Effective Span
It is the portion of beam that effectively participate in bending.
Simply Supported beam
Continuous Beam
Cantilever Beam
Rigid Frame
Here Leff taken c/c distance between the columns
Longitudinal Reinforcement
Case a) Longitudinal Tension R/F
Case B) Longitudinal Compression R/F
Asc, min = no Value
However, Minimum two bars are provided to impart ductility and to hold the stirrup (Hanger Bars).
Asc, max = 4% of gross area = 0.004bD
Side Face Reinforcement
It is provided to take care of shrinkage along the longitudinal direction which leads to development of cracks & to avoid lateral buckling.
Side Face Reinforcement (SFR) = 0.1 % gross web area (0.001 bD), Provided on both sides equally @ spacing not more than (<) 300 mm. It is provided when depth is more than 750 mm (D>750mm).
Minimum Nominal Cover/Clear Cover
Minimum Nominal Cover is governed by following criteria:
a) Type of structural member (beam, Slab, Footing, Columns etc)
b) Exposure condition (Mild, moderate, Extreme, severe etc)
c) Fire resistance (in hours) (30 min-4 hrs)
d) Maximum Permissible width in RCC Structure.
{Or diameter of bar whichever is greater}
Horizontal Spacing of Reinforcement
a) Minimum Horizontal Clear Spacing is kept as maximum of
- Diameter of Bar (if bar is equal dia)
- Diameter of larger bar (if bar are of different diameter)
- Nominal size of coarse aggregate +5mm
b) Maximum Horizontal c/c (It depends upon grade of steel)
Deflection of Beam
Total deflection of beam is due to the following
Total Deflection = Deflection due to Loading + Deflection due to shrinkage + Deflection due to creep + Deflection due to Temperature
Where, Deflection due to creep and Shrinkage is long term deflection and Deflection due to temperature and Loading is short term deflection.
a) The final deflection due to all types of loads including the effect of creep, temperature, shrinkage should not exceed “leff/250“
[Dead load+live load+Temperature+Creep+Shrinkage]
b) The deflection including the effect of temperature, creep and shrinkage occurring after the erection of partitions and finishes must not exceed {“leff/350 or 20mm”}min
Deflection Control
Since calculation of deflection and keeping it within the permissible limit needs a lot of calculations, hence IS 456 has simplified this analysis,
If leff/d ratio satisfy the following condition then beam is safe for deflection.
