Deemed to satisfy slab deflection checks example (Eurocode)
A simple way to assess slab deflection in Tekla Structural Designer is to run a linear analysis using adjusted analysis properties, and then check the resulting deflections by manually determining critical spans.
Download and open the tutorial model
Perform Linear Analysis
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From the Results toolbar,
review 2D deflections for the FE chase-down analysis for the
load combination 1, service load results
Identify critical check locations
We can see that the maximum reported deflection is 38.9mm, occurring in the middle of a corner bay. This should be assessed by taking the slab span diagonally across the bay.
Note: In 'real world' flat slabs some engineering judgment might be required when
assessing which deflections and span lengths require checking.
Guidance exists in How to Design Concrete Structures using Eurocode 2, The Concrete
Centre, Figure 9
In our example, taking the diagonal
dimension across the columns, the deemed-to-satisfy span / 250 rule provides a
deflection of [√(80002+80002)] / 250 = 45.3mm.
In our example, taking the diagonal
dimension across the columns, the deemed-to-satisfy span / 250 rule provides a
deflection of [√(80002+80002)] / 250 = 45.3mm.This compares favorably.
Note: Remember, the method does not predict actual deflections. The total deflection
is simply expected to be less than span / 250.
Concrete properties used in the analysis
The Tekla Structural Designer deflection result is completely dependent upon the concrete elastic modulus used in the analysis which is adjusted by a modification factor to consider such things as creep, cracking and shrinkage.
The modification factor is set from the Settings dialog on the Analyze ribbon. As shown below, for the FE chase-down analysis of flat slabs this defaults to 0.2.
