Text 8 The gravitational force on a structure

Words and word-combinations to be remembered:

dead loads – «мертве» навантаження, власна вага

live loads – рухоме навантаження

accurately – точно

to predict – передбачати

magnitude – величина

uncertainty – невизначеність

Read and translate the text:

The gravitational force on a structure

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 movable, 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 loads exact 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).

Exercise 1

What’s the English for:

неможливо рухомий

мабуть дорівнює

чинити опір розрахувати

досвід безпечний

землетрус застосований

пропорція коливатися

умова сила тяжіння

визначений застосований

протягом можливий

Exercise 2

Give the Ukrainian equivalents for the following English words and word – combinations:

the probable loads, variable and movable, it is impossible, the exact value, rarely change with time, too dangerous, never know, from past experience, for these forces, this condition, may range, the applied loads, engineers never design, during its life, great uncertainty, can be divided, we can never know .

Exercise 3

Answer the questions in English:

1. Як можна поділити сили гравітації?

2. Можна точно визначити «мертве» навантаження?

3. Рухоме навантаження постійне чи змінне?

4. Яким діям повинна протистояти будівля?

5. Чи можемо ми знати точну величину застосованого навантаження чи міцності будівлі?

6. Що означає «фактор безпеки»?

Exercise 4

Answer these questions:

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

2. Can the loads from storage in a building be estimated accurately? Why not?

3. How can an engineer predict the possible loads that will occur on a structure?

4. Why do engineers never design a structure so that the applied loads exact equal the strength of the structure?

5. 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?

6. When does failure occur?