Just like for many kids, The Three Billy Goats Gruff is one of my favorite stories. Not because of the smelly and mean troll, but because of the important part the wooden bridge played to save the goats from starving to death.
When the goats had munched all the grass on their hillside, they needed to get on the other side of the river to have a taste of the delicious grass at their sight. Without the wooden bridge, their story would never exist.
Bridges are important in our lives. They make it possible for us to cross over streams, rivers, canyons, and ridges. Anciently, bridges were only meant to be used by human beings and animals. Today, there exist big bridges for vehicles and highway overpasses in cities and towns that are used to ease traffic congestion.
The ancient people made bridges from fallen trees or stones to make hunting and gathering easy. Over time, engineers have used this idea to develop strong modern bridges from steel, concrete, and other materials.
There are also portable bridges, which are mainly used by the military due to their flexibility. Engineers ensure that bridges are built strong enough not to be destroyed easily as a result of the weight of the vehicles and people using them.
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Bridge Facts for Kids
- They build bridges over rivers, roads, and railway tracks.
- They need to be strong to support people, cars, and trains.
- They need to withstand strong winds, storms, and earthquakes.
- The oldest bridge is in Turkey over the river Meles, build in 850BC
- The longest bridge in the world is Lake Pontchartrain Causeway in New Orleans’s
Types of Bridges
Beam Bridge
Whenever people or cars need to cross over highways, valleys, water bodies, and other spaces between two separate surfaces, they use beam bridges. A beam bridge was the first bridge to be used by human beings because it is easier to build. It is made by placing two rigid pillars on both ends and laying planks of wood across them.
Sometimes, engineers may need a beam bridge to be quite long and extended than usual. In this case, they may be required to place more support material at various intervals in the middle of the bridge. These materials are known as piers. Unlike in the initial times when most beam bridges were only made of logs and wood, today, bridge designers use concrete and steel to make the bridges stronger.
For safety purposes, most beam bridges cover shorter distances. The shorter the distance between the support materials, the stronger the bridge and vice versa. The longest beam bridge is The Lake Ponchartrain Causeway that is found in the United States. It is about 38 kilometers long.
Quick Facts on a Beam Bridge
- Another name for a beam bridge is a girder bridge
- It is the first bridge that humans ever used
- A beam bridge has the easiest design
- A beam bridge is made using strong straight two end supports
- The longest beam bridge is the Lake Ponchartrain Causeway in the United States
Truss Bridge
Over time, human beings made machines like vehicles that needed to be moved from one end of a gap or a water body to the other. Since vehicles are not designed to fly or float on water surfaces, engineers and architects had to design stronger bridges than the beam bridge. One such bridge was a truss bridge.
The first truss bridge was built in the United States in 1820 from wood. It was a development of the beam bridge. The structure of certain shapes can be applied to make bridges stronger. In the case of a truss bridge, engineers used triangles because of their rigid nature. It is hard to break a triangle by applying force at its points.
The triangular units that run across the sides of a bridge are known as trusses. The trusses spread the weight evenly across the bridge to reduce too much tension on a particular point. Trusses are cheaper to build because they require fewer materials.
While designing truss bridges, Engineers can decide where the road should pass. They can place it at the top of the bridge to form a deck truss, through the middle of the bridge to form a through truss, or below the truss. The longest truss bridge is the Ikitsuki Bridge, found in Japan.
Quick Facts on a Truss Bridge
- The earliest truss bridge was made of wood in 1820
- A truss bridge relies on several triangles for support
- Truss bridges can be categorized according to where the roadway passes
- The longest truss bridge is Japan’s Ikitsuki Bridge
- Truss bridges require fewer materials to construct
Cantilever Bridge
As the name suggests, a cantilever bridge is constructed using the cantilever concept A Cantilever has two sections that are attached to one side and joined at the center. A good example of a cantilever is an extension of the human arm. The arm is attached to the body but can still hold heavy objects.
The type of material used to build a cantilever depends on the intended purpose. A simple footbridge may require small beams to construct. On the other hand, a cantilever meant for large vehicles or trains should be made using strong steel supported by prestressed concrete. One advantage of a cantilever bridge is that it is easy to construct over-complicated gaps as it doesn’t require support at the construction time.
The first cantilever bridge was built in the late nineteenth century by Heinrich Gerber. However, the first modern design of the bridge was constructed in Germany in 1867. It is known as the Hassfurt Bridge and has a length of 38 meters. The Quebec Bridge in Canada is the longest cantilever bridge with a length of 1,800 feet. Notably, the Forth Rail Bridge in Scotland is the most famous ancient cantilever bridge. It was built in 1890 and is the second-longest.
Quick facts on a cantilever bridge include
- A cantilever bridge is supported on one end
- Structural steel and prestressed concrete are used to build a strong cantilever bridge
- Heinrich Gerber built the first cantilever bridge
- Hassfurt Bridge was the first modern cantilever bridge
- The Quebec Bridge is the longest cantilever bridge
Arch Bridge
Arch bridges are the most ancient bridges ever to be used by humans. They have been in use for over 3000 years. Initially, they could only be built over small gaps. Today, with technological advancements, arch bridges can be built over longer spans and with more strength.
