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Tomazevic M.,Slovenian National Building And Civil Engineering Institute
Brick and Block Masonry: Trends, Innovations and Challenges - Proceedings of the 16th International Brick and Block Masonry Conference, IBMAC 2016 | Year: 2016

Some aspects of testing and experimental research of seismic behaviour of masonry walls and buildings, based on the experience obtained at Slovenian National Building and Civil Engineering Institute, are discussed. Typical testing methods are presented and the influence of governing parameters, such as boundary conditions, loading protocols and scale effects, on failure mechanisms and test results, discussed. Typical examples of experimental research to investigate various issues of seismic behaviour of masonry buildings are also briefly presented. © 2016 Taylor & Francis Group, London.


Trtnik G.,IGMAT Building Materials Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Ultrasonics | Year: 2014

To summarize some of the most important findings in the field of ultrasonic (US) testing of early age hydration and formation of structure of different cement based materials (CBMs), a review of literature with focus on US P-wave transmission and S-wave reflection methods is presented in this paper. The review shows a great ability of both US techniques to observe setting phenomena and to determine different milestones during the early age formation of CBM's microstructure. Clear physical basis, high accuracy, and non-destructive nature of the method indicate that US methods could become standardized in the near future. © 2013 Elsevier B.V. All rights reserved.


Trtnik G.,IGMAT Building Materials Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Cement and Concrete Research | Year: 2015

In this paper, a possibility of using frequency spectrum of ultrasonic P-waves to determine very early age compressive strength (fc) of cement based materials (CBMs) is analyzed. TG parameter, representing the ratio between maximum amplitudes of high and low frequency ranges that appear in the frequency spectrum of the transmitted signal, is used to observe the changes in the spectrum. Both fc and TG start to increase simultaneously and later develop according to similar trend. Thus, strong correlation between fc and TG is established, regardless of the CBM's composition. By comparing stress-strain curves and time derivatives of TG-t curves, the stage when the material is clearly plastic and stage when material exhibits solid behavior, can be distinguished. These results explain physical meaning of TG parameter in more detail and expand the range of practical applications of methods based on spectral analysis of transmitted P-waves. © 2014 Elsevier Ltd. All rights reserved.


Gams M.,Slovenian National Building And Civil Engineering Institute | Trtnik G.,IGMAT Building Materials Institute
Cement and Concrete Research | Year: 2013

The paper presents a new method to determine the transition of different cementitious materials from liquid to solid state, usually defined as a setting period. The method is based on a ratio between maximum amplitudes of two dominant frequency ranges that appear in the frequency spectrum of ultrasonic (US) P-waves, called a TG parameter. Clear and unambiguous correlation between characteristic points in the evolution of TG parameter and penetration resistance in time is established on samples with different material composition during the early hydration process. The correlation indicates that TG parameter detects the development of rigid bonds between hydrating cement particles. The ability and accuracy of the method to determine setting period is unaffected by the material composition. Non-destructive nature and insensitivity of the method to aggregate size gives it an advantage over penetration methods and other US methods in determining the setting period of cement pastes, mortars, and concretes. © 2013 Elsevier Ltd.


Trtnik G.,IGMAT Building Materials Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Cement and Concrete Research | Year: 2013

In this paper, a possibility of using a frequency spectrum of ultrasonic P-waves to monitor the formation of structure of cement pastes at early ages is studied. A new parameter, labeled as a TG parameter, is defined as a dimensionless ratio between maximum amplitudes of two dominant frequency ranges that appear in a frequency spectrum of received ultrasound signals. Four stages and three characteristic points can be identified on the TG-vs.-time graphs, indicating that the development of the frequency spectrum is closely related to the setting phenomena. By comparing the TG parameter with the P-wave velocity and temperature evolutions in time, important milestones in the process of formation of microstructure were identified, such as the time of reduced workability and a period of intensive setting. The combined use of P-wave velocity and TG parameter results in a comprehensive ultrasonic method that gives a more complete picture of setting. © 2012 Elsevier Ltd. All rights reserved.


Cesen A.,Slovenian National Building And Civil Engineering Institute | Kosec T.,Slovenian National Building And Civil Engineering Institute | Legat A.,Slovenian National Building And Civil Engineering Institute
Corrosion Science | Year: 2013

In the study characterization of steel corrosion in concrete at the macro- and micro-level was performed. Physical (electrical-resistance probes) and electrochemical techniques (coupled multi-electrode arrays) were implemented in order to upgrade the general information that conventional electrochemical techniques can provide. Measurements were performed in mortar exposed to periodic wetting and drying. Steel corrosion damage was assessed by micro X-ray computer tomography (CT) and SEM. The results were compared and interpreted. By combined use of micro-CT and electrochemical methods, new insights into the corrosion mechanisms of steel in concrete were obtained. © 2013 The Authors.


