The ASCE 7-22 Standard [1], Sect. 12.9.1.6 specifies when P-delta effects should be considered when running a modal response spectrum analysis for seismic design. In the NBC 2020 [2], Sent. 4.1.8.3.8.c gives only a short requirement that sway effects due to the interaction of gravity loads with the deformed structure should be considered. Therefore, there may be situations where second-order effects, also known as P-delta, must be considered when carrying out a seismic analysis.
Imperfections in construction engineering are associated with production-related deviation of structural components from their ideal shape. They are often used in a calculation to determine the equilibrium of forces for structural components on a deformed system.
This technical article presents some basics for using the Torsional Warping add-on (7 DOF). It is fully integrated into the main program and allows you to consider the cross-section warping when calculating member elements. In combination with the Stability Analysis and Steel Design add-ons, it is possible to perform the lateral-torsional buckling design with internal forces according to the second-order analysis, taking imperfections into account.
In the world of construction engineering, the word "imperfections" has a specific meaning. In general, it describes the incompleteness of a structure or the deviation of a structural component from an ideal shape caused by the production.
This article describes the different options for determining the allowable deformation of crane runway girders. Since multi-span beams and flexible lateral supports (sway bracing) are used in practice, this article will show how to select the correct method.
According to EN 1993‑1‑1 [1], it is necessary to use the equivalent geometric imperfections with values that reflect the possible effects of all types of imperfections. EN 1993‑1‑1, Section 5.3, specifies basic imperfections for the global analysis of frames as well as member imperfections.
According to EN 1993-1-1 [1], it is necessary to use the equivalent geometric imperfections with values that reflect the possible effects of all types of imperfections. EN 1993-1-1, Section 5.3, specifies basic imperfections for the global analysis of frames as well as member imperfections.
As an alternative to the equivalent member method, this article describes the possibility to determine the internal forces of a wall at risk of buckling according to the second-order analysis, taking imperfections into account, and to subsequently perform the cross-section design for bending and compression.
In the AISC 360 – 14th Ed. C2.2, the direct analysis method requires initial imperfections to be taken into consideration. The important imperfection of recognition is column out-of-plumbness. According to C2.2a, the direct modeling of imperfections is one method to account for the effect of initial imperfections. However, in many situations, the expected displacements may not be known or easily predicted.
RFEM and RSTAB provide the option to create load and result combinations automatically according to the combination expressions defined in the standards. In this case, imperfections can be set differently for each combination expression.
The stability analysis of the steel frame described in my previous post can also be performed in RF‑/FE‑LTB according to the Equivalent Imperfection Method. This post describes how to calculate or determine the critical load factor.