- RT Arch
By Shelley Livingston
Gothic cathedrals originated in Northern France in the 12th century, the first of which was Saint-Denis (fig. 1 and 2). St. Denis was the French royal monastery and was originally a Carolingian basilica.
In 1137, Abbot Suger, advisor to King Louis VI and VII, was commissioned to design renovations to the church. The two additions, the west façade, and choir, were inspired by Suger’s interpretation of the Old Testament’s Temple of Solomon. Like Saint-Denis, gothic cathedrals typically used a cruciform plan (fig. 3). The long axis includes a wide central nave, flanked by aisles. The transept (a horizontal arm of the cross) on the shorter axis is perpendicular to the aisles. A high spire often tops the area where the axes cross. The long axis terminates at the apse in the upper arm of the cruciform plan. The apses were meant to symbolize the crown of thorns. Verticality was also emphasized, with towns competing against one another to build cathedrals reaching ever higher toward the heavens.
In stark contrast to their earlier Romanesque counterparts, Gothic cathedrals were spacious and open, and their ornate stained-glass windows reflected colored light, as described in the Old Testament. The Romanesque cathedrals, on the other hand, were dark and had small windows and thick walls. Thick walls were necessary to support the load from
the roof, and window openings were small because larger ones would have created too much lateral thrust, thereby causing structural failure. However, Gothic structural innovations – the pointed arch, the rib vault, and the flying buttresses – eliminated the structural concerns that had previously necessitated thick walls and minimal fenestration.
The lateral thrust of a pointed arch is only about fifty percent that of a Roman arch (fig. 4),
since most of the load is directed in a more downward direction than in an outward direction. In addition, the pointed arch allowed for thinner and lighter walls. Since there was less lateral thrust with which to contend, bulky piers or walls were unnecessary.
The rib vault (fig. 2, 5), an intersection of two pointed arches, directs loads from above
through the ribs down to point loads at the piers below. Since the pointed arches reduced the lateral stress, it was also possible to use more slender columns. While the lateral stress was significantly less than that of Roman arches, however, builders still needed to counter the horizontal force. The solution to this problem was buttressing. Prior to 1170, pillars were attached to the exterior and functioned as shear walls. Thereafter, the pillars were placed further from the exterior walls and attached by means of the flying buttress.
The flying buttress (fig. 6) sprang from the wall into the air and connected to an external pier on the other end. Heavy pinnacles were set atop the piers to assist in directing the load downward. The pinnacles increased the compressive forces, for which the stone structures were well suited. The upper part of the flying buttress followed the line of force from the
vault. The dead load of the flying buttress was supported by means of the lower arched part of the surface. The flying allowed thinner walls with more openings because it counteracted the lateral thrust of the walls and directed it out and down to buttresses or piers.
Medieval builders constructed these magnificent Gothic cathedrals without modern software to aid in structural analysis, without modern machinery to aid in construction, and without modern building materials, which perform better structurally than stone. Like St. Denis, some of the oldest gothic cathedrals still stand. Having withstood the destructive forces of wars, time, and weather, these cathedrals remain as a testament to the astonishing accomplishments of medieval architects.
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Salvadori, Mario. Why Buildings Stand Up. McGraw-Hill.
“Saint-Denis, Paris, France.” Paris Region Basilica Cathedral of Saint-Denis Skip the Line Entrance Ticket, Viator, 2020, www.viator.com/tours/Paris/Skip-the-Line-Basilica-Cathedral-of-Saint-Denis/d479-37736P9.
Pintson, Allan. “Plan of Abbey Church, Saint-Denis. 1140-1144 (with the Old Structure), French Gothic.” Pinterest, 2020, www.pinterest.com/pin/462393086715532771/.
Arquitectura Antigua.” Pinterest, 2020, www.pinterest.com/pin/365495325992964509/.