What's a BridgeWhat's a bridge?
Miracle of Bridge
And the easiest way is to use a bridge. Might sound simple, but what kind of bridge do you use? How are there so many different guys and how do they all work? It' one of the biggest viaducts in the whole wide open air. More than 150 years after its completion in 1859, the stunning Royal Albert Bridge of Isambard Kingdom Brunel still transports railway traffic 30 metres across the Tamar River, dividing Cornwall and Devon in England.
Is it a hanging bridge, or is it a half-timbered bridge? Well it is certainly a lattice bridge (note the thick, tube-shaped, "lenticular" lattice girders above). Because of the perpendicular bindings that run from the top bend ("chord") of the lattice girders to the bottom bend and down to the decks, the bridge does not press outwards on its falsework although it presses its load on it.
However, there are also other bridge components in here - suspended bridge bit, bow chord pieces (bow arches) - and I think it's a good example that some bridge actually are hybrid that combine several different kinds of bridge in one construction. In the 1960' a contemporary hanging bridge was constructed next door to transport vehicles (see pictures below).
There will always be only one victor in the never-ending human battle against Mother Earth - but human beings can still comfort themselves with casual wins, which are the greatest bridge in the universe. No matter whether we have to traverse a river or a valley, link an island with the land, transport a car, a human being or an artificial waterway, a bridge is a great way to get in touch with outdoors.
History suggests that humans created a bridge when they saw how collapsed tree can help them traverse flat streams. Ever since, the bridge has become longer, more technical and much more impressive, and has gradually evolved from small rock archways to graceful hanging bridge sections several mile long. Whipped by wind from above, washed by river from below, plagued by heavy weather all year long, it is a wonder that viaducts remain erect as long as they do.
With floating tower and charming span widths, their inspirational design is a victory for architects and engineers. Is the Palladian Bridge in Prior Park, Bath, England, constructed in 1755, and allegedly one of only four such bridge worldwide. It can be seen that the lower part of the bridge - basically its decks - is resting on five separated stony archways.
Powers set things in motion, but they also keep them still. It is anything but evident, but when something like a high-rise stands high above us or a bridge extends under our legs, concealed powers are at work: a bridge does not go anywhere because all the powers that act on it are well-balanced.
Bridging engineers, in brief, are power compensators. However, a bridge that spans a stream, a dale, a sea or a street is quite different: the giant decks (the most important bridge horizontally platform) has no direct supporting underneath. As the bridge grows longer, it becomes heavier, bears more weight and has a greater chance of collapsing.
Bridge falls certainly from period to period and quite spectacular, but most stands for years, decade or even century happy still. This is done by meticulously balance two major loads, namely compressive (an inward compressive or crushing force) and tensile (a tensile or elastic effort that acts outwardly) loads, and by directing the loads (the overall bridge mass and the things it carries) onto rests (the rests on both sides) and pillars (one or more rests in the middle).
Though there are many different forms of bridge, practically all of them work by compensating pressure at some points with traction at others, so there is no total load that causes movement and causes shear. Levelling elements in a bridge: Various bridge species bear load by the load of compaction ( "squeezing" - here represented by flashing wires ) and stress ("stretching" - here represented by flashing wires): 1) A girder bridge has its girder partially under traction and partially under pressure, with the abutment (side piers) under pressure; 2) An arched bridge bears load by pressure; 3) A hanging bridge has its columns (towers) under pressure and the ceiling is suspended from thick ropes by thin ropes, all of which are under traction.
4 ) A cable-stayed bridge is similar, but the decks hang directly from the pillars of wires. 5 ) A lattice bridge is a type of strengthened girder bridge. As with a girder bridge, the upper side is under pressure and the lower side under pressure. 6 ) A self-supporting bridge compensates tensile loads above the bridge decks and compressive loads below.
When a bridge is discharged, it only has to bear its own mass (the tare load) so that the stress and pressure in its structural integrity are basically stationary loads (those that do not cause movement) that change little from time to time or from time to time. Strictly speaking, however, a bridge must bear the varying proportions of the mass (payload) of things such as railways, automobiles or humans, which can significantly raise the normal tractive or pressure force.
