Two way slab

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  1. Direct Method ? ? Reinforcement in Two-way Slabs ? Footing Classification ? Footing Design
  2. The reinforcement is for slabs without beams.
  3. Look at Example 13-7 Design of a flat plate floor without spandrel beams - Direct Design Method Look at Example 13-9 Design of a Two-way slab with beams in both directions.
  4. Shear failure occurs when inclined cracks form due to flexural and shearing stresses. Two types of shear failure mechanism in 2-way slabs. (a) One-way shear (b) Two-way shear (Punching shear).
  5. One-way shear Two-way shear
  6. Inclined cracking Slab slides down column Top (negative reinforcement pulls out of slab leaving no connection to the column Inclined cracking
  7. Critical perimeter is located d / 2 from column face, where d = effective depth of slab
  8. Critical perimeter is located d / 2 from column face, where d = effective depth of slab Slabs with Drop Panels
  9. Two-way Shear with Negligible Moment Transfer ACI Eqn. 11-1 Vu Vn where, Vu =Factored shear force (tributary area bounded by lines of zero shear) Vn = Nominal shear resistance of slab 0.85
  10. Two-way Shear with Negligible Moment Transfer Vn Vc Vs where, Vc =Shear resistance of concrete Vs = Shear resistance of steel (in most slabs, Vs = 0)
  11. (a) Two-way Shear with Negligible Moment Transfer For two-way shear in slabs (& footings) Vc is smallest of 4 ACI 11-35 Vc 2 f c b0 d c where, = long side/short side of c column concentrated load or reaction area b0 = length of critical perimeter around the column
  12. (b) Two-way Shear with Negligible Moment Transfer d s ACI 11-36 Vc 2 f c b0 d b0 where, = 40 for interior columns s 30 for edge columns 20 for corner columns
  13. (c) Two-way Shear with Negligible Moment Transfer ACI 11-37 Vc 4 f c b0 d Take smaller of (a), (b) and (c)
  14. Tributary area for Vu calculations Figure 13-41 MacGregor
  15. If V Vn can be increased by: , Vc u (1) Increase slab thickness (2) Use drop panel (3) Increase b0 by increasing column size or adding a fillet or capital (4) Add shear reinforcement