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Tuesday, 29 May 2012
World's longest suspension bridges
1.Akashi Bridge
Also known as the Pearl Bridge, it has the longest central span
of any suspension bridge,[2] at 1,991 metres (6,532 ft). It is located
in Japan and was completed in 1998.
Before the Akashi Kaikyō Bridge was built, ferries carried
passengers across the Akashi Strait in Japan. This dangerous waterway
often experiences severe storms and, in 1955, two ferries sank in the
strait during a storm, killing 168 people. The ensuing shock and public
outrage convinced the Japanese government to develop plans for a
suspension bridge to cross the strait.
2.Xihoumen Bridge
The 5.3-kilometre-long suspension bridge connection has a 2.6-kilometre-long main bridge with a central span of 1,650 metres.
3. Great belt bridge
The Great Belt Fixed Link (Danish: Storebæltsforbindelsen) is the
fixed link between the Danish islands of Zealand and Funen across the
Great Belt. It consists of a road suspension bridge and railway tunnel
between Zealand and the island Sprogo, as well as a box girder bridge
between Sprogo and Funen
4. Runyang Bridge
The Runyang Bridge is a large bridge complex that crosses the
Yangtze River in Jiangsu Province, China, downstream of Nanjing. The
complex consists of two major bridges that link Zhenjiang on the south
bank of the river and Yangzhou on the north. The bridge is part of the
Beijing-Shanghai Expressway.
5. Humber Bridge
The Humber Bridge, near Kingston upon Hull, England, is a 2,220 m
(7,283 ft) single-span suspension bridge, which opened to traffic on 24
June 1981. It is the fifth-largest of its type in the world.
6. Jiangyin Suspension Bridge
It connects the cities of Jiangyin and Jingjiang. The main span
of the bridge is 1,385 metres (4,544 ft) meters long, making it the
sixth-longest span suspension bridge in the world.
7. Tsing_Ma_Bridge
The bridge was named after two of the islands at its ends, namely
Tsing Yi and Ma Wan . It has two decks and carries both road and rail
traffic, which also makes it the largest suspension bridge of this type.
8. Verrazano-Narrows Bridge
The bridge furnishes a critical link in the local and regional
highway system. Since 1976, it has been the starting point of the New
York City Marathon.[4] The bridge marks the gateway to New York Harbor;
all cruise ships and most container ships arriving at the Port of New
York and New Jersey must pass underneath the bridge and thus must be
built to accommodate the clearance under the bridge.
9. Golden Gate Bridge
The Golden Gate Bridge is a suspension bridge spanning the Golden
Gate, the opening of the San Francisco Bay into the Pacific Ocean. It
has been declared one of the modern Wonders of the World by the American
Society of Civil Engineers. The Frommers travel guide considers the
Golden Gate Bridge "possibly the most beautiful, certainly the most
photographed, bridge in the world".
10. Yangluo Bridge
With a main span of 1,280 metres (4,200 ft), it is tied with the
Golden Gate Bridge for the ninth longest suspension bridge in the world
15 Amazing Dams that make India Proud
15 Amazing Dams that make India Proud
The biggest dams in India
Hailed as the "Temples of Resurgent India" by Pandit Jawaharlal Nehru, the country's dams help provide water and electricity to millions citizens. We look at some of the biggest ones.
The Tehri Dam is a multi-purpose rock and earth-fill embankment dam on the Bhagirathi River near Tehri in Uttarakhand, India. It is the primary dam of the Tehri Hydro Development Corporation Ltd. and the Tehri hydroelectric complex. The dam is a 260 metres (850 ft) high rock and earth-fill embankment dam. Its length is 575 metres (1,886 ft), crest width 20 metres (66 ft), and base width 1,128 metres (3,701 ft).
Kerala Government has long been demanding construction of a new dam in Mullaperiyar on the Kerala-Tamil Nadu border. Many believe that the existing 116-year-old dam could pose safety hazard. While the matter rests with the apex court, we look at some of India’s biggest and most famous dams, hailed by Pandit Jawaharlal Nehru as ‘The Temples of a Resurgent India
Bhakra Dam is a concrete gravity dam across the Sutlej River, and is near the border between Punjab and Himachal Pradesh in northern India. The dam, located at a gorge near the (now submerged) upstream Bhakra village in Bilaspur district of Himachal Pradesh, is Asia's second highest at 225.55 m (740 ft) high next to the 261m Tehri Dam. The length of the dam (measured from the road above it) is 518.25 m; it is 9.1 m broad. Its reservoir, known as the "Gobind Sagar", stores up to 9.34 billion cubic meters of water, enough to drain the whole of Chandigarh, parts of Haryana, Punjab and Delhi.The 90 km long reservoir created by the Bhakra Dam is spread over an area of 168.35 km2. In terms of storage of water, it withholds the second largest reservoir in India, the first being Indira Sagar dam in Madhya Pradesh with capacity of 12.22 billion cu m.Nangal dam is another dam downstream of Bhakra dam.
