Difference between Bridges and Flyover
Hi there, Welcome to "thecivilengineer18.com", we travel a lot from the morning till evening travel from our home to our office and vice versa. But have you noticed there are different types of structures that you have crossed? You call them simply roads. But for a civil engineer, there are Roads, Culverts, Flyover bridges, and so on. In this article, my main focus will be on bridges and flyovers.
What is a Bridge
The main purpose of the bridge is the connectivity of two inaccessible points. Let's say a river is flowing but we must make a road over or above the river. At this point, a structure is built which is known as a bridge for the connection of the road.
Types of Bridges
- Arch Bridges
- Beam Bridges
- Cantilever Bridges
- Cable-stay Bridges
- Suspension Bridges
- Tied Arch Bridges
- Truss Bridge
Arch Bridges
Arch bridges are one of the oldest forms of bridges which are made of stones. They are the only form of bridge that was available to mankind. Nowadays too arch bridges are used but they are made of concrete.
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| Chenab Arch Bridge, India |
Load Transfer Mechanism of Arch Bridges
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| Arch Bridge |
Arch bridges work on the principle of comparison and distribution. You see arch bridges are comprehensive of three components: the deck where the traffic flow is supported by numerous hangers or pillars. The load of the pillars transferred to our hero component the arch of the bridges. They transfer the load to their endpoints, known as abutments, and transfer the load to the ground.
Advantages of Arch Bridges
One of the greatest advantages of arch bridges is that they are very suitable to cover longer distances than any kind of bridge because of their stability strength and resistance. That's why some of the highest bridges in the world like the Chenab Bridge in India which is constructed at an elevation of 322m or 1056ft arch bridges.
Disadvantage of Arch Bridges
If the two points that need to be connected are too far then more arches need to be constructed and proper side supports need to be provided until the span's construction.
Arch bridge construction needs a lot of expertise, but a very strong and stable type of bride.
Beam Bridges
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| Lake Pontchartrain Causeway, US |
These kinds of bridges were the simplest form of bridges. They are made up of connecting numerous beams that run parallel to the deck slab and the beams were connected together at regular intervals by connecting beams that are perpendicular to the deck. These beams were in turn connected to the piers that were erected in the ground.
Load Transfer Mechanism of Beam Bridges
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| Beam Bridge |
Normally when load is applied to a beam, the top portion of the beam experiences compression and the bottom layer tends to experience tension hence in beam bridges the moving load of the vehicle and the deck load are applied on the beams that run parallel to them. these beams transfer the load they receive to the connecting beams that run perpendicular to the deck at regular intervals above the Pillars. From the connecting beams, the load gets transferred to the pillars from the connecting beams. The pillars transfer the load to the ground using vertical compression.
Advantage
Beam bridges were the very easiest in the construction of the bridge. The members can be made from various kinds of material like steel, concrete or timber or as a composite material like a combination of Steel and concrete as shown in the diagram. They can be quickly constructed since the members can be made in factories like pre-fabricated structures and transported to the required site location.
Disadvantage
The greatest disadvantage of beam bridges was that they may sag over some time. so periodic maintenance is needed. This can be overcome by making steel beams in steel, but the cost is too high. So periodic maintenance is the only disadvantage with beam bridges.
Cantilever Bridges
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| Forth Bridge, Scotland |
In Cantilever Bridges the Pillar is first constructed on a regular interval, and then the deck slab is projected outwards from the pillars with the help of beams below it. In addition to the below beams, the top layers of the deck are connected to the pillars with the help of bracings.
Load Transfer Mechanism of Cantilever Bridges
Cantilever bridges work in the same manner as like that of a cantilever beam, In a cantilever beam one end is attached to the and the other end is left free. The load transfer in a cantilever beam occurs when all the cantilever load gets transferred to the fixed end. In the same manner in a cantilever bridge, the load in the deck will be transferred to the fixed end by the cantilever mechanism.
Advantages
Cantilever bridges are very suitable for long spans and if the distance is so long the cantilever supports can be constructed simultaneously hence saving a lot of time. Cantilever bridges were a very suitable option for deep terrain like valleys etc. where side supports cannot be provided. The greatest advantage is their lifespan and minimal maintenance.
Disadvantage
The main disadvantage of cantilever bridges was the cost. Since the bridges were constructed with the help of steel or pre-fabricated structures the cost will become expensive. And more expertise is required for the design of the cantilever bridges. They are not suitable for areas like earthquake-prone and other extreme weather conditions like frequent cyclones which may affect the load-carrying capacity of the deck due to the faster winds from the cyclone which in turn creates more momentum in the bridge.
Cable Stay Bridges
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| Incheon Bridge |
The cable stay bridge is also one of the oldest types of bridges used nowadays. Here the main hero is the straight diagonal cables connected to the slab's deck. The pillars were placed at regular intervals from each other, and then the pillars were connected to the deck with the help of numerous straight diagonal cables.
