21 juli 2016

Timber-framed glass triangles in Jeddah

Situated on the 49th floor of the 236-metre high 'Headquarters Business Park' in Jeddah (Saudi Arabia) is the Al-Dabbagh GroupPentagram London designed the interior of the main office with a spectacular six and a half metre high curved wall of wood-framed glass triangles. Smeulders Interieurgroep took on the challenge to realise the wall in collaboration with glass specialists Si-XTobias Nagel for 3D modeling, and ABT as structural design engineer.

An inner wall on the 52nd floor has to meet fundamentally different requirements compared to an inner wall at ground level. Façade panels can fracture or break and need replacing for example. Suddenly facing a severe storm (wind force 8) at that altitude is not uncommon in Jeddah.  

Glass consultant Erwin ten Brincke from ABT: "We had to make the wall withstand against wind speeds of up to 70 kilometres per hour. And since the wall is 6.5 metres high, this turned out to be quite a challenge."

Ten Brincke immediately fell for this magnificent project. However, he was unable to predict its feasibility. "But I considered: we have some of the smartest people on our side; Smeulders, who is great at building elements; SI-X, who is a glass construction company lead by an architect; a great 3D modeller; and myself, with the necessary expertise from  our Glass group... I was confident that we were able to come up with a suitable joint solution."

3D model
The designers first created a 3D model of the entire wall, which was then converted to a 3D structural analysis model. "It is customary to regard a convex wall as a flat wall as this is easier to analyse. But a curved wall is able to distribute forces much more efficient in comparison to a straight wall. Having said this, I even doubt whether a straight wall would have been feasible in the first place. So we first made sure to prepare the computational workflow. This implies  a relatively larger investment in engineering in the initial design stage, but results in added value at the end of the design process. It's not about your price, it's about how much you're worth."

Afbeelding: Foto_intekst_jeddah_businesspark

Glass doesn't need to break
The scale of the wooden structure then started to pose a problem. "Given the wall had to withstand an incredible amount of (wind) load, the dimensions of the wooden frame would have been much larger than the architect originally had in mind. This was solved by abandoning the idea that all panes need to be replaceable. This can be considered a Pavlovian response: with glass, people often immediately think that it is susceptible to breakage and must be replaced. But we make it so strong that the chance of breaking is extremely minimal. So the real question is: do we even need to take this into account? As such, we let go of that concept entirely, which enabled us to prefabricate larger and more slender elements. As a result, the assembly is more precise and requires less effort on site. The wall was eventually entirely built in the factory before it was shipped to Jeddah." 

Invisible connection
So, by abandoning conventional methods, new opportunities arise. The same  principle holds for the design of the connections. "We wanted to create an invisible connection, but it had to be safe as well. There isn't a design guide for wooden diagrid structures with screwed connections. 

We were therefore initially considering bolts through and through, but this can not be regarded as a subtle solution. I thought a system of screws and pins might do the job, but somehow I didn't feel entirely confident with the idea. A six metre high wall and wind speeds of up to 100 kilometres per hour are serious boundary conditions to take into account. That is why we engineered the entire structure successively by means of structural simulations, a full-size mock-up and laboratory tests. Step by step, we refined the design and realised a wall which we are all very excited about. Feel free to challenge me any time with another wood-glass-structure."

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