Ribbed Slab Modelling & Design Procedure

Ribbed Slab Modelling & Design Procedure

There are two approaches in ribbed slab modelling and design as following:-

Analytical Approach:
ProtaStructure considers ribbed slabs as continuous beams and analyses them with  Moment-Distribution Method under G and Q.

FE Approach:
Similar to ordinary slab plates, Ribbed/Waffle slabs can be analyzed separately from building under G and Q, or with the building model under all combinations.
Waffle slabs must be analyzed using FE Approach.

Modelling Procedure:
  1. Insert Ribbed Slabs and Waffle Slabs as required. Usually beam widths are at the order of 800-1000 mm and beam depths are 320 mm.
  2. Insert slab strips. Strip must cover all continuous rib beams. If there is any discontinuity, it is required to insert a new strip. 
    1. Strip must be in the direction of rib beams
    2. During the design stage, the length of the designed rib beam will be calculated depending on the position of the strip (nearest beam to strip). Therefore, you may choose to insert strip along every rib beam or along the most critical one.
    3. If you are using Analytical Method, the strip type must be "Analytical Strip"
    4. If you are using FE Method, "FE Strip" must be selected (refer to snapshot below). 
  1. When create the slab strip, ensure that correct Start/End condition is selected. 
Analysis Procedure:
  1. If FE Method is preferred then perform FE Slab Analysis.
  2. Click on “Concrete Design > Ribbed Slab Analysis”. This will calculate the internal forces either by Moment Distribution method or from existing FE Results.
  3. A report will be displayed. This report summarizes the analysis results.

Design Procedure:
  1. After you have performed Ribbed Slab Analysis, go to Concrete Design > Beam Reinforcement Design > Ribs. 
  2. The beam design menu will be shown and populated by the rib beams instead of storey beams. 
  3. Design the rib beams as usual. 
  4. Rib beams details can be accessed from a separate menu in Prota Details. 
  5. Number of Rib Beams designed will be equal to the strips inserted (nearest beam). 
  6. "Qty" column will be automatically populated and quantities will be multiplied with this quantity. 

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