Tomazevic M.,Slovenian National Building And Civil Engineering Institute | Weiss P.,Slovenian National Building And Civil Engineering Institute
Bulletin of Earthquake Engineering | Year: 2010

The results of shaking table tests of a series of 1:5 scale masonry building models have been used for the assessment of values of structural behavior factor q for masonry structures, seismic force reduction factors proposed for the calculation of design seismic loads by Eurocode 8, European standard for the design of structures for earthquake resistance. Six models have been tested, representing prototype buildings of two different structural configurations and built with two different types of masonry materials. The study indicated that the reduction of seismic forces for the design depends not only on the type of masonry construction system, but also on structural configuration and mechanical characteristics of masonry materials. It has been also shown that besides displacement and energy dissipation capacity, damage limitation requirement should be taken into account when evaluating the values of behavior factor. On the basis of analysis of experimental results a conclusion can be made, that the values at the upper limit of the proposed range of values of structural behavior factor q for unreinforced and confined masonry construction systems are adequate, if pushover methods are used and the calculated global ductility of the structure is compared with the displacement demand. In the case where elastic analysis methods are used and significant overstrength is expected, the proposed values are conservative. However, additional research and parametric studies are needed to propose the modifications. © 2010 Springer Science+Business Media B.V.


Hiti M.,Slovenian National Building And Civil Engineering Institute
Measurement Science and Technology | Year: 2015

This article describes a resistor network for linearity verification of voltage ratio-indicating instruments. The network is based on a resistive divider with low variation of input and output resistance. To compensate for the output resistance change due to a selection of various output ratios, a switched variable compensating resistor network is added to the output leads of the voltage divider. It limits the variation of output resistance to <5% at a ratio of 1:10 and <0.5% for ratios 1:100 or higher. The application of the circuit is shown in the example of an output voltage ratio simulation of a strain gauge bridge transducer, typical in the measurement of mechanical quantities such as force, torque, and pressure. The circuit is suitable for verifying the linearity of voltage ratio measuring instruments by using a combinatorial calibration technique without the need to calibrate the resistor network. Results are shown for the linearity check of a high-precision strain gauge amplifier. © 2015 IOP Publishing Ltd.


Tomazevic M.,Slovenian National Building And Civil Engineering Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Bulletin of Earthquake Engineering | Year: 2012

The response of autoclaved aerated concrete confined masonry buildings to seismic ground motion has been studied. Three 1:4 scale models of residential buildings with the same distribution of walls in plan but different types of floors and number of stories have been tested on a uni-directional shaking table. Lightweight prefabricated slabs have been installed in the case of the three-storey model M1, whereas reinforced concrete slabs have been constructed in the case of three-storey model M2 and four-storey model M3. Model M1 was subjected to seismic excitation along the axis of symmetry, whereas models M2 and M3 were tested orthogonal to it. Typical storey mechanism, characterised by diagonal shear failure mode of walls in the ground floor in the direction of excitation has been observed in all cases. Taking into consideration the observed behaviour, a numerical model with concentrated masses and storey hysteretic rules has been used to simulate the observed behaviour. Storey resistance curves calculated by a push-over method and hysteretic rules, which take into account damage and energy based stiffness degradation hysteretic rules, have been used to model the non-linear behaviour of the structure. Good agreement between the experimentally observed and calculated non-linear behaviour has been obtained. © Springer Science+Business Media B.V. 2011.


Tomazevic M.,Slovenian National Building And Civil Engineering Institute
International Journal of Architectural Heritage | Year: 2011

In the past three decades, significant research has been conducted on seismic behavior of masonry buildings in historic urban and rural nuclei. On the basis of the earthquake damage observations and subsequent experimental simulations of the observed mechanisms, technical measures for the improvement of the seismic resistance have been proposed and methods for seismic resistance verification developed. By in situ and laboratory testing, the basic mechanical properties of the existing and strengthened masonry have been determined. The research results have been used to analyze the requirements of Eurocode regarding the design methods and parameters for structural assessment and retrofitting of buildings. Modifications have been proposed that would lead to more realistic assessment of seismic resistance in the case of historic masonry buildings. For this purpose, the seismic behavior of buildings, subjected to design-level earthquakes for the second time in just a few decades, has been analyzed and correlated with the actually observed earthquake damage. Copyright © Taylor & Francis Group, LLC.

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