Utilization of fibre concrete in building structures, supported by technical standards in preparation, stimulates the development of methods for nondestructive analysis of its structure, crucial for mechanical properties, as fracture resistance under tensile loads. The paper presents an overview of available methods, based i) on image processing and ii) on measurements of electromagnetic quantities.
This report presents a new method for designing composite timber steel-fibre-reinforced concrete slabs with unprotected secondary timber beams subject to fire, taking tensile membrane action into account. The FE-model consists of material tests, push-out shear tests and beam tests, which had formed a preliminary study. The FE-model represents the behaviour of the floor slab tested in experiment, together with a collapse prediction for the slab. The FE-model with characteristic material properties includes a safety concept based on the Eurocode standards, and is applied to define the fire resistance of various types of timber steel fibre-reinforced concrete flooring.
This paper discusses the practical use of microwave technology in construction practice. Opinions on the use of EMW devices are not only among the general public quite different. From boundless praise, to the uncritical condemnation. The reason for this situation is the lack of awareness of experts and the public about what is and what is not possible to expect from this technology.The article conclusions which we reached on the basis of experiments conducted at the Faculty of Civil Engineering Brno and subsequently verified measurements in field practice. The aim is to provide basic information about how to use microwave technology. Their benefits but also the risks that this technology brings along.
Long-time study of fibre-reinforced concrete, i.e. a composite material with a cementitious matrix, whose structure is hardened by usually randomly distributed fibres (steel ones in the most frequent case), demonstrates good mechanical and other technical properties, which makes possible its utilization in bearing structures. This stimulates the development of methods, non-destructive or low-invasive if possible, for the analysis of its structure, which determines crucial mechanical properties, e.g. fracture resistance under tensile loads. This article, coming from research activities of the Faculty of Civil Engineering at Brno University o Technology, brings an overview of available methods, namely direct methods coming from image processing and indirect ones utilizing measurements of electromagnetic quantities.
The article deals with hot-air treatment of a historically valuable Rožnov town office, built in 1770, which was transported to the Wallachian Open Air Museum in Rožnov pod Radhoštěm in 1924 as the first building of the currently extensive premises of this national cultural heritage. The method of wooden structure hot-air treatment was used for the first time in the territory of the Czech Republic in 2010. It has been used in western European countries (especially Denmark and Germany) approximately since 1930. This comprehensive method is governed by the German standard DIN 68 800 – Part 4 [1] and it is especially used for historically valuable buildings where emphasis is put on the preservation of the original wooden structure attacked by wood-destroying insects, usually of the long-horn beetle family (Cerambycidae) oranobium beetle family (Anobiidae). The goal of the article is to explain the hot-air treatment method to professional public using an example of one of implementations.
Water vapour permeability is one of significant material properties. The value of water vapour resistance factor is necessary to know to be able to rehabilitate structures, mainly after floods. One thing is essential – to know what are the values of water vapour resistance factor of the used material to know how long the structure will take to be dried and users can come back to live there.
Sulfate attack is one of the major threats for durability of concrete in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water as well as from biogenic activity of bacteria. Damage due to sulfate interaction can result in the cracking and softening with loss of strength of concrete and it may lead to the concrete desintegration. Gypsum is the primary product of sulfate attack on concrete, after which ettringite is subsequently formed. Ettringite and gypsum are considerably larger in volume than the initial compounds, which leads to increased pressure within the concrete structure. This paper is focused on the sulfate attack on fine-grained concrete where the effect of 12 months contact of 0.5% sulfuric acid, simulating biogenic sulfuric acid corrosion, 5% sodium sulfate solution and solution simulating sewage water on various types of concrete has been investigated. The concrete specimens were characterized after exposition to the corroding media by their mechanical parameters, changes in pH and content of sulfates. It was found that after one-year exposure to sulfuric acid solution, the compressive strengths of all types of concrete significantly decreased. Sodium sulfate solution and the artificial waste water did not represent the significant corrosion environments for the concretes in terms of their strength reduction, increasing of sulfate ions content and the reduction in the pH of their aqueous leaches. The fine-grained concretes containing metakaolin and ground limestone showed the highest coefficient of corrosion resistance for the applied corrosive solutions.
