What is the reinforced concrete deep beam and where it used?
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Reinforced concrete deep beam is defined as that members with clear spans in equal or less than four times the overall member depth or regions of beams that are loaded on one face with concentrated loads within twice the member depth from the support and supported on the opposite face so that compression struts can be developed between the loads and supports.
Use of reinforced concrete deep beam:
Definition of deep beam:
A member who is loaded on one face and supported on the opposite face. Hence, compression strut can develop between the loads and the supports.
The clear span of the reinforced concrete deep beam is equal to or less than four times the overall member depth.
Reinforced Concrete Deep Beam:
R/f’ed concrete deep beam
It is a special structure in beams. In the deep beam, the depth of the beam is greater than eff. span. The assumptions of the normal beam are not applicable in a deep beam. As the depth is more, the distribution of the stress is not uniform. So we found some in finding the values of the lever arm & the other related things.
Defn of Deep Beam as per IS 456: 2000
The beam having greater depth in comparison to its eff. span is called as Deep Beam.
Uses of Deep Beam
IS Codes provisions of a Deep Beam
where, L = Eff span, D = Overall depth.
To calculate eff span = c/c dist betn supports or 1.15 x clear span. (Consider less value)
Lever Arm (Z): As the stress distn along the depth of the beam is non-linear. Due to this the lever arm bent the comp & tensile forces can’t be easily determined.
The values of Lever Arm as per IS 456:2000
Z = 0.2 (L+2D) If 1 ≤ L/D ≤ 2
Z = 0.6 L If L/D < 1
Z = 0.2 (L+1.5D) If 1 ≤ L/D ≤ 2.5
Z = 0.5 L If L/D < 1
R/F provision as per IS 456-2000
In the case of deep beam, tension is still to be extended over the whole length of the span & should be well anchored in the support.
Embedded length = 0.8 x Development length
= 0.8 x (0.87 fy φ / 4 τbd)
Zone of depth = 0.25D – 0.05l
Provided to resist the -ve B.M
Termination of r/f – Half of the r/f may be terminated at a dist of 0.5D from the face of the support & remaining should be extended over the whole span.
When 1 ≤ L/D ≤ 2.5, wholly have to distribute the total tensile r/f in 2 zones
Zone – 1 = 0.2D having Ast1 Ast1 = 0.5 (l/D – 0.5)Ast
Zone – 2 = 0.3D (on either side of mid depth) having Ast2 = Ast – Ast1
If l/D ≤ 1 = zone → 0.89 (evenly distributed)
To resist the effect of shrinkage & temp
It also can be provided in vertical direction & horizontal direction.
% of total c/s’al area is to be provided given in IS 456:2000 cl: 29.3.4 → cl 32.4
Min req’ts of r/s in wall as per IS 456:2000 cl 32.4
Spacing of side face r/f ≤ 3 x thkness or 450mm