Preliminary design of slab
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1) The document outlines the preliminary design steps for a slab with inner dimensions of 4x3.6 meters. 2) In step 1, load calculations are performed to determine the factored load of 9 kN/m. 3) In step 2, design moments are calculated at supports and mid-spans along the short and long spans. 4) In step 3, the effective depth is checked and found to be sufficient at 42.56mm, so the total depth is set at 120mm.
![PRELIMINARY DESIGN OF SLAB
STEP 1:-
LOAD CALCULATIONS
Inner dimensions = (4×3.6) m2
Assuming fy = 415 N/mm2
Fck = 20 N/mm2
Effective span (Lx) = 3.6m
Effective span (Ly) = 4 m
Aspect ratio (Ly/Lx) = [4/ 3.6] = 1.1 < 2
Assume over all depth of slab = 120 m
Effective depth = 120 – 15-10/2 = 100mm
Self weight of slab = 0.12 × 25 =3 kN/m2
Live load = 2kN/m2
Dead load = 1kN/m2
Total weight = 6kN/m2
Load per meter run = 6.0 × 1.0 = 6.0kN/m
Factored load = 1.5 × 6.0 = 9.0 kN/m
Edge condition = Interior panel.
STEP 2:-
DESIGN MOMENTS
Using bending moment coefficients from table – 26 of IS 456:2000, the bending moments are
calculated as follows.
Mx=αxwLx
2 My=αywLx
2
BENDING MOMENTCOEFFICIENTS
AT SUPPORTS AT MID SPAN
ALONG SHORT SPAN (αx) - 0.037 0.028
ALONG LONG SPAN (αy) -0.032 0.024](https://image.slidesharecdn.com/preliminarydesignofslab-170525100219/85/preliminary-design-of-slab-1-320.jpg)
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Preliminary design of slab
- 1. PRELIMINARY DESIGN OF SLAB STEP 1:- LOAD CALCULATIONS Inner dimensions = (4×3.6) m2 Assuming fy = 415 N/mm2 Fck = 20 N/mm2 Effective span (Lx) = 3.6m Effective span (Ly) = 4 m Aspect ratio (Ly/Lx) = [4/ 3.6] = 1.1 < 2 Assume over all depth of slab = 120 m Effective depth = 120 – 15-10/2 = 100mm Self weight of slab = 0.12 × 25 =3 kN/m2 Live load = 2kN/m2 Dead load = 1kN/m2 Total weight = 6kN/m2 Load per meter run = 6.0 × 1.0 = 6.0kN/m Factored load = 1.5 × 6.0 = 9.0 kN/m Edge condition = Interior panel. STEP 2:- DESIGN MOMENTS Using bending moment coefficients from table – 26 of IS 456:2000, the bending moments are calculated as follows. Mx=αxwLx 2 My=αywLx 2 BENDING MOMENTCOEFFICIENTS AT SUPPORTS AT MID SPAN ALONG SHORT SPAN (αx) - 0.037 0.028 ALONG LONG SPAN (αy) -0.032 0.024
- 2. BENDING MOMENTS AT SUPPORTS (kN-m) AT MID SPANS (kN-m) ALONG SHORT SPAN Mx (-ve) = -4.3 Mx (+ve) = 3.2 ALONG LONG SPAN My (-ve) = -3.73 My (+ve) = 2.79 STEP:-3 CHECK FOR EFFECTIVE DEPTH Maximum bending moment (Mu) = 0.138 × fck × bd2 4.3 ×106 = 0.138 × 20 × 1000 × d2 d = 42.56 mm < 100.00mm Therefore, provide total depth of slab( D) = 120mm S.NO SPAN(m x m) EDGE CONDITION REQUIRED DEPTH(mm) PROVIDED DEPTH(mm) 1 3 x 6.1 Two Adjacent edges Discontinuous 51.6 100 2 3 x 3.6 One Long Edge Discontinuous 39 100 3 2 x 3 One Short Edge Discontinuous 27.2 100 4 4 x 3.6 One Short Edge Discontinuous 42 100 5 1.5 x 6.1 One short edge Discontinuous 27.5 100 6 3 × 6.1 One short edge Discontinuous 44.6 100 7 4 × 6.1 One short edge Discontinuous 54 100 8 4 × 3.6 Interior panel 42.56 100 9 4 × 2 Interior panel 29.11 100 10 3 × 3.6 Interior panel 35.5 100 11 1.5× 3.6 Interior panel 33 100 12 3 × 2 Interior panel 26.3 100 13 1.5 × 2 Interior panel 18.15 100