
What was the brief to the Architect?
As a building standing foremost in the center of a developing cosmopolitan area, the client wanted to have a unique building that served the needs of the client, its neighbors, as well as the public in a new, exciting, and smart way.
Was the project envisaged in steel from the start? If not, why was it built in steel in the end?
Yes, Meeting Pods, Atrium, and Media screen.
Meeting Pods: The Meeting Pods can be viewed from the landscaped thoroughfare which forms part of the showpiece of the buildings. The architectural intent for the pods is to be as open as possible, embedded in the glass. These pods are also cantilevered from the concrete frame and was a retrofit.
Atrium: The Atrium structure formed part of the glass façade, spanning over six stories, additionally it formed a part of the glass skylight structure on the Atrium roof. The structure spanned large distances and had to be as slender as possible while limiting deflection.
Media screen: The LED panels required special connections at very particular points, while constrained by the removal time by the crane, steel allowed achieving these challenges.
Give a brief description of the structural framing. What type of sections were used (e.g. hollow, cellular, I-beams etc) and why?
Meeting pods: Gravity loads were the main consideration; therefore, the loads were concentrated around one axis and normal I-section portals bolted to the concrete were the most efficient.
Atrium: The inner–and bottom chord of the Atrium vertical truss and roof truss were determined by architectural constraints. The outer chord is braced by transom beams for the façade glass, however, the inner chord had a large unbraced length due to the omission of regular knee-bracing. Similarly, the bottom chord had a large effective length for the uplift load case, due to knee bracing not being able to pierce the bulkheads of the skylights butting up snug to the truss either side. This resulted in a relatively large PFC inner chord and large I-section for a bottom chord. The purlins (bracing for the top chord) of the roof had to step, due to the skylight glass line and sheeting line being on different levels. Additionally, the purlins form part of the skylight substructure. The load path was fairly two dimensional and an RHS section was used. For the Atrium glass transoms, large SHS were used due to the wind, and gravity load cases being very similar correlating the sections’ similar radii of gyration in each direction, it was also aesthetically preferred.
Media screen: The screen consisted of a large SHS outer frame, as the facade and surrounding over cladding required a 200mm flat fixing face, it was also beneficial at the one end, as a part of the screen had to remain cantilevered to span across the crane void, which would only be filled later with structure. Considering hollow sections’ optimal spread of material away from the center of gravity it gave good results when relating stiffness/size ratios.
Were there any challenges in the fabrication of the project from the Engineer’s design – if yes, please tell? Tell more about fabrication and erection process if it was complex, difficult, innovative etc.
The manufacturing was straightforward, the main difficulty was during erection, the site has virtually no laydown areas with very limited access. The internal cladding support was all done by hand, accurate setting out of beveled columns gave a suitable platform to fix the substructure at awkward angles and positions as per the Architect’s design. The main Atrium roof is very high, and tower cranes were relied on for erection, difficulties were accessed and space as well as supporting lattice columns until the trusses were fixed in place.
What is special/ unusual/ innovative/ aesthetic about the steelwork/cladding in this project?
The final steelwork visual was not part of the architectural intent, therefore hiding it as effectively as possible while forming part of multiple systems and serving its purpose. To accommodate this architecture, it resulted in large unbraced lengths and a peculiar arrangement of members. There was also a large emphasis on keeping the tonnage down to accommodate the Green Star rating.
How did the project team work together (e.g Contractor involved early, challenges/ease of communication etc.)?
Design stage: The Engineer and Architect liaised and correlated intent and final design with BIM level two, this was vital to ensure clash detection as the complex facade shapes where hard to interpret on two-dimensional drawings.
Shop drawing stage: Even though detailed sheets were prepared, it was almost completely unused at this stage. Since such a large emphasis was placed on BIM, the model was an accurate reflection of the drawings. This allowed the Structural Steel Detailers to use the engineering model and import it straight into Tekla Structures software. Member lengths, connections, and positions translated from the model kept turnaround times for shop drawings and queries to a minimum. It also resulted in industry standard repercussions, where certain information pertaining to the length of the member can be omitted from engineering drawings and can technically only be used for design intent and setting out purposes.
Erection stage: The Engineer worked directly with the Sub-Contractor to ensure the complexity of the information was carried over to the final item. BIM was also used on site, as the model was issued directly to the Sub-Contractor, allowing them to interrogate the model on site.
|Tons of structural steel used||115 Tons|
|Structural profiles used||All readily available profiles|
|Project Team Role||Company|
|Nominator||KRU Detailing CC|
|Structural Steel Detailer||KRU Detailing CC|
|Steelwork Contractor||Central Welding Works|
|Steel Erector||Central Welding Works|
|Cladding Manufacturer||Façade Solutions|
|Cladding Supplier||Façade Solutions|
|Cladding Contractor||Façade Solutions|
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.