The object of the research are short, thin-walled columns with an open top-hat cross section made of multilayer laminate. The walls of the investigated profiles are made of plate elements. The entire columns are subjected to uniform compression. A detailed analysis allowed us to determine critical forces and post-critical equilibrium paths. It is assumed that the columns are articulately supported on the edges forming their ends. The numerical investigation is performed by the finite element method. The study involves solving the problem of eigenvalue and the non-linear problem of stability of the structure. The numerical analysis is performed by the commercial simulation software ABAQUS®. The numerical results are then validated experimentally. In the discussed cases, it is assumed that the material operates within a linearly-elastic range, and the non-linearity of the FEM model is due to large displacements.

In this paper, the retrofitting method of thin-walled, cold-formed sigma beams using bonded carbon fibre reinforced polymer (CFRP) tapes is proposed. The effectiveness of the presented strengthening method is investigated by the means of laboratory tests and numerical analysis conducted on simply supported, single-span beams made of 200 × 70 × 2 profile by “Blachy Pruszyński” subjected to a four-point bending scheme. Special attention is paid to the evaluation of possibility to increase the load capacity with simultaneous limitation of beams displacements by appropriate location of CFRP tapes. For this purpose, three beams were reinforced with CFRP tape placed on the inner surface of the upper flange, three with CFRP tape on the inner surface of the web, three beams with reinforcement located on the inner surface of the bottom flange, and two beams were tested as reference beams without reinforcement. CFRP tape with a width of 50 mm and a thickness of 1.2 mm was used as the reinforcement and was bonded to the beams by SikaDur®-30 adhesive. Precise strain measurement was made using electrofusion strain gauges, and displacement measurement was performed using two Aramis coupled devices in combination with the Tritop machine. Numerical models of the considered beams were developed in the Finite Element Method (FEM) program Abaqus®. Experimental and numerical analysis made it possible to obtain a very high agreement of results. Based on the conducted research, it was proved how important is the impact of the applied reinforcement (CFRP tapes) in thin-walled steel structures, with respect to the classic methods of strengthening steel building structures.

The current study investigates the stability and failure analysis of thin-walled composite columns with a top-hat and channel cross section, subjected to axial compression. The analyzed structures were made of composite material (carbon fiber reinforced polymer) by autoclave technique. The study included experimental tests on actual specimens and numerical simulations on numerical models using finite element method (in ABAQUS® program).Experimental-numerical analysis was conducted over the full range of loading (until failure phenomenon). Regarding the experimental tests, postbuckling equilibrium paths as well as acoustic emission signals were registered, which directly allowed for comprehensive analysis of failure phenomenon of composite material. In case of numerical simulations, two independent numerical damage models were used. The first one constitutes the progressive failure analysis, considering the damage initiation criteria using Hashin's theory and damage evolution based on the energy criterion. The second one constitutes the cohesive zone model, which was used to simulate failure of composite material caused by delamination phenomenon. Both experimental and numerical results show high agreement. Furthermore, the obtained results reveal an interesting relationship between buckling, postbuckling, and failure phenomenon of the analyzed structures.

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