using metal in gothic cathedral construction
But buttressing was often not enough, especially if a buttress was mis-positioned - easy enough to do before the days of civil engineers trained in Newton's laws of physics. So to correct impending collapses, metal was used to strengthen and reinforce the cathedral's structure, as well as providing additional support. Iron ties held arches together, while a girdle made of forged iron 'links' held the cathedral's waist (usually at the triforium level) in trim.
This page will discuss and illustrate how metal was and is an integral part of a structurally sound cathedral's construction.
Keep in mind that the development of these structures was greatly mediated by trial and error. Of course, that is the way engineering develops, as can be seen to this day. These methods of using iron have been used in many cathedrals around Europe. Some indications can be found in this, rather sloppy, paper: The role of iron armatures in Gothic constructions: reinforcement, consolidation or commissioner's choice.
the forge building at the Abbey of Fontenay
recreated water-powered trip hammer at the Fontenay forge
The Abbaye de Fontenay at Montbard in the département of Côte-d'Or. Founded and run by Cistercian monks, the abbey complex includes the late 12th-century forge building. Over 50 metres long, it probably housed two furnaces, with several mills operating hydraulic hammers.
The wrought iron supplied to Amiens cathedral and others was probably forged in a Cistercian workshop of this type. This forge is about 300 km from Amiens cathedral. Amiens cathedral was built between 1220 and 1266.
[The Abbaye de Fontenay/Fontenay Abbey is at
Montbard 21500, tel. n°: 03 80 92 15 00,
fax n°: 03 80 92 16 88.
To help protect the cathedral from literally falling apart from the strains generated by building such a large structure that led to it being rather unstable, chains of iron stabilising rods [chaînage, chainage] were added, generally hidden galleries and passages.
There were many combinations of rods, bars, ties that were connected to, and connected by, claws, clamps, crampons, brackets; these being held together by dowels, gudgeons, pins and wedges. Altogether these would be classified as chaînage.
CHAÎNAGE: This word applies to wood stringers, or to successions of iron hooks laid like links in a chain, or even iron bars or rods, laid horizontally along the triforium, all designed to prevent spreading and dislocation of masonry construction.
The building of Amiens cathedral, a huge cathedral only capped in height by Beauvais, was much affected by the then nascent knowledge of structural engineering, and by the ambitions of the builders and the people who commission the construction. The flying buttresses were not always sufficient, or were not placed to apply a counter pressure in the right position to prevent the stone shifting so cracks appear, columns to bow and arches threaten to collapse.
To correct the problems that appeared, the builders at Amiens took two main steps. One was adding better positioned buttressing. The original flying buttresses had been placed so their point of reinforcement was too high, and so not effective. Additional buttressing was added later to correct the problem.
The original buttressing to the south-east crossing of the transept and nave had been designed to support both the clerestory wall and the vaults. However, the buttresses in this area were placed too high to give full support to the vaults, so they were supplemented with a lower strut. For a more detailed discussion see buttressing and chainage at Amiens cathedral.
The second method for correcting the cathedral's structural problems was giving the cathedral a girdle, at first in wood. This was later replaced with an iron armature, probably forged at the Abbey of Fontenay.
As the diagram above illustrates, the iron 'girdle', the ceinture de fer or iron belt, holds together the arches between in the nave and the two sides of the transept at Amiens cathedral. The 'girdle' is made up of solid iron rods, linked together by strong links, and set firmly into the fabric of the cathedral's stone structure at the end points. The rods were up to 4 metres long and had a cross-section of 4 by 8 cm. This iron chain, or chaînage, lies on the floor of the triforium running around the cathedral above the main bay arches. As can be seen in the illustration at the head of this section on chaînage, this is just above where cracks have appeared as parts of the cathedral shift apart.
