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tunnels which can be oriented along the dominating direction of the winds providing adequate natural ventilation.

But the majority of the tunnels need artificial mechanical or forced ventilation and face the problem of estimation the volume of the air required. There is a special estimation technique taking into consideration the tunnel dimensions, the volume of traffic, etc. The general tunnel ventilation involves blowing, exhaust and combined ventilation. The blowing ventilation supplies fresh air from the unpolluted source – usually at the portal. The air is forced through a pipe and discharged at a place where it is needed. The foul air drifts back to the portal. By the exhaust method, foul air is pulled out through the pipe and the fresh air enters at the portal. The combination of these methods uses the fans to draw out the dust and auto emissions and then the fan are reversed.

Many tunnels are designed with ventilation stations including the ventilation tower and machinery rooms equipped with fans, power receiving and transforming equipment, dust collectors, mufflers and ventilation control devices. Some tunnels are equipped with a lateral flow ventilation system. In this system the air taken in at the ventilation station is fed into the tunnel to dilute auto emissions. The air is discharged from the tunnel after the dust has been removed from it. The name of the system derives from the fact that the air for ventilation flows laterally in the motor way through the feeding and discharging ducts.

In a concentrated discharge system, diluted auto emissions are absorbed by force near the entrance of a tunnel and discharged after the dust is removed from them. This system controls the leakage of exhaust gas from the tunnel entrance.

Tunnel lightning is very important from the point of view of safety measures. If an accident occurs in a tunnel road in a city, it will have a major effect not only inside the tunnel, but also on urban activities on the surface because vehicles may carry hazardous loads. That is why special consideration is given to lightning at the design development phase. For instance, some tunnels in Switzerland are equipped with solar batteries which are used in remote areas in the mountains.

IV. Find 11 pairs of synonyms:

disastrous; poisonous; various; catastrophic; safe; necessary; escape; protected; happen; different; proportions; toxic; town; remove; essential; phase; dimensions; exhaust; occur; leak; urban; stage

V. What notion is explained by the following definition?

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-equipment for providing light for a room, building, etc;

-to allow air to enter and move freely through a room, building, etc;

-a device with blades that are operated mechanically to create a current of cool air;

-to allow liquid or gas to get in or out wrongly;

-a device that fix something firmly;

-a thing that is difficult to deal with or understand

VI. Use the following phrases in the sentences of your own and let your partner translate them.

In charge of; needless to say; side by side; depend on; in addition; result in; due to; taking into consideration; from the point of view of.

VII. Complete the following sentences. Choose your answers from the box. There are more words than you will need.

1.Tunnel maintenance includes railway track maintenance, shipping clearances testing, water discharging, ventilation, lightning and … inspection.

2.The dynamics of the running processes in the seismically active areas are tested by…

3.… call for extra maintenance cost under low temperatures.

4.The majority of the tunnels need … ventilation.

5.… must be taken into consideration at the design development phase.

lining lightning forced screens screeds gutters forcing

VIII. Cross out the words/word combinations, which cannot be used in description of tunnel maintenance.

current, careful, difficult, expensive, negligible, necessary, labour-intensive, profitable, interesting

IX. Retell the text using Ex. II and the word combinations below.

1. The title of the story I want to tell you is… 2. First of all… 3. Second I would like to say that… 4. As far as I understand… 5. In fact… 6. As far as I remember… 7. In conclusion I’d like…

Home Exercises

I.Memorize the words from Ex. I page 145.

II. Change the Voice of the sentences where it is possible.

1. Tunnel supervisors gave special attention to the maintenance of the railway

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track.

2.They erected a tunnel in the seismically active area that’s why there are a lot of problems with it.

3.We are going to use the blasting technique.

4.The tunnel was closed because of the damaged ventilation.

5.They need much more money for gutters repairing.

