Applied Mechanics and Materials Vol. 821

Abstract: Mechanical properties and durability of Ultra-High Performance Concretes (UHPC) are closely associated with composition and microstructure of tested samples. In this work, determination of effective elastic properties of UHPC composite was performed for a representative volume element using combination of microstructural investigations (scanning electron microscope imaging, image analysis of back scattered electron micrographs and nanoindentation) and analytical methods of micromechanics. Based on the volumetric content and micromechanical behavior of individual components an effective elastic modulus of the whole composite was predicted and compared with macroscopically measured value with good agreement within 5%.

Abstract: In the study, the bending behavior of high-performance fiber reinforced lime-based mortars is experimentally investigated using four-point bending test. From the experimental data, the influence of the mortar’s composition on its stiffness, cracking strength and ultimate strength are investigated. It is also studied, whether the response has strain-softening or strain-hardening character and whether the material exhibits multiple cracking. Such behavior is very important for the durability of the material, because it allows carrying load during imposed deformations (due to thermal effects, movements of foundations, seismicity, etc.). The number of formed cracks is examined using digital image correlation method. The mortar composition is considered with two types of binder (pure lime, lime-metakaolin), with two types of polyvinyl alcohol fibers in four volume fractions (0.5÷2.0%). As the reference, we consider two sets of specimens made of plain mortar without fiber reinforcement.

Abstract: The influence of foaming agent on the properties of steel-reinforced beams made of recycled plastic material is studied in the paper. The foaming agent creates a porous core in the recycled plastic elements. This core must be reflected when deriving the beam effective properties to be used in macroscopic simulations. To that end, standard image analysis combined with nanoindentation and the Mori-Tanaka micromechanical model is adopted to identify elastic material properties of the plastic material both inside and outside of the core. These are expected to enter an independent macroscopic analysis of the steel-reinforced beams.

Abstract: Thin-walled construction represents a powerful tool for saving steel and thereby for increasing the competitiveness of steel structures. However, on the other hand, as the limit state of thin-walled structures is substantially affected by stability phenomena, the above concept can be implemented just on the condition of post-buckled behaviour being taken into account in the solution to these stability phenomena. The paper first briefly studies the factors on which the intensity of the very favourable post-buckling reserve of strength depends and then in detail turns attention to the most important among them, viz. the effect of the cumulative-damage process that becomes manifest in the case of bridges and other systems subjected to many times repeated loading.

Abstract: This article reports on a new tool for optimized design of reinforced concrete plates based on the yield-line theory. The primary focus is on the development of a computer program which can analyze arbitrary yield-line systems with one degree of freedom. The program includes a GUI for quick and intuitive input, and automatically performs analysis of yield-line systems regardless of the complexity of their analytical solution. Furthermore, optimization of orthotropic reinforcement is implemented. The possibility of yield-line analysis of systems with multiple degrees of freedom by linear programming is examined.

Abstract: The behaviour of reinforced concrete slab-column structures under the impact of accidental loading is very significant due to safety reasons. The failure of the support zone by punching and lack of proper structural integrity reinforcement can lead to a progressive collapse. However, the instructions on how to prevent such situations are not very detailed. According to the guidelines of standard EC2, the structural integrity reinforcement should be continuous throughout the length and consist of at least two bars above the column in every perpendicular direction. EC2 does not state the amount of necessary reinforcement. The article presents a theoretical model of calculation that permits a more detailed analysis of internal forces in reinforcing bars located directly above the column. Adopting a solution in the form of exact equations makes it possible to take into account the influence of a non-linear change of the bar rigidity and considerable deflections. The calculation model was verified on the basis of the results of experimental investigations. It enables to estimate the tensile force of the bar at which it is ruptured during the destruction of the support zone.

Abstract: A great advantage of computer calculations is the opportunity to map the whole floor, including the supporting beams, columns and walls, in one model, with the members fully cooperating with one another. In this way the need for strenuous compiling of the loads on supporting members and independent searching for extreme values becomes eliminated. As a separate part of a floor, in this case a beam appears occasionally. The mapping of a beam in a model can have various forms. The paper presents a comparison of the influence of the way in which a rib is modelled on the results of statistical calculations. As a reference point for substitute shell models a solid spatial model was adopted.

Abstract: In a properly designed slab-column structure the failure of the floor should be signalled by cracks and significant and visible deflections of the floor in the spans. The paper presents two proposed ways of calculating a uniform loading causing the destruction of the central field of a typical slab-column structure. The values obtained in the limit state were compared with the value of the load obtained during the experimental research.

Abstract: The adaptive discretization technique for static discrete models of random geometry based on Voronoi cells is developed here. It is based on adding randomly located nodes into the highly stressed regions and updating the discretization based on those nodes before the crack may initiate in or propagate through the regions.

Abstract: Cement-based composites are traditionally used building materials. Concrete is the basic representative of this type of materials which exhibit the so called quasi-brittle response. Quantification of mechanical fracture parameters is performed using fracture tests on specimens with a stress concentrator. Load versus crack mouth opening displacement (P–CMOD) diagrams are recorded during these tests. In order to correctly evaluate these diagrams, an advanced own developed software tool was used for the data filtering and appropriate modifications. In this paper, the programmed Java utility is generally introduced and its utilization demonstrated on the set of recorded P–CMOD diagrams, which are further evaluated using Double-K fracture model.