Design a roof slab inside dimension 7x3 m if supporting brick walls are 300 mm thick. The Slab will have to carry 75 mm thick additional material as the rooftop finishing, Whose Unit weight 20 KN/m³, service load 2 HYSD Steel bar Fe415, Rec slab simply supported
1. Given Data:
- Slab Dimension (inside):
- Supporting Wall Thickness: 300 mm
- Rooftop Finishing Thickness: 75 mm
- Rooftop Finishing Unit Weight: 20 kN/m³
- Service Load: 2 kN/m²
- Steel Reinforcement: Fe415 HYSD bars
- Slab Type: Simply supported
2. Calculation of Load
a) Self-weight of the Slab
Assume Slab Thickness: Generally, for a simply supported slab, the thickness t is chosen as:
t=20Lshort≈203=0.15m (or 150 mm)Unit Weight of RCC: 25 kN/m³
Self-weight of the slab:
Self-weight=Unit weight of RCC×Slab thickness=25×0.15=3.75kN/m²
b) Weight of Rooftop Finishing
Weight of Finishing=Unit Weight×Finishing Thickness=20×0.075=1.5kN/m²c) Service Load
Service Load=2kN/m²d) Total Load (Design Load)
Total Load=Self-weight+Weight of Finishing+Service Load=3.75+1.5+2=7.25kN/m²3. Bending Moment Calculation
For a simply supported slab, the bending moment M is calculated as:
M=8wL2where:
- w is the total load per unit area.
- L is the shorter span.
Using w=7.25kN/m2 and L=3m:
M=87.25×32=87.25×9=8.15625≈8.16kNm/m4. Area of Steel Reinforcement (Main Steel)
For Fe415 steel:
M=0.138fckbd2
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