Hirakud Dam is built across the Mahanadi River, about 15 km from Sambalpur in the state of Orissa in India. Built in 1957, the dam is one of the world's longest earthen dam. Hirakud Dam is the longest man-made dam in the world, about 16 mi (26 km) in length. It is one of the first major multipurpose river valley project started after India's independence.
Nagarjuna Sagar Dam is the world's largest masonry dam built across Krishna River in Nagarjuna Sagar, Nalgonda District of Andhra Pradesh, India, between 1955 and 1967. The dam contains the Nagarjuna Sagar reservoir with a capacity of up to 11,472 million cubic metres. The dam is 490 ft (150 m). tall and 1.6 km long with 26 gates which are 42 ft (13 m). wide and 45 ft (14 m). tall. Nagarjuna Sagar was the earliest in the series of large infrastructure projects initiated for the Green Revolution in India; it also is one of the earliest multi-purpose irrigation and hydro-electric projects in India.
The Sardar Sarovar Dam is a gravity dam on the Narmada River near Navagam, Gujarat, India. It is the largest dam and part of the Narmada Valley Project, a large hydraulic engineering project involving the construction of a series of large irrigation and hydroelectric multi-purpose dams on the Narmada River. The project took form in 1979 as part of a development scheme to increase irrigation and produce hydroelectricity. It is the 30th largest dams planned on river Narmada, Sardar Sarovar Dam (SSD) is the largest structure to be built. It has a proposed final height of 163 m (535 ft) from foundation. The dam is one of India's most controversial dam projects and its environmental impact and net costs and benefits are widely debated. The World Bank was initially a funder of the SSD, but withdrew in 1994. The Narmada Dam has been the centre of controversy and protest since the late 1980s
The Indirasagar Dam is a multipurpose key project of Madhya Pradesh on the Narmada River at Narmadanagar in the Khandwa district of Madhya Pradesh in India. The Project envisages construction of a 92 m high and 653 m long concrete gravity dam. It provides Irrigation in 1,230 square kilometres of land with annual production of 2700 million units in the districts of Khandwa and Khargone in Madhya Pradesh and power generation of 1000 MW installed capacity (8x125). The reservoir of 12,200,000,000 m3 (9,890,701 acre•ft) was created. less
Tungabhadra Dam
The Bhavanisagar Dam and Reservoir, also called Lower Bhavani
Dam, is located on the Bhavani River between Mettupalayam and
Sathyamangalam in Erode District, Tamil Nadu, South India. The dam is
situated around 16 km (9.9 mi) west to Satyamangalam and 35 km (22 mi)
from Gobichettipalayam, 36 km (22 mi) north-east to Mettuppalayam and 70
km (43 mi) from Erode and 75 km (47 mi) from Coimbatore.
The dam is considered to be among the biggest earthen dams in the country. Bhavani Sagar dam is constructed on Bhavani River, which is merely under the union of Moyar River. The dam is used to divert water to the Lower Bhavani Project Canal
The dam is considered to be among the biggest earthen dams in the country. Bhavani Sagar dam is constructed on Bhavani River, which is merely under the union of Moyar River. The dam is used to divert water to the Lower Bhavani Project Canal
The Koyna Hydroelectric Project
is the largest completed hydroelectric power plant of India It is a
complex project consisting of total four dams with the largest Dam built
on Koyna River known as Koyna Dam hence the name Koyna Hydroelectric
project. The total Installed capacity of the project is 1,920 MW. The
project consists of 4 stages of power generation. Due to the project's
electricity generating potential the Koyna River is considered as the
life line of Maharashtra.
The Idukki Dam, located in Kerala, India, is a 168.91 m (554 ft) tall arch dam. The dam stands between the two mountains - Kuravanmala (839) m and Kurathimala (925)m. It was constructed and is owned by the Kerala State Electricity Board. It supports a 780 MW hydroelectric power station.
It is built on the Periyar River, in the ravine between the Kuravan
and Kurathi Hills in Kerala, India. At 167.68 metres, it is one of the
highest arch dams in Asia and third tallest dam in India.
