Load Bearing Capacity Of Elements Research Articles

Усталостная долговечность изгибаемых железобетонных элементов со смешанным армированием

An experimental-probabilistic analysis of variations in the load-bearing capacity of bending reinforced concrete elements with matrices reinforced by polypropylene fibres was carried out. A numerical ex-periment was conducted using the normative methodology of multi-link and layerwise modelling of el-ement cross-sections and experimental "σ-ε" diagrams of fibrocomposites in initial and post-cyclic (50 cycles with η = 0.8 amplitude and zero asymmetry) states. Probabilistic changes in the load-bearing capacity of bending elements subjected to cyclic loads were estimated by the numerical strength modelling of rectangular beams (b × h = 100 × 200 mm) with the one-sided reinforcement (A400 class) of varying intensity. The observed high value of fatigue life of reinforced concrete ele-ments with fibre-reinforced matrices was found to be associated with the presence of mechanisms compensatory for structural changes, i.e., a decrease in the strength is accompanied by an increase in the ability to redistribute internal forces. A post-cyclic reduction in the strength of concrete causes practically no effect on the load-bearing capacity of bending elements with a large and economically preferable range of their structural reinforcement. The reliability kinetics of elements, estimated by the level of the realised concrete strength potential, was analysed. Moderate (μ ≤ μR) reinforcement was found to result in objective conditions for increasing the completeness of the stress diagram in the compressed cross-sectional part due to the redistribution of forces along the height. In this case, de-spite a significant decrease in the strength of concrete, the load-bearing capacity of elements at μ ≤ 2.5% reinforcement remains practically the same after cyclic effects.

Simulation of Performance of CFST Elements Containing Differentiated Profile Tubes Filled with Reinforced Concrete

The approach to calculating CFST elements is considered in which physical non-linearity of materials, geometric non-linearity of the tube and the effect of increasing the strength of the core are taken into account. Finite element models are developed and proposed as the basis for more accurate method of calculating concrete-filled steel elements consisting of differentiated profile tubes filled with reinforced concrete. The technique uses a step iteration algorithm involving analytical dependencies and finite element simulation. The criterion for determining the load bearing capacity of CFST elements was the achievement of the stresses in the tube of the characteristic strength. The possibility of estimating the load bearing capacity of elements by limiting stresses in the core concrete is also implemented. The result of the calculations was obtaining the stress-strain and limiting state of the differentiated profile tubes with CFST elements, and graphic analysis of the regularities of stress redistribution at different stages of performance of columns. In general, with the accepted problem statement we could establish the exact stress-strain state, take into account the elastic-plastic deformations of concrete, its cracking and destruction, and geometric nonlinearity of the tube. The effect of performance of the corrugated sheet as a tube was established.

Load-bearing capacity of concrete elements reinforced with steel and composite coatings

In the article, the compressive strength of steel-concrete structures defined as CFST (Concrete Filled Steel Tubular) has been checked. The steel elements used in CFST columns have high tensile strength and ductility while the concrete elements have high compressive strength and stiffness. Therefore, CFST elements have a large range of applications in construction. The analysis included 8 examples of elements consisting of a steel tube filled with a concrete core. The examples differed in the thickness of the steel coating and the compressive strength of the concrete core. Analytical calculations and experimental studies for them were carried out. The analytical calculations were based on the author’s method of assessing the load-bearing capacity of concrete-filled steel tubes. In experimental verification, CFST samples were subjected to a static compression test. The calculation method was also used to calculate the load capacity when composites reinforcement is the outer coating for the concrete core. Three types of composites were analysed. The obtained results show a large influence of the steel coating thickness on the compressive strength for the CFST elements. The load-bearing capacity of the elements depends on the appropriate ratio of the surface of the steel coating to the concrete coating.

Analysis of spherical indentations of coating-substrate systems: Experiments and finite element modeling

The influence of surface layers and thin coatings on the load-bearing capacity of elements under contact load conditions has yet to be sufficiently described theoretically. In this study, the deformations of coated surfaces were analyzed using spherical indentation and finite element method (FEM) modeling. The paper presents a complex procedure of indentation result analysis, based on the transformation of load-penetration depth curves into stress–strain curves. Such a procedure was applied for 0.7–2.4μm thick titanium nitride (TiN) coatings deposited by the Pulsed Laser Deposition (PLD) technique on steel substrates. Indentation experiments showed that the critical stress for fracture of TiN coatings deposited on steel substrates is 2–3GPa. The result of the theoretical analysis, FEM modeling and experiments is the map of failure, which shows elastic, elastic–plastic and fracture regimes of the tested coating-substrate systems.