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The gravitational force on a structure can be divided into dead loads and live loads. Dead loads can be calculated accurately because they rarely change with time and are usually fixed in one place. Live loads are always variable and moveable, so no exact figures can be calculated for these forces.

Structures must also resist other types of forces, such as wind or earthquakes, which are extremely variable. It is impossible to predict accurately the magnitude of all the forces that act on a structure during its life; we can only predict from past experience the probable magnitude and frequency of the loads.

Engineers never design a structure so that the applied exactly equal the strength of the structure. This condition is too dangerous because we can never know the exact value of either the applied loads or the strength of the structure. Therefore, a number called a “factor of safety“ is used. The safety factor is defined as the ratio of the probable strength of the structure and the probable loads on the structure. This factor may range from 1∙1 (where there is little uncertainty) to perhaps 5 or 10 (where there is great uncertainty)

Now answer these questions:

a) Can the loads from the internal partitions of a building be estimated accurately? Why?

b) Can the loads from storage in a building be estimated accurately? Why not?

c) How can an engineer predict the possible loads that will occur on a structure?

d) Why do engineers never design a structure so that the applied loads exactly equal the strength of the structure?

e) When there is great uncertainty about the loads on a structure and the strength of a structure, does an engineer choose a high or low safety factor?

f) When does failure occur?

Вариант № 1

Переведите текст, выполните задания №1, №2

Mass construction

Building materials are used in two basic ways. In the first way they are used to support the loads on a building and in the second way they are used to divide the space in a building. Building components are made from building materials and the form of a component is related to the way in which it is used. We can see how this works by considering three different types of construction:

1. In one kind of construction, blocks of materials such as brick, stone, or concrete are put together to form solid walls. These materials are heavy, however, they can support the structural loads because they have the property of high compressive strength. Walls made up of blocks both support the building and divide the space in the building.

2. In another type of construction, sheet materials are used to form walls which act as both space-dividers and structural support. Timber, concrete and some plastics can be made into large rigid sheets and fixed together to form a building. These buildings are lighter and faster to construct than buildings made up of blocks.

3. Rod materials, on the other hand, can be used for structural support but not for dividing spaces. Timber, steel and concrete can be formed into rods and used as columns. Rod materials with high tensile and compressive strength can be fixed together to form framed structures. The spaces between the rods can be filled with light sheet materials which act as space dividers but do not support structural loads.

Now say which paragraph discusses:

a) planar construction

b) frame construction

c) mass construction

1. Copy and complete this table by putting ticks in the boxes to show the functions of the components: