Imperfections are inaccuracies in supports, residual stresses in members, variable thicknesses of plates, out-of-straightness of members, etc. All these imperfections are replaced and simulated by an equivalent geometrical imperfection. All kinds of imperfections are described in the Theoretical background for IDEA StatiCa Member. In short, there are global imperfections applied on the whole structural model and local imperfections applied on single beams, columns, or frames.
IDEA StatiCa Member allows applying the local imperfections in the buckling mode shapes with maximal amplitude chosen by the user in absolute value. Usually, the ﬁrst buckling mode shape with the maximum amplitude according to relevant guidelines is enough.
There are guidelines for each code, how to determine imperfections. For instance, in EN, it is described in EN 1993-1-1, Cl.5.3.2 (3), where the plastic analysis should be used.
The amplitude e0 which you input in Member for GMNIA analysis should be calculated according to the following table.
It must be also decided whether:
- member is predominantly compressed where ﬂexural, torsional or torsional-ﬂexural buckling is expected,
- or if the member is predominantly bent and the main failure mode is lateral-torsional buckling.
For models with more analyzed members, more buckling mode shapes must be analyzed.
After the calculation of MNA (materially non-linear analysis) and LBA (linear buckling analysis), you can input local imperfections to IDEA StatiCa Member and calculate the 2nd order GMNIA analysis (geometrically and materially nonlinear analysis with imperfections).