Text 41 

I. Listen and repeat:

	failures	['feIljq]
	avalanche	['xvqla:nS]
	mayhem	['meIhem]
	mitigation	["mItIgeISn]
	withstand	[wID'stxnd]
	building code	['bIldIN
	precision	'kqud]
	gust	[prI'sIZn]
	bay	[gAst]
	accretion	[beI]
	impending	[q'kri:Sn]
	ablation	[Im'pendIN]
		[xb'leISn]
	scour
		['skauq]
	constriction
		[kqn'strIkSn]
	slimy	['slaImI]
	brittleness	['brItlnIs]

авария, повреждение; неудача снежный обвал, лавина нанесение увечья смягчение, уменьшение противостоять, выдержать

строительные нормы и правила точность; четкость; аккуратность порыв ветра пролет моста прирост; увеличение

предстоящий, неминуемый, грозящий снос; размывание пород; таяние ледников промоина, размыв

сужение, сжатие, стеснение вязкий; скользкий хрупкость

II. You are going to read a text about failures and collapses of the constructional works. Five sentences have been removed from the text. Choose from the sentences A – E the one that fits each gap (1 – 5) to complete the text.

FAILURES AND COLLAPSES OF CONSTRUCTIONAL WORKS

The main reasons causing the failures and collapses of the constructional works can be divided into three groups:

1)insuperable disasters (earthquakes, hurricanes, floods and avalanches);

2)imperfection of the engineering and technical calculations of the structures (knowledge insufficiency concerning true behavior of the structure and the forces acting on the structure);

3)negligence, ignorance and violation of the construction, operational and structural safety.

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Let’s consider some of the well-known cases of failures and collapses of the constructional works caused by different reasons. Of all the frightening things of the world none is so frightful as an earthquake. 1 More than 100,000

quakes occur each year around the globe. Sudden, abrupt and violent shifts of the Earth’s crust result in vertical up to 7m and horizontal up to 4m displacements. In response to such displacements the spans can be thrown off the supports because the piers themselves can be damaged and to a great extent move into an inclined position or even displaced.

But it is worth noting that during the most reported quakes the constructional works have suffered not nearly so much as other civil-engineering works because of the mitigation of earthquake damage. The earthquake in Japan crushed 85 % of dwellings in Tokyo on September 1, 1923. But the bridge works could withstand the disaster and only 337 from a total number of 1028 bridges failed. 2 .

Hurricanes also cannot result in the bridge collapse because at present the building codes take into consideration the forces of the most violent winds and calculate them with great precision. In 1879 the bridge having five spans 75 m long was thrown off the piers on the lake Tay in Great Britain. The train moving along the bridge at the moment of a severe gust added an extra area for the impact of the wind the speed of which was about 140 kph. In 1904 the viaduct supports 90 m high were overthrown and the 76 m long bays fell down under the wind blowing at 280 kph in St. Paul City, U.S.

3 In 1938 the ice accretion or ice jam which was more than 27 m

thick and 120 m long cut the abutment of the arch span 256 m long on the Niagara River, U.S. The bridge had been in service for forty years and the ice level twice reached the impending danger point during its service life. 4 .

The ablation and scour of the support foundations resulted in the bridge collapse on the Uvod-river in Russia in 1881. The speed of the river current increased because of the channel constriction and leads to the 5 m deep hollow in the soft slimy ground.

The lack of the knowledge about the metal behavior led to the bridge collapse in Belgium in 1938. 5 This metal condition is called brittle-

ness or shortness of steel. It is caused by the high carbon content of steel.

AIce impact is also rather dangerous for the bridge works.

BNo place on earth may be safe from the possibility of tectonic mayhem.

CWhen the air temperature dropped abruptly to the low subzero points some of the metal elements of the arch span burst even without any additional loads.

DAnd in fact the Great Tashkent Еarthquake in 1966 did not break down

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or could seriously distract any constructional work.

EThe last ice jam was building up during 36 hours but nothing was done to blast it off.

III. Read the text once again and make words from the letters (all the words are in the text).

aClolseps; tiasseDr; Syfeta; uQkae; vOrewhrto; neDagrsuo; stBru; nuricHare; onrgacneI; fuSref

IV. Match the given words with their common and special meanings (consult the dictionary). In what meaning are these words used in the text?

	Common meaning		Special meaning
work	1)	скорость	a) конструкция
globe	2)	работа	b) дутьё
break	3)	ветер	c) колокол воздушного насоса
wind	4)	металл	d) дроблёный камень
speed	5)	разрушаться	e) жёлоб
metal	6)	канал	f) светочувствительность
channel	7)	земной шар	g) заземление
ground	8)	земля, грунт	h) осветлять

V.Do the puzzle.

1.a large quantity of water;

2.a mass of snow that slides rapidly down the side of a mountain;

3.a place of residence;

4.the solid surface of the earth;

5.land;

6.a hard layer;

7.a sudden fall;

8.a long bridge, usually with many arches, carrying a road or railway across a river, valley, etc;

9.a sudden strong rush of wind

1	d
2	a
3	n
	g
	e
6
7	o
8	u
9	s
	157

VI. Read the text and say if these statements are true, false or not given.

1.In 1883 in Great Britain the 9 m span failed just at the moment when a train was moving with the speed 65 kph.

2.In 1879 in Great Britain the bridge having five spans 75 m long was thrown off the piers.

3.The Tacoma Bridge was destroyed due to the amplification of the vertical and hormonal vibrations created by the resonance in a mild gale.

4.In 1938 in Belgium the hurricane caused a bridge to collapse.

5.The Quebec Bridge in Canada fell into the water because of the technological violation.

6.A stream of water and mud gushed into the Northern-Muya Tunnel and stopped the work for several years.

7.In 1940 the main span of the suspention bridge across the Tacoma River in the USA collapsed.

Home Exercises

I.Memorize the words from Ex. I page 150.

II. Write down the summary of the text in 50 – 70 words and don’t forget to express your own opinion. The phrases below and the key words you have written will be helpful.

I believe…; In my opinion…; The way I see it…; It seems to me that…; As far as I am concerned…; I completely disagree with the idea that…; I fully support… .

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Beyond the ’94 Deauville Confer-

ence...

Since engineers began to build bridges, they have looked for ways to increase span lengths. Bridge design can be seen as the pursuit of minimum of dead load to satisfy a span's required stiffness. This effort becomes more interesting and more important as the span increases. Sound conceptual design, proper detailing and simple methods of construction will lead to good performance of bridges.

Each combination of materials and structural systems imposes its own limits. To understand, indeed to feel how structures and (new) materials

behave and interact is the key to creating new conceptual designs for high performance structures, whereas ever more refined methods of structural analysis probably will not lead to new solutions. The following proposal, a "spatial" suspension bridge for bar- rier-breaking spans, is a highly challenging concept. Among the many possibilities it raises, might it not also find application for other types of longspan structured?

Prof. Eugen Brühwiler

Chairman, IABSE Publications Committee

BREAKING BARRIERS OF SCALE:

A CONCEPT FOR EXTREMELY LONG SPAN BRIDGES

	Christian Menn, Prof. em.		increases.		Moreover, each structural
	Chur, Switzerland		system exhibits, by simple extrapola-
	David P. Billington, Prof.		tion,	an	economically limited span
			length whose location on a cost/span
	Princeton Univ., Princeton, NJ, USA
			diagram can be established where the
	Introduction		cost will increase exponentially. With
			fundamental changes in structural sys-
	For each bridge project, span length is
			tems,	new construction techniques,
	an especially important parameter. It is		new or more efficient construction ma-
	a visual impression of the structure's		terials, the span limit can be increased.
	technical efficiency and it has a con-		The challenge to exceed previous lim-
	siderable influence on	construction	its is probably the most important rea-
	costs: For every structural system, both		son why long spans continually have
	the quantities of construction materials		fascinated bridge engineers.
	and the design and erection problems
	grow disproportionately	as the span

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Fig. 15

Since the beginning of the Industrial Revolution - with its scientifically proportioned bridge designs - the longest spans have been achieved by suspension bridges (Fig. 15).

First were the chain bridges like the Menai Straits Bridge of 1826 with a span of 177 m. After that came the development of the in situ cable spinning technique with wires, whereby the erection problems were significantly reduced. With the great bridge over the Saane River in Fribourg, Switzerland, in 1834 a span of 274 m was reached, and in 1848 the ill-fated Ohio River Bridge at Wheeling, USA, was the first to reach the span of 1000 ft. (308 m). The longest leap in the 19th century was certainly the 487 m long span for the Brooklyn Bridge in 1883. With the construction of the George Washington Bridge in 1931 between New York and New Jersey, O. H. Ammann showed a new way to design suspension bridges.

