The traditional design of a bridge incorporates arches because of the amount of strength this design offers. You can find examples that are more than 2,000 years old thanks to the ambitious efforts of the Roman Empire. Multi-level structures, including aqueducts, used this design as a way to transport people, materials, or supplies into a community.
When you look at the history of the arch itself, there is evidence that the Egyptians discovered the advantages of this design more than 5,000 years ago. Its versatility has long been a part of human culture. It only makes sense to include it with a bridge because it offers two robust abutments that serve as the base pressure points for the span. You receive better strength and flexibility compared to other design options because of this feature.
As the forces in the arch are carried to the ground, it will push outward at the base. This thrust increases as the height of the arch decreases. That is why the soft compression form is such an effective way to create support structures.
List of the Advantages of Arch Bridges
1. There are multiple design options from which to choose.
There are three common true arch configurations that you will find with bridges today: fixed arches, two-hinged arches, and 3-hinges arches. The first is used most often when building a reinforced concrete bridge, but it is also useful for the times when a tunnel might be necessary. It is most effective when spans are short.
The two-hinged arch is useful for longer spans, offering pinned connections at the base that provide rotation. This design gives the structure room to move during thermal contraction and expansion. As for the three-hinged arch, it provides an additional connection at the mid-span so that the structure can move in opposite directions to account for temperature changes.
2. You can span a greater distance when using the arch design for a bridge.
When there is a significant distance to span with a bridge, then the arch design is the one that engineers typically use because of the advantages of strength and flexibility that come with this option. It travels further between two support points than a straight beam does because of how the downward stresses are managed with this option. Not only does this mean you can create a longer deck, but it also means there is more horizontal strength to support heavier loads.
The Rossgraben Bridge that is near Bern, Switzerland, is an excellent example of this advantage. Even with the three-hinged design, it provides a medium-length distance that reduces the need for support pillars.
3. There is a higher level of resistance available with an arch bridge.
The curvature of the arch bridge design gives the deck and overall structure more strength than alternative options can provide. If something heavy were to travel across the bridge, then the weight will modify the bridge with a downward, sagging force. Because the two support columns allow for the weight to transfer along the entirety of the structure with consistency, there is less stress placed on the structure over time. That means communities have fewer problems with wear-and-tear to manage since the equal displacement ensures that the bridge handles thermal and user changes effectively.
4. it is possible to create an arch bridge out of almost any material.
When we look at the typical arch bridges that are constructed today, most of them are made from either concrete, steel, aluminum, or a combination of those materials. If you look at the ancient relics left behind by the Romans with this construction, then you will see that even stone has the capability of lasting for a long time when property built. We are even using some of these old structures still today, like in the construction of the Pula Arena in Croatia.
The arena was built in the 1st century, and it is one of the largest surviving structures of its type in the world. It offers two stories of arches built from stone that continues to host concerts, film festivals, and even two professional hockey games over the years.
5. Arches adapt to the local environment better than other designs.
Romans began to build arches after they perfected the design because they realized that the structure could withstand the natural environment better than the traditional pillars or abutments that were in use during that era. It is an advantage of arch bridges that still exists today. Even when you look at the advantages of the semi-circular design, you’ll see this advantage – although the segmental arches are more effective.
This strength means the bridge can withstand natural disasters, such as earthquakes or flooding, with greater certainty. You can still gain the advantage of distance with the span as well with this option. That’s why there are more than 1,000 total ancient structures in 25+ countries which are still standing today despite being over 2,000 years old.
6. The arch design for a bridge can actually get stronger as it ages.
The arch design for a bridge is already naturally strong, which is why it is such a popular option for tall, lengthy spans. As the structure begins to go through the aging process, this bridge design begins to get stronger. That’s because the compression that gets placed on each side of it will begin to flatten out the arch somewhat, creating a U shape with less rounding. This process helps to distribute the weight of the deck better to the abutments while providing more stability in the crossing surface.
The only way that this advantage is not experienced by a modern bridge is if the structure is made from inferior materials. Concrete doesn’t age as well as the bridge, so ongoing maintenance may be necessary to ensure that the structural integrity remains intact.
7. There are fewer distortions to worry about with an arch bridge.
One of the issues that other bridge designs face is a distortion of the support piers over time because of how the load goes across the deck. When downward force is applied to an arch, then you receive better equality in the process because of the transference effect that exists. This advantage can reduce the ongoing maintenance costs that a community faces when deciding on this design.
8. A variety of forms are possible with the arch design.
Because the arch shape is so effective at carrying loads and spanning distance, there are a variety of forms that are possible for the construction of the bridge. That means engineers have more flexibility available to them when thinking about the overall aesthetics of the structure. You can opt for a lighter, thinner design with a trussed arch if you wish. The Romans often used masonry arches because they could be stacked to provide more height to manage difficult spans.
Bridge designs can also use equilateral points, horseshoes, trefoils, parabolic, triangular, elliptical, and Tudor design elements to create a finished result that is useful and aesthetically beautiful at the same time.
9. Multiple arches can work together to create stability.
The Juscelino Kubitschek Bridge across Paranoa Lake in Brazil is an excellent example of this advantage. It features a three-arch design with supportive cables that carry drivers safely over the water. Each one is tied to the other to create more stability while encouraging a strong deck that can handle significant levels of vehicular traffic. As long as you have a clear span, a consistent rise, and a voussoir that works with the other curved segments of the structure, then you will have an immediately strong bridge design that can handle most environmental conditions.
