How to model voided slab system?

When modeling a voided slab system, first the cross-sectional value (moment of inertia, unit volume and cross-sectional area) of the 𝙸 section formed by disposable formworks are calculated. Equivalent section coefficients are obtained by comparing voided slab cross section values with flat section values. The voided slab model is created by multiplying these coefficients with relevant parameters such as effective section stiffness, modulus of elasticity and concrete unit volume weight in the structural design software used.

Modeling steps:

1. Determine parameters for flat (full) slab

2. Calculate voided slab equivalent coefficients

Flat slab cross-section features with the same geometry as the voided slab cross-section features are determined and the following features of the 2 slabs are proportioned:

Section Area Factor:                  A_voided / A_full

Concrete Volume Factor:            V_voided / V_full

Moment of Inertia Factor:           𝙸_voided / 𝙸_full

These ratios are used by multiplying effective section stiffness in the code.

3. Construct dead and live load combinations

4. Do the preliminary design

5. Check the slab thickness by inspecting moment diagrams

6. Check the punching zones by inspecting shear diagrams

Design table for voided slabs with different openings:

Voided slab system sample designs:

Sample finite elements diagrams:

You can contact our technical team to review the full report on the sample design from which these Finite Element Diagrams were produced.