He increased the record, span from the 564 m of the Ambassador Bridge in Detroit to the unbelievable 1067 m, whereby in View of the high dead weight or rather the "cable stiffness" (a consequence of the great dead weight), he greatly reduced the stiffening truss and even concluded that he could eliminate it entirely when only the upper deck was in place between 1931 and 1962. At the end of the 20th Century the 2000 m span limit will be approached by the Akashi Straits Bridge in Japan.

Structural Systems for the Longest Spans

Great spans are doubtless achieved only with cable-supported bridges. In principle the following cable-support- ed bridge systems are known (Fig. 16):

(a)Suspension bridge with cables anchored in the ground: up to now this is the system used for the longest spans.

(b)Suspension bridge with cables anchored against the deck girder: used only for small bridges and small spans, because the girder must first be constructed on a scaffold.

(с) Cable-stayed bridge with cables anchored in the deck girder: almost all cable-stayed bridges are built with this system. The compressive force introduced into the girder by the cable stays and the cantilevered construction stage is critical limitations for the span length.

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Fig. 16

(d) Cable-stayed bridge with cables anchored in the ground (with expansion joints at either end of the girder): seldom used because the cables must run the entire length between the ground anchorages.

Of the known cable-supported bridge systems, only the classical suspension bridge with cables anchored in the ground is suited for the longest spans. Depending upon the ratio of bridge width to bridge span, suspension bridges are - especially under wind loading - sensitive to vibrations; and for extremely long spans, in the region of 3000 m, this problem will be dominant.

At the IABSE-FIP conference of 12-15 October 1994 in Deauville, Theme 4 was devoted to new developments in the construction of extremely long spans. The main problem for these bridges - as already noted - is their dynamic behaviour. This behaviour can

be improved by an extra-wide deck, a streamlined deck cross section, a V- shaped arrangement of the hangers and by the placement of cable stays in the region near the pylons. In 1968, F. Leonhardt already emphasized the importance of a streamlined cross section and the effectiveness of V-shaped hangers [1]. References [2, 3 and 4] propose combinations of these measures. Reference [5] proposes a concept with spread pylons for the suspension cables, which most likely will present considerable difficulties in construction.

New Structural System for Extremely Long Spans

In the following, a new, constructionally simple and efficient concept for extremely long spans (or narrow, long span bridges) will be briefly introduced. As a basis for this proposal, a six-lane highway with two additional lanes for rail traffic is considered. The vertical load will be taken in large part by a more or less conventional suspension bridge system. In place of the usual frame pylon, however, in consideration of the large dimensions for the cross section, a single central pylon is planned which is simpler to erect, more stable, and aesthetically satisfying (Fig. 17). The dynamic stability of the bridge is assured by placing on either side of the deck girder a sloping cable-stayed system carried by slender pylons which are supported by the central pylon.

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Fig. 17

By means of a cable connection with the central pylon, the danger of buckling in the slender cable-stayed pylons will be practically eliminated. In the vicinity of the pylon, the cable-stayed system will also carry the vertical load; on the central part of the span the more widely spaced cable stays serve primarily for the dynamic stabilization of the deck. If the compressive force in the deck must be limited, then at least a part of the stabilizing cables can be anchored (like he suspension cables) in the ground (Fig. 18).

The construction sequence for this system is relatively simple:

–erect the central pylon

–install the suspension cables (the most difficult process of the erection of the bridge)

–pull up the cable-stayed pylons. which are anchored with temporary and final cables to the central pylon

–build the deck from the cable stays and the suspenders.

The proposed concept considers numerous parameters, which for a bridge with an extremely long span, must he optimized specifically for each design. The following parameters are particularly important:

–height of the central pylon, height and slope of the cable-stayed pylons

–placement of the traffic lanes, rail . lines in the middle of the deck or placed one at each edge

–number of suspension cables: two or three

–form of the deck cross section and length of the deck segments

–length of the region with V-shaped hangers

–construction: installation of the suspension cables, erection of the deck.

What Comes Next?

At the present time, steel is clearly the most suitable material for 3000 m spans. This could change, however, if synthetic materials such as carbon fibers prove reliable in construction and the cost of their production were to decrease substantially. For spans greater than 3000 m, new materials that are significantly lighter than steel are essential.

As spans increase beyond 3000 m, it will become necessary to build an increasingly larger proportion of structural components completely or partly of synthetics.

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