An excellent example of a stone arch bridge is the Landwasser Viaduct in Switzerland. It was built in 1902 as part of a daring railway track that passes through mountains. It consists of six high arches, over which the train is carried and underneath which far below, there is a river.
An arch bridge is among the oldest types of bridges. It has been in existence for thousands of years. Back then, these bridges were mostly made of bricks or stones, and were highly popular. Later, with the industrial revolution and with the introduction of newer materials, other advanced bridge types and designs were introduced. However, arch bridges are still in use. With the introduction of concrete, steel, and other new materials, their arches are built on a much larger scale.
There are many advantages of incorporating this semicircular structure in a bridge. They are as follows.
This bridge is characterized by its arch or curved design that gives it strength. As a result of this curving or bending, the load forces are not pushed straight downwards. Rather, they are carried or transferred along the arch curve to the supports (or abutments) present at each end of the bridge. This semi-circular structure, thus enables a higher level of resistance to the bending forces which may have altered or changed the bridge. In other words, the forces acting on the bridge (horizontal) are distributed equally.
Options in Building Materials
They can be built using a wide range of materials that include natural ones like stones, bricks, etc., as well as man-made materials like reinforced concrete or steel. Natural or local materials aid in sustainability and are strong in compression. However, they are not able to withstand much force in tension and hence, masonry arch bridges are designed to be constantly under compression.
Strengthen with Usage
These bridges tend to strengthen with increased usage. Ancient arch bridges had a keystone (final top stone) which once put in place, undergoes compression, thus making the bridge stronger. Furthermore, the abutments also help enhance the sustainability of these bridges. A great deal of dead weight is introduced above each arch, thus supporting loads as well as gaining strength.
In spite of the various advantages of the arch bridge structure, there are also a few disadvantages that cannot be ignored.
Limited Span Length
These bridges have a limited span length. The arch's size and the materials being used, can determine the weight that the bridge is capable of bearing. Such bridges can be built only of certain sizes. More arches have to be built or other reinforcement materials may have to be added to support the bridge load.
Maintenance is Needed
When natural materials are used for building, additional maintenance or care is needed. This is because the impact of wind forced on the structure or the wind load, causes the bridge to bend and move, which in turn causes the binding mortar to crack and decompose in the long run. Thus, frequent care becomes necessary. This may further give rise to extra maintenance costs.
Long Construction Time
Arch bridges have a long construction time. For the proper and normal functioning of these bridges, they have to be built in a particular way. Thus, their construction requires more time, mostly noticed in the case of natural materials. Also, more labor may be required.
Constraints on Location
Arch bridges can be constructed in only certain locations where the foundation on both sides is solid and stable. This is because this type of bridge needs more support from its sides. However, it is said that in some modern bridges (made of steel or reinforced concrete), the load is tolerated by tension within their structure. Due to this, the transfer of the horizontal load forces to the abutments is reduced or canceled, thus allowing the construction of this bridge type on weaker grounds as well.
We can conclude that the decision of having an arch bridge can be made by considering the aforementioned pros or cons.