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gothic cathedral and church construction |
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franceon first arriving in France - driving Marianne - a French national symbol, with French definitive stamps the calendar of the French Revolution the French umbrella & Aurillac the forest
as seen by francois mauriac, and today the Citroën 2CV: mardi gras! carnival in Basque country what a hair cut! m & French pop/rock country life in France: the poultry fair short biography of Pierre
(Peter) Abelard the greatest show on Earth - the Tour de France
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church and cathedral constructionThe building of gothic cathedrals developed in step with the development of the design process. Through the medieval apprenticeship system, accumulated knowledge was passed down. Over a period of about a century and a half, designs increased in complexity and sophistication as the new techniques developed into a coherent ‘gothic’ style. Added to this accumulating knowledge taken from experience, came the use of small-scale models, constructed similarly to the proposed full-scale building, and used to test the overall stability of a design. Detailed testing was made ‘on the job’, by building the cathedral one bay at a time, while using proven elements from previous designs. So it was that cathedral construction evolved, with ribbed vaults and pointed arches appearing at the start of the eleventh century. This first major innovation in gothic cathedrals - the pointed arch - replaced the rounded Roman arch and enabled the building of more complex and higher buildings. This evolved to include the ribbed, arched vaults of large buildings, which were able to span much large spaces than could the Roman arch.
By trial and error came the flying buttress to counteract outward pressures, so allowing ever taller and more complex structures. Flying buttresses were first recognised as being used in Notre Dame in Paris shortly before 1180. Later, throughout the twelfth century, came the technology that gradually removed the requirement for walls to carry loads. The gothic builders discovered that it was no longer necessary to build curtain walls between the load-bearing skeleton of the church, because the skeleton carried all the weight. This allowed the builders to become much more adventurous, and to fill the spaces between the load-bearing pillars and ribs with glass. The leading person to consolidate all these building techniques was Abbé Suger (Abbot of St. Denis, 1081 - 1151).
how gothic cathedrals stay upGothic cathedrals have large curtain walls filled in with stained glass, walls that do not support the weight of the vaulting and roofs. The cathedrals are often very tall and have to resist considerable side pressures from wind. In general, the further north and the taller the cathedral, the greater the wind pressures. When you reach Britain, the cathedrals are generally lower and with lower-pitched roofs [1], in part because of the higher wind speeds. [based on 19th century drawing of Amiens cathedral]
There gradually developed an external system of buttressing, which applied counter-acting force sideways towards the cathedral wall. This resists the tendency of the walls to bulge out from the lateral pressures. There are no lateral forces exerted by the roof in situ, for the roof is framed in wood and cross-pinned to hold it together; but, of course, the wind forces do transmit force laterally. The upper flying buttress redirects the wind forces from the roof and the clerestory wall, guiding them downwards into the pier buttress. The lower flying buttress performs the same duty, but for the outward lateral forces being exerted by the nave vaulting. The pier buttress, as you can see from the diagram, blocks the equivalent force from the vaulting of the side aisle. The pier buttress also supports the flying buttresses, bracing them so the cathedral wall does not move outwards. The pier buttress also transforms the still sideways forces into downward ones. The pinnacle adds further weight to the pier buttress, helping to anchor it against sideways pressure. Piers are optional and positioned according to the stresses found by the builders. Remember that these arrangements were worked out as the builders noticed problems, modifying the structure if they noticed.
Note the buttresses marching down the side of the cathedral. Between each pair of buttresses in this innovatory construction technique, there is no serious weight coming down from the roof and the vaults. These in-between walls now have to carry relatively very little weight and, therefore, can be opened up to accommodate the glory of large stained-glass windows, thus letting in the light.
let the light flood inRoman arches are fine for spherical domes and barrel roofs, but not for more complex shapes. In the diagram to the left, note that the arches for an oblong bay must span three different distances. This can be handled effectively by the use of pointed arches, by varying the steepness of the arcs, thus terminating all three arch lengths at the same height above the nave. This is shown by the colour coding in the diagram. The gaps between the arches can then be filled by simple curves. In some cathedrals, a sexpartite design is substituted in order to further spread the vault load. For example, an extra arch would run between the two mauve arches, joining with the tip of the yellow arches. Each end of this extra arch will then be supported on two more intermediate pillars, normally of a narrower section, which will thus transmit some the of the weight downwards. (Bourges is an example of sexpartite vaulting. I expect to include a picture of this on the page about Bourges Cathedral.) Further notes on the vaults and the stone out of which they are made. Left: Labelling the parts of the nave
Note how the clerestory stained-glass windows fit between the ribs and up into the associated vaulting. The vaulting is supported by the ribs [see diagram above]. The ribs descend onto the pillars, which reach down to the ground. Outside the cathedral, the flying buttresses press against the cathedral wall in line with the pillars on the inside, leaving the window walls unobstructed. Abbé Suger, who was the effective inventor of this style at the royal church of Saint Denis, had a poetic and imaginative approach to this new light which he had invited into the church. He intended that the beauty that he brought into the church would raise the worshipper from the material to the non-material, bringing him closer to god.