The strength of an arch bridge lies in its curved structure. When force is applied at the arches, it doesn’t travel downwards to bend the bridge. Instead, the force is spread along the arches to supporting pillars known as abutments on each end. The abutments bear the weight of the whole bridge and hold the arches in their desired position
Arch bridges were made popular by the Roman Empire. The Roman architects had arch bridges constructed in parts of Europe and Asia before spreading the technology to North Africa. Some of these bridges were so strong that they still exist up to now.
Arch bridges can be made stronger and more efficient by constructing them with rigid structural steel, iron, and prestressed concrete. When combined with art, arch bridges form some of the most fascinating sights, like the Rialto Bridge in Italy.
There are five major types of arch bridges. They include the corbel arch bridge, aqueducts, and canal viaducts, deck arch bridge, through arch bridge, and a tied arch bridge. The world’s longest arch bridge is the Chaotianmen Bridge found in China. It is 5,712 feet long.
The following are quick facts on arch bridges
- They are some of the most ancient bridges
- They are made strong by the arches and supporting pillars at each end
- The pillars of the arch bridge are called abutments
- The Romans invented them
- Some arch bridges form attractive sights
- The longest arch bridge is the Chaotianmen Bridge in China.
Tied Arch Bridge
A tied-arch bridge is also known as a bowstring arch. It can be seen to combine both the arch bridge and suspension bridge technology. Tied Arch bridges are efficient for short-span distances such as over rivers or the construction of cross-bridges.
During the construction of a tied arch bridge, an arch rib is placed on each roadway side. Each arch rib is reinforced by a tie beam. There are also vertical ties that connect the tie-beam with the arches to make the roadway more rigid. When in use, the force from objects on it is spread over to the top tie beams by the vertical ties. The tie beams then translate the tension to the bridge’s abutments, where it is neutralized.
Tied arch bridges are easier to construct in areas with loose soil. What makes them more convenient on such sites is that they can be assembled from anywhere before being moved to the actual construction place. To make tied-arch bridges stronger, the connections at the arch rib and the tiers must be carefully welded. They also need regular maintenance to keep them in place. The Caiyuanba Bridge, located in China, is the longest tied-arch bridge with a length of 420m.
Some quick facts about a tied arch bridge include:
- It is also known as a bowstring arch
- It uses both the arch bridge and suspension bridge technology
- It is made strong by arch ribs reinforced by ties and vertical beams
- They are convenient over short crosses
- They need regular maintenance
- The Caiyuamba Bridge is the longest tied-arch bridge.
Suspension Bridge
The peak of beam bridges and arch bridges pushed engineers to look for new ways of making advanced modern bridges. As a result, they combined the concept of a simple rope bridge with the rigidity and strength of steel chains and cables to come up with a suspension bridge.
A suspension bridge comprises cables running from one tower to the other and vertical hangers that hold the roadway in place. The suspension cables spread the weight of the objects on the bridge to the towers where it is absorbed.
The first modern suspension bridge was built in Pennsylvania, United States, in 1801 at Jacob’s Creek, Westmoreland County. From the time of their invention, suspension bridges became widespread because they were relatively cheaper to construct. They can also be extended over longer spans with more efficiency compared to other types of bridges. Moreover, suspension bridges are less affected by natural calamities such as earthquakes.
For maximum strength, suspension bridges should be constructed stiffly to resist strong winds. One shortcoming of this kind of bridge is that they are only convenient for lighter traffic. The Akashi Kaikyō Bridge in Japan is the longest suspension bridge in the world.
Here are some quick facts about a suspension bridge
- It is made using suspension cables and vertical hangers
- It is the suspension cables that strengthen a suspension bridge
- It is cheaper to construct
- It is earthquake-proof
- The first suspension bridge was designed in 1801
- It is convenient for lighter traffic
Cable-stayed Bridge
The design of a cable-stayed bridge is similar to that of a suspended bridge. However, what differentiates the two is that in a cable-stayed bridge, the cables connect the roadway to the end-to-end towers directly. It is convenient for pedestrians, bikes, and light traffic. It is also optimal for construction in areas where cantilever bridges can’t fit. One notable advantage of this kind of bridge is that it is cheaper and faster to construct.
The first cable-stayed bridge was designed in Venice, Italy, in 1595 by Fausto Veranzio. However, this type of bridge was made practical in the 19th century when bridges such as the Dryburgh Abbey Bridge and the James Dredge’s Victoria Bridge were built in England. The United States had its earliest cable-stayed bridge in 1889 when the Barton Creek Bridge was constructed.
There are five variations of a cable-stayed bridge. They include the side-spar cable-stayed bridge, cantilever spar cable-stayed bridge, multiple-span cable-stayed bridge, extradosed bridge, and cable-stayed cradle-system bridge.
A side-spar cable-stayed bridge comprises only a single tower on one of its sides. Secondly, a cantilever-spar cable-stayed bridge has one cantilever on one end that resists the bending force resulting from the cables. Thirdly, a multiple-span cable-stayed bridge comprises more than three spans and is quite complicated to construct. An extradosed bridge consists of cables that are connected to the roadway from the towers. Lastly, the cable-stayed cradle-system bridge is the latest design, which is made up of cables that connect within the roadway continuously without anchors.
Quick facts about cable-stayed bridges include:
- They are made up of cables that support the deck
- The cables are connected to towers directly
- They are convenient for light traffic
- They are cheaper and faster to construct than other bridges
- They were first designed in 1595 in Venice
- There are five variations of a cable-stayed bridge
