In masonry, the alternative to spanning an opening is the arch, as shown in the picture above. Like the lintel, the arch can be made of stone, but the arch has two main advantages.
To understand how these massive arches will withstand heavy loads, let’s start.
First, the wall arch consists of many smaller parts, the segments in the shape of wedge-shaped voussoirs, so that finding a large stone fall block without cracks or blemishes is no longer necessary, as is the delicate logistics of handling large stone blocks for the Lintels.
Second, because of the physics involved, the arc can span much greater distances than a stone lintel, and under certain conditions, it can span great distances. The gravitational forces created by the wall above the arch are distributed across the arch and converted in the segments into diagonal forces approximately perpendicular to the bottom of each voussoir.
Every voussoir is exposed to compressive forces. However, one of the disadvantages of arch construction is that during construction all of the voussoirs must be supported by a wooden frame called a centering until the top segment, called a keystone, is inserted and locks the arch in place.
At this very moment, the arch becomes self-supporting and the centering can be removed in order to build the next arch. Traditionally, the centering was semicircular, as this shape was easiest to build with pegs and ropes on the construction site. Unfortunately, the semicircular arc is not really a perfect structural shape for the arch, as the forces at the base of an arch of this shape don’t descend directly. In many forms of construction spanning an opening, lateral forces are created in addition to vertical forces (the forces generated by gravity and directly descending).
This is especially true for the semicircular arch, and the problem increases in direct proportion to the vertical forces that the arch carries. These lateral forces would cause the base of the arch to expand if not properly restrained, like a large arch bridge where the feet of the arch press against the bedrock on either side of a ravine. There is another problem with an arch without a superimposed wall: the weight of the arch itself. A single point load focused on the apex or crown of the arc causes the arc to break or bulge upon its upper surface about 40 ° above horizontal, but this problem quickly diminishes with an additional even Last spans an arch and also presses against the arch.
Several arches that are placed together form an arcade. In an arch, the transverse forces of one arch are counteracted precisely by the opposite transverse forces of the adjacent arch, with the resulting force on the column being purely vertical. With this arrangement, the arches can be placed on pillars or slender columns, as the transverse forces cancel each other out, except at the ends where buttresses must be.
Hope you understood the concept, if you have any doubts feel free to comment.
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