2383

Fig. 5

Fig. 6

IX. Tell your group mates everything you know about suspension and cable-stayed bridges.

Home Exercises

I.Memorize the words from Ex. I page 52.

II. Copy and complete the table.

Text 13 

Steel supports are employed for over bridge and trestle bridges but not so frequently.

The ordinary supports made of concrete may be subdivided into three groups according to the construction technology:

1.Monolithic supports. The concrete is placed against the falsework in situ. The falsework determines the supports shape and dimensions.

2.Precast supports. The supports are mounted of the prefabricated concrete blocks.

3.Combined supports (precast with cast-in-place concrete supports). This sort of supports is practiced on a large scale and represents the structures assembled from the precast concrete blocks and monolithic concrete placed in situ.

Technological process of the support footing erection may be rather various and depends on a support structure. This process may be influenced by the geological conditions, ground firmness, type and dimensions of the supports, loads from the spans and supports.

First, footings are subdivided into two large groups: shallow footings, deep footings.

Shallow footings are usually designed as monolithic ones on the natural bed. This is one of the simplest and rather cheap technologies but it can be employed only for firm grounds. The construction of such footing begins from the pit working. If a pit is excavated rather deep in a dry place for the abutments and over bridge supports as well as viaduct and trestle bridge supports, the builders employ a sheet piling. The same is done if a pit is excavated on a riverbed.

A sheet piling is made of metal bars driven to the calculated depth into the ground by a pile driver. Then several pumps exhaust the water from the sheet piling and after that the builders erect a falsework and install a reinforcement. Then they place concrete against the falsework and ram it in place. As a rule, the reinforcement does not work in tension but resists to the shrinkage cracks appearing during concrete setting.

The most difficult work is to place the concrete for pier footings erected on the riverbed. The matter is that despite the pumps working some water enters the pit. That is why the builders make additional grouting bed to strengthen the surrounding ground in the water. And then they place the footing itself.

IV. Guess the noun which goes with the adjectives. Make up one sentence using all these 5 nouns.

1)timber, concrete, steel _ _ _ _ _ _

2)monolithic, precast, combined _ _ _ _ _ _ _ _

3)reinforced, prefabricated, precast _ _ _ _ _ _ _ _

4)difficult, interesting, home _ _ _ _

5)deep, coal, refuse _ _ _

V.What notions are described below? How are they reflected in the text?

1)This term is a combination of the Greek “art, craft,” with “word, speech,” meant in Greece a discourse on the arts, both fine and applied. When it first appeared in English in the 17th century, it was used to mean a discussion of the applied arts only, and gradually these “arts” themselves came to be the object of the designation. By the early 20th century, the term embraced a growing range of means, processes, and ideas in addition to tools and machines. By midcentury, this notion was defined by such phrases as “the means or activity by which man seeks to change or manipulate his environment.” Today it is the development over time of systematic techniques for making and doing things.

2)These things are designed to convey the weight of a structure to the ground underneath and around it. They may be spread (made with wide bases placed directly beneath the load-bearing beams or walls), mat (consisting of slabs, usually of reinforced concrete, which underlie the entire area of a building), or floating types.

3)It is a boxlike structure used in construction work underwater or as a foundation. It is usually rectangular or circular in plan and may be tens of metres in diameter.

VI. Underline the correct word to complete each sentence.

A box caisson, open at the top/bottom and closed at the top/bottom, is usually constructed on water/land, then launched, floated to position, and sunk onto a previously prepared foundation, leaving its upper edge under/above water level. It serves as a suitable shell for a pier, seawall, breakwater, jetty, or similar work, remaining permanently in place on the sea bottom.

An open caisson, closed/open at both the bottom and the top, is fitted with a cutting bottom edge, which facilitates sinking/floating up through soft material while excavation is carried out inside through a honeycomb of large pipes, or dredging wells. As excavating proceeds and the caisson sinks, additional sections are added to the shaft above. This process is continued until the caisson has sunk to the required width/depth. A floor, usually of concrete, is laid to provide a bottom seal. The dredging wells can then be filled with concrete to complete the structure.

Pneumatic caissons are similar/different to open caissons except that they are provided with airtight bulkheads above the cutting edge. The space between the bulkhead and cutting edge, called the working chamber, is pressurized to the extent necessary to control the inflow of soil and water; thus the excavating can be performed by workmen operating in/out of the working chamber at the bottom of the caisson.

свая-оболочка; drilled pile – буровая свая; coffer – опускной колодец; sinking

–погружение.

Всложных геологических условиях, когда прочные грунты залегают на большой глубине, применяют фундаменты глубокого заложения. Данные фундаменты разделяются на несколько типов.

- Свайные фундаменты, состоящие из свай (т.е. железобетонных элементов небольшого сечения и значительной длины) и ростверка – железобетонного элемента, объединяющего сваи.

- Фундаменты на сваях-оболочках. Их отличие от обычных свай в том, что сваи-оболочки представляют собой пустотелые цилиндры диаметром до 3,0 м и длиной до 30 м.

- Фундаменты на буровых сваях, которые отличаются от свай-оболочек только способом погружения свай.

- Опускные колодцы, представляющие собой железобетонную коробку, которая погружается до расчетной глубины.

- Кессонные фундаменты, которые отличаются от опускных колодцев тем, что работа в них ведется под давлением сжатого воздуха, чтобы оттеснить воду из кессона. Данный способ сооружения фундаментов очень опасен для здоровья рабочих, подвергающихся перепаду давления воздуха в атмосфере и в кессоне.