For example, railway bridge bends and bends every times a heavier pull passes over them, and then "relax" as soon as the weight is over. Connections must also withstand the constantly shifting influences of the environment. For example, arched river crossings have to deal with backwater (their supports often have strategic apertures through which floods can drain).
Suspended gantries that support automobiles generally support the same load throughout the entire working season, but also have to withstand screaming squalls that can build up a torque in the bridge decking, known as twist (modern suspended gantries solve this by having surfaces with aerodynamic cross-sections that can be put to the test in windtunnels and strengthened with underlying crossbars).
Particularly hazardous can be a load that causes a bridge to move back and forth when it causes it to oscillate freely at its own or its own response frequencies. As it is known, response causes wineglasses to break when operatic performers come a little too near; the "singing" of the winds can also have disastrous consequences on a bridge.
Humans find bridge charming and confusing at the same as well. What makes you think there's so many different guys? So why have humans in different eras of the story tend to construct different kind of bridge? An easy response is that over millennia of civilisation, engineering has progressively evolved more complex bridge constructions capable of bridging ever greater distance.
Some of the oldest bridge models, girders and arched structures, can only expand as far as they will break down under their own load; more demanding models of these structures (truss, girders and arms ) can go further; and suspended and cable-stayed structures can go further. Some of the reasons for this progressive bridge building and expansion was a deep technical knowledge, but also the use of much thicker material.
For example, bow bridge constructions were loved in the Middle Ages because they could be quickly and easily constructed from local material and took a long period of times with little or no servicing. In 1779, when the world's first arched cast-iron bridge was constructed in Coalbrookdale, Shropshire, England, in 1779, it revolutionised bridge building; in the nineteenth centuries, several hundred other bridge constructions were made of metal and later mild steels, among them the famed New York Brooklyn Bridge of 1883 with a wingspan of 486 metres (1595 ft).
Suspended gantries and cable-stayed gantries are based on the most reliable advanced material, ferroconcrete and structural steels. Of course, some of the latest bridge designs use the latest composites. Whilst it is simple to argue about bridging in this rather theoretical and abstracted way, it is much more interesting to look at some particularities by studying each larger bridge model in turn.
This is a timber bridge supporting a railroad line across a street in Dorset, England. Observe the thrust bearing on the right that prevents the bridge from falling down the mound to us. Beams are the easiest (and often cheapest) type of bridge: a platform that spans a relatively small stretch and is supported by a couple of rests (the perpendicular columns at both ends).
Place yourself on a board (the deck) that extends between a few stools (the abutments) and you will bend it down in the centre so that it is slightly longer below and slightly shortened above. We are told that the underside of a bar is under stress (pulled longer than normal), while the top is under pressure (squeezed shorter).
Loads onto such bridge are transferred by carrier onto abutment at both ends, which also are pressed down. Since the longer the girder, the more likely it is that it will hang in the centre, simple girder bridge systems are usually quite brief. Today's girder bridge can be much longer if it is constructed with girder beams (huge empty cases made of repeated segments of structural beams and/or ferroconcrete ) or with truss beams (diagonal reinforcement) either laterally or below.
Pulteney Bridge in Bath, England, consists of three rock archways. Archwires are the only types of bridge that are completely carried by compressive force. Some tensions exist under a bow, but it is usually insignificant unless the bow is large and flat. This makes perfect sense when you think about it, because an endlessly broad arc would only be a horizontally stretched bar whose underside is under stress.
An arched bridge decking presses down on the bend of the underlying bricks (or pieces of metal), compressing them firmly and making them actually strong. Loads on a arched bridge are transferred through the middle block (the so-called key block), around the curves of other blocks and into the abutment where the firm floor on both sides presses upwards and inwards again.
Just like timber bridgework, archways are relatively easy and inexpensive to build and do not have to obstruct a street or stream with centerpiles. However, their big disadvantage is that they require large thrust blocks, so they are not always an effective way of crossing something like a motorway when space is at a premium.