Originally, the chainage that prevented arches collapsing from outwards pressures were made from wood, included in the cathedrals as they were built. In some cathedrals, like Saint-Denis and Notre Dame de Paris, there was such a retaining 'girdle' at each level of arches. Viollet-le-Duc, when supervising the dismantling of these cathedrals before restoring and rebuilding them, found quadrilateral-sectioned 'tunnels' through the cathedral structure left by the wood that had rotted away.
As a result, and as the making and manipulation of iron developed, the wooden chainage was supplemented and replaced by iron. However, iron would also have its problems, rusting over time, or as Viollet-le-Duc described it,
This rusting was lessened by enveloping the iron with lead. A more modern rust protector for iron is red lead, that until recently could be seen protecting large structures such as the Golden Bridge at San Francisco and the Forth bridge in northern England. The red lead protection has now been replaced by modern alternatives.
Interestingly, the chapel of Sainte-Chapelle in Paris incorporated a form of iron reinforcement, with two ‘chains’ of hooked bars encircling the upper chapel, the main part of the structure. Further, there were iron stabilisers across the nave (with a vertical tension bar).
Also, an impressive eight-pointed iron star helped hold the apse together. Its iron bars radiated from a central collar. (The drawings above and below were made by Jean-Baptiste-Antoine Lassus during the restoration of Sainte-Chapelle.)
Originally, the iron bars were much smaller, because the technology could not produce enough iron at one time to make longer bars. In those early days, the iron bars (called crampons) hooked one into the next.
As well as crampon bars with a hook at one end and eye at the other, there were also bars with two eyes or two hooks to enable all possibilities on connection, depending on the circumstance.
Because of the rather dodgy stability of the gothic buildings, later additions of iron stabilisation can be seen in many cathedrals, for example at Westminster Abbey and in the cathedral at Saint Quentin.
The tie rods at Saint Quentin are placed higher, nearer the apex of the Gothic arch, than those at Westminster Abbey. A lot of construction development, changes and even improvements, were a matter of trial and error.
It is of interest to note that, at Saint Quentin, the apse tie-rods were removed at the end of the 19th century, while those in the nave were kept. After the First World War shelling, the apse vaults collapsed, while for those in the nave the ribs survived, though the webs between them were damaged. After the cathedral was restored, the nave tie-rods were removed.
On June 4, 1836, following the carelessness of plumbers who were making repairs, a fire broke out in the roofing timbers of Chartres cathedral. The fire spread quickly, destroying the wood frame, the forest, and the cathedral's lead roof. Fortunately, the fire did not advance into the bell tower. There, the great bell was not harmed, sounding for half an hour. Many lower bells were lost, to be replaced in 1840 and 1845 by those still rung today.
The roof was replaced by a beautiful iron frame and a copper roof, built in metal for future safety and for economy, like the partial roof at Southwark Cathedral, London built during the restoration of 1822-25, and the cupola at Mayence [Mainz in Germany], built in 1827 (?). When built, the span over the cathedral's crossing (where the nave crosses the transept) was the largest of any iron-framed construction in Europe. The iron frame looks like a huge boat overturned. The framing has joists of wrought and cast iron, connected by rafters that ensure the rigidity of the structure. During the winter storm in 1997, a portion of the roof was torn and was long covered by tarpaulins. By December 2009, renovations were completed. The metal frame, having suffered from corrosion and expansion due to temperature changes, has been partially restored between 1995 and 1997 by Guy Nicot, chief architect of historical monuments.
The roof structure of Chartres cathedral is one of the oldest iron structures in France. It was built in 1837 by architect Emile Martin and locksmith Mignon. The structure was made combining wrought iron and cast iron. The principal curved beams rising to meet at a point, are cast iron. They support a superstructure in iron carrying the roof of copper tiles. The iron horizontal rafters are connected by several rows of double spacers, forming a very rigid system. The system of segments bolted together and crossed by cast iron bars is inspired by some iron bridges built in England, such as the Severn Bridge at Coalbrookdale, built in 1777. On such constructions, the resistance of cast iron in compression enables the creation of arches. The steep slope of the rafters limits the bending forces, while a series of wrought iron rods take up a portion of the lateral thrust.
