12 An arch is a structure that covers part of the space between two walls or between two columns. It serves as a decorative element in buildings. Arches are built with wedge-shaped stones called voussoirs. These are placed on top of structural supports. The parts of an arch are the span, the rise and the springing line. The voussoir at the top of the arch is called the keystone. It receives the weight of the wall and distributes it sideways. Round arch The round arch or Roman arch is one that is shaped like half a circumference. Its centre point is on the springing line. Segmental arch The segmental arch is one that is shaped like half a circumference. Its centre point is below the springing line. Equilateral pointed arch In an equilateral pointed arch, the centres of the arcs are the points of support called the springing points. To construct a pointed arch, given the springing points A and B, follow these steps: Step 1. Use centre point A and radius AB. Draw an arc. Step 2. Use centre point B and radius AB. Draw an arc that intersects the previous arc, forming a pointed arch. Round Segmental Pointed Horseshoe Three-centred Ogee Trefoil GALLERY The round arch is the basic element of the barrel vault. The pointed arch is one of the characteristics of Gothic architecture. Construction of a round arch Construction of a segmental arch span rise springing line A B keystone voussoirs Con s t r u c t i on o f a r c h e s I Construction of an equilateral pointed arch Each arch has a different name, depending on its shape:
RkJQdWJsaXNoZXIy