Abbé Suger [1081 - 1151] had inscribed above the doorway of Saint Denis,
The symbology of Saint Denis and other cathedrals was often abstruse and esoteric. Thereby, Suger, in the manner of great teachers, sent complex messages to the extremely highly educated classes, while attempting to communicate with all people, by what he termed “analogical vision”, through the jewelled beauty and artistry of his visionary construction. now for a bit on stoneWell, I suppose we all know what stone is, it’s that stuff that’s all over the place on this fascinating planet. Well, that’s mostly what I know about it anyway; but I hear tell that there are people who spend their whole lives studying stuff like stones, so I imagine there must be a lot more to it than that. (Maybe eventually, I will find an enthusiastic expert who can write some plain english on the subject for me.) Just one or two notes relevant to cathedrals. The stone needs to be hard enough to stand up, and to last a thousand or two years, and easy enough for a medieval craftsman to work with rather primitive tools. Stone is very strong in compression, and only about a tenth of that strength in bending and sheering (tension, stretching), while the medieval mortar is about a tenth of that sheering/bending strength.
Notice the greyed stones in the arches of diagrams A and B. On the arches, you will see a small triangular diagram. If nothing were holding the shaded stone place, it would fall to the earth; but locked in place, weight (force) is coming down on the stone (the stone, of course, also has some weight). That force is directed mainly along the stone. As you will see, the stone in the pointed arch [A] is at a more vertical angle than the stone in the Roman (rounded) arch [B]. This means that a greater proportion of the load on the stone is transmitted downward and less outward than is the case with the rounded arch. The differing forces are represented by the differing lengths of the sides of the triangle, and these can be calculated. Those nice vaults under which you are standing can be estimated to weigh towards 300,000 kilograms for the quadripartite vault, and towards 400,000 kilograms for the sexpartite[2] - a nice headache for you if the medieval craftsmen were slacking on the job. Note that the sexpartite tends to cover the equivalent of two quadripartite vaults, thus making the overall weight of sexpartite vaults less and, thereby, reducing the stresses throughout the structure. (Bourges can be thought of as a very special, high-tech cathedral.) Moving to diagram C above, you will note that, at the overhang there are forces inclining the stone to bend downwards. Tensile forces are generated at x and compressive forces are generated at y, and thus the pressure is to pull the stone apart at x and tear it apart. In the arch stones, similar forces are being applied. Note that, were the stone at C to be made of butter, it may tend to sheer rather than bend. And that’s enough about stone for here.
naming parts of a gothic cathedral - interior
Christianist cathedrals and churches are usually built to have a floor-plan shaped like a cross. The head of the cross is generally oriented towards the East, towards Jerusalem. Thus the transept, running north and south, is the cross-bar of this cross. The foot of the cross, at the west end, accommodates the spectacular portals of the main entrance . (Some cathedrals are five-aisle - for example, Bourges. This will probably be discussed on the page about Bourges Cathedral.) Transept: Going across the main body of the cathedral, with north and
south arms, sometimes with side doors.
gothic cathedral building start dates,
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Experiments in gothic structure
by Robert Mark MIT Press 
pbk 0262630958 reprint: 1984 amazon.com / amazon.co.uk |
If you want to understand the structure of the great gothic cathedrals, this is the place to go. Some of it gets a bit technical, Mark used polarised light, epoxy plastic models and wind tunnels to work out the the loadings and stresses in some of the great cathedrals. An absolutely fascinating book to read, if you can stand the hard work and the usual technical manual disorganisation.
As with Painton Cowen , I can not resist giving this book five GoldenYaks, if only because I know of nothing better.
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| email abelard@abelard.org © abelard, 2006, 8 february the address for this document is http://www.abelard.org/france/cathedral-construction.php |
The
main weight of the cathedral structure is carried downwards by the tall
pillars that march along the nave and the side aisles. The pointed arch
vaulting directs more of the force downwards than does the Roman arch,
but there remain 
This
illustration should be studied in concert with the cross-section of Amiens
cathedral, above.
