As per our last article How to Structural Design a Building/House Step by Step Part-1 & 2. In this article, we design slab load, slab depth, slab steel design. Now in this article, we calculated a slab beam design.
Slab Beam Design
Below steps slab beam design.
1. Beam Thickness & Depth Design
2. Find Ast
3. Slab beam Steel Design
Beam Thickness & Depth Design
Mu lim = 0.138 . fck . b d2 | SP. 16, P-10, Table-c
d = 2 b
Find Ast Min Steel Design
Ast = (pt / 100) x b x d | Sp. 16, P – 229
Pt= 50 (fck/fy)x( 1-√(1-(4.6xMu/Fck b.d.d)))
Beam Ring Design
Vus = Vu – τc . b . d
Vu = w l /2
τc | IS 456-2000, P-73, Table-19
Sv = (0.87 x fy x Asv x d) / Vus
Check for Maxminum Spacing
1. 0.75 d
2. 300 mm
3. Sv = (0.87 x fy x Asv) / (0.4 x d) | IS : 456 – 2000, P 47
Beam Thickness & Depth Design- Example
Total Weight = As per Slab total Weight Mu X Area = 11.82 kn.m x 3.0 x 3.0 = 89.438 kn.m.
Beam load per running. m = 89.438 kn.m. / (3.0 + 3.0 + 3.0 + 3.0 ) = 14.031 Kn.m.
Along Lx Beam weight = 7.453 x 3.0 = 22.36 kn.m.
Along Ly Beam weight = 7.453 x 3.0 = 22.36 kn.m.
Along Lx Find Breadth & Depth
Mu lim = 0.138 . fck . b d2
22.36 x 106 = 0.138 x 20 x b x (2b)2
Breadth = 138.9 mm ≅ 230 mm
Depth = 2 x 230 mm = 460 mm
Along Ly Find Breadth & Depth
Mu lim = 0.138 . fck . b d2
22.36 x 106 = 0.138 x 20 x b x (2b)2
Breadth = 138.9 mm ≅ 230 mm
Depth = 2 x 230 mm = 460 mm
Find Ast Min Steel Design
Along Lx
Ast = (pt / 100) x b x d | Sp. 16, P – 229
Pt= 50 (fck/fy) x ( 1-√(1-(4.6 x Mu / Fck b.d.d)))
Pt= 50 (20 / 415 ) x ( 1-√(1-(4.6 x 22.36 x 106/ 20 x 230 x 4602 )))
Pt = 0.131 %
Ast = ( 0.131 / 100) x 230 x 460
Ast = 138.6 mm2
Select = 12 mm dia
ast = ( π / 4 ) x 122 = 113.04 mm2
No Bars. = 138.6/ 113.04 = 1.22 ≅ 2 Nos.
2 Nos – 12 mm Dia
Along Ly
Ast = (pt / 100) x b x d | Sp. 16, P – 229
Pt= 50 (fck/fy) x ( 1-√(1-(4.6 x Mu / Fck b.d.d)))
Pt= 50 (20 / 415 ) x ( 1-√(1-(4.6 x 22.36 x 106/ 20 x 230 x 4602 )))
Pt = 0.131 %
Ast = ( 0.131 / 100) x 230 x 460
Ast = 138.6 mm2
Select = 12 mm dia
ast = ( π / 4 ) x 122 = 113.04 mm2
No Bars. = 138.6/ 113.04 = 1.22 ≅ 2 Nos.
2 Nos – 12 mm Dia
Beam Ring Design
Lx Beam Self Wight = (b x d x l) x Density of RCC = ( 0.230 x 0.460 x 3.0) x 25 = 7.94 Kn.m.
Ly Beam Self Wight = (b x d x l) x Density of RCC = ( 0.230 x 0.460 x 3.0) x 25 = 7.94 Kn.m.
Lx Total Weight = 22.36 kn.m. + 7.94 kn.m. = 30.3 kn/m.
Ly Total Weight = 22.36 kn.m. + 7.94 kn.m. = 30.3 kn/m.
Along lx Vu = ( w . l)/2 = ( 30.3 x 3) / 2 = 45 kn
Along ly Vu = ( w . l)/2 = ( 30.3 x 3) / 2 = 45 kn
Along with lx pt = 0.131%
Along with ly pt = 0.131%
Along with lx τc = 0.28 N/mm2 | IS 456-2000, P 73, Table -19
Along with ly τc = 0.28 N/mm2 | IS 456-2000, P 73, Table -19
Find Vus
Vus = Vu – (τc x b x d)
Along with lx
Vus = 45 – (0.28 x 230 x 460) = 15826 N
Along with ly
Vus = 45 – (0.28 x 230 x 460) = 15826 N
Beam Ring Design
Consider 2 – legged 8 mm ∅ Vertical stirrups of Fe – 415 steel
Asv = 2 x (π /4) x d2 = 2 x (3.14/4) x 82 = 100.51 mm2
Sv -1
Along lx, ly = (0.87 x fy x Asv x d) / Vus = ( 0.87 x 415 x 100.51 x 460) / 15826 = 1054 mm.
Sv -2
Along lx, ly = 0.75 x d = 0.75 x 460 = 345 mm
Sv -3
Along lx, ly = 300 mm | IS 456-2000, P-47
Sv -4
Along lx, ly = (0.87 x fy x Asv) / 0.4 b = (0.87 x 415 x 100.51) / 0.4 x 230 = 238 mm
Minmum sapcing of vartical strips = 238 mm
Slab Beam Design
Slab Beam Calculation /Design Excel Sheet – Download
Video tutorial for better understanding:
Also, read: How to Structural Design a Building/House Step by Step Part-1 (One Way Simply Support Slab)
Also, read: How to Structural Design a Building/House Step by Step Part-2 (Two Way Simply Support Slab)
Also, read : How to Structural Design a Building/House Step by Step Part-4 (Column Design)
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