The Mostar Bridge in Bosnia-Herzegovina and the Charles Bridge in Prague are just two prime example of arched bridge constructions. Half-timbered bridge with a footpath across a railway line in Dorset, England. A way to increase the range of a simple girder bridge is to strengthen it - and designers have found the best way to do this with a system of oblique rectangular triangles on the sides known as traverses.
It is possible to arrange traverses to carry a bridge in many ways, resulting in a multitude of complicated and often eye-catching grid designs; lens-shaped (curved) traverses used in the Royal Albert Bridge in the above photograph are an example. Typically a half-timbered bridge looks like a cavity with open or enclosed sides and top, the sides strengthened with oblique half-timbered structures and the basis supported on beams.
Huey P. Long self-supporting bridge over the Mississippi River near New Orleans, built in the early 1930s. Notice how the seemingly self-supporting span widths at both ends extend outward from the pillars into the open space - the arm type at work. This is the main concept behind the boom bridge. Usually when we speak of a jib, we mean a support that is braced only at one end, like a springboard or seesaw, only much stiffer.
As a rule, in a bridge with arms, there are a couple of arms that extend from each pillar, with a brief bridge of beams between them connecting them; as an alternative, some have a arm that extends from each pillar to the centre, a bridge over it. Jibs are sometimes difficult to see as they are usually strengthened with beams and lattice beams, but much more easily seen when you consider that they have several segments and often have at least one pillar in the centre.
Scotland's most renowned outrigger bridge, the Forth Bridge, has three outriggers (reinforced by a lattice) with two short girder bridge sections in between. Quebec's longest boom in the whole wide sense is the very similar Quebec bridge with a length of just under 1 km (987 metres or 3239 feet to be exact). Further self-supporting bridge projects included the Queensboro Bridge in New York City and the Crescent City Connection in New Orleans.
Tamar Bridge, finished in 1961, crosses the Tamar River, the border between Cornwall and Devon, England, next to the Brunel Railway Bridge of 1859 (from which this photograph was taken). Note the lattice and beam reinforcement under the decks. When you need a bridge that stretches even further, a hanging bridge of some kind is your only one.
One of the geniuses of a hanging bridge is to use very high pillars with enormous, curved cords between them. Several dozen thin ropes of different lengths are suspended from the ropes and carry the enormous load of the decks and its load. And although humans always see the ropes in a hanging bridge, they often don't recognize the beams and traverses that reinforce the underlying decks.
It is a subtile and very important point: most bridge materials are actually composite materials of two or more of the fundamental bridge types...) All of the largest viaducts use the hanging base; the longest in the word, the Akashi Kaiky? in Japan, is 3.9 km (2.4 miles) long. Renowned hanging gantries are the Humber Bridge and the Clifton suspension bridge in England, the Golden Gate Bridge in California and the Brooklyn Bridge in Manhattan, New York City.
Arthur Ravenel, Jr. cable-stayed bridge in Charleston S.C. picture with kind permission of Carol M. Highsmith's America Project at the Carol M. Highsmith Archive, US Library of Congress. One of the major disadvantages of hanging bridge systems is that they have to be fixed to the floor on both sides. Another type of hanging bridge, the so-called cable-stayed bridge, makes this superfluous by compensating for two pairs of supporting ropes on either side of each pillar carrying the weight.
On a " standard " hanging bridge, the decks are suspended from different lengths of wire, which in turn are carried by the enormously powerful primary support ropes. There is only one pair of wires in a cable-stayed bridge that are pulled from each pillar to the bridge decks in a diagonal direction, which tends to be more powerful and voluminous than in a suspended bridge.
Suspended rope gantries are significantly shortened compared to traditional suspended gantries and generally do not bridge much more than 1 km; the longest in the word is currently the Russkybrücke in Vladivostok, Russia, at 1.1 km (3622ft). Further example are the Vasco da Gama Bridge in Portugal, the Millau Viaduct in France, the Hangzou Bridge in China and the Chord Bridge in Jerusalem.