List of the Disadvantages of Arch Bridges
1. Arch bridges provide a finite span with each set of abutments.
You can cover an indefinite span with an arch bridge if you wish, but there is a catch to that process. You’ll need to use multiple arches within the design to make that happen. That’s why you’ll see the stacking design used in the ancient Roman structures that are still standing today – usually 2-3 stories worth of support. If you increase the length of the bridge, then you must add more arches.
If the endpoints of an arch are spaced too far away one from another, then the weight transference benefits disappear with this design. Whenever there is tension and radius added to this design element, the structure weakens.
2. It is a design option which requires an experienced hand.
If given enough time and resources, anyone can build a bridge that can effectively cross almost any span. That might be a simple log or plank that goes across a creek, or it could be the world’s longest bridge. When using this design, there must be an understanding of the interior and exterior pressures that the abutments must handle. You must also place enough strength in the materials and support processes for enough transference to occur.
Builders and designers must have robust skills in blueprint reading, geological understanding of the region, mathematics, and architecture for a successful bridge-building process. If any of these vital components are missing, then it can lead to a premature failure of the structure – a disadvantage that could have life-threatening consequences.
3. The arch must be perfect for the bridge design to be adequate.
If the supportive structures of the bridge are not in perfect alignment with the arch design, then it is impossible to place the keystone accurately. When this issue occurs, then the distribution of weight down to the abutments is no longer balanced. Even when the strength of modern building materials is factored into this process, it only takes a fraction of a centimeter to be off to increase the risk of bridge failure. Discrepancies are almost too challenging to overcome when there is an error in the building process.
4. Arch bridges can sometimes have too much flexibility.
When you look at the two-hinged or three-hinged design for an arch bridge, the advantage of movement can be a tremendous benefit to communities that live in areas where thermal change is frequent and significant. There are also times when the movement or flexibility of the arch can be too much for the deck to handle. When there is too much movement allowed, especially in different simultaneous directions, then this disadvantage can lead to the complete failure of an arch bridge.
5. Some bridges may require additional side supports to manage the deck.
The average arch bridge requires more side supports than other designs because of the nature of settling and movement that occurs with this structure. It is not unusual for artificial supports to be needed if the natural end supports are not strong enough to help the design. This disadvantage is the reason why some locations use pillars or some other form of support. Artificial support can only provide a finite amount of strength, which may not be enough to reach the weight tolerances that are necessary for the upcoming bridge design.
6. Arch bridges are not suitable for some locations.
There must be solid and stable supports on both sides of an arch bridge for it to support a deck of any type. If this option is not available for a community, then there is no way to replicate the result. You must have two placement points that are successful in their support, even for a small span, for this design element to be successful. Modern materials like steel can withstand more tension and stress so that there are more placement options to consider, but you cannot have a one-sided bridge.
If you need a longer span, then you must have multiple distribution points. That’s why the longest arch bridge in the world today is the Chaotianmen Bridge over the Yangtze River, at just 1,814 feet. Modern designs can span for over 30 miles over water.
7. Arch bridges typically need higher levels of ongoing maintenance.
The average arch bridge must receive ongoing maintenance to ensure the supports are distributing weight to the abutments as they should. That means there must be frequent inspections of the span as the structure ages to ensure it is not weakening over time. Wear points are common, even with strong materials like steel, so an early intervention can often lead to repairs and ongoing use of the structure.
If a community is not performing regular checks of their bridge, then it could lead to a catastrophic failure. One of the most famous examples of this issue was the Honeymoon Bridge that connects the U.S. and Canadian sides of Niagara Falls. It collapsed in 1938 because a sudden wind storm sent 100 feet of ice to push against the bridge, changing the weight displacement so that it would eventually give way.
8. It can take more time to build an arch bridge compared to other designs.
Because of the level of specificity that is necessary to complete an arch bridge, it can take longer to finish a project like this compared to other designs. It can take up to triple the time to build this structure, which may not be available to some communities if a span is needed immediately. This disadvantage is also why the cost of building is so much higher with an arch-based design, since there is more labor involved in the project.
Even if the federal government were to subsidize some of these costs for the states in the U.S., the risk of time and cost overruns is significant when looking at the arch design compared to the other choices which might be available.
Verdict on the Advantages and Disadvantages of Arch Bridges
Arch bridges are one of the most effective designs that humans have invented in history. We continue to use this option still today, even with modern materials like steel and concrete, because of the tremendous strength and flexibility that it provides without an increase in the risk of failure.
Every arch has a maximum length and limit that it can support. Engineers must recognize these concepts in the design phase to ensure the structure can offer the advantages of longevity. Then the contractors who are responsible for the completion of the bridge must follow those plans accurately to ensure a positive result.
The advantages and disadvantages of arch bridges are essential to consider when building a span for travel. This information can then apply to other areas of life, such as building a roof or installing a window because the downward forces are essential the same in each scenario.
Keith Miller has over 25 years of experience as a CEO and serial entrepreneur. As an entrepreneur, he has founded several multi-million dollar companies. As a writer, Keith's work has been mentioned in CIO Magazine, Workable, BizTech, and The Charlotte Observer. If you have any questions about the content of this blog post, then please send our content editing team a message here.