One Blackfriars stands out as one of the new icons on the ever-evolving London skyline, but there were a lot of engineering challenges to make a structure like this work. This week I sat down with Jacob-Adrien Béglé (one of the Yuanda Team members) from our Yuanda engineering department to talk about some of the engineering decisions that were involved in creating the unique cap of this structure.
One Blackfriars is a 170-metre tall tower across the river from Blackfriars station here in London. The development includes two smaller buildings adjacent to the primary tower. Designed by SimpsonHaugh Architects the tower provides exceptional views across the capital.
Affectionately dubbed “the vase” the tower consists of a double-skinned facade. Meaning there is an inner facade with a sliding door allowing access to a winter garden with secondary glazing to provide protection from the elements. It has over 9100 panes of glass on the inner and outer facades and at its peak had over 1400 people working on the construction process.
Just the cap alone weighs around 130 tonnes. Believe it or not, this is actually fairly light for a design such as this. This is broken down into the following parts:
Most buildings of this “curved” shape (like The Gherkin) are facetted, meaning that from afar they appear to be curved, but, as you get close you can see that the shape is formed from many flat pieces of glass. This is much easier, but not what was desired in this project. The Cap is unique in that it contains double-curved, twisted, and variating sections of steel, clad with flat, cold bent, single- and double-curved glass.
I like to imagine a soap bubble cut into several parts. If you look at one small part, it has a curve (radius) along both the x-axis and the y-axis. A curve is a radius in one direction only. While this is very common in the natural world, it’s not the kind of shape that is easy to make using 20mm thick laminated glass.
Producing double-curved glass is difficult. Each pane needs to be heat formed over a latticework that needs to match the steelwork that it will eventually be installed on. All panes that make up the cap are different.
On top of that, we would allow for the glass to be cold bent during installation to hold it in the final geometry. During this step, the glass is “pressed” to its final form by a small deflection amount that remains in the glass forever.
There were a lot of calculations required to make sure the glass could handle this.
There were a number of engineering challenges that we had to overcome at each step. Even with all the technology available today we had to double-check (and triple-check!) each calculation to make sure there were adequate tolerances for each element.
Each piece of steelwork and glass was modelled in 3d, piece by piece to match the geometry designed by the architects.
Being a near artisanal product it had to be manufactured by specialist workers in a state of the art facility. The large steel pieces consisted of a twisted profile at one end (to connect to the ones running up the building), this then had to sweep into a doubled curved profile at the other end. All constructed from one single piece of steel.
The structure was put together initially at ground level (at our test facility) to ensure that everything would fit together correctly when installed 170 metres in the air. Trial glazing was installed to test the cold bending process.
When in London we had a team composed of specialists in each of the required fields. We had design & engineers onsite, fabricators, transport management and some of the best heavy lifting specialists in the world to draw knowledge from.
In the end, it’s all in place and I have to say that it looks pretty good! We’re proud of the team here at Yuanda.
Photography by Ben Kepka