What is curtailment of reinforcement in beam, hi guys in this article we know about curtailment of reinforcement in beam and what is curtailment meaning and why do provide curtailment rebar in beam. we know that beam is flexural structure member compromise of compression and tension when it’s undergo bending moment due to applying of vertical axial forces and shear stress.
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Beam have many types like simply supported beam cantilever beam and continuous beam and so many more type. Curtailment meaning is that restricting and limiting of bar.
Curtail bar in beam is a way of reducing the area of tensile reinforcement at points/areas (either on a beam/slab) where bending moment is minimum or zero for the purpose of achieving an economic design.
Curtailment of bars is a way to shorten the length of reinforcement or the tensile bars are curtailed where the bending moment is minimum or zero to achieve an economical design. Let us some discuss about bending moment about beam structure that help you in understanding curtailment.
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● Property structure of beam :- When axial load is acting on simply supported beam resulting compressive and tensile stress. Tensile stress is developed at the midpoint of beam structure in bottom face of concrete fibre and at the Top face of beam junction- joint .
At the midpoint of beam there is positive bending moment that is known as Sagging in which tension fibre in bottom face and compression fibre in top face of beam. Compression fibre bending moment have little effects and easily resist the load applying on it.
But tension fibre in much tension that’s require higher amount of rebar to resist the load. So tension zone is present in bottom face of beam and Top face of both end at beam Junction joint.
Curtailment of reinforcement meaning for beam
Curtailment mean the fact of restricting something or reducing and limiting use of rebar. Reinforcement are curtailed along its length in beam depend on the bending moment at the section.
In other word it is described as to economize the design of flexural (beam) member the tensile bars are curtailed at the section beyond it is no longer required to resist the moment.
Why is curtailment of reinforcement done in beam?
The major reason reinforcement are providing to resist flexure stress. As we know bending moment is not equaly distributed along its length and it is much lower in mid of top face of beam and bottom face at beam junction joint both end so in that Areas where bending moment is minimum or equal to zero the reinforcement in that area are curtailed and not providing of rebar.
In order to make the structure economical the extra part of rebar is of no use to resist moment except making the structural extra safe.
Length of curtailment of reinforcement (rebar)
There is two areas where the curtailment of reinforcement (rebar) is provided
1) Mid point of beam :- top face of midpoint of beam in negative zone there is no need of providing curtailment of rebar (extra bar) along with negative bar in this areas.
But bottom face of midpoint of beam in positive zone and there is need of providing curtailment of rebar (extra bar) along with main bar in this areas. Curtailment length of rebar which was cut in both end is L/8 according to ACI Code.
if total length of span of beam = 20 foot
L/8 part of total span cut in both end
L/8 part of span = 20/8 = 2.5 foot
Cut at both end so = 2.5×2 = 5 foot
●Ans. :- total length of tension Steel provided is equal to 15 foot , and these curtailment piece of tension Steel provided in mid part of the beam 7.5 foot left and 7.5 foot right of beam continuous without breaking along with main reinforcement which was not curtailed.
2) At both end beam-junction point
Bottom face of beam Junction point both end having negative zone so there is no need of providing extra piece of rebar and Curtailment of rebar.
But top face of beam injunction point at both end are in positive zone so there is need of providing curtailment of rebar and extra bar at both end. According to American concrete Institute code length of curtailment of rebar in that areas is equal to L/3 at both end.
if total length of span of beam = 20 foot
L/3 part of total span cut in both end
L/3 part of span = 20/3 = 6.66 foot
6.66 feet length of curtailment piece of rebar (extra rebar)provided at top face of beam Junction point at both end along with main reinforcement so 6.66 foot top face of negative zone is without extra rebar or curtailment bar.
So in this calculation is there is economise of using reinforcement.
Total span at both upper face and bottom face using two curtailment rebar in each face.
Total span = 20 ×4 =80 foot two curtailment piece top and two at bottom)
Length of using curtailment piece
At beam junction = 2×2 ×6.66= 26.64 foot
At mid of beam = (2×20) _2×2×2.5 foot
At mid point = 30 foot
Total Length of using curtailment piece= 30 +26.66 = 56.66 foot
Length of span which was not used = 80_56.66 foot = 23.34 foot
So there is no need of using 23.34 foot of rebar in beam designing that is beneficial and economical for all people that minimise your cost of building structure.