Krishna Raja Sagara, also
popularly known as KRS, is the name of both a lake and the dam that
causes it.Sir. Mokshagundam Visvesvarayya served as the chief engineer
during the construction of this dam. The dam is named for the then ruler
of the Mysore Kingdom, Krishnaraja Wodeyar IV
The Mettur Dam is a large dam in
India built in 1934.[1] It was constructed in a gorge, where the Kaveri
River enters the plains. The dam is one of the oldest in India. The
total length of the dam is 1,700 m (5,600 ft).
The Srisailam Dam is a dam
constructed across the Krishna River at Srisailam in the Kurnool
district in the state of Andhra Pradesh in India and is the second
largest capacity hydroelectric project in the country. The dam was
constructed in a deep gorge in the Nallamala Hills, 300 m (980 ft) above
sea level. It is 512 m (1,680 ft) long, 145 m (476 ft) high and has 12
radial crest gates. It has a reservoir of 800 km2 (310 sq mi).
The Banasura Sagar Dam is
located 21 km from Kalpetta, in Wayanad District of Kerala in the
Western Ghats. It is the largest earthen dam in India and the second
largest in Asia.
Sunday, 27 May 2012
Types of Bridges
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it.
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History
The first bridges were made by nature itself — as simple as a log fallen across a stream or stones in the river. The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Some early Americans used trees or bamboo poles to cross small caverns or wells to get from one place to another. A common form of lashing sticks, logs, and deciduous branches together involved the use of long reeds or other harvested fibers woven together to form a connective rope capable of binding and holding together the materials used in early bridges.
The Arkadiko Bridge is one of four Mycenaean corbel arch bridges part of a former network of roads, designed to accommodate chariots, between Tiryns to Epidauros in the Peloponnese, in Greece. Dating to the Greek Bronze Age (13th century BC), it is one of the oldest arch bridges still in existence and use. Several intact arched stone bridges from the Hellenistic era can be found in the Peloponnese in southern Greece[2]
The greatest bridge builders of antiquity were the ancient Romans.[3] The Romans built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs. Some stand today.[4] An example is the Alcántara Bridge, built over the river Tagus, in Spain. The Romans also used cement, which reduced the variation of strength found in natural stone.[5] One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered.
The Arthashastra of Kautilya mentions the construction of dams and bridges.[6] A Mauryan bridge near Girnar was surveyed by James Princep.[7] The bridge was swept away during a flood, and later repaired by Puspagupta, the chief architect of emperor Chandragupta I.[7] The bridge also fell under the care of the Yavana Tushaspa, and the Satrap Rudra Daman.[7] The use of stronger bridges using plaited bamboo and iron chain was visible in India by about the 4th century.[8] A number of bridges, both for military and commercial purposes, were constructed by the Mughal administration in India.[9]
Although large Chinese bridges of wooden construction existed at the time of the Warring States, the oldest surviving stone bridge in China is the Zhaozhou Bridge, built from 595 to 605 AD during the Sui Dynasty. This bridge is also historically significant as it is the world's oldest open-spandrel stone segmental arch bridge. European segmental arch bridges date back to at least the Alconétar Bridge (approximately 2nd century AD), while the enormous Roman era Trajan's Bridge (105 AD) featured open-spandrel segmental arches in wooden construction.
Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America, just prior to European colonization in the 16th century.
During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first book on bridge engineering was written by Hubert Gautier in 1716. A major breakthrough in bridge technology came with the erection of the Iron Bridge in Coalbrookdale, England in 1779. It used cast iron for the first time as arches to cross the river Severn.
With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.
In 1927 welding pioneer Stefan Bryła designed the first welded road bridge in the world, which was later built across the river Słudwia Maurzyce near Łowicz, Poland in 1929. In 1995, the American Welding Society presented the Historic Welded Structure Award for the bridge to Poland.[10]
Types of bridges
There are six main types of bridges: beam bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges and truss bridges.
Beam bridges
Beam bridges are horizontal beams supported at each end by abutments, hence their structural name of simply supported. When there is more than one span the intermediate supports are known as piers. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges are large box steel girder bridges. Weight on top of the beam pushes straight down on the abutments at either end of the bridge.[11] They are made up mostly of wood or metal. Beam bridge spans typically do not exceed 250 feet (76 m) long, as the strength of a span decreases with increased length. However, the main span of the Rio-Niteroi Bridge, a box girder bridge, is 300 metres (980 ft). The world's longest beam bridge is Lake Pontchartrain Causeway in southern Louisiana in the United States, at 23.83 miles (38.35 km), with individual spans of 56 feet (17 m).[12]
Cantilever bridges
Cantilever bridges are built using cantilevers—horizontal beams supported on only one end. Most cantilever bridges use a pair of continuous spans that extend from opposite sides of the supporting piers to meet at the center of the obstacle the bridge crosses. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. The difference comes in the action of the forces through the bridge. The largest cantilever bridge is the 549-metre (1,801 ft) Quebec Bridge in Quebec, Canada.
