ARCHES - Introduction and types of arches

ARCHES

Arches are the upward convex shaped curved structure comparatively stronger than beams, supported at ends to resist both horizontal and vertical displacements.

Arches are economic for long span compared to beam

1.     Bending moment of the beam always varies with square of the span.

2.      In case of arches the total moment is always obtained by moment below the load detected by the horizontal thrust action at the same span. (M-Hy)

By the above discussion we can conclude that for the same amount of the load Arch structure is efficient than compared to that of long beams.

Arch Action

1.     Arch is basically a compressive member (zero tensile stress member), whenever the external load is applied on the arch structure it is generally resolved into two components

·        Axial compressive stress

·        Thrust at the base instead of bending moments

2.   The important feature of the arch action is one in which the horizontal reaction at the supports is the governing force to resist the externally applied load by preventing arch from collapsing.

3.  As the height of the arch decreases the horizontal reaction at the supports increases in order sustain the serviceability of the arch for the applied load.

Types of Arches

Basically, there are three types of arches used in practice they are

1.     Two hinged arches

Ø The arch supported with only two hinges.

Ø It is statically indeterminate of degree 1.

Ø It is structurally easier to construct.

Ø The normal thrust along the rib which is compressive in nature causes the rib to shorten.

Ø It is likely developing stresses due to sinking of support.

2.     Three hinged Arch:

Ø This is an arch which consists of three hinges.

Ø It is statically determinate structure.

Ø This arch can be analyzed easily, but difficult to construct.

Ø Since it is determinate in nature, there will be no stresses due to sinking of support.

3.     Fixed Arch:

Ø It is the arch which is supported by fixed supports at both the ends.

Ø The degree of redundancy is 3.

Ø Since the fixed ends are restraint for all reactions at both the ends, hence it creates additional stresses in the arch.

Ø This arch can be analyzed by using strain energy method, least energy method, column energy method etc.…