Arch bridges rely on a curved shape for support, allowing them to span great distances without needing additional supports. Their strength comes from their shape, which is always in compression. They can be built using various techniques and materials, including stone, concrete, and steel. Arch bridges are commonly used over water or in areas where it’s difficult to install supports. They can support large loads without disturbing their surroundings and can be built in various arrangements, including with the roadway above or below the arch.
An arch bridge is a type of architectural structure that relies on a curved semi-circular shape for support. Most arches distribute weight equally and are an attractive option for bridges because they can span great distances without needing posts or other support mechanisms to be sunk into the ground. Most post-and-beam bridges, on the other hand, need columns or other supports placed at regular intervals. Arch bridges are common across wide rivers, ravines, and other locations where it may not be practical to install intermediate supports.
Source of strength
The strength of this type of bridge comes from its shape. As the bow presses down from its top, the ground pushes up with equal force. Often additional support is also placed along the shoulders, or sides, of the structure to prevent the arch from bending outward when heavy loads are pressed upon it, but in most cases nothing should touch the ground at any point along the span. As a result, the bow is always in compression, which makes it stiff and retains its strength.
How are they built?
These types of bridges must be built in a way that they can handle the strong compressive forces that help them hold their shape, which often requires some engineering expertise. There are a couple of different techniques, but most involve starting with a basic shape and adding supports along the way. Some builders start with a wooden frame, for example, which helps hold the shape of the arch during construction. This is more common for stone or concrete decks.
Once the full arch is in place, the temporary wood frame can be removed. Ancient stone bridges relied on the final topstone, or capstone, to be put into place for the bridge to experience the compression that would make it strong. Supports along the side of the deck can also help hold its shape as loads press down from above.
Types of building material
Many of the oldest arch bridges are made from cut stone. The ancient Romans and Greeks built a number of these structures as did civilizations across Asia, and many of these bridges still exist today. In some respects this may be due to the material as much as the engineering. Stones are some of the best materials for resisting compression due to the way they absorb and transfer energy. Stone and brick are certainly still used in modern bridge construction, although steel and poured concrete, which can be more easily shaped, are also quite common.
Modern bridges that rely on reinforced concrete can often retain their strength from the concrete itself, meaning no additional supports are needed along the sides. Supports are very common in metalworking, however, particularly if a bridge is designed to support large weights. For example, train trestles often have to be much stronger than bridges used primarily by pedestrians or even passenger cars.
Variants and uses
There are many types of arch bridges and many different ways they can be used. They are perhaps most popular over water as they do not require poles or supports to be sunk halfway, which can be both detrimental to water flow and costly to install and maintain. Depending on how high the arch is, they can also allow for easy passage of water vessels such as boats.
It’s also common to see these bridges over steep gorges, mountain valleys, or anywhere else cars or trains need to go but where it might be difficult to sink supports. When built correctly, they can usually support large loads without disturbing much of their surroundings.
One traditional arrangement has the roadway above the arch, while in others the arch rises above the roadway. In some cases they can even be built on top of each other to cover a much higher height. This is common in the case of aqueducts, which move water from one place to another.
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