Arch Bridge Diagram: How Do Arches Transfer Load?
An arch bridge is a type of suspension bridge which consists of two or more arched spans connected together with beams and trusses. The term “arch” refers to the vertical span of the structure. A typical arch bridge is made up of three spans; one above and below ground level, and another at grade.
These spans are supported by a series of columns and piers. The purpose of these supports is to keep the structure from tipping over when it’s not being used. Arch bridges are especially useful when spanning wide valleys. They are also great for spanning over waterways. Many famous bridges such as the Brooklyn Bridge in New York and the Forth Bridge in Scotland are arch bridges. The traditional design of an arch bridge is known for being strong and rigid, but also elegant
The purpose of an arch bridge is to channel the weight and force of the road above it into the ground.
Advantages of Using an Arch Bridge
Arches are stronger than other bridge types under the same weight. No arch bridge can be permanently damaged or destroyed by earthquakes or the elements. The bridge’s abutments and piers act as pillars which support the weight of the bridge.
The arch, or vault, is the center of the bridge where the road or pathway is located. The weight of the bridge is channeled through the vaults and into the abutments and piers at each end.
In this way, the weight of the bridge is transferred down through the bridge structure into the ground. The downward force is distributed around the abutments and piers and into the ground below. Stresses from earthquakes and other major events are absorbed into the ground, making the bridge very strong against external damage.
How Does an Arch Bridge Work?
The bridge structure consists of an upper and lower horizontal span which support the vertical arch. This arrangement distributes the weight of the bridge into the ground through the pillars or columns at each end of the bridge. Each span may consist of a high arch, low arch or any combination of both.
The high and low arches allow the bridge to span a wider range of river heights. The relatively narrow pillars support the ground and reduce the possibility of the bridge being damaged. This type of bridge is particularly strong and flexible which make it very popular.
Why Do Bridges Have Arches?
The strength of an arch is derived from the strength of its material. The shape of an arch, however, makes it inherently strong and rigid. Arches can be used for many different types of bridges.
The type of material used for the bridge will determine how heavy the bridge can be and how far it can span. The basic design of an arch bridge will ensure that the bridge is durable and strong. The strength of the bridge, however, also makes it very rigid. This means that the bridge does not move or bend easily. The advantage of a rigid bridge is that it will stay in place and not move, even when heavy vehicles pass over it. This rigidity, however, can cause the road to be uneven and bumpy. This can be a particular disadvantage to cyclists.
Other Types of Bridge Designs
In addition to the traditional beam bridge and the arch bridge, there are several other bridge types. These include:
Continuous Span Bridge – A continuous span bridge has no supports or columns. Instead, the bridge is constructed with a series of arches which support the deck. The deck of the bridge can be constructed from steel, concrete or a similar material.
This arrangement is sometimes known as a ‘beam and slab bridge’. Continuous span bridges are suitable for locations where supports or columns would be problematic. This type of bridge is also known as a ‘Pin Connected Deck Arch Bridge’.
Cantilever Bridge – The cantilever bridge is similar to the continuous span bridge in that it has a rigid design. It has cantilever arms which support the bridge deck. The advantage of the cantilever bridge is that it is very strong and can span gaps where other bridges would not be possible.
The disadvantage of a cantilever bridge is that it is rigid and unsuitable for locations where the roadbed needs to be well supported or rebuilt often. This type of bridge is also known as a ‘Cantilever Deck Arch Bridge’.
Suspension Bridge – The suspension bridge is the type of bridge that most people think of when they think of a bridge. The design of a suspension bridge uses cables, which span between towers, to support the bridge deck. The ends of these cables are attached to the ground at each end of the bridge.
The weight of the deck is supported by these cables. These types of bridges require tall towers to support the cables and a stiff deck to transfer the loads from the deck to the ground. The stiffer the deck, the better the bridge will handle heavy loads. The deck is often reinforced with steel. This type of bridge can handle heavy loads and span long distances. The main disadvantage of this type of bridge is that it must be supported on both sides and the cables must be secured at each end. The cables can also be vulnerable to extreme loads or weather conditions. These bridges are often very expensive to build. This type of bridge is also known as a ‘cable-stayed bridge’.
Other Bridge Types – There are many other types of bridges which fall into more specialized categories. The Michigan Toll Bridge Photos website looks at some of these other specialized types of bridges.
Why are Some Bridge Girders Orange?
While not exactly a common sight, some bridge girders and beams are painted orange. These girders are painted orange for a couple of different reasons.
The first reason is that painting a girder orange makes it easier to see the girder against the natural backdrop of the environment. Some girder types are very similar in color to their natural surroundings making them difficult to see. Painting the girder a bright color makes it much easier for drivers, pedestrians and workers to see the beams when they are nearby.
