Jack Arch Floor Of Concrete

Construction of upper floors cont b.

Jack arch floor of concrete.

Jack arch roof construction where trapezoidal reinforced concrete beams are used at intervals between which hollow terra cotta blocks form small elongated multiple vaults. The rise of the arch is kept 1 12th of the span. Jack arch floor consisted of i section steel beams supported on gap and walls between i sections beams filled with concrete arch. The second type of arch is the major arch where span rise and loading may exceed those of the minor.

These floors are formed through constructing brick or concrete arches called jack arches on the lower flanges of mild steel joists. Alternate names are flat arch and straight arch. Above them concrete fill is laid providing a level surface upon which the flooring finish can be if there is another level in the structure. Concrete arches may be built either plain concrete or reinforced.

Cement concrete jack arch flooring is made of 1 2 4 cement concrete supported on the lower flanges of m s. A jack arch is a structural element in masonry construction that provides support at openings in the masonry. Instead they are flat in profile and are used under the same circumstances as lintels unlike lintels which are subject to bending stress jack arches are composed of. Given figure shows a typical jack arch flooring.

It was largely superseded by the introduction of thinner and more fire resistant concrete encased steel and reinforced concrete floors later in the 20th century. The centering consists of 3 mm thick mild steel plate bent to the exact shape of intrados and having holes at the two ends at 75 cm c c longitudinally i e along the length of the plate. The development of concrete jack arches is comparatively simple. The minimum depth at the crown is kept at 150 mm.

The jack arch was an economical way of building a strong non combustible floor structure that could be left as a visible ceiling with a satisfying structural logic. This gives an idea that when the arch is used at lintel level the wieight of the brick masonry above the lintel and the floor loads is carried by the arch. Unlike regular arches jack arches are not semicircular in form. Construction of concrete jack arch floors the construction of concrete jack arch floors is comparatively simple.

At the present time r c c. The centring consists of a 3 mm thick mild steel plate bent to the shape of an arch and having pair of holes at ends spaced at 75 cm c c. The joists are spaced 1 to 1 5 m centre to centre and are supported at their ends either on the walls or on longitudinal girders.