Structures 0-3: Compare and Contrast

hello i'm paul casabian and i'm a structural engineer and we're talking about how to understand structures and as part of that i always think it's helpful to look at the structures in the world around us to compare them to to see the differences between them and before i show some of these i do want to say highly aware that the choices we make as a society for the built structures that surround us are not driven by only structural behavior there are a lot of needs above those that drive many of the decisions on what they are how they behave not just structurally how they look how they're perceived by others so understanding some very critical elements that can drive what something is i think it's still helpful to at least be aware of what they mean structurally right so that we have an understanding of that piece that's the part that i think is important i actually wanted to start with a building that i used to see um uh when i was on the bus going to school and watching it get built it's the sainsbury wing next to the national gallery at trafalgar square in london and on this side you can see this is the facade of the building you're seeing columns this debate sort of closely in space next to each other not in a very standard way it's probably obvious to everyone that those are not structural columns this is essentially a facade decoration on the exterior of the building in fact if you go around the corner down the side street where it's actually a brick uh facade in many ways actually this building is part of the architectural intent um it essentially acts as a bit of a mirror to the buildings that are opposite it the structure is inside it's it's hidden it works it's safe and architecturally what you see on the outside is a facade an architectural set of choices that's fine and here i'm going to contrast it with another museum the pompidou center in paris now a lot of people at the time it was built and still today feel that it is somewhat ugly or harsh and not in keeping with paris again that is not the discussion that i would like to have right now so much as to point out in contrast the structure of this building is very much on show the exterior of the building everything you're seeing is the building structure which of course is not very typical for buildings but it's certainly very interesting and this side view um in fact shows a lot of what's going on for these very long spans it's taken at the end in a push-pull so compression and then tension to balance out the ends of these very long span trusses it's a fascinating building it's very sort of obvious in how it works also a museum but in many ways an interesting visual clarity to the structure and i want to take a moment to talk for a second about structural honesty this is something that a lot of people talk about and often sort of say that a building should be structurally honest and i think to some extent that's supposed to mean that if something looks like structure it is the structure and from my personal opinion i think there's as i said some issues that are above structure for the reasons that we build the buildings and infrastructure around us and also for reasons we'll get into as we go things it's maybe not always so clear what structural honesty or pure structure might be or even why it would then be perfectly useful after all at some point we need flat flaws and one might argue that those are not structurally honest they don't express the forces in them so i just wanted to take that moment here while we're going so i love this one this uh this is you may have seen these around this is uh an antenna right for signals and clearly uh whoever was in charge felt that the antenna itself wasn't good enough to look at and they have chosen to design manufacture and install cladding around the antenna to make it look like a tree and pretty sure all of us can tell that's not a tree but still someone's chosen to do this so we have structure covered fine and essentially covered by yet another structure with little cantilever branches coming out i'd like to contrast this with another antenna a radio antenna the eiffel tower right also quite controversial at the time it was built currently essentially one of the symbols of paris and france it's interesting how things can change over years and acceptability um but very much uh on view structure right it is um you can it's the metal structure there's no real cladding to this um it it's for overall form is is essentially linked to how uh the wind forces go on it it tapers so that the wind at the top is less it broadens at the base to be more stable against wind but you know just just while we're talking the area down at the base that arch looking area down there those parts that form the curve shape those are decorative those are not necessary to the structure but in terms of the overall form you might consider that they are necessary to the look it might look a little bit more harsh or industrial if it didn't have that and i think many people might even think that they're structural that's fine but it is interesting to compare what what you might have thought i was showing to you as a fully exposed structure still has some decorative elements on it so i'm showing the parthenon here and i want to talk about it in the use of material and i want to be very careful here with all due respect to my close friend yani and all greeks his ancestors thank you for democracy and geometry but let's talk about the parthenon from a structural point of view there are stone columns and then there are stone beams and stone doesn't do well as a beam stone doesn't do well in tension beams need to carry tension so what you see are some very short spans of beams which subsequently have very closely spaced columns again the parthenon was built and was meant to represent things above and beyond structure but if we're talking about structure only you can see here in the temple of zeus also in athens top right one of those stone beams has a crack in it just at the area of maximum tension so there are consequences to using and structural materials in a certain way or making certain design choices that we should be aware of right doesn't mean that it should drive the process or the design but it needs to be part of it but what if we understand how to work with a material like stone that works well in compression what else could we do with it if we choose to vault with stone then you get something like kings college chapel in cambridge large open spans it may be hard to see in the photograph but wide spaced columns down the side with large stained glass windows beautifully letting in letting in light uh into the interior it's a magical wonderful space to be in and this is with choices of how to use stone and even further than this let me show you a project by uh the famous engineer peter rice this is for the seville expo in 92 where stone is used in a shape and a form with the loads applied to it such that is always maintained in compression and just shows you what we generally think of as a heavy mass of material that stone has to be being able to work span hold its own weight safely and yet be airy and light so this is a fascinating way of thinking about the world around us contributing to what the design might be and how parts of it behave within the whole of what the project should be

Channel: Paul Kassabian

Views: 1,164

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Id: 0HFLA4g0D64

Length: 9min 1sec (541 seconds)

Published: Sun Sep 13 2020