Text A. ARCH

If we return to the basic masonry wall once again, we find there is an alternative for spanning an opening — the arch.

Like the lintel the arch can be made up of stone, but the arch has two great advantages. First, masonry arch is made up of many smaller parts, the wedge-shaped voussoirs, the critical necessity of finding a large lintel free of cracks or flaws is eliminated, as are the logistics of handling large blocks of stone. Second, because of the physics involved, the arch can span much greater distances than can a stone lintel. The gravitational forces generated by the wall above the arch are distributed over the arch and converted in the voussoirs to diag­onal forces roughly perpendicular to the lower face of each voussoir. Each voussoir is subjected to compressive forces. One of the drawbacks of arch construction is that dur­ing construction all the voussoirs must be supported by a wooden framework, the cen­tering, until the uppermost voussoir, the keystone, is put in place. At that instant the arch becomes self-supporting and the cen­tering can be removed to be used to build the next arch.

Traditionally, centering was semicircular in form, as this shape was the easiest to lay out on the job site. Unfortunately the semicircular arch is not a perfect structural form, for the forces at the base of an arch of this shape are not going straight down. In almost every- traditional structural form, there are lateral (sideways) forces in additional to vertical forces (those generated by gravity and going straight down). This is especially true of the semicir­cular arch, and the problem increases in direct proportion to the vertical forces the arch carries. These lateral forces would cause the base of the arch to spread unless suitably restrained, as in a large arched bridge in which the feet of the arch push against the bedrock on either side of a gorge. In an arch that has no wall bearing down on it there is another problem – the arch’s own weight.

Exercise 4. Translate the words:

stone, part, eliminate, generate, involve, force, voussoir, support, uppermost, put, semicircular, shape, lateral, cause.

Exercise 5. Choose the right translation from A to B:

A: involve, distribute, keystone, remove, restrain, bedrock, framework, increase, lay out, advantage.

B: вовлекать, ограничивать, опалубка, увеличивать, преимущество, подстилающая порода, распределять, прокладывать, удалять, замковый камень.

Exercise 6. Are these meanings correct or incorrect? Correct the mistakes:

eliminate – поддерживать

drawback – преимущество

force – сила

voussoir – кирпич

bridge – свод

generate – устранять

support – подвергать воздействию

subject – вовлекать

Exercise 7. Translate the following word combinations:

masonry wall, block of stone, stone lintel, gravitational forces, compressive force, arch construction, wooden framework, structural form, arched bridge, job site, bear down.