1) Decide whether the following statements are true or false according to the text:

1. A beam bridge consists of a rigid horizontal member.

2. Beam is supported at each end by some kind of pile.

3. Less beam bridges are made from concrete and steel to hold out against the forces of compression and tension.

4. Beam bridges are rarely used in highway construction.

5. The biggest limitation of this type of bridge is still its length.

6. The deck of beam bridge is composed of one or several beams, which are supported by piers across the space.

7. Beam bridges typically span the greatest distance.

8. Today beam bridges are not built as foot-bridges.

2) List advantages and disadvantages for the beam construction used. Divide them into two columns:

Limited span; inexpensive relative to other bridge types; does not allow large ships or heavy boat traffic to pass underneath; easy to build; design generally not considered very interesting or eye-catching; used widely in urban and rural settings.

Advantages:	Disadvantages:

3) Learn information in the text how tension and compression forces impact bridges. Look at the figure 1 and decide what sort of force is it? Write down the force in the box.

FORCE:	DESCRIPTION OF FORCE ACTING:
	As live loads, such as cars and trucks, travel across the bridge, this force acts on the top of the roadway and passes down into the piers.
	This force acts on the underside of the roadway, which is pulled apart by the live loads pressing down on the top of the roadway.

4) Fill in the missing words from the list:

Adjacent, roadway, vertical piers, span, design, horizontal beams, strength.

Beam bridges are the oldest known bridges and tend to be the simplest to …… and build. Roughly half of all bridges in the world are beam bridges. They consist of……and …… A beam bridge’s ……. depends on the strength of the ……… and can be increased by adding additional piers. While beam bridges can be quite long, the …………, or distance between …….. piers, is usually small.

5) Make up the word combinations using the derivatives from the words in brackets:

(strong), of the material, bridge (construct), (suspend) bridges, (available) of steel, to be (embed) into the banks, (addition) support, ropes (suspend) from rocks, elaborate (scaffold), period of railroad (expand), to cost (consider), one of the most (common) used, concrete (reinforce) with steel bars.

.

References: http://en.wikipedia.org/wiki/Beam_bridge

Unit 5. Timber and Masonry Bridges.

Vocabulary.

masonry — каменный

limit — ограничивать

durable — долговечный

weather proof— погодоустойчивый thawing — оттепель limestone — известняк adorn — украшать elimination— сокращение density — плотность pile — свая cribs — сруб pine — сосна larch — лиственница arid — высушенный dowel — шпонка log — бревно square sawn timber - брус plywood — фанера

The early bridges were made of stone and timber because these building materials could be easily found everywhere. The earliest type of stone bridge is one that re­quires no designing. When large flat stones could be found it was a simple enough matter to build piers of square stones in the stream and lay the large flat slabs on the tops of the piers. Obviously, such a construction was very limited in application, for to find a flat stone large enough to span a reasonable distance was hard enough to start with, and when found would be difficult to handle with primitive tools owing to its weight. The local name for these is clapper bridges, and the Postbridge clapper bridge has three spans of 15 feet each. Such bridges are examples of beam or girder bridges in stone.

Stone used for bridge construction must be durable, weather proof and resistant to freezing and thawing. Some­times the builders use the artificial stone i.e. concrete made of cement, crushed rock or pebbles, sand and water.

As the stones were “dressed”, that is cut, shaped and finished by stone masons, build­ings in dressed stone are called masonry. The greater the skill of the masons the longer does the building last, and this applies to bridges as well as houses and castles. Of course, wars and weather play their part too, but other things being equal, a bridge built of carefully wrought masonry will last longer than one stuck together, as it were, with cement or mortar. The Romans knew this, although they were experts at making concrete. But the Romans frequently depended entirely on a good fit between the stones for many of their greatest works.

Today it would require quite careful design by engineers to construct a bridge by up-to-date methods, using modern materials. But the Romans had nothing to guide them but common sense and experience.

The masonry bridges offer the following advantages:

1. Long durability. Some Roman bridges survive to our days. The only reasons for their destruction are wars and disasters.

2. Aesthetic values of these bridges adorn many cities.

3. Greater rigidity under the extra heavy super load.

4. Considerable elimination of maintenance cost.

Possible disadvantages of masonry bridges are:

1. Greater dead weight as a stone density is between 2 and 2.7 t/m3

2. Only the arch structure may be used. It produces the horizontal force – the thrust, which requires powerful founda­tions and solid ground to rest on.

3. Masonry bridge construction is difficult to be mech­anized. It requires much handwork. So it takes the builders much more time to erect a masonry bridge in comparison with other bridge types.

Timber bridges are used as temporary structures during 10 – 15 years. Piles and cribs made of wood are often applied as bridge foundations. But metal spans save much time during bridge construction because they may be much longer than those made of wood.

The best timber for bridge building is pine, fur-tree and other soft wood as well as larch, arid cedar. The expensive timber species such as oak, hornbeam, and beech are used only for the most important elements – the caps and dowels.

To increase its waterproof, timber is impregnated with antiseptics. It results in the service life prolongation up to 25 – 30 years. Plywood structures are widely used abroad and the spans made of this material are more durable, rigid and lighter than those made of logs and square sawn timber.

A. Examples of bridges of this type are found in Cornwall and Devon, owing to the prevalence of flat granite slabs on the moors, and a good example is still to be seen at Postbridge on Dartmoor.

B. Some of their bridge piers had, in fact, to be demolished by dynamite when the bed of the River Humber was deepened some 1500 years after their construction.

C. This sound wood is easily treated and does not decay.

D. Most favorable rock for this purpose is granite, basalt, dolomite and widespread and rather cheap sandstone and limestone.

E. Wood is also used for bridge supports and spans.

Answer the questions:

1. What were the earliest building materials for bridges?

2. What is the most durable material for bridge building?

3. What building materials are used for stone bridges?

4. Why were the bridges the Romans built very solid and durable?

5. What bridges are difficult to mech­anize?

Exercises: