HISTORY OF BRIDGE DEVELOPMENT

INTRODUCTION

A bridge is a structure which provides passage facilities over an obstacle without

closing the way underneath. The required passage may be for a railway track, road or

pedestrians etc. The obstacle to be crossed may be deep valley full of water, road,

railway etc.

Its origin may have been man’s first attempt to control the forces of nature. A

bridge has always offered man the satisfaction of successfully crossing an

obstruction-be it a primitive of the ancients or a bewildering modern bridge of

immense spans. The concept of bridge is one of the oldest ideas of man brought about

by the requirement of crossing an obstruction. He discovered this much before he

conceived the idea of a wheel.

In this topic, we consider the role of critical analysis played in the history of

bridge building. Throughout history each important structural problem has been

solved by producing a few alternatives and undertaking an investigation to arrive at a

solution. Knowledge of bridge engineering from world practice has great value. For

this reason we begin our topic from a historical perspective. It is not possible to show

all the bridges ever constructed. Here, only those which illustrate the most important

engineering and design developments are being considered.

We know that certain natural bridges were formed, that sustained themselves

by the geometric principles of the arch. We also may reasonably surmise that the first

bridges were such simple structures. There remains evidence of the “clapper” (from

the Latin, claperius, meaning pile of stones) bridges in England, primitive rocks

arranged for passage over rivers. These first beams or stringer bridges were formed

simply by laying a flat stone or log on supports without need for complex

mathematical calculations or resolution of engineering problems.

By the same token, ropes and vines were used for carrying people over ravines

and canyons. Perhaps someone first swung from one point to another, and later kept

the vine or rope attached to two points so that cargo or persons could slide along from

one end to the other. Eventually, these supports would hold another vine or rope over

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which people would walk, ultimately becoming a “roadway” in itself. Such may have

been the origins of the suspension bridge.

The pioneers used empirical methods .They made some intelligent guesses as to the

strength required and built the bridge accordingly

Importance of bridges

The bridges serve as the most useful links connecting big towns and cities, and

hence in case of war or calamities, the destruction of bridges stops the mobility of

army or essential goods. The importance of bridges has been felt from the very

primitive age and cities have sprung up at the bridge head or where they could be

crossed over any time. International trade and travel depend on shipping and air

routes, but efficient distribution networks depend on bridges.

HISTORICAL DEVELOPMENT OF BRIDGES

A Mythological Insight

Valmiki Ramayana provides mythological accounts of bridges constructed from India

to Lanka by the army of Rama in verse 2-22-76. So the first available information in

the development of bridges is during this period. The saying of the verse (translated)

goes like this

“When Rama is about to release a missile presided over by Brahma from his

bow, the sea-god appears in person before him with joined palms and advises him to

get a bridge constructed by Nala across the ocean. The ocean god disappears after

giving this advice to Rama. Nala accordingly constructs a bridge across the sea with

the help of other monkeys “

Another verse from the Ramayana (translated) goes like this

“ That beautiful and lovely bridge constructed by Nala across the ocean the

abode of alligators, shone brightly like a milky way of stars in the sky “

The Ram Sethu also known as Adam's Bridge is a chain of limestone shoals,

between the islands of Rameswaram, off the southeastern coast of Tamil Nadu, India,

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and Mannar, near northwestern Sri Lanka. Geological evidence indicates that this

bridge is a former land connection between India and Sri Lanka

Fig 1. Adam's Bridge (Ram Sethu)

Nala, the son of Viswakarma, was probably the first Indian bridge engineer.

The Arthashastra of Kautilya mentions the construction of dams and bridges. A

Mauryan bridge near Girnar was surveyed by James Princep. The bridge was swept

away during a flood, and later repaired by Puspagupta, the chief architect of Emperor

Chandragupta I. The use of stronger bridges using plaited bamboo and iron chain was

visible in India by about the 4th century. A number of bridges, both for military and

commercial purposes, were constructed by the Mughal administration in India

Ancient Period-Early Developments in Bridge Construction

It is said that the history of bridges is the history of civilization. However

achieving progress in bridge engineering was not an easy task. Bridges, as most other

engineering structures, began with the “cut and try” process. The pioneers used

empirical methods. They made intelligent guesses required and built the bridge

accordingly. Many centuries passed before man created the five basic types of

bridges: the beam, the cantilever, the arch, the suspension and the truss. The first four

types were copied from nature long before recorded history began.

Primitive man must have built many crossings over shallow streams by

pilling rocks for piers and covering them with slabs of stones, logs, or falling trees so

as to span small rivers.

Early forms of Suspension Bridges: Suspension bridges across the water were built

from the overhanging branches of opposite trees. Thus, it may be seen that the

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evolution of bridge engineering resulted from the evolution of the form of structure,

the materials of construction, and the methods of design, fabrication and erection.

Initially ropes were thrown across a narrow gorge or river, from which people could

hang as they crawled across. This was the earliest suspension bridges. Later, wooden

footways were added between the ropes. The suspension or cable bridge is illustrated

in nature by the swinging vine, utilized by animals and people to pass from one tree to

another over a stream. In its simplest form a suspension bridge consists only of cables

and unstiffened roadway. Many primitive bridges of this kind were built.

Fig 2. Hanging creepers used as monkey trains

Fig 3. A swinging vine

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Bridges made of timber

The natural example of the simple beam bridge is that of a fallen tree spanning a

stream.

Fig 4. Accidentally fallen tree used as bridge

Then the purposefully felled trees/logs and two or more felled logs with

transverse type platform were also used as bridges. A log bridge is a bridge that uses

logs that fall naturally or are intentionally felled and placed across streams. The first

man made bridges with significant span were probably intentionally felled trees. Such

log bridges have a severely limited lifetime due to soil contact and subsequent rot and

wood-eating insect infestation.

Fig 5. A Log Bridge

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Bridges made of stone

The Natural stepping stones

Fig 6. A rough creek crossing

A step-stone bridge is a simple means for a pedestrian to cross a watercourse

during periods of low flow while keeping feet dry. This type, along with the log

bridge is likely the oldest bridge types. Unlike all other bridges, this bridge has no

spans. Water is allowed to course between the stones that form the steps. Step-stone

bridges are often seen in gardens in China and Japan. It is one of several principal

types found in such gardens. Sometimes one will find these as informal crossings of

small streams when hiking, as they are often built by hikers during the drier seasons

and are subject to being swept away (or at least disarranged) during periods of high,

fast water

Clapper bridge is an ancient form of bridge formed by large flat slabs of

granite or schist supported on stone piers (across rivers), or resting on the banks of

streams. Although believed to be of prehistoric origin, most were erected in medieval

times, and some in later centuries. They are often situated close to a ford where carts

could cross. According to the Dartmoor National Park, the word 'clapper' derives from

an Anglo-Saxon word, Cleaca, meaning 'bridging the stepping stones’.

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Fig 7. The Clapper Bridge at Post bridge, Devon-England

Early forms of Arch Bridge: An arch bridge is a bridge with abutments (supports at

either end) at each end shaped as a curved arch. The arch is in compression and

pushes its load out horizontally and vertically into the supporting ground. Natural

bridges of stone have also been formed, where the action of water has worn away rock

until only an arch was left, high above the river bed.

Fig 8. Natural Arch Bridge

Early forms of Cantilever bridges: Quite probably, primitive man discovered the

principle of the cantilever bridge at a very early stage of the development. He made

use of cantilever to construct longer spans than he was able to build with simple

beams. Timber beams or stone slabs projecting out one above the other represented

such bridges.

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Fig 9. A Cantilever Bridge

The earliest bridge of which there is any authentic record was built over the Euphrates

at Babylon at about 780 B.C.

THE ROMAN PERIOD:

The Roman Period dates from 300B.C and covers a period of about 600 years.

The Romans were the first real bridge engineers. The greatest bridge builders of

antiquity were the Romans. They applied a civil engineering repertoire on an

unprecedented grand scale and achieved impressive results .They built bridges in

wood, stone and concrete. They abandoned Timber bridges in favour of stone bridges

which required the arch to be perfected. They solved the complicated engineering

problems of how to rest their massive spans on underwater piers and how to protect

the piers from floods. Today, Roman arches still stand in Italy, Spain and France. The

Greek writer Herodotus in his Histories, records several pontoon bridges. For

Emperor Darius I The Great of Persia (522 BC - 485 BC), the Greek Mandrocles of

Samos once engineered a pontoon bridge that stretched across the Bosporus, linking

Asia to Europe, so that Darius could pursue the fleeing Scythians as well as move his

army into position in the Balkans to overwhelm Macedon

Roman engineering introduced four significant developments to the art of

bridge building that never had been prominent before:

1. The discovery and extensive use of natural cement.

2. Development of the coffer dam.

3. Perfection and widespread application of the semi-circular masonry arch.

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4. The concept of public works.

Typical characteristics of Roman Bridges

Many are more than 5 meters wide

Most of them slope slightly

Many have rustic work

The stonework has alternating stretcher and header courses ; i.e. one layer of

rectangular stones is laid lengthwise, and the next layer has the ends facing

outwards

Stones linked with dovetail joints or metal bars

Indents in the stones for gripping tools to hold onto

The Romans mixed cement, pozzolana, found near the Italian town of Pozzuoli

(ancient PUTEOLI), with lime, sand, and water to form a mortar that did not

disintegrate when exposed to water. It was used as a binder in piers and arch

spandrels, and mass-formed in foundations.

The oldest roman bridge according to history was the Pons Sublicius,

named for the sublicae, or wooden beams, from which it was built across the river

Tiber in 620B.C. The most celebrated of all the Roman bridges was Caesar’s pile

trestle (55B.C) which was founded on groups of wooden piles. A series of these piles

and cross beams were carried right across the river, and then logs were laid along

them to form the roadbed of the bridge. The Roman’s greatest undertaking was the

large timber arch bridge over Danube in 104A.D. It contained 20 wooden arch spans

resting on cut-stone piers.

Fig 10. Pons Sublicius

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To erect underwater piers, the Romans made use of Coffer dams. They are

temporary enclosures built in river beds to keep the water out while the foundations

were established. They were made by driving timber piles into the river bed,

removing water from the area enclosed, and then excavating the soft ground inside.

Despite the use of coffer dams, Roman bridge foundations typically were not deep

enough to provide sufficient protection against scour. The most well known existing

Roman aqueduct is the Pont Du Gard, near Nimes in France. It is a three tiered bridge,

the lowest of which consists of six large arches and the topmost tier carries the water

channel.

Fig 11. Port de gard near Ninnes, France - A 3-storyed aqueduct

The aqueduct of Segovia of Spain is another example. The Romans abandoned

timber bridges in favour of stone bridges, which required that, the arch to be

perfected. The Romans also used the strong semicircular arch. The Romans, while

certainly not the originators of the arch (credit has been given to the Babylonians for

that), can fairly be said to have perfected its application and principles. Some of the

stone arch bridges built by Roman engineers survive to this day.

Development in China

Following the decline of the Roman Empire with its many engineering

achievements, little developments in beam, arch, suspension, and cantilever bridge

took place in China and other parts of the world. Chinese bridge builders

experimented with forms and materials, perfecting their techniques. China was the

origin of many bridge forms. Marco Polo told of 12,000 bridges built of wood, stone,

and iron near the ancient city of Kin-sai. The first chain-link suspension bridge, the

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Panhogiao or Panho Bridge (206 BC), was built by General Panceng during the Han

Dynasty. Also, one suspension bridge is said to have been built in china about 65

A.D. Another early form of bridge was the cantilever span. The Chinese are believed

to have constructed cantilever bridges many centuries back. The Chinese have

developed the true semicircular arch for ages, although their old spans were always

short. The ancient China, the Zhou Dynasty Chinese text of the Shi Qing (Book of

Odes) records that King Wen of Zhou was the first to create a pontoon bridge in the

11th century BC. However, the historian Joseph Needham has pointed out that in all

likely scenarios, the temporary pontoon bridge was invented during the 9th century

BC - 8th century BC in China. During the Eastern Han Dynasty (25-220 AD), the

Chinese created a very large pontoon bridge that spanned across the width of the

Yellow River.

Post Roman Era

After the fall of the Roman Empire, progress in European bridge building

slowed considerably until the Renaissance. Fine bridges sporadically appeared,

however. Medieval bridges are particularly noted for the Ogival or pointed arch. With

the pointed arch the tendency to sag at the crown is less dangerous, and there is less

horizontal thrust at the abutments. Medieval bridges served many purposes. Chapels

and shops were commonly built on them, and many were fortified with towers and

ramparts. Some featured a drawbridge, a medieval innovation. The most famous

bridge of that age was Old London Bridge, begun in the late 12th century under the

direction of a priest, Peter of Colechurch, and completed in 1209, four years after his

death. London Bridge was designed to have 19 pointed arches, each with a 7.2-metre

(24-foot) span and resting on piers 6 metres (20 feet) wide. There were obstructions

encountered in building the cofferdams, however, so that the arch spans eventually

varied from 4.5 to 10.2 metres (15 to 34 feet). The uneven quality of construction

resulted in a frequent need for repair, but the bridge held a large jumble of houses and

shops and survived more than 600 years before being replaced.

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Fig 12. Old London Bridge

FURTHER DEVELOPMENT OF BRIDGES

Development in Arch Bridges

Stone Arches

Corbelled Arches

Masonry Arch Bridges

R.C.C Arch Bridges

Steel Arch Bridges

The construction of arches began before the days of recorded history. Corbelled stone

arches were used by the Egyptians in the pyramid of Gizeh dating back some 3000-

4000 years ago. The inhabitants of the valleys of Euphrates and Tigris were also

familiar with the arch at a very early period. The Chinese have employed the true

semicircular arch for ages although their spans were always less. But the Romans

pioneered the building of arch bridges, which with their familiar parabolic shape

allowed for longer spans than beam bridges. Because the reach of the beam bridge is

limited, arch bridges provide a natural mechanism for spanning greater distances.

Stone Arches: Stone arch bridges are the oldest of the arch bridges, as early engineers

made use of this available material. However, there is an aesthetic appeal to the use

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of stone, and stone was used in the twentieth century in construction of some very

beautiful and important bridges. Stone as a material handles the massive compressive

forces acting on the bridge. To the extent that concrete is comprised of sand and

gravel, they are included here as "stone" arch bridges, though might be considered

separately.

Fig 13. A Stone Arch Bridge

Corbel Arches

The corbel arch bridge is a masonry, or stone, bridge where each successively higher

course (layer) cantilevers slightly more than the previous course. The steps of the

masonry may be trimmed to make the arch have a rounded shape.

Mayan civilization: Corbelled arches are a distinctive feature of certain pre-

Columbian Meso-american constructions and historical/regional architectural styles,

particularly in that of the Maya civilization. The prevalence of this spanning

technique for entrances and vaults in Maya architecture is attested at a great many

Maya archaeological sites, and is known from structures dating back to the Formative

or Pre classic era.

India: The arches in Indian buildings were trabeate or corbelled. The tomb of

Sultan Ghari is an example of a corbelled arch from 1231 AD, located in New Delhi,

India.

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Fig 14. A corbel arch in Vasant Kunj, New Delhi

In addition to stone, arch bridges were also fabricated from wrought or cast iron as

well as steel

Masonry Arch bridges

The end of the 16th century marked the start of new evolutionary era in the building of

masonry arch bridges. The Renaissance took the structures and forms of construction

of the Romans as its models. Due to its rise/span ratio of 1:2 the semicircular arch

permits only very restricted functionality and is therefore unsuitable for urban

structures in particular. This functional disadvantage gave rise to new arch forms

which were considered shallower than Roman arch.

More than 2000 years certainly passed before the Etruscan’s masonry arch

with specially cut joints appeared. But the span of time from the first masonry arch

theories of the late 17th century to the elastic arch theory is less than 200 years. And

the analysis of masonry arch bridges based on the ultimate load method did not appear

on the scene until the 1960s.

The largest masonry-arch span in the world, 89.9 m (295 ft), is the Syra Bridge at

Plauen, Germany, completed in 1903. No major masonry-arch bridges have been built

in the U.S. in recent years because of their high construction costs.

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Development in Suspension bridges

A simple suspension bridge is an early type of bridge that is supported entirely

from anchors at either end, and has no towers or piers. The simple suspension bridge

is the oldest known type of suspension bridge and there were at least two independent

inventions of the simple suspension bridge, in China and South America. It was also

used in remote ages in Japan, India and Tibet. The cables of these primitive types

were made of wines twisted onto straps of hide and fastened to trees or other

permanent objects on shore. Iron chains for suspension cables were adopted in both

India and Japan more than 500 years ago.

Fig.15. Suspension Bridge in South America

A rope bridge is a bridge constructed chiefly of rope. In its simplest form, it can be

one or two ropes that bridge a river, enabling the traveler to be supported in their

crossing and not be swept away. One rope above another, for feet and hands, may be

referred to as a commando bridge.

More complicated rope bridges can involve the use of multiple ropes, and boards as

footpaths. One of the most complex examples of a culture using these as permanent,

rather than temporary crossings, is the Inca civilization

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Fig.16. A Rope Bridge in China

A Chinese multi-span simple suspension bridge with bamboo cables is

reported at Quan-Xian, documented from 960AD. Simple suspension bridges using

iron chains are also documented in China and the Himalayas, although their earliest

date is unclear. The Luding Bridge dates from 1703, spanning 100 m using eleven

iron chains. Several are attributed to Tibetan monk Thang-stong rGyal-po, who

reportedly built several in Tibet and Bhutan in the 15th century, including one at

Chuka. Claims that more modern suspension bridges with a horizontal deck also

originated in Tibet or China remain largely unsubstantiated.

In South America, Inca rope bridges predate the arrival of the Spanish in the Andes in

the 16th Century. The oldest known suspension bridge, reported from ruins, dates

from the 7th Century in Central America (see Maya Bridge at Yaxchilan). This bridge

has been proposed as the earliest known suspended-deck suspension bridge, but may

have been a simple suspension bridge. Development of wire cable suspension bridges

dates to the temporary simple suspension bridge at Annonay .

The first chain suspension bridge did not appear in Europe until 1741, when the 70ft

(21m) span Winch Bridge was constructed over a chasm of the River Tees (UK), with

the flooring laid directly on two chains. The grandfather of all great suspension

bridges is the mania straits bridge, England. Built by Thomas Telford in 1825, which

was 60 years ahead of its time. The Menai Bridge was twice rebuilt before the entire

suspension system was replicated in steel in 1940 and the arched openings in the

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towers were widened. Simple suspension bridge designs were made largely obsolete

by the 19th Century.

The inherent tendency of suspension bridges to sway and undulate in wavelike

motions under repeated rhythmic loads such as marching soldiers or the wind was not

completely understood by engineers until the 1940s, following the collapse of the

Tacoma Narrows Bridge. Credit for designing the first suspension bridge rigid enough

to withstand wind loads and the highly concentrated loadings of locomotives belongs

to John Roebling. His first masterpiece was the Niagara Suspension Bridge, with a

span of 821ft (250m) on the Grand Trunk Railway below Niagara Falls

Fig 17. Niagara Bridge (USA)

Iron bridges

Though extremely versatile, wood has one obvious disadvantage - it burns.

There was another material, however, whose use at the end of the 18th century offered

bridge engineers an alternative to the traditional materials of timber, stone, and brick.

The Greeks and Romans had used it to reinforce stone pediments and columns in their

temples and iron links had been forged by the Chinese and used in suspension

bridges.

The successful smelting of iron with coke, rather than charcoal, by English ironmaster

Abraham Darby in 1709 freed iron production from fuel shortage restrictions, made

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large castings possible, and facilitated creation of the arch ribs for the world's first

iron bridge, built seventy years later. Bridges were one of the first structural uses of

iron, preceded only by columns to support the floors of textile mills.

The first successful all-iron bridge in the world was designed by Thomas Farnolls

Pritchard, an architect who suggested using the material as early as 1773. The Iron

Bridge was followed by a succession of cast-iron arches built throughout Europe. One

iron arch, however, merits mention, as it is the oldest iron bridge in America. Dunlaps

Creek Bridge (1839), designed by Captain Richard Delafield of the Army Corps of

Engineers for the National Road in Brownsville, Pennsylvania, survives to this day,

still carrying traffic (Figure 7). Because the material could be moulded into elaborate

shapes, extravagantly decorative iron arches were used for pedestrian bridges on the

grounds of estates and imperial palaces or urban pleasure grounds.

Fig 18. Dunlaps Creek Bridge (1839), Brownsville, Pennsylvania (USA)

Following the construction of the Iron Bridge at Coalbrookdale, Thomas Telford, a

gifted, self-educated Scottish engineer, built a number of cast-iron arches throughout

the British Isles. These included canal aqueducts, which were extraordinarily

innovative arrangements in which the cast iron had real structural value. Telford's

most ambitious notion, however, was his proposal of 1800 for a single cast-iron arch

of 600ft (183m) span over the Thames to replace Old London Bridge.

Today, several collections of cast-iron arches survive in different countries. Rio Cobre

bridge in Jamaica is another example. By 1800, most European engineers were open

to using cast iron.

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Fig 19. RioCobre Bridge ,Jamaica

Steel bridges

Structural steel is strong and supple compared to Cast or Wrought iron, and

allows greater design flexibility. The last thirty years of the 19th century witnessed

the phasing in of steel plates and rolled shapes, leading to the enormous production of

steel trusses and plate-girder spans of ever-increasing lengths throughout the world.

Steel arches and cantilevers were favoured for long spans because they better

withstood the impact, vibration, and concentrated loads of heavy rail traffic.

The earliest known use of steel in bridge construction was the 334ft (102m)

suspension span across the Danube Canal (1828) near Vienna (Austria). Steel halved

the weight of wrought iron, but remained prohibitively expensive for another forty

years before steelmaking processes such as the Bessemer and the Open-hearth were

perfected. The first major bridge utilizing true steel was the Eads Bridge (1874), one

of the Mississippi River crossings in the USA. The crowning achievement of the

material during the 19th century was the mighty Forth Railway Bridge in Scotland

(1890). Its design was motivated by the Tay Bridge disaster. Steel arches of enormous

span were built during the first few decades of the 20th century.

In India, for example, the British built several long-span railway bridges, such as the

Hooghly and the Sukkur bridges called Howrah Bridge which exceeded 1000ft

(300m) in span and are interesting because they were constructed using the simplest

equipment and armies of unskilled labour.

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Fig.20. Howrah Bridge, Calcutta

Railroads and Viaducts

Railroads, the transportation mode that revolutionized the 19th century, generated a

bridge type that merits special attention. The limited traction of locomotives forced

the railroad engineer to design the line with easy gradients. Viaducts and trestles were

the engineering solution for maintaining a nearly straight and horizontal line where

the depth and width of the valley or gorge rendered embankments impracticable.

These massive, elevated structures were first built in Roman style of multiple-stone

arches and piers. Later, when wrought iron and steel became available, engineers built

viaducts and trestles of great length and height on a series of truss spans or girders

borne by individual framed towers composed of two or more bents braced together.

Fig 21. Kinzua Viaduct,Pennsylvania (USA)

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Development in Cantilever bridges

To solve the problem of increasing the span distance, other alternatives to

beam and arch bridges included suspension and cantilever bridges. Cantilever bridges

are a modified form of Beam Bridge, with the support being placed not at the end, but

somewhere in the middle of the span. Engineers in the nineteenth century understood

that a bridge which was continuous across multiple supports would distribute the

loads among them. This would result in lower stresses in the girder or truss and meant

that longer spans could be built. The use of a hinge in the multi-span system presented

the advantages of a statically determinate system and of a bridge that could handle

differential settlement of the foundations. Engineers could more easily calculate the

forces and stresses with a hinge in the girder.

Heinrich Gerber was one of the engineers to obtain a patent for a hinged girder

(1866) and is recognized as the first to build one. The Hassfurt Bridge over the Maine

river in Germany with a central span of 124 feet (38 meters) was completed in 1867

and is recognized as the first modern cantilever bridge.

The Kentucky River Bridge by C. Shaler Smith (1877), the Niagara Cantilever

Bridge by Charles Conrad Schneider (1883) and the Poughkeepsie Bridge by John

Francis O'Rourke and Pomeroy P. Dickinson (1889) were all important early uses of

the cantilever design. The Kentucky River Bridge spanned a gorge that was 275 feet

(84 meters) deep.

The most famous early cantilever bridge is the Forth Rail Bridge. This bridge

held the record for longest span in the world for seventeen years

Fig 22. Forth Rail Bridge -Scotland

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Scientific analysis of bridge design during the 19th century

It took the worst bridge disasters of the century in the USA, Great Britain, and

France to usher in the development of standards, specifications, and enough

regulation to protect the travelling public. The loss of 83 lives caused by the collapse

of a cast- and wrought-iron truss in Ashtabula prompted an investigation by the

American Society of Civil Engineers. The loss of 80 lives by failure of a section of

the two-mile-long Tay Bridge resulted in similar inquiries in Britain.

The reasons for these major failures were similar: ignorance of metallurgy resulted in

uneven manufacturing methods and defective castings, and inadequate inspection and

maintenance were inherent at both bridges. For the Tay Bridge, exceptionally strong

vibrations due to dynamic wind stresses under a moving load created a lack of

aerostatic stability and eventual failure. It took engineers another quarter-century to

perfect bridge design according to advanced theories of stress analysis, understanding

of material properties, and renewed respect for the forces of nature. A definitive

understanding of the physical oscillations and vibrations of structures did not occur

until the middle of the 20th century after the Tacoma Bridge collapse in the USA

in1940

Truss bridges and Girder bridges

Advances in design theory, graphic statics, and knowledge of the strength of

materials by engineers such as Karl Culmann and Squire Whipple were achieved in

the second half of the 19th century, but the factor that most influenced the scientific

design of bridges was the railroads. Engineers had to know the precise amount of

stresses in bridge members to accommodate the thundering impact of locomotives.

Founded on the pioneering work of the American Squire Whipple and other European

engineers as Collignon, the last quarter of the 19th century witnessed broad

application of both analytical and graphical analysis, testing of full-size members,

comprehensive stress tables, standardized structural sections, metallurgical analysis,

precision manufacturing and fabrication in bridge shops, publication of industry-wide

standards, plans, and specifications, inspections, and systematic cooperation between

engineers, contractors, manufacturers, and workers. The combined experience of the

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railroads, bridge manufacturing companies, and the engineering communities enabled

the railroads successfully to tackle long-span iron and steel bridges and long-span

trussed-roof train sheds , the two engineering icons of the 19th century.

The metal truss bridge features a network of metal beams arranged in a pattern based

on triangles that work to support the bridge. The metal truss bridge was essentially the

result of the transition from wood to metal for use in bridge building. Although

experiments in metal bridges had been going on for many years, it was not until the

1870s that metal bridges began to take off and began to be the preferred material over

wood.

Steel-truss construction has been used extensively in bridge building because

of its low cost. Modern developments have increased the attainable length of span,

and continuous trusses are increasingly employed. A notable example of this type is

Lindenthal’s Sciotoville Bridge (1917), over the Ohio River, with a truss 472.4 m

(1550 ft) long in two spans of 236.2 m (775 ft) each. The Astoria Bridge (1966) over

the Columbia River in Oregon is the longest continuous truss bridge, with a 375.5-m

(1232-ft) span.

Fig.23.A Truss Bridge

A girder bridge, in general, is a bridge built of girders placed on bridge abutments and

foundation piers. In turn, a bridge deck is built on top of the girders in order to carry

traffic. The girder is the simple form of Beam Bridge. Originally wood, girders then

were made from iron or steel, or even reinforced concrete.  Following World War II

and the expansion of highways, steel and concrete girder bridges became

commonplace.

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Fig 24. Girder bridge

Modern developments

Reinforced concrete Bridges

Prestressed Concrete Bridges

Movable(swing or bascule)bridges

Cable stayed superstructure

Reinforced concrete bridges

Soon after the turn of the 20th century, the development of reinforced concrete

brought about great progress in concrete bridge construction. Just when the masonry

arch bridge was reaching its peak around the beginning of the 20th Century,

reinforced concrete arrived on the scene. Since then, it has become the major

construction material for bridges as it has for most structural and civil engineering

applications, with its intrinsic versatility, design flexibility and, above all, natural

durability.

The Esla Bridge over the Esla River, Spain, with a 196.6-m (645-ft) span, was

completed in 1940 and The Gladesville Bridge (1964) at Sydney, Australia, rises 45.7

m (150 ft) above the Parramatta River on a 304.8-m (1000-ft) are the few examples

of reinforced concrete arch span in recent times.

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Fig 25.RCC Bridge over NH-9 in Andhra Pradesh

Prestressed concrete bridges

The most important innovation in the history of reinforced concrete

technology was the development of prestressed concrete. It had also been used to a

limited extent in masonry construction. Its application to reinforced concrete

revolutionized bridge construction. In prestressed concrete, a prestress force is applied

to a concrete member and this induces an axial compression that counteracts all, or

part of, the tensile stresses set up in the member by applied loading. In the field of

bridge engineering, the introduction of prestressed concrete has aided the construction

of long-span concrete bridges. These often comprise precast units, lifted into position

and then tensioned against the units already in place, the process being continued until

the span is complete. For smaller bridges, the use of simply supported precast

prestressed concrete beams has proved an economical form of construction. The

introduction of ranges of standard beam section has simplified the design and

construction of these bridges.

The earliest investigations of prestressed concrete beams were conducted in

the nineteenth century. Further application in construction was made during the first

three decades of the 20th century. Dischinger was the person who built the world’s

first prestressed concrete bridge in Aue, Germany, which was completed in 1937.

Further developments were the Mass River Bridge built in 1949 by Gustave Magnel,

which was the world’s first prestressed continuous girder bridge.

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A stressed ribbon bridge is a tension structure. The suspension cables are

embedded in the deck which follows a catenary arc between supports. Unlike the

simple span the ribbon is stressed in compression, which adds to the stiffness of the

structure. Such bridges are typically made from concrete reinforced by steel

tensioning cables. Where such bridges carry vehicle traffic a certain degree of

stiffness is required to prevent excessive flexure of the structure, obtained by stressing

the concrete in compression. The Maldonado Bridge, located in Maldonado, Uruguay

is an example for stressed ribbon bridge which is a modern development in

prestressed concrete bridges.

Fig.26.The Maldonado Bridge, located in Maldonado, Uruguay,

Movable or Transporter Bridges (Bascule or Swing)

The bascule or draw span was developed by Europeans during the middle Ages. This

is the descendent of Beam Bridge. There was a resurgence of moveable bridges

during the late 19th century. Reliable electric motors and techniques for

counterbalancing the massive weights of the bascule lift, or swing spans marked the

beginning of modern moveable-bridge construction. They are usually found in flat

terrain, where the cost of approaches to gain high-level crossings is prohibitive, and

their characteristics include rapidity of operation, the ability to vary the openings

depending on the size of vessels, and the facility to build in congested areas adjacent

to other bridges. This type of bridge also reaches back into history, integrating ancient

technology such as the rope ferry with new structural forms and materials such as the

iron beam and the strongest steel cables.

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Fig.27.Bascule (Movable Bridge)

Cable-Stayed type Superstructure

A cable-stayed bridge is a bridge that consists of one or more columns (normally

referred to as towers or pylons), with cables supporting the bridge deck. This is the

descendent of Suspension-type bridges.

Cable-stayed bridges can be dated back to the 1784 design of a timber bridge by

German carpenter C.T. Loescher. Many early suspension bridges were of hybrid

suspension and cable-stayed construction, including the 1817 footbridge at Dryburgh

Abbey, and the later Albert Bridge (1872) and Brooklyn Bridge (1883). Their

designers found that the combination of technologies created a stiffer bridge, and John

A. Roebling took particular advantage of this to limit deformations due to railway

loads in the Niagara Falls Suspension Bridge.

Fig 28. Cable-Stayed Bridge

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FACTORS THAT AFFECTED THE DEVELOPMENT OF BRIDGES:

The factors which are mainly responsible for this are as follows:

1. Advancement of construction material

Bridge is a massive structure, which needs sufficient quantity of construction

material. In olden days, the means of transport was not as quick as that of today;

hence the difficulty of transport of materials gave rise to the practice of using local

available materials. Thus in places where good quality timber was available in

abundance, wooden bridges flourished and where timber was scarce and stones was

available in plenty, stone were developed. In tropics, the existence of strong creepers

led to the evolution of suspension bridges.

2. Advent of new materials

With advent of new materials, new ideas came to light in the bridge

engineering. The invention of cast iron replaced timber and stone or trussed bridges

by cast iron bridges. Later on cast iron was replaced by wrought iron and wrought

iron by steel. In the beginning of 20th century, much headway was made in the

production of good quality concrete and a new horizon was opened. By the thirties of

the 20th century R.C.C bridges took the place of steel bridges. Further advancement in

the production of high tensile steel and high strength concrete gave rise to the

development of prestressed concrete bridges. Now a day’s big span bridge are

constructed of prestressed concrete as it is economical in material and has longer life.

3. Advancement in theory and scientific research

The design of the bridges was empirically based on past experience gained by

success or failure of the bridges constructed. The well known Hook’s law came into

existence in the middle of 17th century and Euler’s formula for columns and struts was

published in 18th century. The theory of bending was put forth in 1826. All these

theories led to the theoretical analysis of bridge engineering which enabled modern

bridges design and construction. The development of plastic theory and prestressed

concrete technique further advanced the knowledge of bridge engineering.

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4. Improvement of constructional methods

The improvement in constructional methods has contributed very much to the

advancement of bridge engineering science. The use of compressed air has helped to a

great extent in the construction of bridge piers foundation waters which otherwise

would have been impossible.

5. Advancements in other branches of science

The research work in hydraulics, structural engineering, highway engineering

has considerably contributed to the development of bridge engineering and are closely

related to it.

CONCLUSION

The developments of bridges in the early stage took place in different countries

independently more or less at the same time. Of course the pace of development could

not be kept at par due to many factors. Developments in different countries could not

travel fast to benefit each other by mutual exchange of knowledge and the progress

made in each country remained of local nature. Along with development of other

branches of science, the science of bridge engineering also has been progressed and

very rapidly in the 19th century.

It is certain that technological advancement will continue to influence the type of

bridges in future. New structural concepts in connection with engineered materials

offer a wide range of possibilities for future bridges.

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