The arch bridge is a traditional architectural design which you can see on display throughout many of the world’s significant human civilizations. Romans are often credited with the modern implementation of this technology, but there are archways that have been found as far back as Ancient Egypt inside of buildings, tombs, and storage structures.
It is the versatility of the arch that makes it such a useful design, even with today’s modern technologies. When you have two strong abutments which can serve as a base point for the pressure on the bridge, then this design options offers more flexibility and strength than other architectural design options.
There are definitive pros and cons to consider when evaluating the design of an arch bridge.
List of the Advantages of Arch Bridges
1. It offers higher levels of resistance compared to other designs.
The curved design of the arch bridge gives the structure an added element of strength that is not always found in alternative designs. When heavy objects travel over a bridge, the weight attempts to modify the structure through the creation of a bending force. The structure of the arch allows the weight to transfer along the entirety of the structure, even when that action occurs right along the top of the arch itself. This equal displacement is the most significant advantage to consider with this bridge design.
2. It offers the option to span a greater distance.
Arch bridges are often used when there is a significant distance to span with the structure. This design option can go further between two points of vertical support than a straight beam because of the unique way it handles to downward vectors that occur when elements cross it. That makes it possible for an arch bridge to handle more loads compared to horizontal support designs. Because there is a reduced need for reinforced vertical support, it is usually cheaper to construct this type of bridge compared to other options.
3. It can be construction from almost any material.
If you look for arch bridges in modern infrastructure, then you will find most of them are constructed with a combination of steel and concrete. History shows us that this design stays strong when built with alternative materials as well, such as stone. Some of Rome’s most impressive arch structures, such as the aqueduct of Pont du Gard, use multi-level arch designs to create a system which could still be used today for the same purpose it was created almost 2,000 years ago.
4. It provides an advantage when carrying loads.
The arch design of a bridge does an excellent job of managing compression. That aspect of its construction makes it able to carry more weight than a flat plank or beam could over the same span. Flatter arches will create more force that is sent to the ground in a safe manner. It is this process which allows the arch bridge to have a higher level of durability when compared to other designs. When the advantages in length and strength are combined with this advantage, it is clear to see why it was the preferred way to traverse over a span in the ancient world.
5. It continues to provide support without distortion over time.
The half-circle shape that defines the arch design ensures that no distortion occurs when downward force is applied to the span. That includes the elements of gravity which weigh on the bridge once the structure is entirely constructed. This feature reduces the costs of long-term maintenance for the bridge because of the overall consistency that the structure provides.
One of the oldest existing arch bridges in the world is a prime example of this force. The Mycenaean Arkadiko bridge, located in Greece, dates to about the 14th century BC. It features a stone corbel arch that the local population still uses to this today. Another example is the Eleutherna Bridge, which features a triangular corbel arch.
6. It can become stronger over time.
The natural design of the arch bridge is already strong when compared to other designs that are used when trying to cover a span. As this structure ages, the compression placed on each side of the structure will flatten out the arch, which gives it added strength. Even if the shape of the inverted “U” is minimal, this advantage will be present in the overall usage of the structure. That is one of the reasons why there are more ancient arch structure still available (and in use) from the ancient world compared to those that were built with pillars.
7. It adapts to local environmental conditions better.
The Romans started out by building arch bridges and aqueducts that offered a semicircular design to them. As they learned more about this design, they began to shift to segmental arches instead. The updated building technique allowed for more significant water levels to pass underneath the bridge, which lessened the risk of the structure being swept away during a flood. It was such an effective design that the Romans built almost 1,000 of these structures in 26 different countries.
List of the Disadvantages of Arch Bridges
1. It offers a finite span length to use.
Although arch bridges do offer an advantage in their ability to cover long spans, this design offers a natural restriction to its length as well. When you place the end points of the bridge too far apart from one another, then it will weaken the joint area where they come together. That’s why you see bridges use multiple arches when they must cover a long distance. There is no way for a single arch to provide the benefit. Adding radius and tension to the structure will always weaken the span.
2. It is a time-consuming project to complete.
Because of the specificity which must be met when constructing an arch bridge to gain its benefits, the time investment required to construct this span is often three times greater than it would be for other bridge types. That means the capital costs of construction are often higher with this option as well. Labor tends to be the significant factor in the initial expense of this structure, which is why you typically see it implemented more often when this cost is subsidized or available at a lower rate because of changes to the standard of living.
3. It is a structure which requires careful maintenance.
All bridges suffer from the effects of entropy over time. Because of the unique weight displacement properties of the arch bridge, it must have frequent inspections occur as it ages to recognize cracks or identify damage that could shift this feature. Even steel bridges can develop wear points that may eventually cause the structure to fail if it is not given the correct level of attention throughout the year.
4. It is a bridge option that cannot be built in some locations.
Arch bridges require a location where both sides have access to stable, solid supports that will permit the span to extend for the length required. There must be a minimum of two placement points for even small bridge installations to occur successfully. Although reinforced steel or concrete can withstand higher levels of tension in the structure that open up new options for construction, longer spans still require places where multiple distribution points can be placed, which is not always any option.
5. It requires more side support to complete a successful span.
Arch bridges require more support along their sides than other bridge designs to create a usable span. That means their structures must be situated along abutments or banks that are sound for the span to work. Artificial supports can be used to reinforce weak areas if all the other elements required for the design will work, but this need is typically one of the greatest disadvantages which are associated with the use of an arch bridge.
6. It can sometimes be too flexible.
Arch bridges, like any other span, are built to withstand a certain level of flexing and movement from wind impacts, weather incidents, and higher levels of traffic. That feature improves its durability, but it is an advantage with finite resources. There are instances when these bridges responded with too much movement to their surrounding conditions, resulting in the eventual failure of the structure.
7. It cannot have any design flaws for it to work as intended.
The architectural design and construction implementation must be perfect for the benefits of the arch design to be realized with a new span. If the supportive structures are not perfectly aligned with the arch to create the accurate placement of the keystone, then the weight distribution for the structure will become unbalanced. The strength of the steel, stone, or other building materials must also be consistent for this structure to stand. Any discrepancies may create a weakness that is too difficult to overcome.
8. It requires expertise to build.
Although almost anyone can build a bridge when given instructions and materials, the implementation of an arch design is a different story. There are two different arcs, called the “intrados” and “extrados,” which must be built with specific placement values for this structure to be effective. Builders must know how to calculate the correct striking point for the span, understanding the elements used in its construction, to complete the process correctly. One must be strong in mathematics, blueprint reading, architectural concepts, geologic understanding, and be well-versed as a contractor to build a long-lasting structure.
These arch bridges pros and cons look at the practical side of this beautiful structure. It is a design which offers high levels of flexibility, allowing for the span to gain in strength over time as the impact of compression and gravity wear on it. If the disadvantages of this option can be evaluated before construction begins, then we can learn from the example set by the Romans. An excellent design, combined with world-class materials, can create structures which may last for centuries.
Natalie Regoli, Esq. is the author of this post and the editor-in-chief of our blog. She received her B.A. in Economics from the University of Washington and her Masters in Law from The University of Texas School of Law. In addition to being a seasoned writer, Natalie has almost two decades of experience as a lawyer and banker. If you would like to reach out to contact Natalie, then go here to send her a message.