Steel Bridge & Forms of construction: Steel is widely used worldwide for the construction of bridges from large to very small. It is a versatile and effective material that provides efficient and sustainable solutions. … It dominates the markets for long bridges, railway bridges, bridges and intermediate bridge embankments.
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Why Is steel good for bridges?
Steel is an ideal material for bridges. It is an important part of modern bridges, because it is strong, can bend without breaking and has a long life, even in the harshest conditions. It can be used to build bridges of any length due to its durability and ease of manufacture and maintenance
Steel is widely used worldwide for the construction of bridges from large to very small. It is a versatile and effective material that provides efficient and sustainable solutions. Steel has long been recognized as the economic opportunity for a number of bridges. It dominates the markets for long bridges, railway bridges, bridges, and intermediate bridge embankments. It is increasingly also the choice for shorter voltage path structures. In many ways, society gets the benefits of steel bridge solutions. Landmark steel bridges show good design, they are quick to build and have stimulated the regeneration of many former industrial, dock and canal areas.
Steel bridges are an important feature of the country’s infrastructure and landscape. Few man-made structures combine the technical with the aesthetics in such an evocative way. Look close to the next ‘landmark’ bridge you see; The chances are that it is made of steel.
Over the past thousand years, bridges have served one of the most important roles in the development of our earliest civilizations, the dissemination of knowledge, local and worldwide trade and the rise of transport. Initially made from the simplest materials and designs, bridges quickly developed and enabled the transport of wide terraces, spanning vast distances over rivers, canyons, inaccessible terrain, heavily elevated surfaces, and pre-built urban infrastructures. From the beginning of the 13th century BC Greek Bronze Age scattered arches bridle all over the world, which ultimately led to the increase in the use of steel, iron and other materials in bridges that can span kilometers.
To be able to operate different roles, carry different types of weight and span terrain of different sizes and complexities, bridges can vary greatly in their appearance, carrying capacity, structural elements, presence of moving sections, building materials and much more.
Forms of construction
Beam Bridges
A beam and washer or a composite bridge is one in which a concrete cover plate sits on top of steel I-beams and works with them in bending. There are two main forms of this beam and disc construction; multi-beam construction and ladder deck construction. Between them, they account for the majority of the intermediate bridges that are currently built in the UK and are suitable for ranges from 13m to 100m. The choice between the two forms depends on economic considerations and area-specific factors such as the form of intermediate support and access to construction.
Box beams bridges
Box beams consist of two lanes joined at the top and bottom by a common flange that creates a closed cell that provides very good torsional stiffness, which may be required on high curved bridges. In beam and slab beams, book rods are an alternative to plate beams at the upper end of the span where they provide a lower steel weight, although this must be balanced against increased manufacturing costs. Such composite box carrier covers may take the form of several closed steel boxes, with the cover plate over the top or an open top trapezoidal box closed by the cover plate.
Longer voltages of 100 to 200 meters typically use either a single box or a few boxes of crossbeams. For such long stresses and for bridges as lifting bridges, where minimization of structural weight is very important, an all-steel orthotropic tire can be used instead of a reinforced concrete slab. Over 200m, box beams are probably part of a cable bridge or a spring bridge, where they are specially shaped for optimum aerodynamic performance.
Truss bridges
A truss is a triangulated framework of individual elements or members which act primarily in tension or compression. Trusses have been used in a similar way to beams in composite decks (Oresund Approach Spans), as arches (Sydney Harbour Bridge), as cantilevers (Forth Rail Bridge) or as stiffening girders to suspension bridges (Forth Road Bridge).
Today, the pantiliner construction usually shows expensive to manufacture because of the large amount of labor-intensive work to build members and create connections so that they are rarely used for ordinary engineers. However, for through or half forms, truss bridges offer very rigid, lightweight solutions with minimal structural depth. Therefore, they are widely used in the United Kingdom for footbridges, demountable bridges (Bailey bridges), gantries, and longer tire bridges (over 50m).
Arch bridges
In the traditional form, a steel arch has a similar structural action to old masonry arch bridges. The arch springs from the foundations and exerts horizontal thrusts on them. The arch elements act primarily in compression. The deck may either be supported on struts, resting on arch below, or it may be suspended on hangers from the arch above.
A tied-arch or “bow string” arch is a particular development of the arch form. The horizontal thrusts from the arching action are resisted by tension members between the arch springings. Effectively the deck acts as a tension tie, and is supported by hangers from the arch above. This form is suited to the soft soils of riverbanks, where the ground cannot withstand the large horizontal thrusts from arching action.
In recent years, arches and tied-arches have become a little more common, partly because the use of an arch from which to hang the deck allows the construction depth of a suspended deck to be kept shallow, even at longer spans, and partly because arches make a clear architectural statement. Arches are sometimes skew to the line of the deck and sometimes the arch planes are inclined for dramatic visual effect.
Suspension bridge
A suspension bridge is fundamentally simple in action: two cables are suspended between two supports (‘towers’ or ‘pylons’), hanging in a shallow curve, and a deck is supported from the two cables by a series of hangers along their length. The cables and hangers are in simple tension and the deck spans transversely and longitudinally between the hangers. In most cases the cables are anchored at ground level, either side of the main towers; often the side spans are hung from these portions of the cables.
In addition to its action in carrying traffic, the deck acts as a stiffening girder running the length of each span. The stiffening girder spreads concentrated loads and provides stiffness against oscillation; such stiffness is needed against both bending and twisting actions.
Because of their fundamental simplicity and economy of structural action, suspension bridges have been used for the longest bridge spans. The graceful curve of the suspension cable combined with the strong line of the deck and stiffening girder generally give a very pleasing appearance. The combination of grace and grandeur in such situations leads to the acknowledged view that many of the world’s most exciting bridges are suspension bridges.
Fixed Bridges
Fixed – Majority of bridges constructed all around the world and throughout our history are fixed, with no moveable parts to provide higher clearance for river/sea transport that is flowing below them. They are designed to stay where they are made to the time they are deemed unusable due to their age, disrepair or are demolished. Use of certain materials or certain construction techniques can instantly force bridge to be forever fixed. This is most obvious with bridges made out of construction masonry, suspension and cable-stayed bridges where a large section of decking surface is suspended in the air by the complicated network of cables and other material.
Cable-Stayed Bridges
Cable-stayed bridges – use deck cables that are directly connected to one or more vertical columns (called towers or pylons) that can be erected near abutments or in the middle of the span of the bridge structure. Cables are usually connected to columns in two ways – harp design (each cable is attached to the different point of the column, creating the harp-like “strings” and “fan” designs (all cables connect to one point at the top of the column). This is a very different type of cable-driven suspension than in suspension bridges, where decking is held with vertical suspenders that go up to main support cable.
Originally constructed and popularized in the 16th century, today cable-stayed bridges are a popular design that is often used for spanning medium to long distances that are longer than those of cantilever bridges but shorter than the longest suspension bridges. The most common build materials are steel or concrete pylons, post-tensioned concrete box girders and steel rope. These bridges can support almost every type of decking (only not including heavy rail) and are used extensively all around the world in several construction variations.
The famous Brooklyn Bridge is a suspension bridge, but it also has elements of cable-stayed design.
Source – Google
NPEC has a team of expert workmen for Fabrication of Penstock for Hydro Projects. We have several SAW machines to cater to the requirement of Plate Girders required in Bridges and ROB (Rail Over Bridge).
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