How do Bridges workWhat are bridges like?
It' one of the biggest bridges in the whole wide open space. More than 150 years after its completion in 1859, the stunning Royal Albert Bridges of Isambard Kingdom Brunel still carry railway cars 30 metres across the Tamar River, dividing Cornwall and Devon in England.
Is it a hanging gangway, or is it a half-timbered gangway? Well it is certainly a lattice girder jumper (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 bridges on their falsework do not press outwards even though they press their load on them.
However, there are also pieces of other bridges in here - suspended bridges bit, curved tendon pieces (arches) - and I think it's a good example that some bridges are actually hybrid bridges that combine several different kinds of bridges in one construction. In the 1960' a contemporary hanging bridges 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 bridges 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, bridges are a great way to get in touch with our natural surroundings.
History suggests that humans created bridges when they saw how collapsed tree can help them traverse flat streams. The bridges have since become longer, more technical and much more impressive, and have gradually evolved from basic rock archways to graceful hanging bridges 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 bridges 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 Bridges in Prior Park, Bath, England, constructed in 1755, and allegedly one of only four such bridges worldwide. It can be seen that the lower part of the viaduct - 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 footbridge extends under our legs, concealed powers are at work: a footbridge does not go anywhere because all the powers that act on it are well-balanced.
Bridging engineers, in brief, are power compensators. However, a viaduct that spans a stream, a dale, a sea or a street is quite different: the giant decks (the most important horizontally supported platforms of a viaduct) has no direct supporting underneath. Longer bridges weigh more, carry more, and are more likely to break down.
The bridges certainly drop from year to year and quite dramatically, but most of them remain standing for years, even years or even years. 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 mass of the structure 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 bridges, 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 bridges bear load due to the strength of compaction ( "squeezing" - here represented by flashing wires ) and stress ("stretching" - here represented by flashing wires): 1) A girder bridges has its girder partially under traction and partially under pressure, with the abutment (side piers) under pressure; 2) An arched bridges bears load due to pressure; 3) A hanging bridges 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 gantry is similar, but the decks hang directly from the pillars of wires. 5 ) A lattice girder is a type of strengthened girder structure. As with a girder jumper, the upper side is under pressure and the lower side under pressure. 6 ) A self-supporting gantry compensates for tensile loads above the gantry and compressive loads below.
Once a jumper 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. Bridges, however, by their very nature, must bear varying proportions of the weights (the payload) of things such as railways, automobiles or humans, which can significantly raise the normal tractive or pressure loads.
For example, railway bridges always curve and curve each and every day a heavier pull across them, and then "relax" as soon as the weight is over. The bridges must also withstand the constantly shifting influences of the environment. For example, arched bridges over a river have to deal with damming waters behind them (their supports often have strategic apertures through which floods can drain).
Suspended bridges that support automobiles tended to support the same load throughout the entire working season, but also had to withstand screaming squalls that could build up a torsional effect on the decking of the bridges (modern suspended bridges 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 jumper 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 bridging work.
Humans find bridges enchanting 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 sorts of bridges? An easy response is that over millennia of civilisation, engineering has progressively evolved more complex bridges capable of bridging ever greater distance.
Some of the oldest bridges, girders and archways, can only expand so far before they break down under their own load; more demanding version of these constructions (truss, girders and arms ) can go further; and hanging and cable-stayed bridges can go further. Some of the reasons for this progressive expansion and expansion of bridges were a deep technical knowledge and the use of much thicker material.
For example, bow bridges 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 upkeep. In 1779, when the world's first arched cast-iron viaduct was constructed in Coalbrookdale, Shropshire, England, in 1779, it revolutionised the building of bridges; in the nineteenth centuries, several hundred other bridges of metal and later carbon were constructed, among them the famed New York Brooklyn Viaduct of 1883 with a wingspan of 486 metres (1595 ft).
Suspended bridges and cable-stayed bridges are based on the most reliable advanced material, ferroconcrete and structural steels. Of course, some of the latest bridges use the latest composites. Whilst it is simple to argue about bridges in this rather abstract and theoretic way, it is much more interesting to look at some particularities by studying each larger kind of bridges in turn.
This is a timber girder viaduct supporting a railroad line across a street in Dorset, England. Observe the thrust bearing on the right that prevents the footbridge 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 bridges 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 bridges are usually quite brief. Today's girder bridges can be much longer if they are 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.
