Example. The thickness of glass to be applied in different positions mist be considered by the designers.
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1) Different conditions govern the thickness of the unit to be glazed.
2) The shape of the window or door also affects the thickness of glass to be chosen.
3) The breakage to occur in such glazed units as swing doors is very dangerous.
4) Wired glass to be used in dangerous positions has a wire mesh embedded in the thickness of the material.
5) Glass to meet fire regulations must be used for doors leading to fire escape routs.
III. Use the following word combinations in sentences:
1. The type of glass to depend on the conditions of use...
2. Breakage to occur...
3. Wire reinforcement to be used is wired glass...
4. Doors to lead to fire escape route
5. Glazed doors to be broken easily...
IV. Answer the following questions:
1. What does the thickness of glass depend on?
2. What shapes need less strength?
3. What is the size of glass governed by?
4. What special types of glass are used for the purpose of safety?
5. In what positions is wired glass usually used?
6. 6.What proportion of the radiant heat from sunshine does sheet glass transmit?
7. Hw is the heat effect of the direct sunshine overcome?
8. Does the thickness of glass affect the thermal transmission of glass?
TIMBER.
There are so many types of timber available for use in buildings that architects will find some difficulty in choosing the best for an particular purpose. This is especially the se with the woods used for joinery and for the more decorative parts of a building. Possibly the best advice to acquire good knowledge of the timbers i most general use for structural purposes.
A usual broad classification is into softwoods and hardwoods. Softwoods are used for most structural work and for painted joinery.. Hardwoods are usually employed for more decorative purposes and for places such as the floor where resistance to abrasion is required, or where the patterns of the timber is to be exposed to polishing. It is also important to point out that there are some quite important exceptions to the general rule that hard woods are hard and "softwood s" are soft. The division is in fact, a botanical one. The hardwoods being broad.-leaved species, the softwoods -conifers. A tree grows of the addition layer upon layer.Usually one fresh layer is added each year to the outside of the tree, though in the tropics the growth of the trees is more or less continuous and layers are not necessary added at annual intervals. In. the centre of the tree is the heart, and in the. outside is the bark with a certain thickness of sapwood beneath. Where branches occur there will be knots. The general structure is cellular and the arrangement of the cells varies in different types. These features-cell structure, knots and annual rings will vary not only from one type of the tree to another but also within each type of because of the variable conditions under which the trees grow. A tree growing rapidly in a warm climate will produce a different grade of wood to that from a similar type of the tree growing under colder conditions and a forest tree will differ from an isolated one. All this means that wood is an extremely variable material and that if it is to be used to the best advantage it must be carefully selected or it must b used as a basic for a manufactured product which by reason of its manufacture overcomes this variability. Production of plywood is a good example of a manufacturing process which eliminates much of the variability of ordinary timber.
EXERCISES.
I. Find out sentences with the verbs of obligations and give their equivalents.
