What are these architectural features on churches/cathedrals for?
November 5, 2015 12:32 PM Subscribe
You are not my architect but maybe you can explain these concrete things to me.
I regularly pass by a church with these things on it and have often wondered what they are.
Big grey concrete extrusions on outside of local church
It occurred to me that I saw these on a recent trip to England at Westminster Abbey as well (or they looked similar enough):
http://theenchantedmanor.com/wp-content/uploads/2014/10/Westminster-Abbey-Cloister-exterior.jpg
What are they called? Do they have a specific engineering purpose or strictly aesthetic? Why aren't they on other buildings?
I regularly pass by a church with these things on it and have often wondered what they are.
Big grey concrete extrusions on outside of local church
It occurred to me that I saw these on a recent trip to England at Westminster Abbey as well (or they looked similar enough):
http://theenchantedmanor.com/wp-content/uploads/2014/10/Westminster-Abbey-Cloister-exterior.jpg
What are they called? Do they have a specific engineering purpose or strictly aesthetic? Why aren't they on other buildings?
They are buttresses. From Wikipedia
A buttress is an architectural structure built against or projecting from a wall which serves to support or reinforce the wall. Buttresses are fairly common on more ancient buildings, as a means of providing support to act against the lateral (sideways) forces arising out of the roof structures that lack adequate bracing.posted by JackBurden at 12:34 PM on November 5, 2015
Best answer: Depending when this church was built and what other types of architectural features it has, it's possible that those buttresses are ornamental (modern brick buildings don't usually require buttressing). Because people have a certain idea of what a church is "supposed" to look like, and old-fashioned stone ornamentation is often a part of that.
But, yes, the above answers are right that this is a buttress and that's what it's traditionally been used for within architectural history.
posted by Sara C. at 12:45 PM on November 5, 2015
But, yes, the above answers are right that this is a buttress and that's what it's traditionally been used for within architectural history.
posted by Sara C. at 12:45 PM on November 5, 2015
Best answer: A church has a high, broad interior. Other buildings tend not to have this. The force of the massive roof pressing down wants to thrust the walls out to the side. The buttresses counteract this. Other buildings will have trusses within the ceiling that tie the walls together and keep the force of the roof from pushing them out.
posted by Midnight Skulker at 12:49 PM on November 5, 2015 [3 favorites]
posted by Midnight Skulker at 12:49 PM on November 5, 2015 [3 favorites]
Best answer: Like people said, those are buttresses. The pretty airy-fairy ones on gothic cathedrals are flying buttresses. The alternative to buttresses if you are trying to build a large stone building is to just build the walls really thick (e.g. like medieval castles, and those often had buttresses anyway) or to not have a lot of open space inside because of internal structural support. Since churches generally do have a big indoor space with a vaulted ceiling of some kind they often have buttresses. Sara C is right that more modern construction usually doesn't actually need them but they still get added on for the churchy look.
posted by Wretch729 at 12:52 PM on November 5, 2015
posted by Wretch729 at 12:52 PM on November 5, 2015
You are not my architect
If you hire my firm, I can be.
Yes, they're buttresses, and they serve a structural purpose. They're basically necessary because (historically at least) churches had masonry walls and arched/vaulted ceilings. Currently, they're included in church design because they "signify" a church, just like a gothic arched window does, although neither the arch nor the buttress has the structural necessity that they used to.
So, stone was about all they used to have to make churches with when any degree of permanence was desired. You can't get stone in large enough pieces to create the kind of spaces required for a pilgrimage cathedral, as many gothic churches in France were meant to be, and if you could, the stone wouldn't be able to actually span the distance without failing. The solution is the arch, or vault (which is basically an extruded arch). An arch is any form of construction where all its members are in compression, i.e. they're being smooshed rather than stretched. Stone doesn't smoosh very easily, so it does really well when made into arches, and not so well as beams (which partially smoosh and stretch at the same time). With an arch, you can create a large open space entirely out of stone, and the majority of the load will be transferred down to the base of the arch into its supports. However, some of the load will be translated into a horizontal force called "thrust" which pushes outward, and needs to be resisted by whatever's supporting the arch.
Having a wall resist thrust is basically asking it to perform like a beam, and as already stated, stone doesn't work too well as a beam. A masonry wall has three basic failure modes: 1) toppling 2) buckling and 3) crushing. Buckling and crushing both happen when the vertical load is more than a wall can stand, so parts of it either get crushed, or the wall decides it's easier to bow out and collapse rather stay standing. Toppling is when there's a force perpendicular to the face of the wall that pushes it over, which is what the thrust from an arch can do. To resist the thrust, the wall can either be thickened so that its total mass resists the thrust, or you can add buttresses, which effectively thicken the wall at certain points. Pretty much all the load from the roof and above the windows in a gothic church is channeled into the portions of the wall where there are buttresses. The buttresses are there more to resist the thrust of the arches, not really because the roof load is especially massive. If it were, the walls could always easily fail by buckling towards the interior of the church. In some other conditions, the thrust from arches is resisted by metal tie rods that tie the bottoms of the arch together and keep them from separating.
