all about civil engineering.
Friday, 3 April 2015
Welcome to civil engineering world: TRUSS BRIDGES
Welcome to civil engineering world: TRUSS BRIDGES: We can see the beam bridges every where, but the difference from one another will be its type of design.The key differences, however, all...
TRUSS BRIDGES
We can see the beam bridges every where, but the difference from one another will be its type of design.The key differences, however, all come down to the design, location and composition of the truss.
"A truss bridge is that in which truss will be the load supercomposing structure"
SIMPLE DEF : Truss is a formation produced by triangular components, in accordance with the truss bridge drawings, and coupled at joints known as nodes. The triangular units forming the truss are slim and straight in form.
.The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads.
"A truss bridge is that in which truss will be the load supercomposing structure"
SIMPLE DEF : Truss is a formation produced by triangular components, in accordance with the truss bridge drawings, and coupled at joints known as nodes. The triangular units forming the truss are slim and straight in form.
.The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads.
STRUCTURE AND DESIGN :
The structure and design of the truss bridge has been done by using newtons' laws of motion according to statics. Int he bridge vertical members are in tension,lower horizontal members in tension, shear, and bending, outer diagonal and top members are in compression, while the inner diagonals are in tension.
And there's another reason why a truss is more rigid than a single beam: A truss has the ability to dissipate a load through the truss work. The design of a truss, which is usually a variant of a triangle, creates both a very rigid structure and one that transfers the load from a single point to a considerably wider area.
The truss may carry its roadbed on top, in the middle, or at the bottom of the truss. Bridges with the roadbed at the top or the bottom are the most common as this allows both the top and bottom to be stiffened, forming a box truss. When the roadbed is atop the truss it is called a deck truss (an example of this was the I-35W Mississippi River bridge). When the truss members are both above and below the roadbed it is called a through truss (an example of this application is the Pulaski Skyway), and where the sides extend above the roadbed but are not connected, a pony truss or half-through truss.
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| THROUGH TRUSS |
A single beam spanning any distance undergoes compression and tension. The very top of the beam gets the most compression, and the very bottom of the beam experiences the most tension. The middle of the beam experiences very little compression or tension. This is why we have I-beams, which provide more material on the tops and bottoms of beams to better handle the forces of compression and tension.
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| DECK TRUSS |
And there's another reason why a truss is more rigid than a single beam: A truss has the ability to dissipate a load through the truss work. The design of a truss, which is usually a variant of a triangle, creates both a very rigid structure and one that transfers the load from a single point to a considerably wider area.
TRUSS USED IN BRIDGES:
Allan truss :
It is on the based on the Howe truss.
Bailey bridge :
Designed for military uses, the prefabricated and standardized truss elements may be easily combined in various configurations to adapt to the needs at the site. In the image at right, note the use of doubled prefabrications to adapt to the span and load requirements. In other applications the trusses may be stacked vertically.
BALTIMORE BRIDGE :
The Baltimore truss is a subclass of the Pratt truss. A Baltimore truss has additional bracing in the lower section of the truss to prevent buckling in the compression members and to control deflection. It is mainly used for rail bridges, showing off a simple and very strong design.
Bowstring arch truss :
The bowstring arch through truss bridge was patented in 1841 by Squire Whipple. While similar in appearance to a tied-arch bridge, a bowstring truss is a truss and thus has diagonal load-bearing members. These diagonals result in a structure that more closely matches a Parker truss or Pratt truss than a true arch.
CANTILEVER TRUSS :
Most trusses have the lower chord under tension and the upper chord under compression. In a cantilever truss the situation is reversed, at least over a portion of the span. The typical cantilever truss bridge is a "balanced cantilever", which enables the construction to proceed outward from a central vertical spar in each direction. Usually these are built in pairs until the outer sections may be anchored to footings. A central gap, if present, can then be filled by lifting a conventional truss into place or by building it in place using a "traveling support".
Howe truss :
A truss having upper and lower horizontal members, between which are vertical and diagonal members; the vertical web members take tension, and the diagonal web members are under compression.