In our articles on the functioning of building structures, bars are described in more detail. Pulteney Bridge in Bath, England, consists of three rock archways. Archwires are the only types of bridges 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 bridging platform presses down on the bend of the underlying bricks (or pieces of metal), compressing them firmly and making them actually more powerful.
Loads on a arched rock viaduct are transferred through the middle rock (the so-called keystone), around the curves of other rocks, and into the abutment, where the firm floor on both sides presses upwards and inwards again. Just like timber bridges, archways are relatively easy and inexpensive to build and do not have to obstruct a street or stream with center buttresses.
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 bridges.
Half-timbered viaduct with a footpath across a railway line in Dorset, England. A way to increase the range of a simple girder gantry is to strengthen it - and the engineer has found the best way to do this with a system of oblique three-cornered rods on the sides known as traverses.
It is possible to arrange traverses to carry a jumper in many ways, resulting in a multitude of complicated and often eye-catching grid designs; lens-shaped (curved) traverses used in the Royal Albert Bridges in the above photograph are an example. Typically a half-timbered structure 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 river crossing 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 overpass. Usually when we speak of a jib, we mean a vehicle that is braced only at one end, like a springboard or seesaw, only much stiffer.
As a rule, in a bracket arm span, there are a couple of bracket arms that extend from each pillar, with a brief joist span in between connecting them; as an alternative, some have a bracket arm that extends from each pillar to the centre, a joist spanning them. Jib bridges are sometimes difficult to see as they are usually strengthened with beams and trusses, 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 boom viaduct, the Forth in Scotland, has three booms (reinforced by a lattice) with two short girder viaducts in between. Quebec's longest boom in the whole wide sense is the very similar Quebec viaduct with a length of almost 1 km (987 meters or 3239 feet to be exact). Further self-supporting bridges are the Queensboro Bridges in New York City and the Crescent City Connection in New Orleans.
Tamar Bridges, built in 1961, span the Tamar River, the border between Cornwall and Devon, England, next to the Brunel Railway Bridges of 1859 (from which this photograph was taken). Note the lattice and beam reinforcement under the decks. When you need a span that' s even wider, a hanging jumper of some kind is your only one.
One of the geniuses of a hanging gantry 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 gangway, they often don't recognize the beams and traverses that reinforce the underlying decks.
It is a subtile and very important point: most bridges are actually composite materials of two or more of the fundamental bridges types...) All of the largest bridges use the hanging base; the longest in the word, the Akashi Kaiky? in Japan, is 3.9 km (2.4 miles) long. Renowned hanging bridges are the Humber and Clifton suspension bridges in England, the Golden Gate bridges in California and the Brooklyn bridges in Manhattan, New York City.
Arthur Ravenel, Jr. cable-stayed 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 bridges is that they have to be fixed to the floor on both sides. Another type of hanging gantry, the so-called cable-stayed gantry, makes this superfluous by compensating for two pairs of supporting ropes on either side of each pillar carrying the weight.
On a " standard " hanging gantry, the decks are suspended from different lengths of wire, which in turn are carried by the enormously powerful primary ropes. There is only one pair of wires in a cable-stayed viaduct that are pulled from each pillar of the viaduct obliquely to the viaduct decks, which tends to be more powerful and voluminous than in a suspended viaduct.
Suspended bridges are significantly shortened compared to traditional suspended bridges and usually do not bridge much more than 1 km; the longest in the word is currently the Russky Bridge in Vladivostok, Russia, with 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 temporal deck structure, swimming a decks on a row of boats is a possible option. This type of swimming viaduct is known as a jetty and is often used by the army for irregularly crossing rivers (e.g. when bridges have been blasted for strategical reasons).
Well organised armed forces have prefabricated segments of barge bridges that they can hover and screw in place wherever and whenever they need to. One of the major issues with barge bridges 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 jetty bridges 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 Bridges, a continuous railway in New York City, taken between 1915-1920. Notice how the bridging decks cut horizontal through the arc (so that part of the arc is above and part below the deck) and the large abutment at both ends that hold the arc in place. Suspend a girder jumper from a ceiling arc and what you get is referred to as a gangway (when the decks intersects through the arc) or a tie bar (when the decks attaches the arc to its base).
The two species are a little like hanging bridges, 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 arc brigde, as in a traditional rock or tile arc, and must be pushed back through the abutment.
