Ribbed or waffle slabs

Current practices for determining forces in ribbed and waffle slabs may also be used for designs to Eurocode 2.Where a waffle slab is treated as a two-way slab refer to previous section, but note that their torsional stiffness is significantly less than for a two-way slab and the bending moment coefficients may not be appiicabie.Where it is treated as a flat slab reference may be made to Chapter 7, originally published as Flat slabs4

The position of the neutral axis in the rib should be determined, and then the area of reinforcement can be calculated depending on whether it lies in the flange or web (see flow chart in Figure 6). The main differences compared with BS 8110 are that the assessment of the flange width is more sophisticated (see Figures 7 and 8).

Where a slab is formed with permanent blocks or a with a topping thickness less than 50 mm and one-tenth of the clear distance between ribs it is recommended that a longitudinal shear check is carried out to determine whether additional transverse reinforcement is required (see BS EN 1992-1-1, CI 6.2.4).

Table 8

Bending moment coefficients for two-way spanning rectangular slabs supported by beams

Table 8

Bending moment coefficients for two-way spanning rectangular slabs supported by beams

Type or panel and moments considered

Short span coefficients for values of ly/lx

Long-span coefficients for all values of ly/lx

1.25

1.5

1.75

2.0

Interior panels

Negative moment at continuous edge

0.031

0.044

0.053

0.059

0.063

0.032

Positive moment at midspan

0.024

0.034

0.040

0.044

0.048

0.024

One short edge discontinuous

Negative moment at continuous edge

0.039

0.050

0.058

0.063

0.067

0.037

Positive moment at midspan

0.029

0.038

0.043

0.047

0.050

0.028

One long edge discontinuous

Negative moment at continuous edge

0.039

0.059

0.073

0.083

0.089

0.037

Positive moment at midspan

0.030

0.045

0.055

0.062

0.067

0.028

Two adjacent edges discontinuous

Negative moment at continuous edge

0.047

0.066

0.078

0.087

0.093

0.045

Positive moment at midspan

0.036

0.049

0.059

0.065

0.070

0.034

Greener Homes for You

Greener Homes for You

Get All The Support And Guidance You Need To Be A Success At Living Green. This Book Is One Of The Most Valuable Resources In The World When It Comes To Great Tips on Buying, Designing and Building an Eco-friendly Home.

Get My Free Ebook


Responses

  • Michael
    How to design check continuous two way ribbed slab?
    7 years ago
  • lena k
    How to determine the distance o f waffle in Bs?
    3 years ago

Post a comment