Types of Arches

Intrados is a combination of arcs of various radii. Based on the number of centres, arches may be classified as follows:

1. One-Centred Arch

Under this category, semi-circular arch, segmental arch (which is less than a semi-circle), horse-shoe arch (which includes more than a semi-circle) and stilted arch (which consists of semi-circular arch with two vertical portions at the springings) are included. Figure 19.2(a–d) schematically represent these arches.

Figure 19.2 Types of arches

2. Two-Centred Arches

There are different types of two-centred arches. Three of them are shown in Figs. 19.2(e), (f) and (g). They are as follows:

(i) Blunt Arch

The two centres of the arch are within the arch itself.

(ii) Gothic Arch

This is also called as equilateral arch. Here the radius of intrados are equal to the span length and the centres are on the springing line.

(iii) Acute Arch

In this type, the centres of the arch are outside the arch.

3. Three-centred Arches

Here there are two types. In the first type, the central portion of the arch is drawn with one centre and the other two centres are used for making up the ends of the arch (Fig. 19.2(h)). In the other type, the procedure is reversed (Fig. 19.2(k)).

4. Four-centred Arches

Here the centres for the lower section do not coincide as in the case of three-centred arches (Fig. 19.2(i)).

(i) Two Cusped Arch

It is used mainly for decorative purposes (Fig. 19.2(j))

(ii) Elliptical Arch

It has an elliptical shape for its intrados.

(iii) Flat Arch

In this type of arch there is no size (Fig. 19.2(k))