Discharging arch

A discharging arch or relieving arch is an arch built over a lintel or architrave to take off the superincumbent weight.

The earliest example is found in the Great Pyramid, over the lintels of the entrance passage to the tomb: it consisted of two stones only, resting one against the other. The same object was attained in the Lion Gate and the Treasury of Atreus, both in Mycenae, and in other examples in Greece, where the stones laid in horizontal courses, one projecting over the other, left a triangular hollow space above the lintel of the door, which was subsequently filled in by vertical sculptured stone panels.

The Romans frequently employed the discharging arch, and inside the portico of the Pantheon the architraves have such arches over them. In the Golden Gateway of the palace of Diocletian at Split the discharging arches, semicircular in form, were adopted as architectural features and decorated with mouldings. The same is found in the synagogues in Palestine of the 2nd century; and later, in Byzantine architecture, these moulded archivolts above an architrave constitute one of the characteristics of the style. In the early Christian churches in Rome, where a colonnade divided off the nave and aisles, discharging arches are turned in the frieze just above the architraves.

The first examples of discharge arches can be seen in ancient Rome. The enormous growth of the capital of the empire forced the architects to build large structures, for which the lintel architecture was insufficient. The arch was then used , which, unlike the beam , did not require great traction efforts for which brick and stone were not suitable. In all periods, the purpose of the discharge arch has served two similar purposes: to relieve the load on areas of the wall built with materials or equipmentweaker, or reduce the weight on the areas in which it was planned to open a gap, although often both functions concurred in the same point.

For this reason, it is not uncommon to see this type of arches in walls of churches or medieval temples of lower budget, both brick and stone , because they allowed to use materials or building systems of less resistance in the enclosures, and thus concentrate the effort economic in representative areas, such as the main facade , or the most delicate areas of the structure, such as corners. It was also frequently used in neoclassical architecture , which meant a return to the flat aesthetics of Greece and Rome, where it was used for the same purpose of expanding the gap then. By using discharge arcs over the holes, thelintel , by supporting less weight, could save a wider span .

With the popularization of steel started in the mid-nineteenth century, the architecture has provided a suitable material to withstand the traction efforts. Since then, the use of load-bearing walls has been abandoned in favor of the more efficient structures of beams and pillars , which is why these types of arches are no longer used today. It is convenient to specify that not all blind arcs are necessarily discharge arcs. Sometimes they have been used for merely decorative purposes, as in the blind arcades of Italian Romanesque architecture, or more recently, in the European fascist architectures of the twentieth century in Germany, Italy and Spain.

The arch of discharge is a useful constructive solution, but not elegant from an architectural point of view, so in the most emblematic buildings, its use used to hide behind a final finish in the form of plaster , plaster or stone cladding.

Source From Wikipedia