I. Decide whether the following statements are true or false according to the text:

1. An incomplete structure may be subjected to tension and compression

2. Serious research is done before any actual construction is done.

3. The construction of bridges is always greeted by the public.

4. The collapse of several girder bridges in the 1960’s helped to understand the stresses better.

5. The variation in stresses during construction demands jacking.

6. Excavation for foundation is always taken through unsuitable ground before solid rock is reached.

7. The pillars of the towers of suspension bridges are stabilized by cables which are removed after the completion.

8. Arches are usually supported by towers.

9. ‘Keystone’ is an important part of a finished arch.

II. Answer the questions

1. What are the most ingenious parts of bridge building?

2. Why is the construction work a grave hindrance to normal life in the area?

3. What is done before any construction work?

4. How can computer simulations supplement the tests?

5. How can the stresses of the structure differ?

6. When must jacking be provided?

7. What are the difficulties in excavation for foundations?

8. How can the pillars of the towers of big suspension bridges be stabilized?

9. What is a keystone?

LANGUAGE FOCUS

III. Match the words with their synonyms.

1. complicated a) accessible

2. ingenious b )suggestion

3. available c) destruction

4. investigation d) complex

5. proposal e) inventive

6. collapse f) research

7. feat g) connect

8. join h) exploit

IV. Match the words with their opposites

1. top a) mild

2. solid b)above

3. severe c) proper

4. below d) to forget

5. unsuitable e) to disappear

6. temporary f) bottom

7. to remind g) constant

8. to arise h) soft

V. Insert the prepositions.

To subject … sth, … the form of sth, in conjunction … sth, in case … sth, a great variety … sth, an opposition … sth, to differ … sth, a set … sth, to prevent … sth, the origin … sth, the value … sth, to deal … sth.

VI. Insert the words from the list

spans, cantilevers, jack, rams, completion

1. The four legs of the Tour Eiffel were provided with … which were adjusted from time to time as the structure grew. Even after … a concrete structure may be subject to creep and the ground may settle.

2. Above ground, until … are joined wind, can be a great hazard.

3. Before the Pont de Normandie was completed? There was serious discussion about the use of active stabilizers to keep the long thin … in place.

4. Large weight would have been moved by … .

VII. Make the precis of the text

Text 2. Bridge Construction (According to the Types).

There is nothing especially complicated about the lifting process, and the stresses in the beam are more or less as they will be in the final position. Nevertheless, a heavy object suspended in space is potentially dangerous, and accidents do happen. During the lifting of the suspended span of the Quebec bridge, something broke, and the span fell into the river and was destroyed. During the lifting of one span of the Britannia bridge, a jack burst, and the end of the span fell. Fortunately, Stephenson had given strict orders to insert packing after every few inches of lifting. Nevertheless, a slight distortion of the beam did occur. The incident shows the importance, not only of correct instructions, but of good communications. Accidents have happened because instructions were not received, or if received, modified or ignored. An exception of the method of lifting may be adopted in the case of the suspended span of a cantilever bridge, as in the case of the Forth railway bridge. Here, the beams were built out from the ends of the cantilever arms until they could be joined in the middle. Only then were the temporary rigid connections removed. Such an operation has to be done with great care, because large stresses are released and created. The bending moment at the join completely disappears, for example, while the stress in the top chord of the beam changes from tension to compression. Some continuous box girder beams and concrete beams are constructed as cantilevers until they are joined up. New parts may be taken along the existing part of the bridge, or they may be lifted up from below. Sections of a segmented prestressed concrete bridge may be lifted by a crane which rests on previously attached segments, or they may be manipulated by means of a launching girder which is slowly advanced along the already built part of the span. Another method is to use moving formwork which progresses with the construction. Because the cantilevered part span is subject to stresses for which the complete span is not designed, temporary stays are sometimes attached between the segments and a temporary tower, turning the span into a cable-stayed one until closure is complete.

Yet another technique, when the lower surface of the span is horizontal, is to rest the formwork on the steel girder which reaches to the next pier. The casting of each segment is often done using the previous segment as a part of the formwork. This technique, called match-casting, ensures an almost perfect fit at assembly time, and greatly reduces the tendency for misalignments to occur during erection. A film of epoxy may be spread between segments. After each segment is placed, steel pre-stressing wires, or tendons, are fitted to hold it in position. The pre-stressing tension prevents the concrete ever reaching a tensile state with any foreseeable load. This method of pre-stressing is called post-tensioning, because the stress is added after placement. When the wires are tensioned before the concrete is poured, the process is called pre-tensioning. The tendons are equivalent to the ties in the lattice truss, while the concrete is roughly equivalent to the struts. Thus the concrete and the steel are both used in the roles for which they are best suited.

The joints between the concrete segments are subject to vertical shear forces, which can be resisted by the use of matching corrugated surfaces.

COMPREHENSION CHECK