Another method can be seen at Noyon cathedral with the roof off and the rather more tidy concreting, the modern idea of rubble. Of course, this much reduces the fire risk from the traditional and medieval forest.
The central lantern
tower, combined with its spire, is the tallest in France at 151m or
495 ft. Building started in the thirteenth century, the spire being
raised in the sixteenth century. The present cast iron spire was raised
in 1876 to replace the previous wooden spire, covered in gilded lead,
which had been placed there in 1544. That wooden spire had been destroyed by fire in 1822.
Elise Whitlock Rose commented about the lantern tower:
The Germans smashed Beauvais cathedral in 1940, as can be seen in this image. The upper flying buttresses were destroyed (see right).
Therefore, I am unsure quite what is being claimed here. Maybe some of the bars had been recovered from the rubble.
Lead in cathedrals is frequently used to cover the roofs. Cathedral roofs are often intricate, with complicated shapes and curves. Lead is manipulable, and so is a very effective, if heavy, protection from 'the elements'. However, lead has always been an attraction to thieves and vandals.
Lead is also used as the grouting, or caulking, that holds the myriad pieces of coloured glass that make up the glorious windows of the great cathedrals of France. The modern piece of lead came [right] would have panes of coloured glass slotted in on either side.
But here described are other widespread, yet not much discussed, uses of lead in cathedral construction - for protecting iron bolts, and for levelling the footing of arches and pillars. Iron rusts easily unless protected from the damp air. Using lead to protect the iron chainage has been mentioned above, but this is only one example of iron protection. The others are hidden.
Iron bolts were put between the blocks of stone making up pillars and arches to reinforce them against movement [see left]. However, there were two problems: the iron rusting, and the difficulty in chiselling exact holes in the stone to hold the bolts. The solution was to encase the rod in molten lead, that also surrounded the bolt in its hole, the bolt becoming immovable when the lead solidified.
Lead also provided a easy-setting mortar between relatively rough-cut stones, to ensure the stones have a good seating the ensemble of arches or pillars [see right]. In some situations, molten lead was poured into a pre-fashioned 'tunnel', so molten lead could be introduced into the centre of a wide column or arch.
cathedrals – introduction: reading stained glass
gothic cathedral and church construction
Chartres - wonder of the world
history of ugly stained glass: Auch, Bazas, Dreux
Auch cathedral choir and stalls
Rouen and Monet
Dax and church iconography photographs, Dax
Bazas - iconography and architectural styles
Poitiers, neglected masterpiece photographs, Poitiers / photos 2
Angers, heart of the Angevin Empire photographs, Angers
Laon, the midst of the gothic transition, with added oxen photographs, Laon
Saint-Jean-Baptiste de Lyon
Notre Dame of Lausanne
Senlis - how a typical cathedral changes through the ages
Saint-Bertrand-de-Comminges - the cathedral of the Pyrenees
Le Mans and Bourges cathedrals - medieval space technology
Lausanne rose window - photo-analysis
cathedrals in Lorraine - the Three Bishoprics
cathedral giants - Amiens and Beauvais
Clermont-Ferrand and Agde - from volcanoes to cathedrals
Germans in France - Arras cathedral
Germans in France - Reims cathedral
Germans in France - St. Quentin cathedral
Germans in France - Noyon cathedral
Germans in France - Cambrai cathedral
Germans in France - Soissons cathedral
cathedral plans, and facts
using metal in gothic cathedral construction
cathedral labyrinths and mazes in France
cathedrals and cloisters of France by Elise Whitlock Rose
|abstracts||briefings||information||headlines||loud music & hearing damage||children & television violence||what is memory, and intelligence?||about abelard|
© abelard, 2016, 31 january
the address for this document is http://www.abelard.org/france/using-metal-in-cathedral-construction.php