The Project entails the development of the new Head Office for Discovery Health in the Sandton Precinct and consists of three towers with glass façades and large skylight roofs on the two larger towers and required extensive steelwork support for the facades at roof level and between the three towers.
There were two key factors within Discovery’s brief.
First was to create an architectural statement that captured the essence of the Discovery brand, and that it could be identified with going forward. They wanted a building that embodied their core values.
The second factor, that follows on from the first was to improve efficiencies in the day to day working of the company.
The Discovery building was conceived from the inside out. This concept resolved itself into two large, sun filled internal atria around which the open floor plates were arranged. The atria are enclosed by 2800sqm of glazed roof, with all pause areas and agile spaces opening into them. Connecting these atria to one another is a central concourse, within which a stack of escalators links double volume bridges that stitch the floorplates together. The concourse space was conceived as a “grand central station”, a literal and figurative interchange between the company and its clients.
The roof of the building is a landscaped retreat, accessible to all employees, where the philosophy of holistic approach to health, an integral part of the company’s core values, is physically expressed.
A key feature of the building is the floating “nose” of the west tower which projects over the Katherine/ Rivonia intersection. To make a statement that fitted with the scale of the building, we needed to cantilever 17.5m over 6 floors. This posed a significant structural challenge that was eventually solved with the introduction of 3 massive concrete beams that project over the length of the cantilever. The floors are then suspended from these beams on steel, concrete filled, columns.
Another challenge was the large atrium roofs. We wanted these to provide as much light as possible which meant the engineering of a bespoke support solution that was visually unobstructed, but structurally stable. The solution from the façade engineers is an elegant tension truss lattice that supports both the weight of the glazing as well as resisting the up forces created by the movement of air over the top of the glazed panels.
There are a number of separate steelwork structures on the Project many of which are worthy of exposure and as such a brief description of the major elements is covered below.
The Skylight Roofs are probably the most iconic and interesting structures within the development and encompass an extremely innovative design concept allowing them to convey a minimal structural expression of openness.
The major construction challenge presented by the design was the requirement to effectively pre-stress the Main and Secondary (‘so called ‘Glass) Trusses post installation to ensure their bottom chords remain in tension under all loading conditions. The pre-stress is achieved by the incorporation of ‘ so called ‘ light pull-down bars which were then post tensioned on the main support trusses after installation using purpose made tensioning brackets and permanently installed strain gauges to ensure correct tensioning was applied. The ‘ Glass ‘ trusses were post tensioned using a much simpler ‘ nut turning ‘ method on their pull-down bars.
The bottom chords on the Main Support Trusses plus pull-down bars are all imported high tensile KINEX Bars from China with aesthetically pleasing end connection clevises and couplers. The Glass Trusses utilise normal structural steel round bars throughout.
The Fabrication of the steelwork had its own challenges particularly with respect to the Main Support Trusses which are of tubular construction with high tensile KINEX Bar bottom chord members. The main challenge here was in the design of the truss intersections which involved many hours with the design Engineers and careful component fabrication and fit-up in the workshop to achieve the required result.
Cantilevered Floating ‘Nose’:
The Cantilever floating ‘nose’ is a stunning architectural feature and an engineering marvel which enables the large cantilevered six storeys to be supported by the massive post-tensioned concrete beams at roof level.
This steelwork needed to be accurately manufactured with beams rolled to seven different radii seamlessly butt welded together to form the perimeter of the floors which supports the façade which follows the ever changing curvature of the building. The six floors were assembled and supported on five temporary columns at ground level, each floor has five 508mm diameter CHS columns which are concrete filled and hang from three massive post-tensioned concrete beams at roof level. After all the floors had been erected and the top of the CHS columns cast into the concrete beams, the temporary columns at ground level were slowly and methodically cut out while the structure was closely monitored for settlement deflection. This steelwork was on the critical path with a very tight programme. The final result talks for itself.
Façade Support Structure at Roof Level:
The façade support structure requires a 200x200x4.5 SHS to follow the three dimensional curvature of the top edge of the buildings, as this member could not be successfully rolled to the required radii with the required finish we opted for a purpose made curved SHS using plates which were laser cut to the required radius and shop welded to form the 200x200x4.5mm curved SHS which is curved in plan and segmented in elevation. The entire structure was erected to tight tolerances required by the façade glazing contractor and finished to the high standard required by the architect.
