One of the oldest existing bridges in the world today is the Mycenaean Arkadiko Bridge. It is located in Greece and formed part of a road network that was present during the Greek Bronze Age. It may have been built as early as the 14th century BC. The Romans would then see the full potential of using an arch bridge for their construction needs. More than 900 structures from the Roman Empire have been cataloged and some of them are still in use.
The primary advantage of an arch bridge is that it doesn’t require complicated materials or complex architecture to create a functional structure. Bricks and stone were commonly used to constructed arch bridges in the past with great success. As long as the materials remain strong during compression and are somewhat resistant to shear, it can be used to construct a functional bridge.
The disadvantage to the arch bridge design is that it is effective for short distances only. If you look at the length of Roman aqueducts that use the arch design, you’ll find multiple arches and multiple levels had to be constructed to maintain the strength of the bridge. A single arch is only effective for a short span.
Here are some additional arch bridge pros and cons to discuss today.
Top Pros of an Arch Bridge Design
1. It distributes pressure effectively.
When weight is placed onto an arch bridge, the compression comes straight downward. That allows each part of the bridge to support the full weight of what is crossing instead of having it be dispersed throughout the entire span of the bridge. It is a design which allows every part of the bridge to support other parts, ensuring that no single spot receives all the pressure, all the time.
2. It is a cheap design option.
Concrete is often used to construct arch bridges today. Any material that is based on natural components can, in theory, be used to construct an arch bridge. That means every community can focus on their local resources to enhance their infrastructure instead of relying on imports. That also means each arch bridge can have its own personality.
3. It offers better resistance.
The arch is one of the strongest designs ever invented. With a proper keystone, the arch offers one of the best levels of resistance to any force that may attempt to modify its shape. Both ends of an arch are fixed, which creates equal displacement throughout the structure. That dispersant process reduces the chances that warping or distortion may occur over time.
4. It is easier to maintain.
Because of the natural strength of the arch design, maintenance costs for the bridge will be naturally lowed compared to other bridge designs. The natural materials which often make up the bulk of an arch bridge’s composition are easier to maintain than iron or steel as well. That makes it easier for communities to keep their bridges in good working order.
5. It opens new transportation networks.
Small obstacles can create large gaps in trade and travel for some communities. The Romans utilized numerous arch bridges for their roads because it was a simple way to increase the reach of their transportation networks. Because these bridges are such an economical option, almost any community can build their own and benefit from the better network it creates.
6. It is a design option that is structurally sound.
As an arch begins to compress under pressure, it becomes stronger. That is because the compression forces the arch to operate at maximum dispersion. Heavy weights are often placed on top of the arch to encourage compression before the bridge is ever used. Over time, as more compression occurs, more strength is added to the design. That is how some Roman bridges can still be used more than 2,000 years after they were built. It is one of the most structurally sound designs that can be found today.
Top Cons of an Arch Bridge Design
1. It must be perfect for it to be effective.
The design of an arch bridge must be 100% perfect for it to have the strength that it will need to last. It relies on the skill of the builder more than the designer to ensure the arch will function as intended. If the starting point on one side is just a little off or there is a weakness in one of the building blocks of the bridge, the entire structure might come down one day.
2. It needs more supports than average.
For an arch bridge to work effectively, it must have a bank foundation that is structurally sound. Abutments are required to provide stability to the base. For longer spans that require multiple arches, there must be pillar supports installed in equal lengths to ensure weight distribution has been equalized. Because of this need, the locations where an arch bridge can be installed are somewhat limited.
3. It may need more maintenance than average.
Natural materials can withstand the elements very well and corrosion is never really a threat to stone or brick. The one problem that does exist from a maintenance point of view is the flexibility in the arch. When there is too much flex within an arch, any mortar or sealant can degrade over time, reducing the strength of the bridge as it crumbles. In some high-wind locations, an arch bridge might be costlier to maintain than other design options.
4. It takes time to build.
Although arch bridges have proven their longevity, there is a certain time investment required to construct them in the first place. It may take more than a decade to construct a span that includes multiple arches. For a single-arch bridge, the process may still take 6-12 months. When estimating the cost of installing a new bridge, the time investment must be one of the considerations in the decision-making process.
5. It requires a specific skill-set to build.
Knowing how to build an arch requires more than basic construction skills. One must know how to ensure the springing line for each arch can remain level. Constructing the intrados and extrados arc requires specific placement values. One must be able to calculate a striking point and understand the components of the keystone, key brick, or other item that serves as the mid-point of the arch. It is a process that can be mathematically intense.
These arch bridge pros and cons show that when this structure is built correctly, one of the best bridges in the world can be constructed. It is a technology that has been known for potentially 3,500 years. As long as the negatives are accounted for in the design and construction process, the arch bridge is easily one of the best innovations humanity has ever achieved.