Applied Mechanics and Materials Vol. 827

Abstract: Relocation of existing concrete structures requires full or partial demolition, which consumes a lot of energy and thus has a negative impact on the environment. From environmental point of view, demountable precast structures are sustainable. They allow “recycling” to the level of precast elements and so they save significant amounts of energy and materials. Another advantage of these structures is quick assembly without wet processes. A characteristic component of precast reinforced concrete construction system for multi-storey buildings are demountable joints of load-bearing precast reinforced concrete elements. This paper is focused on experimental verification of demountable precast column structure and its demountable steel joints. The experimental research was carried out within TA02010837 “Multipurpose dismantleable prefabricated reinforced concrete building system with controlled joint properties and possibility of repeated use”.

Abstract: This paper is focused on the assessment of serviceability of the footbridge structure, which has been excited by pedestrians and vandals. The three dimensional FE model of the footbridge structure was created for the necessities of theoretical modal analysis. Computed mode shapes and natural frequencies were subsequently used for the forced vibration analysis as an input files into MATLAB code. Results obtained by the theoretical analysis were compared with the experimental results. At the end of this paper, the comfort criterion of crossing pedestrians has been evaluated.

Abstract: This paper is focused on the mechanical properties development of fine recycled aggregate (FRA) concrete. FRA was obtained from recycling plant in the Czech Republic. There were prepared four concrete mixtures in the laboratory. The first mixture was reference (REF) with fine natural aggregate (FNA). FNA was replaced in concrete mixtures R10, R20 and R30 in varying replacement ratio. The concrete mixtures R10, R20 and R30 contained 10 %, 20 % and 30 % FRA. There were tested properties of concrete. Finally, it is possible to say that the use of the FRA in concrete influences concrete properties. It is necessary to verify of probably an improvement of compressive strength of FRA concrete in future research. However, FRA concrete is possible to be used in the manufacturing of building structures, but it is necessary to test durability and lifespan of FRA concrete.

Abstract: This article deals with experimental testing of the textile reinforced concrete samples. The main topic of this article is determination ultimate tensile strength of the textile reinforced concrete. The testing samples were in form “dogbone” for good fixing in testing machine. There are 12 samples totally in experimental program. One type cement matrix and three types (difference in their weight 125 g/m², 275 g/m² and 500 g/m²) glass textile reinforcement were used for the production of samples. The textile reinforcement is made of alkali-resistant glass fibres. Three samples were made of cement matrix and nine samples were made of cement matrix reinforced textile reinforcement (three of each type of reinforcement). The samples were tested in special attachment in one-axial tensile. Experimental tests were controlled by speed of rate of deformation (0.0005 m/min). The textile reinforcement has very good influence to behaviour of the textile reinforced concrete in tensile stress.

Abstract: The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions, especially in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water and from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to sulfate interaction can result in the cracking and softening, with loss of strength of concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of one-year contact of 0.5% H₂SO₄, and 5% Na₂SO₄ on changes of pH and content of sulfates in 7 types of concrete has been analyzed. It was found that after one year of sulfate attack on concrete, significant growth of content of sulfates is observed in the lowermost layer of the samples. Samples treated by 5% Na₂SO₄ contain slightly more sulfates in the upper layers than samples treated by sulfuric acid. The reduction in pH of aqueous leaches occurred in all layers of the samples. However, even in the lower layers of the samples, the reduction of pH below 9.5 did not turn up (except for SRS sample), and thus the conditions for the depassivation of reinforcement were not met.

Abstract: A numerical model for unreinforced masonry columns and masonry columns reinforced by FRP wrapping is presented in this paper. Both, the bricks and the mortar are modeled as 3D continuum and to the interface between these two materials a non-linear contact law is assigned. The accurate 3D modeling of masonry units and mortar joints within the numerical model leads to high computational cost, but on the other hand, an appropriate analysis tool delivering detailed information about the behavior of masonry columns is obtained. A concrete damaged plasticity model was adopted for mortar and brick. External wrapping by a perfectly-adherent composite based strips and contact between strips and masonry is defined in the next step. The behavior of reinforcement was assumed isotropic and linearly elastic. The response and failure mechanism of masonry columns can be investigated. For all simulations the commercial software package ABAQUS was used. By comparison with results from experiments [1], the performance of the numerical model is evaluated and the obtained numerical results are discussed.

Abstract: This paper analyzes critical forces and stability of steel thin-walled C-cross-section beams without lateral restraints. Mechanical properties of the rods material are determined by testing standard specimens in a laboratory. Based on the obtained data, the stability analysis of rods is carried out and critical forces are determined: analytically by using the theory of thin-walled rods, numerically by using the finite element method (FEM), and experimentally by testing the C-cross-section beams. The analysis of critical forces and stability shows that the calculation according to the theory of thin-walled rods does not take the effect of local buckling into account, and that the resulting critical global forces do not correspond to the actual behaviour of the rod. The FEM analysis and experimental test show that the simplifications, which have been introduced into the theory of thin-walled rods with open cross-sections, significantly affect final results of the level of the critical force.

Abstract: Records of fracture tests on steel fibre reinforced concrete notched specimens in a three-point bending configuration are evaluated in detail and selected results are discussed in the paper. The values of fracture parameters are determined using work of fracture method and double-K fracture model. Primarily, the role of plain concrete as a matrix in steel fibre reinforced concrete specimens is studied with regard to the recorded fracture response.

Abstract: Glass fiber-reinforced lime-based mortars have been studied. Two different fiber reinforcement amounts were used as an addition to the mixtures. Compressive strength and post-cracking behavior of mortars were observed and compared with reference mixture without any reinforcement (marked R). The fibers were added in the amount of 1.8 kg/m³ (mortar samples MA) and 93.75 kg/m³ (mortar samples MB). Destructive compression tests were chosen to compare the performance of the individual mixtures. The maximum compressive strength reached during the testing was the highest for reference samples, while those samples together with MA exhibited the elastic-brittle behavior. Only MB had post-linear hardening behavior and after reaching the maximum compressive strength a slow softening was present.

Abstract: This paper is dedicated to the use of fly ash in cement and concrete. Using fly ash in cement and concrete has ecological and economic benefits. However, it is important to correctly apply the fly ash. If the substitution is close to 50% or more by weight of clinker (HVFAC - High-Volume Fly Ash Concrete), it is necessary to monitor the material and mechanical properties. This paper describes an analysis of a frost resistance of a cement paste with fly ash. The destructive and non-destructive tests were carried out.