To simulate the effect of variable strains on steel grades S275 and S355, an experimental displacement control test of plate specimens was performed. Specimens were tested under monotonic and cyclic loading according to the standard loading protocol of SAC 2000. During experimental testing, strain values were measured with an extensometer at the tapered part of the specimen. Strains obtained by the experimental tests are disproportional to the applied displacements at the ends of the specimens. This phenomenon occurs due to the imperfections of the specimen, hardening of the material, and the buckling behaviour that appears in real structures due to the high deformation experienced during earthquakes. Due to the relative simplicity and wide applicability of the Chaboche hardening model of steel, the calibration of hardening parameters based on experimental test results was conducted. For the first time, calibration of steel hardening parameters was performed following the Chaboche procedure to define the cyclic behaviour with variable strain ranges. The accuracy of the hardening model with variable strain ranges, which were simulated using ABAQUS software, was verified using the experimental results.

The aim of this paper is the development of the two different numerical techniques for the preloading of bolts by the finite element method using the software Abaqus Standard. Furthermore, this paper gave detailed guidelines for modelling contact, method for solving the numerical error problems such as numerical singularity error and negative eigenvalues due to rigid body motion or the problem of the extensive elongation of bolts after pretension which is occurring during the analysis. The behaviour of bolted joints depending on the two different approaches of pretension was shown on the example of an extended end-plate bolted beam-to-column connection under the monotonic loading. The behaviour of beam-to-column connection was shown in the form and moment-rotation (M-ϕ) curves and validated by experimental test. Advantages and disadvantages of pretension techniques, as well as the speed of numerical models, were also presented in this paper.

Industrial hemp, as a natural plant fiber, has received increased research attention recently. Potassium fertilization is one of the most important fertilizers for plant stem thickness, but how the formulation of K fertilizer influences stem morphology and stem tensile strength remains unclear. This study aims to examine the influence of K fertilizer sources on industrial hemp stem properties, with a specific focus on the fibers, to evaluate their potential applications as reinforcement material for stabilizing rammed earth in sustainable construction. A field experiment was set up with different K fertilizer types applied as pre-sowing fertilizer in the following doses: K₀—control, K₁—100 kg ha⁻¹ KCl, and K₂—100 kg ha⁻¹ K₂SO₄. Different K fertilizations did not have significant influence on stem height, which was on average 71.2 cm, nor on stem diameter, which was on average 3.4 mm. Regarding the macronutrient content of the industrial hemp stem (N, P, and K), K fertilization treatment significantly influenced (p < 0.05) their accumulation. The N, P, and K content in the stem within fertilization treatment averaged 0.78, 0.72, and 1.26%, respectively. The average content of cellulose, hemicellulose, and lignin was not significantly different in relation to K fertilization treatments. In the stem, dry weight cellulose content varied from 57.8% (K₀) to 59.0% (K₁), hemicellulose from 11.0% (K₂) to 11.6% (K₀ and K₁), and lignin from 10.2% (K₂) to 10.5% (K₀). The tensile strength and Young’s modulus of the industrial hemp stem were non-homogenous within K fertilization treatments. The highest tensile strength (388.52 MPa) and Young’s modulus (32.09 GPa) were on K₁ treatment. The lowest industrial hemp stem tensile strength was determined at K₂ treatment (95.16 MPa), whereas stems in the control treatment had the lowest Young’s modulus (21.09 GPa). In the mixtures of hemp fibers with rammed earth, the higher compressive strength was determined on cubic samples than on cylindrical samples. This study contributes to the industrial hemp K fertilization of the newer genotypes, but there has been a lack of research in recent times. Since industrial hemp has great potential in various industry branches, this study also contributes to using fiber extracted from the stem in eco-friendly and renewable forms in mixtures with rammed earth.

