Search Results

You are looking at 1 - 10 of 52 items for

  • Author or Editor: I. Kovács x
Clear All Modify Search

Abstract

The present paper of a series deals with the experimental characterisation of compressive strength and compressive behaviour (stress-strain relationship) of different structural concrete containing different volume of steel fibre reinforcement (0 V%, 0.5V%, 1.0V%, 75 kg/m3, 150 kg/m3) and different configuration of steel fibres (crimped, hooked-end). Compressive tests were carried out on standard cube (150 mm × 150 mm × 150 mm) and cylinder (Ø = 150 mm, l = 300 mm) specimens considering random fibre orientation. Since the fibre orientation may significantly affect the compressive behaviour, test series were also performed on cylinders (Ø = 70 mm, l = 100 mm) drilled out of fibre reinforced concrete beams and prisms (100 mm × 100 mm × 240 mm) sawn out of steel fibre reinforced deep beams. Throughout the tests stress-strain relationships were registered on the standard cube and cylinder specimens as well. In conclusion, behaviour of steel fibre reinforced concrete was examined in compression taking into consideration different experimental parameters such as fibre content, type of fibres, fibre configuration, fibre orientation, size of specimens (size effect) and concrete mixture.

Restricted access

Abstract

The papers of the series deal with experimental characterisation of mechanical as well as structural properties of different steel fibre reinforced concretes that can be used for several structural applications. An extensive experimental programme (six years) has been developed to investigate the effect of steel fibre reinforcement on the mechanical performance and structural behaviour of concrete specimens. Specimens and test methods were selected to be able to detect realistic behaviour of the material, representing clear effect on the structural performance. Material compositions, test methods, type of test specimens will be detailed in the presented paper (Part I).

Furthermore, compressive strength (Part II), stress-strain relationship (Part II), splitting strength (Part III) and toughness (Part IV) will also be discussed. In the light of the motivation to determine the structural performances of 1D concrete structural element affected by steel fibre reinforcement, bending and shear behaviour (Part V) as well as serviceability state (Part VI) of steel fibre reinforced concrete beams will be analysed. Since normal force — prestressing force — can affectively be used to improve the structural performances of RC element flexural tests were carried out on prestressed pretensioned steel fibre reinforced concrete beams (Part VII). Moreover, focusing on the in-plane state of stresses for 2D structures, behaviour of steel fibre reinforced concrete deep beams in shear and steel fibre reinforced concrete slabs (Part VIII) in bending will be explained. Finally, based on the wide range of the experimental and analytical studies on the presented field, a new material model for the 1D uniaxial behaviour (Part IX) and its possible extension to the 3D case (Part X) will be described hereafter. All papers will put emphasis on the short literature review of the last four decades.

Restricted access

The present paper of a series deals with the experimental characterisation of tensile splitting strength and compressive behaviour of different structural concrete containing different volume of steel fibre reinforcement (0 V%, 0.5 V%, 1.0 V%, 75 kg/m3, 150 kg/m3) and different configuration of steel fibres (crimped, hooked-end). Tensile splitting tests were carried out on standard cylinder (∅ = 150 mm, l = 300 mm) specimens (so-called Brazilian test) considering random fibre orientation. Since the fibre orientation may significantly affect the tensile behaviour test series were also performed on cross-section (100 mm × 100 mm) of steel fibre reinforced concrete beams (100 mm × 100 mm × 240 mm) sawn out of steel fibre reinforced slab elements. Taken as a whole behaviour of steel fibre reinforced concrete was examined in tension taking into consideration different experimental parameters such as fibre content, type of fibres, fibre configuration, fibre orientation, size of specimens (size effect) and concrete mixture.

Restricted access

The present paper of a series deals with the experimental characterisation of flexural toughness properties of structural concrete containing different volume of hooked-end steel fibre reinforcement (75 kg/m3, 150 kg/m3). Third-point flexural tests were carried out on steel fibre reinforced concrete beams having a cross-section of 80 mm × 85 mm with the span of 765 mm, hence the shear span to depth ratio was 3. Beams were sawn out of steel fibre reinforced slab elements (see Part I) in order to take into consideration the introduced privilege fibre orientation (I and II) and the position of the beam (Ba-a, Ba-b, Ba-c) before sawing (see Part I). Flexural toughness properties were determined considering different standard specifications, namely the method of the ASTM (American Standards for Testing Materials), the process of the JSCE (Japan Society of Civil Engineering), and the final proposal of Banthia and Trottier for the post cracking strength. Consequently, behaviour of steel fibre reinforced concrete was examined in bending taking into consideration different experimental parameters such as fibre content, concrete mix proportions, fibre orientation, positions of test specimens in the formwork, while experimental constants were the size of specimens, the type of fibre used and the test set-up and test arrangement.

Restricted access
Restricted access

The time-series ofδ18O values measured weekly in Lake Balaton gave a chance to estimate the period time. To do this, we used a recently worked-out psd estimation method, the Lomb-Scargle periodogram (Lomb 1976, Press et al. 1992), in which the type of distribution can be given exactly to the power values, so confidence interval can be calculated. The result, however, is only a characteristic mean value of the time-interval examined, so the changes of the period-time were examined by demodulation. The essence of the method is that the process (time-series) is let through a filter that is permeable at merely one frequency, all the other frequency components are filtered out, so the difference from the mean period time can be placed in time. We also examined to what extent the water samples coming from one bay of Lake Balaton are representative of the whole lake. Hierarchical clustering was carried out on the hydrobiological and hydrochemical parameters of water samples coming from ten sites of Lake Balaton to determine the similar sampling sites. After the clustering, part of the sampling sites fell into different groups in the examined 16 sampling times. So the groups were marked in all the 16 sampling times with a code that shows to which group that actual sampling site belongs. In this way, each sampling site was placed in a 16-dimension space. Thus, another clustering became possible, so the grouping related to the given time period could be determined. The result was checked by statistical calculations.

Restricted access

A widely described phenomenon all over Europe is that reed decline begins from greater water depths - i.e. clumping is more expressed at the open water fringe while stands towards the lakeshore are homogeneous and intact. To understand the possible background processes, the present paper examined the differences between the element concentrations of reed organs (root, rhizome, stem and leaf), and the substrate (i.e. sediment or soil) along water depth gradients in Lake Balaton, Hungary. Differences between the mineral compositions of reed organs and the substrate and the impact of water depth on element concentration of samples were investigated. Relations between water depth and element concentrations of substrate and plant organs and interelement correlations in the samples were also considered. In addition to other results, element concentrations provided indirect evidence for increasing hypoxia (anoxia) in the sediment under greater water depths possibly contributing to reed decline. Although, the greater water depth is associated with higher element concentrations in the substrate, the uptake of minerals in reed are impeded by anoxia. Towards the greater water depth, for instance, the higher N concentration of substrate was not associated with more N in leaves (even a slight decrease was observed). On the other hand, elements (e.g. Fe and S) with increasing availability in reduced state, reached high concentrations in reed leaves from greater water depth, which may also indicate the insufficient O2 level in the rhizosphere

Restricted access