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Umm Al-Qura University Department of Civil & Structural Engineering

Design of reinforced concrete II Design of Flat Slab Floors Lecture (3). Umm Al-Qura University Department of Civil & Structural Engineering. Flat Slab Floors. A Flat slab floor is supported directly by columns without the use of beams.

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Umm Al-Qura University Department of Civil & Structural Engineering

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  1. Design of reinforced concrete II Design of Flat Slab Floors Lecture (3) Umm Al-Qura University Department of Civil & Structural Engineering

  2. Flat Slab Floors • A Flat slab floor is supported directly by columns • without the use of beams. • The slab may be with constant thickness or in the • area of the column it may thickened as a drop panel. • The column may also be constant section or it may • be flared to form a column head or capital, see • Fig 8.10 • The drop panels are effective in: • Reducing the shear stresses. • Provide an increased moment resistance.

  3. The flat slab advantages: • 1. Simplified formwork. • 2. Reduced storey heights make it more economical. • 3. Windows can extent up to the underside of the slab. • 4. No beams to obstruct light and air circulations. • 5. Absence of sharp corners gives greater fire resistance. • Deflection requirements will generally govern slab thickness • which should not be less than 180 mm for fire resistance.

  4. Interior panels of the flat slab should be divided as • shown in figure 8.11 into: Column strip Middle strip • Drop panels should be ignored if their smaller • dimension is less than one third of the smaller panel • dimension lx. • Moments are distributed between the strips as • shown in table 8.7.

  5. If the column strip is narrower because of drops, the • moment resisted by the column and middle strips should • be adjusted proportionally as illustrated in example 8.7.

  6. The reinforcement should be arranged according to • the rules illustrated in figure 8.2. • At least two bottom bars in each orthogonal direction • should pass through the internal columns to • enhance robustness. • EC2 requires that the design shear force be increased • above the calculated value as follows: • V eff = 1.15 VEd for internal columns with approximately • equal spans • = 1.4 V Ed for edge columns • = 1.5 VEdfor corner columns

  7. Punching Shear Reinforcement for Flat Slabs • The shear stress should be checked first with respect • to the maximum permissible shear force, VRd, max Where u = punching shear perimeter d = effective depth of tension reinforcement. VRd,max = Design value of maximum punching shear resistance.

  8. The reinforcement should be provided in at least two • perimeters of links. • The spacing of link perimeters (see the figure 5.10) • should not exceed 0.75d. • The spacing of link legs around a perimeter should • not exceed 1.5d within the basic control perimeter • (2d from the column face) . • And should not exceed 2d for perimeters outside • the basic control perimeter where that part of the • perimeter is assumed to contribute to the shear • capacity (see Figure 5.10).

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