Over the Euphrates in Iraq. Boots obviously swim on the waters, so if you need to quickly construct a bridge, swimming a decks on a row of boats is a possible option. This type of bridge is known as a barge and is often used by the army for irregularly crossing rivers (e.g. when a bridge has been blasted for strategical reasons).
Well organised armed forces have prefabricated segments of barge bridge that they can hover and screw in place wherever and whenever they need it. One of the major issues with bridge pontoons is the fundamental fragility and relatively low load they can withstand. Due to the fact that the decks swim very near the water line, a bridge of pontoons block the use of a stream even though it is normally possible to release one or two stretches from the centre and swing them to the side to allow flow of water through.
Picture: Hell Gate Bridge, a continuous railway bridge in New York City, taken between 1915-1920. Notice how the bridge decks cut horizontal through the bow (so that part of the bow is above the decks and part below) and the large abutment at both ends that hold the bow in place. Suspend a girder bridge from a ceiling arc and what you get is referred to as a through bridge (when the decks intersects through the arc) or a rod bridge (when the decks attaches the arc to its base).
The two species are a little like hanging bridge, because the ceiling and its cargo are hanging from the bow. Although they look very similar, they compensate powers in different ways. The ends of the archways are pushed outwards ("thrust") in a passage bridge, as in a traditional rock or tile bridge, and must be pushed back through the abutment.
This is why such a bridge is sometimes referred to as a push-bow. The Sydney Harbor Bridge in Australia, the Hell Gate Bridge in New York City (shown here) and the Tyne Road Bridge in Newcastle, England, are just a few good example of a transmitted light bridge. the Ohio River.
Notice how the bow is placed at the bottom of the bow (in other words, the entire bow is placed above the deck) and attached in place; therefore, no large thrust bearings are required to keep the bow in place. Inside a bow bridge, while the bow carries the decks, the decks also prevent the bow from sliding outwards and being held in place so that the bow and decks compensate each other.
In the same way that a cable-stayed bridge is more self-supporting than a suspended bridge because it dispenses with anchor wires, tensioning band bridge is more self-supporting than a traditional curve because it requires less stable thrust blocks. Bows are sometimes referred to as string bows because they are similar to the bows of a bows that are drawn out to fire an arrows, and because the cross-bar connects the bows in a similar way.
The Puente de la Barqueta in Spain and the St. Georges Bridge in Delaware, USA are just two typical example of this. Chaotianmen Bridge in China is both a through bridge and an arcuate bridge. El Ferdan Bridge bears a railway line across the Suez Canal in Egypt. With a span of 340 meters (1100 ft) it is the longest swivel bridge in the word.
Traditional footbridges are not practical when something like a low street has to traverse a stream or channel through which high vessels have to sail. We need a mechanic bridge with a decking that can be raised or swung to the side if necessary. The Tower Bridge in London, England, is a kind of twin drawbridge: it has a divided decks that rise in the middle.
We have many example of swivel bridge construction all over the globe. In the same way that bridge design compensates for competitive loads from different angles, engineering must consider all possible factors when planning a new bridge. What does the bridge have to go to? This usually determines the kind of bridge that is needed.
Extremely small spans (across a small stream, a street or a railway line) could only deserve an inexpensive girder or traverse; suspended bridge and cable-stayed bridge will usually be needlessly complicated and costly; and curved bridge are much less frequently constructed than in the Middle Ages, in part because other kinds of bridge make more efficient use of available area.
We have already seen that the bridge model largely defines the material used. However, there may be possibilities for the use of locally sourced material so that a bridge fits into its surroundings. This was certainly a characteristic trait of the ancient arch bridge, often constructed of rocks or stones.
Today's bridge is usually constructed of iron and cement and relies instead on designs to blend into its environment. Truss girders are often produced in off-site segments so that they can be assembled very quickly. Also the place where a bridge is constructed is an important one.
