Design of a Two Way Slab

Design and Analysis of a two-way Spanning Slab

A two-way spanning slab is a slab with main reinforcements in both directions. The reinforcements parallel to the shorter dimensions are designed first and act as the main reinforcements while the reinforcements parallel to the longer side are deigned later and distribute onto the shorter side reinforcements.  Two-way designed is adopted if the longer side exceeds 4.5m, if the slab is loaded heavily or if the shorter span exceed 4.0m.

Below is the example of a two- way spanning slab design:

how to design a slab

Using 25-410 concrete.

Loading

Self-weight:   = 24 x 0.15 = 3.6KN/m2

Finishes and felting =  2.00KN/m2

Total = Gk = 5.60KN/m2

Live load = 1.5KN/m2

Thus, F = 5.6×1.4 + 1.5×1.6

= 10.24KN/m

K = ly/lx = 7200/4200 = 1.71

αsx = 1.714/8(1+1.714) =           0.112

αsy = 1.712/8(1+1.714) = 0.038

 

Short Span

M = 0.112 x 4.22 x 10.24

= 20.231KNm

h = 150mm, d = 150-20-6 = 124mm

K = M/ Fcubd2

= (20.231×106)/(20x1000x1242)

= 0.053

La = 0.95, Z = lad = 0.95×124 = 117.8

As = M/0.95FyLad

= (20.231×106)/(0.95x410x117.8)

= 441mm2

Provide Y12 @ 150mm c/c BTM (754mm2)

 

Long Span

M = 0.038 x 4.22 x 10.24

= 6.864KNm

h = 150mm, d = 150-20-6 = 124mm

K = M/ Fcubd2

= (6.864×106)/(20x1000x1242)

= 0.018

La = 0.95, Z = lad = 0.95×124 = 117.8

As = M/0.95FyLad

= (6.864×106)/(0.95x410x117.8)

= 150mm2

Provide Y12 @ 250mm c/c BTM (450mm2)

how to design a slab

 

 

 

One Response

  1. Faridahmad July 29, 2019

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