Such bridges are therefore sometimes referred to as push-bows. The Sydney Harbor in Australia, the Hell Gate in New York City (shown here) and the Tyne Road in Newcastle, England are just a few typical example of a transmitted light structure. 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 bridging 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 gantry is more self-supporting than a suspended gantry because it dispenses with anchor wires, a tensioned gantry is more self-supporting than a traditional gantry because it requires less stable thrust blocks. Bows bridges are sometimes referred to as string bridges 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-Brücke in China is both a through and an arched one. El Ferdan swings a railway line across the Suez Canal in Egypt. With a span of 340 meters (1100 ft) it is the longest swivel crane in the word.
Traditional bridges 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 jumper with a platform 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 bridges all over the globe. Like bridges compensate for competitive loads from different angles, when planning a new viaduct, the engineer must consider all possible factors. What does the brigde have to reach? This usually determines the kind of jumper 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 bridges and cable-stayed bridges will usually be needlessly complicated and costly; and arch bridges are much less frequently constructed than in the Middle Ages, in part because other kinds of bridges make more efficient use of available area.
We have already seen that the material used is largely determined by the kind of bridges. However, there may be possibilities for the use of locally sourced material so that a bridging structure can be integrated into its surroundings. This was certainly a characteristic trait of the ancient arch bridges, which were often constructed of rocks or stones.
Today's bridges are mostly constructed of iron and cement and depend instead on designs to blend into their environment. Truss girders are often produced in off-site segments so that they can be assembled very quickly. Also the place where a viaduct 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 in which to anchor ropes (and if not, would a cable-stayed gantry be better)? Crossing a stream on the bridges, how can pillars and turrets be securely lowered into their beds so they don't get washed away by the sound of sound?
Precise positioning of a viaduct is meticulously selected to facilitate building, lower costs and make sure the viaduct is stable and long-lasting. However, it is not always possible for bridges to traverse in a perfect line; bridges sometimes have to traverse at an angle along a bend (resulting in a so-called oblique bridge), a bend or a shift in course from one section to another.
State-of-the-art hollow-frame bridges, which are constructed from cover profiles, can be easily bent even through very drastic corners. What incidental, temporary loads must the viaduct endure in addition to the death and traffic loads? Is there an earthquake or hurricane and if so, how can the viaduct be shaped to outlive it?
Do you think a flood control dam will 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 viaduct 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 structure, engineering must consider all other possible parameters. Does a viaduct, for example, have to transport different modes of transport (rail, car and pedestrian) and how is it separated?
How about security aspects (preventing car submersion in the air) and questions like minimising the suicide risks (a particular issue for some of the highest bridges in the world)? Which kind of service does the gantry require, from periodic inspection of concretes to systematical varnishing to prevent anticorrosion? Scientists, technologists and engineers give us the trust that we can construct bridges of rock, ice, steel o r cement that will last for many years.
However, a viaduct has much more to offer than just remaining erect when boring burdens fly over it. Remember some of the largest bridges in the wide 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 soon realise that big bridges are as stunningly impressive as big structures.
If you are seated in a stream or spanning a hollow, you could say that a viaduct disturbs the equilibrium of the natural state. However, bridges link peoples and societies, and many would deny that great bridges are real miracles of the earth that improve their environments. For example, who can think of San Francisco Bay without the Golden Gate Bridges?
It is perhaps just as truthful to say that the great thing about a great bridging art is to build a relationship between man and place so that technology and natural world can coexist in happiness. Building of bridges by Jim J. Zhao and Demetrios E. Tonias. This is a guide for builders of bridges (and chairs) with many case histories, pictures and pictures.
The bridges of the world: Contains the designs and histories of bridges with many samples and many illustration and photo. Bridges: Bridges: Celebrating the bridges of one of the most renowned British architecture scholars. Build bridges: Astonishing bridges in the world by Michael Hurley. This 32-page guidebook for children aged 8-10 concentrates on a good choice of renowned bridges, 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. Bridges supported by two hands...and some more thrilling samples of stunning bridging architectures! Each year China opens about 50 new bridges, but payment is not simple. Three new bridges are rising in New York, with an appearance that could stop the flow of David W. Dunlap.
History behind the latest cable-stayed bridges in New York City. An alternative viaduct 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 bridging and a few more facts and stats. The longest hanging gantry in the world is opened in Japan:
This is a much more technically and detailled paper about the Akashi Kaiky? by James D. Cooper. Dave Ansell's Kartoffelbogen, The Naked Scientists. This is how you construct your own bow brigde from a potatoe! Influence of structure of bridge on bearing capacity of Terik Daly and Andrew Olson, Science Buddies.
Building different types of bridges and see which can bear the most load.