These segmental arch bridges had one crucial design advantage which separated them from ordinary semicircular bridges — they enabled bridge builders to more arch of the bridge much higher and lower the mass of the entire structure.
These changes enabled bridges to much easier survive stresses of floods and strong rivers. During the life of Roman Empire, they built many wondrous bridges, lengthy aqueducts with multiple arches, bridges with flood openings on the piers, and many others. As centuries went on, medieval architects improved the designs of Romans, creating arch bridges with narrower piers, thinner arch barrels, lower span-rise rations, pointed arches, and increased spans of arches increasing to over 70 meters, most famously on the bridge at Trezzo sull'Adda who was in use from 17th to the end of 18th century.
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, 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, 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. 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.
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. 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. Mobile Newsletter chat dots.
Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Prev NEXT. Civil Engineering. Cite This! Print Citation. It can be of any shape, a parabolic, catenary, straight lines, etc. But how can we decide the shape? A shape of an arch is one of the most critical thing. The shape depends on the type of load applied on the arch. If it is just a point load at the center then it will be two straight lines as shown in figure 2. If two point loads then the shape will be as shown in figure 4.
If it is uniformly distributed load then the shape of the arch will be a parabolic one. How can we come up with such shapes and why? Take a normal cable or a thread and tie it up at two ends but don't pretension it. Then apply different loading like a point load, half uniformly distributed and a point load, full uniformly distributed, etc whatever you can imagine and see the shape of the cable.
If you invert this shape and see it will be the best possible shape of the arch for that particular loading. These arches are called funicular arches. Funicular means a particular shape of chord in tension which you already found when applied a type of load.
These particular shapes are the most efficient. Now one can ask why? What happens when you load a cable? It takes all the load in pure tension and it is because of it's flexibility. This gives the most efficient design possible. So that is why if we give a similar shape to arch for a particular loading you will find only compression acting in the arch.
Isn't that awesome? We will not be dealing with bending and shear forces anymore..!! But wait that is not possible. We cannot give any desired shape to an arch. Because it is in compression.
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