Question

1. A 3.5 m clear span singly reinforced cantilever beam has a rectangular section of b=300mm and D=500
mm is reinforced with 2 bars of 32 mm diameter and 1 bar of 25mm diameter in the tension zone. The
live load taken by the beam is 19 kN/m. Check if the beam is safe to carry the above load . Use M25
and Fe500.

Answer 1

Answer:

Given that:

A 3.5m clear span singly reinforced cantilever beam has a rectangular section of b=300mm and d=500mm is reinforced with 2 bars of 32 mm diameter 1 bar of 25mm diameter in the tension zone.

Here

b=300mm and d=500mm.

  

Assuming clear cover 25mm

eff cover =25+32/2=41mm

assuming it to be 50mm

d = D-50mm

=450mm

Smaller of above effective length = 3.5 + 0.45/2 = 3.725m

Self weight of beam = 0.3 * 0.5 * 25

=3.75kN/m

By assuming unit weight of concrete as

Live loade = 19 kN/m

Total loade = 3.75+19

= 22.75 kN/m

Total factored lode = 1.5 * 22.75

= 34.125 kN/m

For a cantilever beam,Maximum bending moment

=

ultimate moment = 239.94 kNm

Moment that can be taken by this beam

Here

Moment capacity of the given beam is only 90 kNm.Ultimate moment comes is 239.94kNm so the beam is not safe to carry the livelod 19kN/m.