Concrete

1. Warming up:

What materials may be used as construction ones?

2. Look through the text and give Russian equivalents to the underlined words, word combinations and terms.

Concrete has many properties that make it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal.

Good-quality concrete has many advantages that add to its popularity. First, it is economical when ingredients are readily available. Concrete's long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape. Building of the molds and casting can occur on the work-site which reduces costs.

C oncrete is a non-combustible material which makes it fire-safe and able withstanding high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters.

Concrete does have some limitations despite its numerous advantages. Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.

Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste. It is molded or placed as desired, consolidated, and then left to harden. Concrete does not need to dry out in order to harden as commonly thought.

The concrete (or specifically, the cement in it) needs moisture to hydrate and cure (harden). When concrete dries, it actually stops getting stronger. Concrete with too little water may be dry but is not fully reacted. The properties of such a concrete would be less than that of a wet concrete. The reaction of water with the cement in concrete is extremely important to its properties and reactions may continue for many years.

3. Read the text attentively and answer the following questions:

   1. What are the advantages of concrete?

   2. Where is concrete used?

   3. What materials are used for concrete preparation?

   4. What is curing?

   5. What does concrete need to hydrate and harden?

   6. What is important to properties of concrete?

4. Retell the text using the following expressions:

The text is entitled…; It describes…; It mentions about…; According to the text…; Owing to…; The fact is that…; In addition, …; It turns out that…; In conclusion…

Skyscrapers

1. Warming up:

What famous skyscrapers do you know?

2. Look through the text and give Russian equivalents to the underlined words, word combinations and terms.

T hroughout the history of architecture, there has been a continual quest for height. Thousands of workers toiled on the pyramids of ancient Egypt, the cathedrals of Europe and countless other towers, all striving to create something awe-inspiring. People build skyscrapers primarily because they are convenient – you can create a lot of real estate out of a relatively small ground area.

Up until relatively recently, we could only go so high. After a certain point, it just wasn't feasible to keep building up. In the late 1800s, new technology redefined these limits. Suddenly, it was possible to live and work in colossal towers, hundreds of feet above the ground.

The main obstacle in building upward is the downward pull of gravity. There has to be more material at the bottom to support the combined weight of all the material above. Every time you add a new vertical layer, the total force on every point below that layer increases. If you kept increasing the base of a pyramid, you could build it up indefinitely. This becomes infeasible very quickly, of course, since the bottom base takes up too much available land.

In normal buildings made of bricks and mortar, you have to keep thickening the lower walls as you build new upper floors. After you reach a certain height, this is highly impractical. If there's almost no room on the lower floors, what's the point in making a tall building?

Using this technology, people didn't construct many buildings more than 10 stories – it just wasn't feasible. But in the late 1800s, a number of advancements and circumstances converged, and engineers were able to break the upper limit.

The main technological advancement that made skyscrapers possible was the development of mass iron and steel production. New manufacturing processes made it possible to produce long beams of solid iron. Essentially, this gave architects a whole new set of building blocks to work with. Narrow, relatively lightweight metal beams could support much more weight than the solid brick walls in older buildings, while taking up a fraction of the space. Steel, which is even lighter and stronger than iron, made it possible to build even taller buildings.

The central support structure of a skyscraper is its steel skeleton. Metal beams are riveted end to end to form vertical columns. At each floor level, these vertical columns are connected to horizontal girder beams. Many buildings also have diagonal beams running between the girders, for extra structural support.

In this giant three-dimensional grid – called the super structure – all the weight in the building gets transferred directly to the vertical columns. This concentrates the downward force caused by gravity into the relatively small areas where the columns rest at the building's base. This concentrated force is then spread out in the substructure under the building.

In addition to the vertical force of gravity, skyscrapers also have to deal with the horizontal force of wind. Most skyscrapers can easily move several feet in either direction, like a swaying tree, without damaging their structural integrity.

The most basic method for controlling horizontal sway is to simply tighten up the structure. At the point where the horizontal girders attach to the vertical column, the construction crew bolts and welds them on the top and bottom, as well as the side. This makes the entire steel super structure move as one unit. For taller skyscrapers, tighter connections don't really do the trick. To keep these buildings from swaying heavily, engineers have to construct especially strong cores through the center of the building.

Experts are divided about how high we can really go in the near future. Some say we could build a mile-high (5,280 ft, or 1,609 m) building with existing technology, while others say we would need to develop lighter, stronger materials, faster elevators and advanced sway dampers before these buildings were feasible. Speaking only hypothetically, most engineers won't impose an upper limit. Future technology advances could conceivably lead to sky-high cities, many experts say, housing a million people or more.

2. Divide the text into logical parts

3. Write out the sentence or sentences expressing the main idea of each logical part.

4. Entitle each part and make a plan of the text.

5. Retell the text in your own words making use of the plan and the sentences.

WHAT IS A PERSONAL COMPUTER