Main image: The completed d-school (Image courtesy of Terry February Photography)

LEAF Structures was approached by KMH Architects for assistance with the design of the building’s feature roof element. Having looked at the initial design and renderings of the roof by KMH, LEAF Structures could assist with design input for the design, supply and installation of the steel and glass roof.

Striking and unique roof

The striking roof element of the building is its 75m long glass-clad, steel gridshell structure. The gridshell roof was identified as an important feature of the building. At the atrium, the gridshell acts both as a skylight – bringing light into the building and assisting with the building’s six-star Green Star rating – and also as a canopy, as it spans over the entrance facade, folding down to the ground. This creates a welcoming indoor/outdoor space in which the d-school community and members of the greater University of Cape Town (UCT) campus could meet.

The d-school site. (Image courtesy of KHM Architects)

Canopies as beacons

Since the d-school is located on a small triangular site, with high foot traffic passing the eastern and western sides of the building, the canopies function as beacons and encourage students to enter the building, while assisting in beautifully rounding out the sharp corners of this triangular building. Having visited the site, LEAF Structures understood the site conditions and limitations clearly, which then helped them in their logistics and site layout planning.

The initial rendering of the d-school illustrating the gridshell roof structure. (Image courtesy of LEAF, Novum and KMH Architects)

Light structural grid

A large 4,5m structural grid was chosen. This meant that the structure is lighter and more transparent than a typical free-form grid. However, it introduced an additional challenge for the glazing, as the large structural grid exceeded the maximum width size of a single glass panel width.

To solve this problem, four triangular glass panels were used in each triangular structural grid opening. The middle glass panel is point-supported at its corner via stainless steel rotules, while the surrounding three panels are supported on two sides with edge clamps. To transfer the load between the adjacent glass panels, “floating” edge clamps were used. A total of 521 laminated glass panels, and each glazing consisting of two fully tempered clear glass lites with a low-e coating and 50% coverage dot frit, were used on this project.

The layout and arrangement of the glass panels within a single-triangular steel grid.

Gridshell structure

The final form of the gridshell structure was tweaked in the detailed design phase to ensure there was adequate slope for drainage and to more evenly distribute the loading throughout all the gridshell members. The gridshell structure is made up of 252 unique galvanised rectangular hollow steel beams, with Novum custom cast end adapters welded to each side end. These beams are then site-bolted to custom machined steel nodes. 

Collaborative design the key to success

The collaborative design phase has put this project on the path to success. The on-site collaboration and attention to detail by the general contractor, Haw & Inglis, and LEAF’s installation teams were equally important factors to this project’s overall success. Managing, sorting and installing thousands of unique components was a difficult task.

However, with a competent team, a clear sequence and a methodology of the installation process working in a collaborative manner, this complex task was broken down into a series of simple steps, which were implemented diligently and successfully.

Challenges

• Pressure on timeline: This entire process was complicated by the Covid-19 pandemic, which severely impacted the movement and availability of materials, putting great pressure on the project timeline.
Since the completion of the roof was required to close the building envelope in order to allow for building finishes to commence, its installation was thus on the project’s critical path. In addition, the glass installation could not be undertaken in damp or windy conditions.
As a result of these factors, accelerating the installation process was not possible. To mitigate the risk of delays, the main contractor installed temporary waterproofing measures and hoardings to cordon off areas of the building from the weather to permit the internal fit-out work to continue.

Freeform steel installation.

• Limited site space: A further installation challenge was posed by the limited site space. The construction site only allowed for a single tower crane, which limited the speed at which the glass could be installed, as the installation of the larger glass panels required the use of the crane to hold each panel in position while being fixed to the steel sub-frame.

    Quick assembly process

    Once the supporting structure had been installed by Haw & Inglis and embed locations were checked by LEAF, the freeform installation could begin. The structural installation started in the atrium roof section of the building. The bolted connections of the gridshell structure made the assembly process quick and easy. Smaller sections of the freeform structure (beams and nodes) were bolted together, assembled as per the method statement, and then the atrium section was installed.

    For more information, contact LEAF Structures:
    Tel: +27 11 462 5701
    Email: info@leafstructures.co.za
    Website: www.leafstructures.co.za

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