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Our Ask an Engineer Q&A series was created to answer questions we get asked by design professionals in the AEC industry—about using natural stone.
Category: Stone Engineering
Q&A: What are some design/engineering considerations for stone arches?
Arches can be broken down in two categories:
1. Self supporting arch (True arch)
2. Hung arch
Ideally, True arches are always in compression. These arches can be made of one piece if the span is manageable or multiple pieces for larger openings and more curved shapes. A keystone is used at the apex that locks all the stones in position and creates the continuous line of force that allows for arching behaviour. The compression forces in the arch produces horizontal thrust at the spring points of the arch which need to be resisted by building structure. The presence of thrust leads to a fundamental difference in behaviour between arches and beam–bending moments in arches are generally eliminated, as long as the curvature is properly designed, and matches the load distribution. Advantages of arches over beams increase as the length of a span increases. The presence of thrust requires structure at the spring point that can resist the horizontal force. During construction of such arches, a temporary formwork is required that supports the stone pieces until the keystone is placed.
Hung arches are individually supported cladding pieces. More coordination of the backup structure is required for these types of arches since all of the stonework needs to be anchored to the backup structure with load-bearing connections. During construction, no temporary formwork is required since the stones are fully anchored and supported as they are laid up.
Answered by: Afsheen Khan, P. Eng., Senior Structural Engineer
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