At the University of Chicago's new building in Paris, Lucas and his colleagues are both limiting overall materials use, and picking the right material for each part of the job.
LG : It's a combination of materials that were precisely chosen to reduce the carbon footprint but that's not the only factor, that the whole building is located on top of the railway and the way we distributed the materials we use for the structure is very much a consequence of the fact that it's located on top of the railway.
LG : At the rail level you have an existing durable and robust concrete structure. That means you have a predefined location for your supports and a predefined capacity as well. So you need to minimize the weight of your building but you also need to reach these supports and transfer the loads from the superstructure with a certain structural grid to the predefined supports below.
For these transfers, strong and light steel was the right choice. Timber was then used as much as possible, in order to cut carbon impacts. Other material choices were made to reflect the character of Paris, while still being sustainable.
LG : Jeanne Gang, the architect, came up with a very interesting idea to use external shading sticks made of natural stone. And I think for someone who grew up in Paris, there's a very natural and strong connection between this material and the history of construction in our city, right? But here we need to make them lightweight, so we combine them with a composite material to reduce the weight.
On another new structure, a residential tower, the benefits of materials substitution are being pushed to a new level.
LG : When we talk about timber on medium-rise and high-rise buildings at the moment, usually we're talking about spruce, glue-laminated timber.
LG : And in this particular case, we went for beech timber, which is stiffer and stronger, but we used it only for the vertical columns, the load-bearing columns.
Elsewhere, more standard timber beams were used, along with just a little concrete for parts of the core and foundations.
LG : When Elioth by Egis was chosen to provide structural engineering services for the redesigned restaurant on the Eiffel Tower, the team took the ultimate approach to sustainability: doing the absolute minimum possible. Here, understanding this venerable structure was key.
LG : The whole structure of the Eiffel Tower is made of puddled iron, or fer-puddlé in French. And that's the material that we're not really using anymore nowadays. But basically, the specificity of puddled iron is the refining process of the iron in order to have something relatively homogeneous as a result. And there's a step in that process where the worker would use, let's say, a long hook to activate the chemical reaction of the refining of the iron.
That manual mixing makes the material quite variable.
LG : You need to investigate your material and you need to talk a lot with the engineers in charge of the structural integrity of the tower to get as much information as you can.
And the minimal approach requires further investigation, to identify just those changes needed to bring the restaurant up to modern safety standards.
LG : The lateral facades needed to be completely removed and replaced in theory because of the new fire requirements. And the whole organization of the plan was changing. We needed to create floors in some areas, to create holes for a new staircase in another.
LG : The easy solution would have been to just keep the bare minimum in terms of the existing structure and just create a new one for the rest of the floors. But we try to really understand accurately the role of each structural element of the existing restaurant to have a very minimal intervention.
The team worked within tight weight restrictions. This both ensures the structure is sound, but also minimises carbon impacts and materials use.
A project like this illustrates the new challenge structural engineers face.
It’s not about pitching a client to accept more work.
It’s about making the case for less work.
LG : It's not always easy to go to the client and explain you should actually go for less than what you have in mind when you thought of your project. And I think in order to convince the client that that's the right way to go, you need to be able to demonstrate that you would still have a very high quality result.
