Exercises

I. Match the terms (a) and their definitions (b).

1. roof; floor; slab; beams; wall; column; ceiling;

• a vertical structure of stone, brick, etc;

• the top covering of a house or other building;

• a long piece of timber or iron used horizontal or vertically to support the rafters of a building;

• the part of house, room, etc., on which one treads;

• the inner roof of an apartment;

• a flat piece of marble or stone;

• a round pillar to support a building;

II. Explain in English

• non-structural reasons;

• the nearest equivalents;

• a very extravagant use of material;

• fireproof;

• a composite system;

• to have a great advantage;

• a good horizontal diaphragm;

Lesson 5

Foundations

Warming-up

1. What is the function of foundation?

2. What types of foundations do you know?

3. What is the pneumatic caisson?

Read the text and say what means were practiced in Roman times to spread the load that a structure imposed on the ground.

The loads that a structure imposes on the ground normally reach the ground (or the level of the lowest floor if that is below the outside ground level) through walls, piers, or columns. Ideally, if the ground surface is a firm stratum of natural rock, able to take the loads directly without noticeable settlement, the walls, piers, or columns can simply be ended when they reach it. They can also be built up directly from it after some preliminary levelling. Unfortunately, such strata have rarely been found in the places where men have wanted to build. Therefore, some means have had to be provided to spread the loads more widely or carry them down to rock or firmer ground at a lower level.

Apart from shallow excavation to reach rock close to the surface, there were three means that were widely practiced in roman times.

These were the spread footing, piling, and the continuous raft. The first and last spread the load fairly near the surface, simply by providing each wall, pier, or column with a substantially wider base.

The second, piling, carried the load further down without necessitating deep excavation. The piles were almost of timber. Once hammered into the ground, they acted as columns usually transmitting part of the load to firmer ground at the foot and spreading part of it through the intermediate strata by surface friction.

With the exception of the continuous concrete raft these methods continued in use well into the 19^th century, with little change except in such matters as methods of pile driving and of working below water level.

For deep underwater foundations the answer was the pneumatic caisson. This was a development of the earlier cofferdam – a wall within which, after pumping out the water, it was possible to excavate and then build the base of the pier in the dry.

The new requirements for tall buildings were mainly met by the substitution of grillages of steel beams for the less efficient, earlier spread footings. These have since given way to footing and piles of reinforced concrete, while there have been parallel developments in piling with the substitution of steel and reinforced-concrete piles for the previously universal timber pile. The heaviest reinforced-concrete piles are nowadays cast in situ in prebored hole.

Equally significant has been the increasing exploitation of the buoyancy principle – that of creating open basements below ground level of sufficient volume to displace a weight of earth comparable with the total weight of the building, so that there is only a small net change in pressure at foundation level when construction is completed.