Load Transfer Mechanism of Cable Stay Bridge
Here the load transfer will be made in a manner that the vehicles moving loads will be transferred to the deck, from the deck they are transferred to the pillars with the help of the numerous straight diagonal cables which in turn the pillars transfer those loads to the ground using vertical compression.
Advantages of Cable Stay Bridge
Cable stay bridges can be constructed at a much faster rate than that of any other type of bridge. They are more appealing to the eyes than any other bridges, i.e., they have more aesthetic value. It is more cost-effective. Cable stay bridges are more rigid than suspension bridges.
Disadvantages of Cable Stay Bridges
Cable Stay Bridges were only suitable for Short to medium distances. Also, that is not suitable for areas that will have a greater impact from earthquakes or cyclones since the cables may tend to get damaged by natural calamities easily. Also, the cales may corrode due to the continuous exposure so proper periodic maintenance is required which will add up the maintenance cost of the Cable Stay Bridge.
Suspension Bridges
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| Golden Gate Suspension Bridge, US |
Suspension Bridges are one of the oldest forms of bridges that were made using ropes and wooden planks in the early days. But Modern-day Suspension bridges use Cables nowadays that are made from Galvanized Steel Wires and their casing is also made of Galvanized steel in place of ropes, there are two types of rope one is the main horizontal suspended rope which is suspended with the help of the Vertical tower or Phylons. The deck is made up of Steel and concrete that are suspended with the help of numerous vertical ropes that were attached to the horizontal Suspended ropes.
Load Transfer Mechanism of Suspension Bridges
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| Suspension Bridge |
The Moving load of the vehicles and the dead load of the deck were first transferred to the Vertical Suspension cable which in turn gets transferred into the Main suspension cable which were both in tension due to the load from the deck. This load gets transferred to the Vertical towers or phylon which will transfer the load through vertical compression.
Advantages of Suspension Bridge
Suspension bridges get the first place if you want to construct longer-span bridges with minimum pier or pillars. If you want to construct a bridge without disturbing the Water transport below it then suspension bridge is the best solution for you. Since almost 99% of the work can be done in a suspended manner the waterways below it can't be affected. The maintenance of the bridge also can be done from above, so it has a lot of advantages on this front.
Disadvantage of Suspension Bridge
These bridges were economical but they are the easiest to fail. Some fast winds like cyclones can cause the total bridge to vibrate and wobble the entire deck. The failure of one cable leads to the collapse of the entire bridge. Also, the maintenance and access of the under the deck is very difficult because they are usually constructed very high above the water body. In some areas if the soil type and the hard strata are not available at a suitable depth more efforts like pile foundation need to be deployed since the pylon/pier needs to be very high to suspend the cable. Hence these bridges were not that suitable for extreme climatic conditions areas.
Tied Arch Bridge
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| Fort Duquesne Tied Arch Bridge, USA |
Tied Arch Bridge is a mixture of suspension and arch bridges. In normal arch bridges the arch present below the deck but in tied arch bridges the arch lies above the deck of the slab and the deck is connected to the arch through the vertical cables to support the deck. The arch ends up above the pillar or pier.
Load transfer mechanism of Tied arch bridge
In the Tied Arch Bridge, the load of the moving vehicles and the dead load of the deck were transferred to the arch by the vertical cable through tension. In the arch, the tension from the cable gets converted into compression and the arch transfers it to the Pillars or Piers. The Piers receive the force and transfer it to the ground through vertical compression.
Advantages of Tied Arch Bridge
We can easily construct the tied arch bridge somewhere, and then transport and fix it. So it's very convenient for the construction in a controlled environment. They are arguably very strong and they give less force on abutments than any other bridges.
Disadvantages of Tied Arch Bridge
They are the strongest but they are the shortest, yes the span that you can produce with the help of a tied arch bridge is very small when compared to other bridges. But you can bargain that with the help of the stronger span that you can get. They are more expensive to build than other types of bridges since the span length produced is small so numerous piers or pillars need to be deployed to cover longer distances.
Truss Bridge
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| Truss Bridge |
A Truss Bridge is usually made of Steel sections, where the steel sections are attached to each other in a triangular shape by using welded or riveted joints. Truss bridges were the most popular and suitable choice for places where extreme climatic conditions attack a bridge.
Load Transfer Mechanism of Truss Bridge
Truss Bridges have both Vertical and Diagonal steel members. The load from the deck creates tension in the vertical members which is then transferred to the diagonal member as compression and this process of transfer of load continuously happens through the joints until the load gets transferred to the support of the bridge where the load gets transferred to the ground.
Advantages of Truss Bridge
The strongest of all the bridge types and it is more economical than other types of bridges. They can be fabricated outside and fixed on-site. They are lighter yet they can withstand extreme weather conditions.
Disadvantages of Truss Bridge
Need more expertise in construction. The joint needs to be properly designed to withstand the required load. It is not that much attractive to the eyes. Since they are mostly made of steel proper maintenance is required to prevent it from corrosion.
What is a Flyover
Flyovers are a type of bridge that is constructed over the road or above a bridge to reduce congestion or traffic. Literally, the word itself's days flyovers are meant to fly over the traffic.
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