Arch bridges
Arch bridges have abutments at each end. The weight of the bridge is thrust into the abutments at either side. The earliest known arch bridges were built by the Greeks, and include the Arkadiko Bridge.
With the span of 220 metres (720 ft), the Solkan Bridge over the Soča River at Solkan in Slovenia is the second largest stone bridge in the world and the longest railroad stone bridge. It was completed in 1905. Its arch, which was constructed from over 5,000 tonnes (4,900 long tons; 5,500 short tons) of stone blocks in just 18 days, is the second largest stone arch in the world, surpassed only by the Friedensbrücke (Syratalviadukt) in Plauen, and the largest railroad stone arch. The arch of the Friedensbrücke, which was built in the same year, has the span of 90 m (300 ft) and crosses the valley of the Syrabach River. The difference between the two is that the Solkan Bridge was built from stone blocks, whereas the Friedensbrücke was built from a mixture of crushed stone and cement mortar.[13]
Dubai in the United Arab Emirates is currently building the Sheikh Rashid bin Saeed Crossing, which is scheduled for completion in 2012. When completed, it will be the largest arch bridge in the world, with a main span 667 metres (2,188 ft) long.[14]
Tied arch bridges
Tied arch bridges have an arch-shaped superstructure, but differ from conventional arch bridges. Instead of transferring the weight of the bridge and traffic loads into thrust forces into the abutments, the ends of the arches are restrained by tension in the bottom chord of the structure. They are also called bowstring arches.
Suspension bridges
Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river. The longest suspension bridge in the world is the 12,826 feet (3,909 m) Akashi Kaikyo Bridge in Japan.[15] See simple suspension bridge, stressed ribbon bridge, underspanned suspension bridge, suspended-deck suspension bridge, and self-anchored suspension bridge.
Cable-stayed bridges
Cable-stayed bridges, like suspension bridges, are held up by cables. However, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately shorter.[16] The first known cable-stayed bridge was designed in 1784 by C.T. Loescher.[17] The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China.
Movable bridges
Movable bridges are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. These are generally electrically powered.
Double-decked bridges
Double-decked or double-decker bridges have two levels, such as the San Francisco – Oakland Bay Bridge, with two road levels. Tsing Ma Bridge and Kap Shui Mun Bridge in Hong Kong have six lanes on their upper decks, and on their lower decks there are two lanes and a pair of tracks for MTR metro trains. Some double-decker bridges only use one level for street traffic; the Washington Avenue Bridge in Minneapolis reserves its lower level for automobile traffic and its upper level for pedestrian and bicycle traffic (predominantly students at the University of Minnesota). Likewise, in Toronto, the Prince Edward Viaduct has five lanes of motor traffic, bicycle lanes, and sidewalks on its upper deck; and a pair of tracks for the Bloor–Danforth subway line on its lower deck.
Robert Stephenson's High Level Bridge across the River Tyne in Newcastle upon Tyne, completed in 1849, is an early example of a double-deck bridge. The upper level carries a railway, and the lower level is used for road traffic. Other examples include Britannia Bridge over the Menai Strait and Craigavon Bridge in Derry, Northern Ireland. The Oresund Bridge between Copenhagen and Malmö consists of a four-lane highway on the upper level and a pair of railway tracks at the lower level. The George Washington Bridge between New Jersey and New York has two roadway levels. It was built with only the upper roadway as traffic demands did not require more capacity. A truss work between the roadway levels provides stiffness to the roadways and reduced movement of the upper level when installed. Tower Bridge is different example of a double-decker bridge, with the central section consisting of a low level bascule span and a high level footbridge. The George Washington bridge is also the most used bridge in the world.