Внастоящее время не существует геологических и гидрологических условий, в которых нельзя было бы возвести фундамент глубокого заложения, являющийся более универсальным. Современные механизмы и технологии сооружения фундаментов и опор достигли высокого уровня.

IV. You have heard that a construction company is going to build a bridge across the river you live by. Write a letter of complaint. Use the following expressions for your choice.

I am writing to complain about…; I am writing to express my strong dissatisfaction with…; I was shocked by…; I insist that you…; I trust the matter will receive your immediate attention….; this is unacceptable…; I hope this matter will be resolved….

Text 14 

II. Read the text and pay attention to various techniques of superstructure erection (while reading you may make notes for better understanding).

BRIDGE SUPERSTRUCTURE ERECTION

Erection technology depends on the span type, its dimension and material. The simplest erection technique is applied for the standard beam spans. The standard reinforced concrete beams are produced at the precast works. The length of the spans for the motor way bridges ranges between 6 and 42 m. The railway bridge spans may be up to 34.2 m long.

The first method is described as following: the beams are transported by motorway or railway to the job site where one or two cranes hoist them to the designed position. When a bridge is designed as a continuous one the builders put the ordinary beams on two supports and join them into a continuous beam.

The next method of span erection is the following: reinforced concrete continuous girders are cast on the bank and then the prefabricated segments are installed by the incremental launching to the designed position. While being pushed the girder works as a cantilever resisting the dead weight. As reinforced concrete has a high density the builders use a false nose to reduce the bending moments in the girder. This method is used to construct very long span bridge. The technique has its disadvantages, which clearly limit its area of use: the concrete has to be prestressed before and it needs time to reach certain age.

Two erection methods are used for framed suspended bridges, framed overbridges and trestle bridges. The first one represents the built out concreting of a span in the sliding formwork. This structure is considered to be a monolithic one.

The next erection method represents the balanced cantilevering of framed

structures from ready-made reinforced concrete segments produced at the precast works. The segments are stuck together with epoxy resin or with cement. The reinforcement free length is welded. This method of construction leaves no possibility for later correction; the elements must be fixed exactly in the right position.

The most complicated erection technology is employed for arch bridges. The classical method demands temporary piers and centering to reproduce the shape of the arch superstructure to-be constructed. The precast reinforced concrete blocks are placed on centering. The monolithic concrete arch is erected in the curvilinear formwork.

The erection of arches afloat is a much more advances technique. The arches and semi-arches are assembled on the bank and launched by the building ways to the barge, which carries these structures to the location.

III. Replace the underlined words in each sentence with one word that has the same meaning.

1.Erection technology depends on the type of a distance between the supports.

2.As reinforced concrete has a high relation of weight to volume the builders use a false nose to reduce the bending moments in the girder.

3.While constructing very long span bridge, the segments are stuck together with a grey powder, made by burning clay and lime that sets hard after mixing with water.

4.The erection of arches floating in water is a much more advances technique.

IV. Match the similar words/word combinations:

V. What process from the given below is described?

1.Bridge construction

2.Erection of metal spans

3.Assembling of trusses

For this process standard girders or unified lattice trusses are used. The length of a standard girder is 55 m and of a unified lattice truss varies between 33 and 132 m. Metal beams are lighter than those made of reinforced concrete that is why they may be mounted by one or two cranes. When a girder is 55 m

long it is cut into four blocks to facilitate its delivering to the site. A temporary pier is specially erected in the middle of the span. While erecting these blocks are placed by cranes on centering and supports. The blocks are joined by the high strength bolts.

VI. Think of a span erection method, describe it to your partner using the text and let him guess.

VII. Fill in the gaps with the words given below.

foundations; arch; support; falsework; superstructure; cables; cranes; self-supporting; welded; beam.

All bridges need to be secure at the _____ and abutments. In the case of a typical overpass _____ bridge with one support in the middle, construction begins with the casting of concrete footings for the pier and abutments. Where the soil is especially weak, wooden or steel piles are driven to _____ the footings. After the concrete piers and abutments have hardened sufficiently, the erection of a concrete or steel _____ begins. Steel beams are generally made in a factory, shipped to the site, and set in place by _____. For short spans, steel beams are usually formed as a single unit. At the site, they are placed parallel to each other, with temporary forms between them so that a concrete deck can be cast on top. The beams usually have metal pieces _____ on their top flanges, around which the concrete is poured. These pieces provide a connection between beam and slab, thus producing a composite structure.

Arches for _____ bridges are normally fabricated on-site. After the building of abutments (and piers, if the bridge is multiarch), a _____ is constructed. For a concrete arch, metal or wooden falsework and forms hold the cast concrete and are later removed. For steel arches, a cantilevering method is standard. Each side of an arch is built out toward the other, supported by temporary _____ above or by falsework below until the ends meet. At this point the arch becomes _____, and the cables or falsework are removed.

VIII. What assembling methods are shown in the pictures below (fig. 7 – 9)? assembling of long arches

assembling of aches on falsework assembling of discontinuous beams

Fig. 9

IX. Discuss the following questions:

1.How many erection methods are described in the text?

2.What common features do the methods of erection have for assembling steel girders and reinforced concrete beams?

3.What joint elements are used for the erection of framed bridges?

4.What types of spans are erected with the aid of jack-pushing the girders towards the designed position?

5.Describe the erection of arch bridges.

6.What is a temporary pier built for?

7.What is a false nose and why is it built up?

8.Why is a girder cut into blocks?

9.Why do the builders use centering for the arch assembling?

10.What is a formwork erected for?

Home Exercises