So is the floor strong enough to accommodate large supports for a bow? Do you have a stable base where you can anchor ropes (and if not, would a cable-stayed bridge be better)? When the bridge has to pass a stream, how can pillars and turrets be securely lowered into their beds so that they are not washed away by the roaring waters?
A bridge position is meticulously selected to facilitate building, lower costs and make sure the bridge is stable and long-lasting. However, it is not always possible for a bridge to traverse in a perfect line; a bridge sometimes has to traverse at an angel (resulting in a so-called oblique bridge), a bend or a shift in orientation from one section to another.
State-of-the-art hollow case gantries, which are constructed from cover profiles, can be easily bent even through very drastic corners. What incidental, temporary loads must the bridge endure in addition to the death and traffic loads? Is there an earthquake or hurricane and if so, how can the bridge be shaped to outlive it?
Can a bridge over a stream be able to deal with flooding? In the case of a viaduct, how much transport is expected to grow in the next few years and years, and will the viaduct always be sufficiently large to manage it? If several of these transverse powers appear at the same moment, what happens?
Assuming that a bridge has to cope with strong wind, enormous pressures from increasing sea level and strong transport at the same time? In addition to the base model, position and rigidity of a bridge, engineering must consider all possible other factor. Must a bridge, for example, transport different modes of transport (rail, car and pedestrian) and how is it separated?
How about security aspects (preventing car submersion) and questions like minimising the suicide risks (a particular issue for some of the highest bridge in the world)? Which kind of service does the bridge need, from periodic inspection of the concretes to systematical varnishing to prevent rust? Scientists, technologists and engineers give us the trust that we can construct bridge structures of rock, ice, steel o r cement that will last for many years.
However, a bridge has much more to offer than just remaining erect when boring burdens fly over it. Remember some of the largest viaducts in the wide variety of places in the globe - the Stari Most Arc in Mostar, the Brooklyn Hanging Bridge in Manhattan, the Forth Railway Canadian Bridge or the latest inclined Millau Viaduct in France - and you'll find that big viaducts are as stunning ly catchy as big ones.
If you are seated in a stream or spanning a hollow, you could say that a bridge disturbs the equilibrium of the natural state. However, bridging connects humans and societies, and many would deny that great bridging is a real wonder of the planet that improves their environments. For example, who can think of San Francisco Bay without the Golden Gate Bridge?
It is perhaps just as truthful to say that the great thing about a great bridge is to build a relationship between man and place so that technology and the natural world can enjoy a happy coexistence. Building of bridges by Jim J. Zhao and Demetrios E. Tonias. This is a guide for bridge builders (and chair builders) with many case histories, pictures and pictures.
The world' s bridges: Contains the designs and histories of bridge constructions with many samples and many pictures and pictures. Bridge: Bridge: Ceremony of the bridge of one of the most well-known British architecture scholars. Build bridges: Michael Hurley's most stunning bridge in the world. This 32-page guidebook for children aged 8-10 concentrates on a good choice of renowned bridge projects, among them current ones such as the Millauer Viaduct and classic ones such as the Golden Gate.
The best step forward: the most distinctive footbridges in the whole wide range by Antonia Wilson. The bridge supported by two hands...and some more thrilling samples of astonishing bridge design! Each year China opens about 50 new bridge-buildings, but payment is not simple. There are 3 new viaducts rising in New York, with a look that could stop the flow of David W. Dunlap.
History behind the latest cable-stayed bridge in New York City. An alternative bridge stands in the bay: The way the San Francisco-Oakland Bay Bridge is built for seismic events. Large building: Akashi Kaikyo Bridge: An easier tutorial on the bridge and a few more facts and stats. The longest hanging bridge in the world is opened in Japan:
This is a much more technically and detailled paper about the Akashi Kaiky? by bridge designer James D. Cooper. Dave Ansell's Kartoffelbogen, The Naked Scientists. This is how you construct your own bridge bow from a potatoe! Influence of bridge construction on the bearing capacity of Terik Daly and Andrew Olson, Science Buddies.
Building different types of bridge and see which can bear the most load.