Concrete arches may be built either plain concrete or reinforced.
Jack arch floor of concrete.
The development of concrete jack arches is comparatively simple.
Jack arch roof construction where trapezoidal reinforced concrete beams are used at intervals between which hollow terra cotta blocks form small elongated multiple vaults.
Given figure shows a typical jack arch flooring.
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.
The rise of the arch is kept 1 12th of the span.
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.
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.
The more common concrete masonry arch is the minor arch where maximum span is limited to about 6 feet 1 8 m with a rise to span ratio not exceeding 0 15 and carrying loads up to 1500 lb per foot of span 21 891 n m.
Construction of concrete jack arch floors the construction of concrete jack arch floors is comparatively simple.
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.
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.
The second type of arch is the major arch where span rise and loading may exceed those of the minor.
The joists are spaced 1 0 to 1 5 m centre to centre and are supported at their ends either on walls or on longitudinal girders.
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.
At the present time r c c.
Jack arch roof is composed of arches of either brick or lime concrete supported on lower flange of r s j s.
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.
Jack arch floor consisted of i section steel beams supported on gap and walls between i sections beams filled with concrete arch.
Unlike regular arches jack arches are not semicircular in form.
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.
Construction of upper floors cont b.
Alternate names are flat arch and straight arch.
