Installation of Centering for Arches

The construction of arches is commenced at their springing points and is brought up uniformly towards the crown, whereas the key block is finally fixed and inserted. Centering is the temporary structure needed to support brick, stone or concrete arch during its construction, till it has gained enough strength. The centering is installed in such a way in which its upper surface corresponds along with the intrados of the arch. For minor works, centering might be made of mud masonry constructed to match along with the inner soffit of the arch, and then plastered. This masonry is dismantled later while the arch has been constructed and cured.

The common centering is made of timber or steel. Wooden centering is the easiest and cheapest, used for moderate span. It is simple to construct and easy to dismantle and it can be used various times. Figure 14 shows a thick wooden plank, along with horizontal bottom and the upper surface shaped to the underside of the soffit. Such a plank is called as centre or turning piece. Its width is generally 10 cm, and is supported on vertical timber posts known as props, with wooden wedges to tighten or loosen the centering.