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The paper presents a static analysis of the buckling and post-buckling state of thin-walled cold-formed steel (TWCFS) lipped channel section beam-columns subjected to eccentric compression. Eccentricity is taken into consideration relative to both major and minor principal axes. An analytical–numerical solution to the buckling and post-buckling problems is described. The solution is based on the theory of thin plates. Equations of equilibrium of section walls are derived from the principle of stationary energy. Then, to solve the problem, the finite difference (FDM) and Newton–Raphson methods are applied. Linear (buckling) and nonlinear (post-buckling) analyses are performed. As a result, pre- and post-buckling equilibrium paths are determined. Comparisons of the obtained numerical results, FE simulation results, and experimental test results are carried out and presented in comparative load-shortening diagrams. Additionally, a comparison of the buckling forces and buckling modes obtained from theoretical analysis and experiments is presented. [ABSTRACT FROM AUTHOR]

The work includes the results of numerical, analytical-numerical and experimental study into the influence of load eccentricities with regard to major axis on post-buckling behaviour and load-carrying capacity of thin-walled cold-formed steel lipped channel section columns. The study was solved by using the finite element method (code Ansys) with taking into consideration a full material characteristics in logarithmic strain system and geometric nonlinearities. The analytical-numerical solution was based on Koiter's theory with an application of finite difference method (FDM). Some chosen results of numerical simulations have been compared to experimental results. The deformations of columns were registered by means of Digital Image Correlation Aramis System (DICAS) to observe the maps and the magnitude of displacements for adequate point of a load. The analyses showed that the decrease in maximum load in a dependency on the eccentricity value can be even 3 times minor in a comparison to the load-carrying capacity of axially loaded column. [ABSTRACT FROM AUTHOR]

Flexible polyurethane foams are commonly used materials in automotive applications, especially for internal cockpit parts and seats. During accidental impact, passenger's head has to be stopped by the headrest. Because padding material of a headrest has a significant influence on a head deceleration, mechanical properties of two types of polyurethane foams with a certain range of densities and components proportion have been studied. Dynamic impact tests have been carried out. Results are presented below. Analytical constitutive model of compression has been proposed, which assumes that density, components proportion and strain rate are separable functions. The model has been verified by experimental results of static tests. Impact tests have been conducted due to two objectives: to investigate impact behavior of examined material and to validate numerical solution based on the method of lumped mass.

Thin‐walled cold‐formed steel elements represent an attractive structural solution due to the fast manufacturing and erection time on‐site. Their small thickness leads to imperfection and sensitivities to eccentricities. An experimental programme was performed on short members with lipped channel cross section, subjected to eccentric compression about the minor and major axes, in a large range of eccentricities. The specimens were manufactured on a folding machine. Before testing, the dimensions of all specimens were measured. Shortening of all specimens was measured in two ways, i.e., 1) using the displacement gauge integrated with the machine crosshead beam and 2) from deformation fields obtained using digital image correlation (DIC) system. The quantitative results, presented as the ultimate loads versus the eccentricity curve, emphasise the influence of the eccentric load on the capacity of the element. Finite element (FE) analyses were performed to simulate the behaviour of short members in eccentric compression using the commercial FE software ABAQUS/CAE and ANSYS. Static non‐linear analyses were conducted in displacement control. Both geometrical and material nonlinearities were included. An isotropic linearly elastic‐perfectly plastic constitutive model was considered, with von Mises yielding the criterion and associated flow rule. Failure modes were identified due to numerical and experimental tests. Plastic mechanism models were derived, resulting in the derivation of post‐ultimate, rigid‐plastic curves, characterising a post‐ultimate structural behaviour. [ABSTRACT FROM AUTHOR]

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