The subject of this paper is a comparison of two experiments of timber-fibre concrete floors in fire, which consist of steel fibre reinforced concrete boards and glue-laminated timber beams. Main aim of this project is to assess the using of steel fibre reinforced concrete board, which work together with glue-laminated timber beams to increase fire resistance and investigate its behaviour in loaded construction.
Steel frame structures are commonly analyzed three dimensionally by 1D elements. Connection of elements to joints is assumed to be perfectly rigid, nominally pinned or semi-rigid. The new CBFEM method allows to properly model the connection. The bending/deformation stiffness, resistance and deformation capacity of connections of individual members is evaluated. CBFEM model is loaded with appropriate internal forces obtained by global analysis. The article explains loading of a detailed 3D model of a joint. It also addresses situation where actual structural design of the joint does not match theoretical expectations of the global analysis.
The paper is focused on comparison of different types of compressive tests of samples exposed to high temperature. The tests could be divided into two basic types. The first type of the test is an ambient temperature testing to obtain residual compressive strengths and the second type is a hot state testing to obtain mechanical parameters of concrete exposed to high temperature.
The removal of unwanted material from the surface of historical artefacts is one of the most important and also the most delicate operations in the restoration of cultural heritage. In the Center for innovations in the field of nanomaterials and nanotechnologies a novel design concept of the cleaning microemulsions was developed based on a combination of the two functions, implemented by two components, namely a micellar solution or microemulsion of nonionic surfactants with the addition of co-surfactants and the specific solvents, which are selected according to the respective substances to be removed. The patented cleaning compositions can very effectively and selectively remove coatings of many substances important for the restoration practice, such as waxes, resins (e.g, Damara), paraffins, oils, water acrylate dispersions, hydrophobization coatings (both monomeric and polymeric) etc. Besides the efficient cleaning, the developed procedures have wider applications, such as in a new method of the hydrophobization of sandstone and limestone materials with a thin hydrophilic surface layer, which has been certified by the Ministry of Culture of the Czech Republic.
Non-aqueous dispersions of nanoparticles of calcium hydroxide and magnesium are principally suitable means for the consolidation of wall paintings and limestone materials because they are compatible with the material of historical artefacts. They are also suitable for the deacidification of paper and wood. In the Center for innovations in the field of nanomaterials and nanotechnologies procedures were developed which provide nanoparticles of calcium hydroxide and magnesium ranging in size from about 10 nm to about 200 nm. The procedures are relatively experimentally challenging and put them into practice will require further technological research. Thanks to the good stability of the dispersion a sufficiently long shelf life is ensured and premature aggregation on the surface or just below the surface of treated materials is prevented. There are several alternative methods of the consolidation stone, as exemplified by the use of alkoxides of calcium or magnesium. In converting the alkoxide to calcium carbonate, the sole by-product is alcohol, which naturally evaporates from the stone.
The paper introduces selected parts of the methodology for the technical state evaluation of the steel cylindrical tanks affected by the corrosion weakening. Technical conditions have been mainly worked out for the energetic company experts who are responsible for the realization and evaluation of the steel tanks diagnostics. Simplified analytical procedures have been developed to evaluate the influence of the measured corrosion weakening on the reliability of steel tank structures. The technical conditions serve mainly for a decision about the relevance of the corrosion damage: the corrosion weakening is insignificant with respect to the structural reliability or the corrosion failures are potentially dangerous with respect to the structural reliability and a detailed statistical assessment of the steel tank is necessary.
For rational design of concrete structures, it is necessary to take into account all types of loads to which the structure is exposed during the execution, operation and reconstruction. Biogas tanks belong to the group of constructions where the indirect and environmental loads represent a high risk to the reliability, particularly in terms of their serviceability and durability. The article analyses the effects of these loads as well as the causes of separation cracks formation.
The paper introduces modified arrangement of the test in axial tension for cement composites. Specific shape of the specimen and special steel grips to fix the specimen in testing machine are described. The arrangement of the test enables recording of the load-deformation diagram in the central part of the specimen and direct derivation of the stress-strain diagram.
