Three New Arches

The Building Committee of the Cathedral announced its intention not only to complete the choir structure, but also to continue to the westward and construct the Crossing. The providing of necessary funds would accomplish the three new arches and cover for the crossing.

The pillars being in place, the next step will be the erection of three more arches. They will be precisely the same as the great eastern arch already erected. These four arches complete the square of the crossing. The Belmont Chapel is about complete and the Chapel of St. Columba has started. The Committee needs an additional $500,000 beyond funds on hand and other commitments. Regarding the Crossing area, The Building Committee of the Board of Trustees said the following:

“It is estimated that $200,000 would complete the choir. If finished it would easily accommodate a comparatively small number of worshippers. It is in the judgement of the committee, highly desirable that, in addition to the great stone arch now standing, there should be three similar ones needed to enclose the ‘crossing.’ Were the ground thus bounded to be temporarily roofed over and walled in, we should have an interior capable of accommodating from four to five thousand worshippers.”

– The Building Committee

Completing the Arches

All of the piers and columns for the next three arches came up from bedrock in an orderly way. Granite blocks for these structures kept arriving at the site. The western arch was the first to complete.

The North Arch was the next to complete

Voussoirs on the arches and buttresses

Keep in mind, when Heins & La Farge designed the arches, they were to support a massive lantern and tower. The lantern would fill the crossing with light from large windows. With that in mind, the arches would need to be quite massive. Arch construction depends essentially on a wedge. If a series of wedge-shaped blocks, ones in which the upper edge is wider than the lower edge, are set flank to flank, the result is an arch. Voussoir is the term for these blocks on both the arches and the buttresses.

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Notice the staggered joints on the voussoirs that are side by side. A row a two voussoirs is flanked on each side by three voussoirs. This design further strengthens the arch.

Additionally there are three sets of these voussoirs front to back to further create these massive arches. Numbering the stone determines its exact location. Each voussoir must be precisely cut so that it presses firmly against the surface of neighboring blocks and conducts loads uniformly. The pressure downward on an arch has the effect of forcing the voussoirs together instead of apart. These stresses also tend to squeeze the blocks outward radially. Loads divert these outward forces downward to exert a diagonal force called thrust. These forces will cause the arch to collapse if it is not properly buttressed. Therefore the vertical supports upon which an arch rests must be massive enough to buttress the thrust and conduct it into the foundation.

Voussoir

The word is a stonemasonry term borrowed in Middle English from French verbs connoting a “turn”. Each wedge-shaped voussoir turns aside the thrust on to the supports. Voussoir arches distribute weight efficiently, and take maximum advantage of the compressive strength of stone.

• Photo Credits – All photos from the Irma and Paul Milstein Division of the United States History, Local History and Genealogy, The New York Public Library. Manhattan: Amsterdam Avenue – Cathedral Parkway