Steps for design of
cantilever beam
1.
Basic data
Enter the values of b, clear span(L), fck, fy, clear cover, superimposed load, Overall depth (D), dia. Of bar(∅) and calculate effective depth provided,
∅
dprov = D – clear cover -
2
2.
Effective span
Leff = min. of { L + 𝑏𝑠 and L + 𝑑}
2 2
3.
Factored SF & BM
Self wt. of beam = b*D*unit wt. of concrete Factored load, wu = 1.5*(S.D.L + self wt.)
Factored BM, Mu
= 𝑤𝑢∗𝐿2𝑒𝑓𝑓
2
Factored SF, Vu = wu * Leff
4.
Design parameters
Find 𝑋𝑢𝑚𝑎𝑥= 700 &
𝑑 1100+0.87∗𝑓𝑦
Qlim = 0.36*𝑋𝑢𝑚𝑎𝑥 ∗ (1 − 0.42 ∗ 𝑋𝑢𝑚𝑎𝑥) ∗ 𝑓𝑐𝑘
𝑑 𝑑
·
Find the effective depth required to satisfy the
deflection criteria as follows:
𝐿 = 7 * M.F ((For cantilever beam as per IS
456-2000, pg-37)
𝑑
Find M.F from graph given on pg-38 of IS 456-2000)
d = 𝑳
𝟕∗ 𝑴.𝑭
·
Find effective depth required for balanced section as follows:
𝑑𝑏𝑎𝑙
= √ 𝑀𝑢
𝑄𝑙𝑖𝑚 ∗ 𝑏
Check:
Effective depth provided (dprov) should be more than the depth required to satisfy the deflection criteria as well as depth required for balanced section. If not, increase the overall depth.
·
Calculate percentage of R/F required:
𝑓𝑐𝑘 4.6 ∗ 𝑀𝑢
𝑝𝑡𝑟𝑒𝑞 = 50 ∗
𝑓𝑦 ∗ {1 − √1 − 𝑓𝑐𝑘 ∗ 𝑏 ∗ 𝑑2}
Ast,req = pt∗b∗d
100
A = N*pi*φ2
and check A <A
st,provided 4
5) Design of shear
R/F
st,req
st,provided
Same as singly reinforced beams (Check the video in the channel below)
6) Check for deflection
As per IS 456-2000, to satisfy the deflection critieria,
·
(L/d)actual < (L/d)permissible
·
(L/d)permissible = 7 * M.F (For
Cantilever beams as per IS 456-
2000, pg-37)
And M.F from graph on pg-38 of IS 456-2000.
7) Check for development length
Same as singly reinforced beams (Check the video in the channel below)
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