Design of RCC Slab

SECTION (MM)

PI (constant) LONG SPAN SHORT SPAN COVER MATERIAL: GRADE OF CONCRETE GRADE OF STEEL - MAIN GRADE OF STEEL - SECONDARY LOADS (Kn/m2) : LIVE LOAD FF LOAD PARTITION LOAD MISCELLANEOUS LOAD SAFETY FACTOR: FORCES CONDITION: R 3

3.14159265 6700 4300 15 M15 Fe 415 Fe 415

ASSUME OVERALL THICKNESS OF SLAB EFFECTIVE DEPTH AS PER DESIGN ADOPT EFFECTIVE DEPTH AS OVERALL DEPTH

3.00 0.60 0 0 1.50

125 mm 79.72 mm 105 mm 125 mm

REINFORCEMENT: DIA OF MAIN REINFORCEMENT IN MM DIA OF DISTRIBUTION REINFORCEMENT IN MM DIA OF TORSION REINFORCEMENT IN MM

10 8 8

Reinforcement in middle strip: Steel along short span: Dia of reinforcement Spacing of bars c/c PROVIDE SPACING OF BARS c/c Total area provided Area of tension steel Aty along long span: since required area is greater than minimum required area, hence o.k., provide area

754 mm2 10 mm 104.16 mm 100 mm

O.K.

785.4 mm2 226.08 mm2

Dia of reinforcement Spacing of bars c/c PROVIDE SPACING OF BARS c/c

226.08 mm2 8 mm 222.35 mm 150 mm

Total area provided

335.13 mm2

O.K.

Reinforcement in edge strip: Minimum reinforcement Dia of reinforcement Along short span : Spacing of bars c/c PROVIDE SPACING OF BARS c/c

150.00 mm2 8 mm 335.13 mm 200 mm

Revise O.K.

Total area provided Along short span : Spacing of bars c/c PROVIDE SPACING OF BARS c/c

251.35 mm2

O.K.

335.13 mm 300 mm

O.K. O.K.

Total area provided

167.57 mm2

O.K.

Corner Reinforcement: Length of corner reinforcement Area of each layer of reinforcement Dia of reinforcement Spacing of bars c/c

876 mm 566 mm2 8 mm 83 mm

Check for shear at short edge: Nominal shear stress,τv

0.21 N/mm2

In slabs τc'

0.32 N/mm2 The Slab panel is SAFE in shear.

Check for development length at short edge: Dia of bar used 8 mm Ø ≤ 8.13 mm Dia of bar used is less than required one , hence o.k. Check for deflection: Allowable L/d =α β γ λ Actual L/d Deflection requirements are O.K.

44.8 41.95

DESIGN OF R.C.C. SLAB (IS456-1978) DESIGN DATA : SECTION (MM): LONG SPAN, Ly SHORT SPAN, Lx COVER MATERIAL: GRADE OF CONCRETE GRADE OF STEEL - MAIN GRADE OF STEEL - SECONDARY LOADS (Kn/m2) : LIVE LOAD FF LOAD PARTITION LOAD MISCELLANEOUS LOAD SAFETY FACTOR: FORCES

6700 4300 15 M15 Fe 415 Fe 415 3.00 0.60 0 0 1.50

CONDITION: RESTRAINED SLAB ONE LONG EDGE DISCONTINUOUS DESIGN: σck =

15 N/mm2

σy(main) =

415 N/mm2

σy (secondary) = N.A. factor =

415 N/mm2 0.48 1.56

Ly / Lx = This is two-way slab. Assume overall thicness of slab, D Effective depth, d Effective spans will be lx = Lx + d ly = Ly + d ly / lx = Moments along short span Mx and along long span My are given by : Mx = βx w lx² My = βy w lx² Corresponding ly /lx, For positive moment at mid span βx = βy = For negative moment at continuous edge βx = βy =

125 mm 105 mm 4.405 m 6.805 m 1.5

0.05 0.03 0.07 0.04

DESIGNED & DEVELOPED BY IDCS BASTI, INDIA contd. On next page

DESIGN OF R.C.C. SLAB (IS456-1978) Dead load of slab, wd = D x 25

3.13 kN/m2

Live load, wl

3.00 kN/m2

Finish load, wf

0.60 kN/m2

Partition Load, wp

0.00 kN/m2

Miscellaneous load, w'

0.00 kN/m2

Total load, w = wd+wl+wf+wp+w'

