Материал: Types of Movable Bridges. задания по английскому языку для студентов-магистрантов направления подготовки 08.04.01 «Строительство». Мордовцева Т.В., Зотова М.М

opening angle - угол раскрыва; угол раствора trunnion – ось качания, ось поворота resembling – аналогичный

rocking chair – кресло-качалка refinementулучшение, очищение

folding bridge – складной мост, откидной мост, подъёмный мост drawbridge –подъемный, разводной

curling bridge – скручивающийся мост conceive – постигать, понимать collapse - сжимать

conceale скрывать, утаивать piston – поршень

octagonal shape – восьмиугольная форма cable – канат, трос

mountдержатель; крепление; опора, стойка; основание. benefit – преимущество, выгода, польза

restriction – ограничение vessel – судно

retractable bridge – отводной мост submersible bridge – погружной мост

tilt bridge –мостовое полотно поворачивается на концах по концам на определенный угол

swing bridge –разводной мост с подъемным механизмом, располагающимся под мостом

VII. Name the types of movable bridges

UNIT 3

TRUSS BRIDGE

I.Read the text and answer the questions.

1.What is the main difference between truss bridges and beam or girder ones?

2.What is a truss?

3.Where may the trusses be placed?

4.Why are truss bridges used for railroads and military bridges?

Truss bridges are similar to beam or girder designs but are capable of supporting heavier loads. The sides of the bridge are made from a series of triangles that form a steel web known as a truss. The trusses may be placed below the deck so that traffic rides overtop, or they may be placed on either side to allow vehicles to pass between the trusses. Truss bridges have a high strength-to-weight ratio due to their triangular structure. They are often used for railroad and military bridges because

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they are cost-effective and capable of supporting heavy loads.A truss is constructed of a simple supporting lattice-work of triangles that support the beam or the span by adding rigidity. It increases the beam's ability to dissipate the compression and tension forces. The members of a truss are the chords or horizontals, verticals and diagonals, which will only act in compression or tension.(fig. 9).

Fig. 9. Truss bridge

Piles or pilings are the vertical members of a truss bridge. They are long columns of wood or steel driven into the ground to support vertical loads. The members are pinned together at the nodes where the straight members meet. This allows for some movement of the members without snapping (fig. 10).

Fig. 10. Three-sided truss:

а) diagram б) profile

в)intermediate fixing of take-up г) end fixing of take-up;

1 - tensive elements of a string

Word list profile – сечение

intermediate fixing of take-up – промежуточное крепление натяжного устройства end fixing of take-up концевое крепление

tensive elements of a string –напрягающие элементы затяжки

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II. Try to make the text using the following questions as a plan:

1.What does lattice-work of triangles support. How does it act

2.What are the members of a truss? When do they act

3.What are piles or pilings? Why do they move without snapping

III. Find English equivalents to the expressions from the text.

строительный материал __________________________________________

базируется на простоте строительства ______________________________

податливый и упругий ___________________________________________

строительные лесоматериал _______________________________________

в форме эстакады ________________________________________________

The initial popularity of the truss bridge was based primarily on its simplicity of construction and economics of building the bridges. In the 1800s, wood was cheap and plentiful. Wood was an ideal construction material because it was flexible and elastic to some degree and could withstand the variety of forces that acted against it. The early truss bridges were built from wooden timbers and were constructed in trestle forms where they were composed of a braced framework of timbers, piles or steel beams built to carry roads or railroads over a depression in the landscape topography

IV. Find the information about Iron Bridge (G.B. Wales) in internet and describe the bridge

Fig.11 Iron bridge

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V.Translate the abstracts from English into Russian using t he word list.

Compression and Tension Forces

Compression and tension are seen in a bridge in the road deck, which shortens on top as traffic weight loads bear down directly on it. The compression on the upper side of the decking causes t he underside to go into tension and stretch. The diagonals and horizontal members of a truss transfer the forces to the pilin gs. At these points, most of the downward load or weight of compression applied to th e structure is dissipated or transferred into the earth. Dissipation means to spread the force out or transfer it to a larger area so that no one point bears the entire concen trated focus of the force (fig. 12).

Fig. 12 Arrows are forces on hinges

VI. Complete the sentences using the following words only once.

To shorten, shortening , com pression, forces, bears down, lengthens, lengthening Forces Acting on Truss Bridges

a)There are two major forces that act on bridges: _____________ and tension.

b)The compression force __ __________on an object ___________or compress it, while tension is the directly opposing force that __________and stretches the object.

c)A spring is a good example of a simple mechanism that works w ith both________.

d)Compression pushes the c oils together, thus ____________the

spring and tension pulls the coils further apart, __________the spring (fig. 13)

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Fig. 13. Arrows suggest forces acting on the structure

VII. Read the text. Name the forces which cause stress on bridges. Characterize them orally.

Other Forces Acting On Truss Bridges

Other forces, such as torsion, resonance and seismic forces from earthquakes cause stresses on bridges. Torsion is a rotational or twisting force produced during storms with high hurricane or near hurricane strength winds. Truss construction allows the winds to blow through both the substructure and the superstructure of the road deck so that torsion is minimized.

Resonance refers to standing waves that can run through a bridge causing it to fail through fatigue. Fatigue refers to the repeated bending up and down of horizontal members causing them to fail. A simple example when an army marches across a bridge, the soldiers are ordered to "break step" so that the cadence is broken and wave forms cannot set up. The simple truss construction disperses forces through the members so that no single member can be overstressed in this manner.

Seismic waves caused by earthquakes move through the ground and perturb the surface in all three dimensions. Waves move back and forth, up and down and from side to side and it's very difficult for any structure to resist this kind of punishment.

Truss bridges are just as vulnerable as any other structure to this kind of failure. Railroads have replaced almost all truss bridges in areas prone to seismic disturbance (fig.14)

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