On the Non‐Linearity and Time and Temperature Dependence of the Torsional Restraint Provided by Sandwich Panels

Abstract The rotational spring stiffness provided by sandwich panels to members prone to lateral‐torsional buckling shows both a non‐linear as well as a time‐ and temperature‐dependent characteristic. This is generally acknowledged both in scientific publications and in technical regulations such as recommendations and standards. However, there is a lack of information on how these characteristics can be considered in practical design. This paper aims to close this gap. The first part focuses on the non‐linear characteristic of the moment‐rotation relation that gives the rotational spring stiffness. The influence of both cross‐section geometry and loading is discussed. This results in a focus on hot rolled sections, for which the results of a parametric study are presented, in which the influence of the various simplifications (linearization) on the lateral torsional buckling resistance was investigated. The second part deals with the time‐dependent change in rotational spring stiffness. Only a few studies are available on this, and their implementation in the technical regulations is either based on simplifications or incomplete, as they do not distinguish between creep and relaxation. The paper explains the consideration of the time‐dependent characteristic in design, considering the respective design situation, combination of actions and loading history. The last part deals with the effect of temperature. Here the technical regulations are based on investigations into the temperature‐dependent wrinkling resistance of sandwich panels but neglect the difference in the temperature of the internal and external faces. If this is considered, higher rotational spring stiffnesses can be used in design basically of hot rolled sections.