Experimental research on axially compressed columns made from reinforced concrete (RC) and RC columns strengthened with a steel jacket and additional fill concrete is presented in this paper. A premade squared cross-section RC column was placed inside a steel tube, and then the space between the column and the tube was filled with additional concrete. A total of fourteen stub axially compressed columns, including nine strengthened specimens and five plain reinforced concrete specimens, were experimentally tested. The main parameter that was varied in the experiment was the compressive strength of the filler concrete. Three different concrete compression strength classes were used. Test results showed that all three cross-section parts (the core column, the fill, and the steel jacket) worked together in the force-carrying process through all load levels, even if only the basic RC column was loaded. The strengthened columns exhibited pronounced ductile behavior compared to the plain RC columns. The influence of the test parameters on the axial compressive strength was investigated. In addition, the specimen failure modes, strain development, and load vs. deformation relations were registered. The applicability of three different design codes to predict the axial bearing capacity of the strengthened columns was also investigated.

This paper presents a calculation method for axially compressed cold formed stainless, high strength and carbon steel profiles. Results of different authors in this field published in international journals depict current trends in this field. Paper also presents author’s numerical and experimental analysis of cold-formed centrally compressed elements. Numerical analysis was carried out by finite element method and program for the nonlinear static and dynamic structural analysis - PAK. The results obtained by experimental and numerical methods included boundary conditions, maximum force, buckling curve etc. Small difference observed in the values obtained by these different methods. Results werw compared to values predicted by international designing code in order to analyze if they are too conservative for cold formed steel sections.

Experimental and computational research on the behavior of small-scale and large-scale fiber-reinforced concrete (FRC) beams is presented in this paper. The experimental part included the small-scale bending tests, which were conducted on three 1.3 m long by 0.1 m wide by 0.15 m high rectangular simply supported beams, and the large-scale test that was conducted on 12.8 m long by 0.2 m wide by 1.3 m two-chords girder. The concrete mixture in the large-scale test was designed with environmentally more justifiable supplementary materials (binder and fibers), striving for sustainable excellence. To accurately predict the mechanical behavior of tested models, a numerical model incorporating the real nonlinear materials laws is used. A numerical model based on finite element analysis (FEA) is developed. The FEA model is created using a smeared crack approach with a constitutive law for the tensile behavior of FRC derived from an inverse analysis based on prism bending tests. The numerical model is validated against experimental results and the accuracy of numerical predictions based on finite element modeling showed a good correlation with the test data. The FEA-based model makes it easier to predict how FRC structures fail under transversal loading and can serve as a foundation for creating new design processes. Additionally, the presented research is aimed at the feasibility of recycled steel FRC field application in building structures. The usage of recycled steel fibers could achieve environmental benefits through the adoption of sustainable materials. The present study showcased the possibility of modeling reinforced concrete structural building parts made with recycled steel fibers using available software.

Purpose: The purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.Design/methodology/approach: The problem of fatigue damage is formulated based on the rheological–dynamical analogy, including a scalar damage variable to address the reduction of stiffness in strain softening. The modal analysis is used by the finite element method for the determination of modal parameters and resonance stability of the selected frame cross-section. The objectivity of the presented method is verified by numerical examples, predicting the ductility in bending of the frame whose basic mechanical properties were obtained by non-destructive testing systems.Findings: The modal analysis in the frame of the finite element method is suitable for the determination of modal parameters and resonance stability of the selected frame cross-section. It is recommended that the modulus of elasticity be determined by non-destructive methods, e.g. from the acoustic response.Originality/value: The paper presents a novel method of solving the ductility in bending taking into account both the creep coefficient and the aging coefficient. The rheological-dynamical analogy (RDA) method uses the resonant method to find material properties. The characterization of the structural damping via the damping ratio is original and effective.