Arch System and Arches
Arch is a curved structure designed to carry loads across a gap mainly by compression. The mechanical principle of the arch is precisely the same as that of the portal frame. The straight pieces of material joined by sharp bends are smoothed into a continuous curve. This increases the cost of construction but greatly reduces the stresses.
The geometry of the curve further affects the cost and stresses. The circular arch is easiest to construct, the cattery arch is the most efficient. Arches can be three pinned, two pinned or rigid.
– It is important to minimize the arch THRUST so as to reduce the dimensions of the tie rod, or to ensure that the soil will not move under the pressure of the abutments.
– The THRUST is proportional to the total LOAD & to the SPAN, and inversely proportional to the RISE of the arch.
– In arches rise to span ratio should not be less than 1/8 and Riser minimum should be 1/8 of the span & 2/3rd maximum.