STAIRS – PERGOLAS – GREEN WALL:
When asked to write a report upon the above-mentioned project, immediate feeling of pride and achievement come to mind. This undoubtedly is one of Spiral Engineering’s finest sets of stair ever produced. The project team management and general site feel was on another level of professionalism and hence the success of the project.
We were set out the task of creating 11 features Spiral stairs which created an illusion of stairs which are ‘falling’ through concrete voids combining glass and plate balustrades. Together with this, we had 4 additional sweep stairs (2 in either atrium) to complete the access to the lower floors. Other works completed were the Executive Pergola and Smokers Canopy at Roof level, all boasting subtle curves in plan and elevation to the highest quality standards. Added to this was the design supply of the reception Green wall spanning over 6 floors creating a magnificent welcome to the Discovery staff and guests.
Feature Spiral stairs. (88 tons)
Each one of these stairs were double box stingers 600mm deep which alternated between glass and plate balustrades. The stairs spanned from floor to floor with no intermediate support thus the requirement for full penetration site welding to cast in channel systems to handle the eccentric loads. The handling of these stairs posed challenges in the accuracy and the very strict structural welds were required. Due to program restraints the stairs were hoisted using block and tackle off specially designed structural scaffold systems and were positioned to within very tight tolerance requirements. Full penetration site welding was carried out with every weld preparation and weld inspected and tested by Sotiralis Consulting Engineers. It was a complete team effort from the Contractor, Sub Contractor, Engineer, Quantity Surveyor, Architect and Project Manager to achieve the desired effect. The real challenge was to perfect the flawless smooth white look that the Architects were looking to achieve. Special attention was placed on weld preparation as well as high quality welding and dressing thereof. The final product having the sense of multiple floating steel stairs throughout the Atriums. This really created the WOW FACTOR which you experience when entering these amazing spaces. The stairs were finished off with 16mm laminate full frameless glass and stainless steel grab rail. The sweep stairs on the lower level also consisted of the same high quality finish. Special attention to the tapering entrances and exits did add to detail during fabrication but the smooth clean look was definitely achieved. The full package was completed on time and a great experience for all parties involved.
Jakob green wall (1 Ton Stwk, 2400m Jakob Rope, 3750 No Jakob components)
This unmistakable green wall greets you at the entrance of Discovery Sandton. The green wall spans over 6 floors and primarily comprised of grade 316 stainless steel 10mm cables, fittings, climbing ladders all fixed to slimline bracketry spreading the loads and minimizing any further stresses to the already loaded slab edges. The Green wall follows the curve of the slab edges and spans in length sections suitable to accommodate a dynamic green wall loads throughout the Growth formations. There are curved supporting channels which are staggered between floors which are perfectly set out creating a continuous slim look. This one of a kind green wall did come with its own challenges. Testing of the plant growth as well as a full pre made mock up off site were carried out to ensure the forces, loads and greenery were all covered to ensure the best possible quality for the client. There was no second chance as this installation was scheduled to be installed as a finishing trade, hence the fit first time and mockup requirements were critical to the success of the installation.
Pergola and Canopy (22.5 Tons)
Similar to the Stair structures these were high class fabrication with subtle curves in plan and elevation assembled and installed on the roof without overhead crane access. The attention to detail by the Architect on these structures was exemplary and was cause for much consternation for our finishing teams. There was no shortcut and every curve and detail were thought of by the professional team and placed as much of a challenge as the Atrium stairs in that these were not just secondary structures and we were expected to maintain all the quality and fabrication standards as we had done for the stairs.
|1. Completion date of full project||± NOVEMBER 2017|
|2. Tons of structural steel used||TASS – 700 TONS
SPIRAL – 112 TONS
NANCY – 500 TONS
TOTAL = 1350 TONS
|3. Structural profiles used||UB/UC, ANGLES, CHANNELS, CHS, SHS, RHS, PLATE AND PURPOSE MADE SHS.|
|Project Team Role||Company|
|Client/ Developer||Growthpoint / Zenprop JV|
|Architect||Boogertman & Partners|
|Structural Engineer, Skylight||Pure Consulting|
|Structural Engineer, Main Building||Sotiralis Consulting Engineers|
|Quantity Surveyor||RLB Pentad Q.S.|
|Project Manager||Morta Project Managers|
|Main Contractor||Tiber / WBHO JV|
|Steelwork Contractor||TASS Engineering|
|2nd Steelwork Contractor||Spiral Engineering|
|3rd Steelwork Contractor||Nancy Engineering|
|Steelwork Erector||Onpar Steelwork Erection|
|DRAM Industrial Painters|
|Photographer, Photo competition||Megapix Digital|