Stone has been used extensively for construction since ancient times. The versatility of this material makes it ideal for construction of large building, monuments and other architectural structures. Stones are able to bear indefinite load when placed in the form of arch because of its incredible strength while under compressive force. Thus the ancient Romans used arches while building aqueducts and bridges. This tradition continued until the renaissance era. Today there are many stone arch bridges throughout the Europe.
The keystone plays an important part in arch stone bridges as it holds the arch together. In the absence of the keystone, the arch would not be able to withstand the pressure and would collapse. It is a wedge shaped stone piece which is at the apex of the arch and is placed in the end of the construction of the arch, as it fastens all the stones into their positions. The arch cannot be self supporting until the keystone is placed, yet the keystone is not a weight bearing stone and experiences the least stress.
The masonry techniques used in arch bridges differed considerably. A basic stone arch bridge was built using wedge like or flat fieldstones which were laid up to form an arch. But most architectures and bridge builders used cut stone for the arch ring as proper shaping of the ring stone resulted in a perfectly shaped arch. The spandrels made of rubble or ashlar (rectangular cut stone blocks.) didn’t play a major role, except they retained the fill for the roadway. Architectures would first build a wooden arch, upon which the stones for the arch were laid. This gave a proper shape to the arch. One the bridge was completed, the wooden arch was removed.
Arch Bridges: Pont Du Gard
There are countless stone arch bridges throughout Europe, but one of the most remarkable bridges is the famous Pont Du Gard Bridge. This bridge is the perfect example of architectural and engineering skills. Located in South France, this bridge is a man-made marvel that has been recognized as a heritage site by UNESCO. This amazing structure is visited by many tourists wanting a glimpse of its sheer brilliance.
This man-made structure is made from aqueduct stone as is devoid of mortar use. Aqueduct stones weigh nearly 6 tons thus there was no need for mortar. The bridge comprises of three levels, Upper level that is 275 meters long, the Middle level which is 242 meters long and the Lower level which is 142 meters long. The mid level is 4 meters thick whereas the lower one is 6 meters thick. The engineers and architects of the bridge curved the upper levels of the bridge in upstream direction in order to increase the resistivity of the bridge against the water flow. It is remarkable to note that without the use of modern machinery and equipments, engineers were able to build such a magnificent structure. Pont Du Grad is an example of architectural brilliance and engineering skills of the Roman Empire.