Old Yamuna Bridge (Delhi) or Bridge No. 249 in technical railway parlance, was constructed in 1866 by the East India Railway at a cost of £16,16,335. It was built with a total length of 2,640 feet (800 m) and consisted of 12 spans of 202.5 feet (61.7 m) each. With the completion of this bridge, two principal cities of North India, Kolkata and Delhi, were connected by the railways; this being the last link of the trunk line on this route. In 1913, this was converted into a double line by adding down line girders of 12 spans of 202 feet (62 m) each and 2 end spans of 42 feet (13 m) to the bridge. For the movement of road traffic, two road bridges were provided below the lines. The entry of trains into Delhi Junction Railway station, in such close proximity to the Red Fort, never ceases to impress the rail traveler,[citation needed] reminding all that after the Uprising of 1857, Delhi was a fortified city. The old Yamuna Bridge has an identical twin, a bridge further downstream at Naini on the Allahabad — Mughalsarai section of the now North Central Railways.
By use
A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height. A road-rail bridge carries both road and rail traffic.
Bridges are subject to unplanned uses as well. The areas underneath some bridges have become makeshift shelters and homes to homeless people, and the undersides of bridges all around the world are spots of prevalent graffiti. Some bridges attract people attempting suicide, and become known as suicide bridges.
To create a beautiful image, some bridges are built much taller than necessary. This type, often found in east-Asian style gardens, is called a Moon bridge, evoking a rising full moon. Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream. Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.
By material
Until the end of the 18th Century, bridges were made out of timber, stone and masonry. Modern bridge are currently built in concrete, steel, fiber reinforced polymers (FRP), stainless steel or combinations of those materials. The Iron Bridge completed in 1779 was the first cast iron bridge.
Structure
Bridges may be classified by how the forces of tension, compression, bending, torsion and shear are distributed through their structure. Most bridges will employ all of the principal forces to some degree, but only a few will predominate. The separation of forces may be quite clear. In a suspension or cable-stayed span, the elements in tension are distinct in shape and placement. In other cases the forces may be distributed among a large number of members, as in a truss, or not clearly discernible to a casual observer as in a box beam. Bridges can also be classified by their lineage, which is shown as the vertical axis on the diagram.[clarification needed]
Efficiency
A bridge's structural efficiency is the ratio of load carried to bridge mass, given a specific set of material types. In one common challenge students are divided into groups and given a quantity of wood sticks, a distance to span, and glue, and then asked to construct a bridge that will be tested to destruction by the progressive addition of load at the center of the span. The bridge taking the greatest load is by this test the most structurally efficient. A more refined measure for this exercise is to weigh the completed bridge rather than measure against a fixed quantity of materials provided and determine the multiple of this weight that the bridge can carry, a test that emphasizes economy of materials and efficient glue joints (see balsa wood bridge).
A bridge's economic efficiency will be site and traffic dependent, the ratio of savings by having a bridge (instead of, for example, a ferry, or a longer road route) compared to its cost. The lifetime cost is composed of materials, labor, machinery, engineering, cost of money, insurance, maintenance, refurbishment, and ultimately, demolition and associated disposal, recycling, and replacement, less the value of scrap and reuse of components. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site and the cost of labor is low. For medium spans, trusses or box beams are usually most economical, while in some cases, the appearance of the bridge may be more important than its cost efficiency. The longest spans usually require suspension bridges.
Other functions
Some bridges accommodate other purposes, such as the tower of Nový Most Bridge in Bratislava, which features a restaurant. Other suspension bridge towers carry transmission antennas.
A bridge can carry overhead power lines as does the Storstrøm Bridge.
Costs and cost overruns frequently occur in bridge construction. Flyvbjerg et al. (2003) found the average cost overrun in bridge building is 34%.[18]
In railway parlance, an overbridge is a bridge crossing over the course of the railway. In contrast, an underbridge allows passage under the line.
Bridge failures
See also: List of bridge failures
The failure of bridges is of special concern for structural engineers in trying to learn lessons vital to bridge design, construction and maintenance. The failure of bridges first assumed national interest during the Victorian era when many new designs were being built, often using new materials.
In the United States, the National Bridge Inventory tracks the structural evaluations of all bridges, including designations such as "structurally deficient" and "functionally obsolete".
Bridge monitoring
See also: Structural Health Monitoring
There are several methods used to monitor the stress on large structures like bridges. The most common method is the use of an accelerometer, which is integrated into the bridge while it is being built. This technology is used for long-term surveillance of the bridge.[19]
Another option for structural-integrity monitoring is "non-contact monitoring", which uses the Doppler effect (Doppler shift). A laser beam from a Laser Doppler Vibrometer is directed at the point of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface.[20] The advantage of this method is that the setup time for the equipment is faster and, unlike an accelerometer, this makes measurements possible on multiple structures in as short a time as possible. Additionally, this method can measure specific points on a bridge that might be difficult to access.
Please
Find out the presentation on Suspension Bridges which was presented by me and my friend at College
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