Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

Two Way Edge Supported Slabs

Two-Way Slabs

Slab resting on walls or sufficiently deep and rigid beams on all sides. Other options are column supported slab e.g. Flat slab, waffle slab. Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

Two-way slabs have two way bending unlike one-way slab. Analysis and Design of Slabs Two Way

Design MethodsAnalysis and Design of Slabs Two Way

1.ACI co-efficient method
2.Direct design method
3.Equivalent frame method
4.Finite element method

Notes

1.In two-way slabs shorter direction strip carry greater %age of load.
2.Steel will be more in shorter direction.

Shorter direction steel will be placed near the outer edge to get more “d” means more lever arm to get more flexural capacity.

ACI Co-efficient Method

Unit width strip is taken in both directions. The strip is designed separately  for +ve and –ve moment

eq

“C” depends upon the end conditions of slab and the aspect ratio

Three tables are available for “C”

  •  Dead load positive moment
  •  Live load positive moment
  •  -ve moment

M+ coefficients are increased by 25 % and M- coefficients are reduced by 10 % to get the result more closer to accurate solution. Analysis and Design of Slabs Two Way

Minimum Depth of 2-Way Slab for Deflection Control

According to ACI-318-1963

hmin = (inner perimeter of slab panel)/180
≥ 90 mm

det

Example:

Design the 4 marked slab panels of an ordinary house. Use US customary bars. fc’= 17.25 MPa fy = 300 MPa Analysis and Design of Slabs Two Way

example

Solution:





Panel Edge Conditions Analysis and Design of Slabs Two Way

Sol

lylx

Panel # 1
Lx = 4.5m ,  Ly = 7.0m
m = 0.64 > 0.5, 2-way slab

Panel # 2
Lx = 6.0m ,  Ly = 7.0m
m = 0.86> 0.5, 2-way slab

Panel # 3
Lx = 3.5m ,  Ly = 6.0m
m = 0.58 > 0.5, 2-way slab

Panel # 4
Lx = 6.0m ,  Ly = 6.0m
m = 1 > 0.5, 2-way slab

Slab Thickness
Generally same depth is preferred for one monolithic slab Calculate hmin for all the panels and select the largest value Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two WayAnalysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

Analysis and Design of Slabs Two Way

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