(TYPES OF TRUSS BRIDGES WILL BE CONTINUED IN THE NEXT POST:)
Thursday, 2 April 2015
welcome to civil engineering world: BRIDGES
welcome to civil engineering world: BRIDGES: Well there are very few posts about bridges on net. i'd like to provide the info about the bridges to my blog's visitors. &...
welcome to civil engineering world: CABLE STAYED BRIDGES (one of the most innovative i...
welcome to civil engineering world: CABLE STAYED BRIDGES (one of the most innovative i...: A complete look over the cable stayed bridges. "Cable-stayed bridges may look similar to suspension bridges—both have roadways that...
CABLE STAYED BRIDGES (one of the most innovative in man creations.)
A complete look over the cable stayed bridges.
"Cable-stayed bridges may look similar to suspension bridges—both have roadways that hang from cables and both have towers."
. Cable-stayed bridges differ from their suspension predecessors in that they don't require anchorages, nor do they need two towers. Instead, the cables run from the roadway up to a single tower that alone bears the weight.
The tower of the bridges will play a major role in balancing compressional forces.The cables attach to the roadway in various ways. For example, in a radial pattern, cables extend from several points on the road to a single point at the tower, like numerous fishing lines attached to a single pole. In a parallel pattern, the cables attach to both the roadway and the tower at several separate points.
PARALLEL ATTACHMENT PATTERN
RADIALLY ATTACHMENT PATTERN
Today in this modern world, these bridges are the first choice for every civil engineer.due to its less cable requirement, faster to build which inturns gives the best result.
HOW DO IT WORK :
Stand up and hold your arms out horizontally at each side. Imagine that your arms are a bridge, and your head is a tower in the middle. In this position, your muscles are holding up your arms.
Try making cable-stayeds to support your arms. Take a piece of rope (about five feet long), and have a partner tie each end of the rope to each of your elbows. Then lay the middle of the rope on top of your head. The rope acts as a cable-stayed and holds your elbows up.
Illustration of person with rope supporting arms Have your partner tie a second piece of rope (about 6 feet long) to each wrist. Lay the second rope over your head. You now have two cable-stayeds. Where do you feel a pushing force, or compression? Notice how the cable-stayeds transfer the load of the bridge (your arms) to the tower (your head).
BRIDGES
Well there are very few posts about bridges on net. i'd like to provide the info about the bridges to my blog's visitors.
"A bridge is a structure built over a river, seas, and so on, that allows people or vehicles to cross from one side to the other."
It is a structure which is used to span the physical obstacles like sea,rivers,etc.different designs will be used for construction of bridges that suits the topography of that particular place. Designs of bridges vary depending on the function of the bridge.
TYPES OF BRIDGES :
Classification of bridges depends on the structure and its functions bridges and by how the forces of tension, compression, bending, torsion and shear are distributed through their structure.
BEAM BRIDGE :
Beam bridges are horizontal beams supported at each end by substructure units and can be either simply supported when the beams only connect across a single span, or continuous when the beams are connected across two or more spans. When there are multiple spans, 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 can range from small, wooden beams to large, steel boxes.
TRUSS BRIDGE :
A truss bridge is a bridge whose load-bearing superstructure is composed of a truss. This truss is a structure of connected elements forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. The basic types of truss bridges shown in this article have simple designs which could be easily analyzed by nineteenth and early twentieth century engineers. A truss bridge is economical to construct owing to its efficient use of materials.
CANTILEVER BRIDGE :
Cantilever bridges are those which gets it support on only from side.
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.
ARCH BRIDGE :
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.
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. Sub-types include the simple suspension bridge, the stressed ribbon bridge, the underspanned suspension bridge, the suspended-deck suspension bridge, and the self-anchored suspension bridge.
CABLE STAYED BRIDGES :
These are just like suspension bridges which are held by cables from the towers of the bridge .The only difference is cable usage can be reduced in this bridge . And the towers holding the cables are proportionally higher.
( EXPLANATION INDETAILED FOR THE ABOVE BRIDGES WILL BE VERY SOON :)
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