In a large enough wall, modern masonry construction does require buttressing (even with reinforced walls), but that's usually provided by intersecting walls which perform the same function, and the needs aren't the same because modern buildings rarely have vaulted roofs any more.
posted by LionIndex at 4:23 PM on November 5, 2015 [7 favorites]
If you hire my firm, I can be.
Yes, they're buttresses, and they serve a structural purpose. They're basically necessary because (historically at least) churches had masonry walls and arched/vaulted ceilings. Currently, they're included in church design because they "signify" a church, just like a gothic arched window does, although neither the arch nor the buttress has the structural necessity that they used to.
So, stone was about all they used to have to make churches with when any degree of permanence was desired. You can't get stone in large enough pieces to create the kind of spaces required for a pilgrimage cathedral, as many gothic churches in France were meant to be, and if you could, the stone wouldn't be able to actually span the distance without failing. The solution is the arch, or vault (which is basically an extruded arch). An arch is any form of construction where all its members are in compression, i.e. they're being smooshed rather than stretched. Stone doesn't smoosh very easily, so it does really well when made into arches, and not so well as beams (which partially smoosh and stretch at the same time). With an arch, you can create a large open space entirely out of stone, and the majority of the load will be transferred down to the base of the arch into its supports. However, some of the load will be translated into a horizontal force called "thrust" which pushes outward, and needs to be resisted by whatever's supporting the arch.
Having a wall resist thrust is basically asking it to perform like a beam, and as already stated, stone doesn't work too well as a beam. A masonry wall has three basic failure modes: 1) toppling 2) buckling and 3) crushing. Buckling and crushing both happen when the vertical load is more than a wall can stand, so parts of it either get crushed, or the wall decides it's easier to bow out and collapse rather stay standing. Toppling is when there's a force perpendicular to the face of the wall that pushes it over, which is what the thrust from an arch can do. To resist the thrust, the wall can either be thickened so that its total mass resists the thrust, or you can add buttresses, which effectively thicken the wall at certain points. Pretty much all the load from the roof and above the windows in a gothic church is channeled into the portions of the wall where there are buttresses. The buttresses are there more to resist the thrust of the arches, not really because the roof load is especially massive. If it were, the walls could always easily fail by buckling towards the interior of the church. In some other conditions, the thrust from arches is resisted by metal tie rods that tie the bottoms of the arch together and keep them from separating.
In a large enough wall, modern masonry construction does require buttressing (even with reinforced walls), but that's usually provided by intersecting walls which perform the same function, and the needs aren't the same because modern buildings rarely have vaulted roofs any more.
posted by LionIndex at 4:23 PM on November 5, 2015 [7 favorites]
You've got your answers, so I'll add this. The historical fiction epic "The Pillars of the Earth" by Ken Follett is about the lives and times of people from the birth to the completion of a cathedral in 12th Century England.
It features a young man, Jack Jackson, who comes under the spell of Euclidean geometry and, after the first roof of the Cathedral fails, he envisions a means of fixing them and he invents the buttress.
The collapse of the first roof and the construction of the second are depicted in a somewhat informative way in the 2010 miniseries, which I thought was pretty good. In 2010, I hadn't yet heard of Eddie Redmayne, who played Jackson.
posted by Sunburnt at 5:29 PM on November 5, 2015 [2 favorites]
It features a young man, Jack Jackson, who comes under the spell of Euclidean geometry and, after the first roof of the Cathedral fails, he envisions a means of fixing them and he invents the buttress.
The collapse of the first roof and the construction of the second are depicted in a somewhat informative way in the 2010 miniseries, which I thought was pretty good. In 2010, I hadn't yet heard of Eddie Redmayne, who played Jackson.
posted by Sunburnt at 5:29 PM on November 5, 2015 [2 favorites]
Pleasing fact: the buttresses at Westminster Abbey are under the care of the architect Donald Buttress.
posted by verstegan at 2:20 AM on November 6, 2015 [2 favorites]
posted by verstegan at 2:20 AM on November 6, 2015 [2 favorites]
I am not an architect, but I am a historian ...
You could build large buildings of stone without buttresses - BUT you couldn't put in huge windows. So you have your pre-Gothic cathedrals and other great churches (Romanesque, Byzantine) which were huge, but dark inside.
For the medieval person, the true revolution of the Gothic movement wasn't the pointy arches that we instantly think of, but the sudden appearance of so much more light inside churches. The whole Gothic movement was about being airy and light - lighter appearing in weight, but (more importantly) filled with natural light in the interior.
posted by jb at 6:51 AM on November 6, 2015 [2 favorites]
You could build large buildings of stone without buttresses - BUT you couldn't put in huge windows. So you have your pre-Gothic cathedrals and other great churches (Romanesque, Byzantine) which were huge, but dark inside.
For the medieval person, the true revolution of the Gothic movement wasn't the pointy arches that we instantly think of, but the sudden appearance of so much more light inside churches. The whole Gothic movement was about being airy and light - lighter appearing in weight, but (more importantly) filled with natural light in the interior.
posted by jb at 6:51 AM on November 6, 2015 [2 favorites]
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posted by Jacen at 12:33 PM on November 5, 2015 [2 favorites]