[00:00.00] W: An arch is the spanning of a wall opening by means of separate units, such as bricks or blocks, which are assembled into an upward curve. [00:09.43]The invention of the arch made it possible to span wide openings without large timbers. [00:15.43]Before the arch, large window and door openings required a large wooden timber, and a supply of large trees. [00:23.83] The arch was very important in regions where there were few large trees. [00:28.43]The Babylonians, Egyptians, and Etruscans all used the arch, and it was later adopted by the Romans. [00:37.43]The arch became a basic principle in the Roman system of construction in brick and concrete. [00:43.43] The Romans contributed a lot to the development of architecture, especially its engineering aspects. [00:49.43]They perfected a system of arch and vault construction. [00:54.03] As a result, a larger variety of buildings appeared, each with a form suited to its function. [01:00.43]The Roman approach to the building arts was always practical. [01:04.43]The Romans undertook huge public work projects, including a network of bridges and aqueducts, all of which utilized the arch. [01:13.43]To supply their vast public baths and fill the water needs of their citizens, they needed water in large amounts for their cities. [01:21.43]Using their considerable engineering skills, the Romans built aqueducts so sturdy that many are still standing. [01:29.43]The Roman semi-circular arch is the most common and most elementary type of arch. [01:35.43]It was made by taking wedge-shaped blocks—large bricks with angled sides—and placing them side by side, forming an upward curving, semi-circular opening. [01:46.43]The block at the highest point—the center of the arch—is called the keystone. [01:53.43]The keystone is the most important block because it holds the other blocks in place. [01:58.73] The keystone locks the other stones together. [02:02.43]The round arch is extremely strong and stable. [02:06.43]It’s primarily the wedge shape of the blocks that gives the arch its stability. [02:10.43]The wedge-shaped blocks are locked together tightly, transferring their weight downward on either side. [02:17.43]The arch is very sturdy and can support a heavy load. [02:21.93]The arch is supported only from the sides. [02:25.43]This is because of lateral thrust. [02:28.43]The downward pressure is transformed into lateral thrust through the piers, the two vertical structures on either side of the opening. [02:38.23]What I mean is, the ... um ... the weight of the arch and its load is converted from downward pressure into sideways—lateral—pressure. [02:49.43]The massive piers that frame each side of the opening receive the pressure and therefore support the arch. [02:56.43]Until the nineteenth century, arches were still widely used in public buildings in North America. [03:02.81]However, the invention of steel beams in the nineteenth century—yes, did you have a question?
[03:09.81]M: Yes. I was wondering ... um ... what you said implies that we don’t see arches in public buildings anymore, I mean, in newer buildings. [03:18.16]But what about the arches in our administration building, here on campus? [03:21.81]It has lots of arches, and I’m pretty sure the building is fairly new.
[03:25.81]W: I’m glad you mentioned our administration building because that’s a perfect illustration of the decorative arch. [03:31.81]You see, behind all that beautiful brickwork is a system of steel beams. [03:36.81]The beams are doing the real work of holding up the building. [03:39.81]The brick arches are just for show. [03:42.81]Steel beams for wide spans have reduced the arch to a mostly decorative function. [03:48.81]And, as you can see in our administration building, decorative arches remain popular today.
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