The other reason some beams are painted orange is to provide additional safety for people working close to the bridge. This is especially important on bridges which carry traffic. If a person working near the bridge is struck by a vehicle there is a good chance they could be killed.
Painting the beams a highly visible color makes it more likely that drivers will notice the beams and avoid them.
Bridge girders are painted in several different colors. Some girders are painted blue, yellow, red and even green. Some government entities specify that girders should be a particular color for the benefit of drivers and workers.
Each of the major U.S. Highways has its own unique hue.
The base color for Interstate Highways is yellow. A silver stripe is added to the outside edges of each lane. The stripes help drivers stay in their lanes and keep them from drifting into another lane.
Blue girders are most commonly found on U.S. Highway routes.
Most systems, such as state turnpikes, county-controlled roads, etc., will use yellow girders. Red girders are also common, but these are typically reserved for state-controlled roads.
Bridge builders and highway officials can select from a range of colored beams to meet traffic safety needs.
Safety is a top priority when building any bridge and selecting the right colored beams can help to make sure everyone stays safe.
How are Bridge Decks Constructed?
Bridge decks are typically constructed from reinforced concrete. However, bridge decks can also be made out of other materials such as bitumen, bricks, steel, wood and even grass.
The specific choice of material used in the construction of a bridge deck will depend on several factors including cost, practicality and weight. Each material type comes with its own benefits and drawbacks.
One of the most popular materials for bridge decks is concrete. This material is easy to construct, relatively inexpensive and strong. It can also be made to have a variety of textures or patterns if desired.
There are two main types of concrete that can be used in bridge construction:
Portland Cement – This is the most common type of concrete used in highway construction. It is relatively strong and inexpensive. It is usually gray in color.
Rapid-hardening Concrete – This type of concrete is used in areas where speed of construction is a priority. It is stronger and more expensive than Portland cement concrete. It is usually beige or brown in color.
Other materials that can be used for bridge decks include:
Brick – This type of material is commonly used in historic bridges located in city centers.
Steel – Depending on the strength and thickness of the steel, this material can be very strong. As it is less expensive to install than some other materials, it is often used for small bridges located in rural areas.
Grassed – In areas where a bridge is being built over low-traffic volume roads and the waterway does not require a large clearance, a grassed bridge deck can be installed. These require very little maintenance and are cheaper to construct than most other types of bridge decks, but they can only be used where the waterway requires a low clearance.
Painting and Restoring Bridge Decks
Painting and restriping a bridge deck may be necessary to extend the life of the structure or improve its appearance.
Painting a bridge deck can help to prevent the concrete from eroding. The surface of a concrete bridge deck can be very rough. When vehicle tires roll over the bridge, they can cause small bits of concrete to break off and grind against the top layer of the deck.
Eventually, this grinding process can eat through the top layer of concrete and cause the underlying layer to become exposed. Once the underlying layer has been compromised, it can no longer support the weight that rests on it. This can lead to the bridge deck collapsing.
Painting a bridge deck can prevent this from occurring as the paint creates a protective barrier between the eroding materials and the underlying concrete.
Painting a bridge is relatively simple as long as the necessary precautions are taken. First, the bridge must be closed to all traffic and all vehicles parked away from the work area. The bridge should be swept clean of any loose materials before the paint can dry properly.
The surface of the bridge should then be inspected for any damage. All damaged areas need to be repaired before painting can begin.
Once the surface has been prepared, the painters can begin applying the paint. Painters typically use an oil-based paint as it offers superior protection against erosion. The paint needs to be applied in multiple coats to ensure that it adheres to the bridge properly.
It is very important that no paint drips form as these can erode the bridge deck. Once the painting process is complete, the bridge should be inspected daily for the first week to ensure that no paint drips have formed. Once the painter is confident that all paint drips have been removed, the bridge can be opened to traffic.
In addition to extending the life of a bridge deck, painting can also improve its aesthetics. Where road crews have neglected to paint a bridge, the concrete can take on a gray or beige color as traffic causes the surface to erode. In some cases, the concrete can become so badly damaged that it resembles an unpolished granite stone.
Painting a bridge a contrasting color can make the bridge appear to stand out instead of blending in with the landscape. Some bridge painters even apply artistic designs to their work as a way to add a unique artistic touch.
Striping a bridge deck can also be done to improve its appearance. While most bridge decks are painted a solid color, they can also be striped to create a wide range of visual effects. Typically, road crews will paint alternating horizontal or vertical lines on the bridge deck.
In some cases, the lines may be of varying widths.
Striping a bridge deck is a relatively simple process that involves nothing more than a paint sprayer and a stencil.
Sources & references used in this article:
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