6.73 kN/m2

Factored load, wu = safety factor x w Positive moment at mid span Mx = βx w lx² My = βy w lx² For negative moment at continuous edge Mx = βx w lx² My = βy w lx²

10.09 kN/m2 10.02 kNm/m 5.48 kNm/m 13.16 kNm/m 7.24 kNm/m

The effective depth shall be designed for maximum of moment,i.e. 13.16 kNm/m The effective depth d of the slab is given by 0.138σckbd2 d = 79.72 mm Adopt effective depth,d 105 mm Adopt overall depth,D 125 mm Along the long edge: Length 0f the middle strip 5.10 m Length 0f the edge strip 0.85 m Along the short edge: Length 0f the middle strip 3.304 m Length 0f the edge strip 0.551 m Minimum area of steel 0.12% Hence, Minimum area of steel Reinforcement in middle strip: Steel along short span: Atx = 0.36 σck b Xm / 0.87σy Dia of reinforcement Area of bar Spacing of bars c/c Providing spacing of bars c/c Total area provided, Atxp Area of tension steel Aty along long span: d' = d - dia of bar a = 0.87 x σy / σck x 1000 b = 0.87 x σy x d' c = Mx 2

Aty =( b±√b²-4ac) / 2a

150.00 mm2

754 mm2 10 mm 78.54 mm2 104.16 mm 100 mm

O.K.

785.4 mm2

O.K.

95 mm 9.99 34299.750 7244000 226.08 mm2

DESIGNED & DEVELOPED BY IDCS BASTI, INDIA

contd. On next page

DESIGN OF R.C.C. SLAB (IS456-1978) since required area is greater than minimum required area, hence o.k., provide area Dia of reinforcement

226.08

mm2 8 mm

Area of bar Spacing of bars c/c Providing spacing of bars c/c

50.27 mm2 222.35 mm 150 mm

O.K.

Total area provided, Atyp

335.13 mm2

O.K.

Curtail alternate bars at 1/10 th of effective span in each direction in accordance with clause C-2.1.1 of the Code. Provide 50% of the maximum positive steel at top near the supports to resist bending moment due to partial fixity. This steel is provided in length 0.1l from the face of supports.

Reinforcement in edge strip: Minimum reinforcement = Dia of reinforcement Area of bar Along short span : Spacing of bars c/c Providing spacing of bars c/c

150.00 mm2 8 50.27 mm2 335.13 mm 200 mm

Revise O.K.

Total area provided, Atyp Along long span : Spacing of bars c/c Providing spacing of bars c/c

251.35 mm2

O.K.

335.13 mm 300 mm

O.K. O.K.

Total area provided, Atyp Corner reinforcement: Length of corner reinforcement=0.2 lx

167.57 mm2

O.K.

876 mm

Area of each layer of reinforcement= 75% 0f area required for maximum midspan moment Dia of reinforcement Area of bar no. of bars per rm Spacing of bars c/c

566 mm2 8 mm 50.27 mm2 12 83 mm

Check for shear at short edge: Maximum SF, Vu = 0.5wLx

21.69 kN/m

Nominal shear stress,τv= Vu/bd Percent tension steel = 100As / bd Shear strength of concrete,τc =

0.21 N/mm2 0.11 %

DESIGNED & DEVELOPED BY IDCS BASTI, INDIA

contd. On next page

DESIGN OF R.C.C. SLAB (IS456-1978) β = 0.8 σck / 6.89 Pt > 1.0 τc = 0.85/6β √0.80σck (√(1+5β) -1) In slabs τc' = k τc The Slab panel is SAFE in shear. Check for development length at short edge: d' = Moment of resistance, M1 = 0.87σy At(d'-(σy At / σck b)) Vu = Anchorage value of bars,Lo =60+ 8Ø Development length, Ld = 56Ø Ld ≤ 1.3 M1/Vu + Lo 56Ø ≤ 1.3 M1/Vu + Lo Ø ≤

15.833 0.25 N/mm2 0.32 O.K.

96 mm 5527464.11 Nmm 21.69 kN 124 mm

455.29 mm 8.13 mm

Dia of bar used is less than required one , hence o.k. Check for deflection: Percent tension steel at midspan = 100As / bd γ = β = λ = α = Allowable L/d =α β γ λ Actual L/d = Deflection requirements are O.K.

0.32 1.4 1 1 32 44.8 41.95

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