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  • Prestresed Concrete
    • Introduction to prestressed concrete
    • Methods of prestressing
    • Design of PSC members
    • Prestressing force and Ecentricity
    • Ecentricity limits and tendon profile
    • Losses in prestressed concrete structures

  • tanks
    • Introduction to water tanks
    • Load conditions and flexure details for water tanks
    • Minimum and Maximum reinforcement for tanks
    • Slab design for Tanks
    • Design Requirement of Concrete in tanks
    • General design requirements for members of a tank
    • Circular tank Analysis
    • Numerical on the analysis of Circular water tank
    • Design of Rectangular tanks
    • Numerical on Rectangular water tank
    • Underground Tanks
    • Overhead tanks

  • Retaining walls
    • Retaining walls and their types
    • Earth Pressure and Stablity requirements
    • Proportioning and design of cantilever and counterfort walls
    • Numerical on design of a Retaining wall

  • footings
    • Introduction to footings
    • Soil Pressure under Isolated footings
    • General Design Considerations for Footings
    • Special case of Footing
    • Numerical on footings
    • Design of Combined Footing

  • Flat slabs
    • Introduction to flat slabs
    • Proportioning of flat slabs
    • Determination of bending moment and shear force
    • Slab reinforcement
    • Numericals of flat slab

Branch : Civil Engineering
Subject : Design of Concrete Structures-II
Unit : Flat slabs

Numericals of flat slab


Example 1. 

Design an interior panel of a flat slab with panel size 6 x 6 m supported by columns of size 500 x 500 mm. Provide suitable drop. Take live load as 4 kN/m2. Use M20 concrete and Fe 415 steel.

Solution

Thickness : Since Fe 415 steel is used and drop is provided, maximum span to thickness ratio permitted is 32

Thickness of flat slab  

Provide 190 mm thickness. Let the cover be 30 mm and Overall thickness D = 220 mm
Let the drop be 50 mm. Hence at column head, d = 240 mm and D = 270 mm

Size of Drop

It should not be less than


Let us provide 3 m x 3 m drop so that the width of drop is equal to that of column head.
hence Width of column strip = width of middle strip = 3000 mm.

Loads

For the purpose of design let us take self-weight as that due to thickness at column strip

= 17.625 x 6 x 5.5

= 581.625 kN

Design Total Moment

Total moment

Total negative moment = 0.65 x 400 = 260 kNm
Total positive moment = 0.35 x 400 = 140 kNm

The above moments are to be distributed into column strip and middle strip

Width of column strip = width of middle strip = 3000 mm

= 476.928 kNm

Thus Mu lim > Mu. Hence thickness selected is sufficient

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