What is the reinforced concrete deep beam and where it used?

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:

There are many useful applications of the reinforced concrete deep beam in:

Foundation beam Transfer girders Wall footings Foundation pile caps Floor diaphragms Shear walls

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:

Definition:

• It is simply a member with clear spans in equal or less than four times the overall member depth of beams.
• That member are loaded on one face with concentrated loads within twice the member depth from the support and it is supported on the opposite face so that compression struts can be developed between the loads and supports.
• In case of the building system which is composed of bearing wall and moment frame as upper and lower part, respectively, then a load of the upper part is transferred to the column of another lane through the transfer girder.
• The result is that the transfer girder is to be under very high shear stress and that’s why the depth of it is to be very very deeper.
• For such type of beam, the importance related to the bonding of reinforcement and its anchor has been increased. The main reason behind this anchorage increase is that the high stress following the demand for the bulky and high rise building development and transferred into the concrete structure, which maximizes the concentrated stress at anchorage.

Thank You.

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

1. Foundation beams: The foundation beams transferring the conc column load to the supporting soil.
2. Transfer girder or wall beams at an intermediate floor level of a bldg where some columns are read to be stopped for some particular reasons.
3. Bunker or tanks where the walls itself act as a deep beam

IS Codes provisions of a Deep Beam

• As per IS 456:2000, a beam shall be deemed as deep beam,

1. If 1 ≤ L/D ≤ 2 – For Simply supported
2. If 1 ≤ L/D ≤ 2.5 – For Continuous 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

• For simply supported beam:

Z = 0.2 (L+2D)  If 1 ≤ L/D ≤ 2

Z = 0.6 L      If L/D < 1

• For Continuous beam:

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.

• +ve moment r/f: 

1. It should resist the +ve bending moment & extended w/t curtailment betn the supports.
2. This r/f should be embedded beyond the face of each support.

Embedded length = 0.8 x Development length

= 0.8 x (0.87 fy φ / 4 τbd)

Zone of depth = 0.25D – 0.05l

• -ve moment r/f:

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.

Distribution

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)

• Vertical r/f: Hanging action → Bars or suspension stirrups to be provided.
• Side face r/f: 

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