The growing interest in Cannabis sativa as a highly used crop is present worldwide. There are limited data about the effect of potassium (K) fertilizer on industrial hemp yield for dual purposes (seed and stem production). The current study aimed to investigate the influence of adding two different K fertilizers, KCl and K₂SO₄, at two growth stages (flowering and ripening) on the productivity and chlorophyll a fluorescence (ChlF) of Cannabis sativa, variety Finola. Before sowing, different K treatments were applied: K₁—100 kg ha⁻¹ KCl (60% K) and K₂—100 kg ha⁻¹ K₂SO₄ (52% K, S 17%). The OJIP (O stands for “origin” (minimal fluorescence), P for “peak” (maximum fluorescence), and J and I for inflection points between the O and P levels) data were recorded and used for ChlF transients and individual ChlF parameters during vegetation. At harvest, the stem morphology parameters and yield (plant height, stem weight and diameter, and stem and seed yield), tensile strength, and the modulus of elasticity were determined. The results show the sensitivity of minimal (F₀) and maximal fluorescence (F_m), electron transport from Q_A to intersystem electron acceptors (ET₀/(TR₀ − ET₀)), and electron transport flux until PSI acceptors (RE₀/RC) to K fertilization. The parameters that described electron transport (ET₀/RC, ψE_0, and φE₀), performance index on absorption basis (PI_ABS, TR₀/DI₀, and φP₀), dissipation (DI₀/RC), and electron transport to photosystem I (φR₀ and δR₀/(1 − δR₀)) had a reaction only at the growth stage, indicating a change in their activity during the aging of the Cannabis sativa plants. The average stem height was 67.5 cm, and the stem diameter was 0.41 cm. The different K sources did not significantly influence the stem height and diameter, nor the dry stem (on average 12.2 t ha⁻¹) and seed yield (on average 1.85 t ha⁻¹). The tensile strength of individual hemp stems was the highest with K₂SO₄ (53.32 MPa) and the lowest with KCl (49.25 MPa). The stem stiffness by modulus of elasticity was about 5 GPa on average for all the treatments. In general, the photosynthetic parameters in this study varied more between the growth stages than between the different K fertilizer formulations. Moreover, based on the results of this study, it can be recommended to use both fertilizers, KCl and K₂SO₄, in dual-purpose industrial hemp production since no significant effect was found for the stem morphometric and biomechanical parameters as well as for the agronomic parameters.

Sandwich structures are well-known and frequently used solutions in marine applications, especially when structural stiffness is required. An important part of the sandwich structure is the core, which usually carries shear loads. Therefore, choosing a reliable test method and knowing the exact shear properties of the particular core used in the structural design is beneficial for every engineer. Shear properties of the FlexyFoam M-55, a closed-cell, lightweight PVC foam with an apparent density of 60 kg/m³, have been investigated according to the ASTM C273 standard, using the tensile and compressive loading of metal supporting plates glued to the PVC foam sample. A digital image correlation (DIC) technique was used to monitor the crack propagation, and the appearance of secondary stresses at the foam-adhesive interface and strain field for the representative sample was presented. Displacement was measured using the testing machine sensors and compared to the measurements from the DIC technique. Specimen manufacturing details, surface preparation, and the gluing sequence were described, and measuring equipment and experiment settings were presented. Stress-strain curves have been presented and shear modulus and ultimate shear strength of the foam were compared for each test approach. The results were discussed and compared with the manufacturer’s data, as well as with foams of similar densities. The well-established approach in testing the core material was discussed, and recommendations were given to improve the testing procedure.

In this study, a hysteresis envelope mathematical model for the double extended end-plate bolted beam-to-column joint is proposed. The aim of a proposed joint model is to provide a more realistic behaviour of steel frames under seismic loading by using nonlinear static pushover analysis. The hysteresis envelope model defines the ratios between the monotonic properties of the joints and the properties of the joints during cyclic deformation. The proposed models are based on the hysteresis curves of the joints obtained by numerical simulations. The numerical model takes into account the geometric nonlinearity of the connecting elements, preloading of bolts, contacts between plates and bolts, and nonlinear properties of steel. Nonlinear static pushover analyses of steel frames are performed where the behaviour of the joints is described using the proposed hysteresis envelope models. The results are compared with the nonlinear static pushover analyses of steel frames with a trilinear monotonic joint model. Based on the results, the values of maximum peak ground acceleration for moment-resisting frames with the monotonic model of joints and hysteresis envelope model are estimated.