Arch Bridge

Arch Bridges

1. History of arch bridges
   An arch bridge is one of the most popular and oldest types of bridges, which came into use over 3000 years ago and remained in the height of popularity until industrial revolution and invention of advanced materials enabled the architect to create other modern bridge designs. However, even up till today, arc bridges remain in use. They were originally built of stones and bricks. With the help of modern materials such as reinforced concrete and steel, their arches can be built on much larger scales.
   
2. Construction of arch bridges
   Building an arch bridge is not easy as the structure is very unstable until the two spans meet in the middle. Hence, civil engineers use a technique called centering, of which a wooden support carried both spans until they locked together at the top. A newer method supports the spans using cables anchored to the ground on either side of the bridge.
   
3. How an arch bridge works
   When a force is applied, instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the supports at each end. The weight is transferred to the supports at either end. These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out. The load at the top of the key stone makes each stone on the arch of the bridge press on the one next to it. This happens until the push is applied to the end supports or abutments, which are embedded in the ground. According to Newton's third law, there is an equal and opposite reaction for every action. Hence, the ground which pushes back on the abutments creates a resistance which is passed from stone to stone, until it is eventually pushing on the key stone which is supporting the load.
4. Types of arch bridges
   There are many types of arch bridges, such as:
1. Corbel arch bridge

Even though this bridge does not function in the same way as a true arch bridges, they can be created to look very similar like them. They are created by laying successive layers of masonry or stone with each having successfully larger cantilevers.

2. Aqueducts and canal viaducts To bridge large distances, ancient romans built series of supports which were connected with stone arches. These series of arched structures were not only in one layer like ordinary bridge, but with several layers that could reach very impressive heights.
3. Deck arch bridges
   Common type of arch bridges, where the deck is situated on top of the arch.
4. Through arch bridge
   It is a bridge, where the deck is not situated completely above the arch, but it travels in one part below it and is suspended to it via cables or tie bards. The Sydney Harbour Bridge is the best example of this design.
5. Tied arch bridge
   Also known as bowstring arch bridge, it incorporates a tie between two opposite ends of the arch.
   

5. Advantages and disadvantages

1. Advantages
1. It is very strong and has great natural strength. It also gets stronger over time as arch bridges are designed to compress, this compression causes the materials to become more compact and closer to each other, which firm the foundation and enabling the bridges to withstand heavier loads.
2. Good for small spans.
3. Can be made with many common local building materials such as stone and brick being used in the past. Today, concrete is more likely to be used.
4. Wider distances can be spanned by building more arches.
2. Disadvantages
1. Uses a lot of material, even on short spans.
2. Limited span. It is important for the foundations to be fixed and for the arches to be of certain radius. The higher the arch radius, the higher the tension, and the weaker the bridge. For longer arch bridges, more arches are built. However, the cost and time needed to create multiple arches considerably limit the span or length of arch bridges.
3. Time-consuming to build. It can take at least the double time to build arch bridges than other similar bridges. Arches have to be made with precision to ensure its strength and longevity. They also need to be symmetrical to ensure equal displacement of weight.
4. Maintenance is expensive and constantly required, as simple cracks due to weather and natural wear and tear can compromise the bridges’ safety. The mortar that binds the materials together also become weaker over time and needs regular upkeep.