Papers by Nikolina Živaljić
Structural Engineering and Mechanics, Apr 25, 2016
The aim of this study is to investigate the seismic resistance of dry stone arches under in-plane... more The aim of this study is to investigate the seismic resistance of dry stone arches under in-plane seismic loading. For that purpose, several numerical analyses were performed using the combined finitediscrete element method (FDEM). Twelve types of arches with different ratios of a rise at the mid-span to the span, different thicknesses of stone blocks and different numbers of stone blocks in the arch were subjected to an incremental dynamic analysis based on excitation from three real horizontal and vertical ground motions. The minimum value of the failure peak ground acceleration that caused the collapse of the arch was adopted as a measure of the seismic resistance. In this study, the collapse mechanisms of each type of stone arch, as well as the influence of the geometry of stone blocks and stone arches on the seismic resistance of structures were observed. The conclusions obtained on the basis of the performed numerical analyses can be used as guidelines for the design of dry stone arches.
Materialwissenschaft Und Werkstofftechnik, May 1, 2019
This study presents the performance of a combined finite-discrete element method for prediction o... more This study presents the performance of a combined finite-discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretization of the concrete with triangular finite elements is coupled with one-dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non-linear behavior of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free-falling drop-weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams. Keywords: Crack pattern / finite-discrete element method / impact loading / numerical simulation / reinforced concrete beam Diese Studie zeigt die Leistung der kombinierten Methode der Finite-Diskrete-Elemente zur Vorhersage der Reaktion in der Struktur von Stahlbetonträ gern bei Stoßbelastung. Eine Kombination der Methoden der finiten und diskreten Elemente ermö glicht die Modellierung und die Bewehrung des Betons bevor dieser Risse aufweist sowie eine diskontinuierliche Beschaffenheit des Betons, verursacht durch Bruch und Zersplitterung unter hoher Stoßbelastung. Die Diskretisierung des Betons mit dreieckigen finiten Elementen ist mit eindimensionalen Bewehrungsstä ben verbunden, die in die finiten Elemente des Betons eingebettet sind. Die Rissbildung im Beton aktiviert die Verbindungselemente, die eingesetzt werden um das nichtlineare Verhalten von Beton und Bewehrung zu simulieren. Es wurde eine numerische Analyse aufgrund experimenteller Testdaten durchgefü hrt, um die Hauptmerkmale der Stahlbetonträ ger zu simulieren, beeinflusst durch frei fallende Gewichte. Es wurde eine hohe Genauigkeit bei verschiedenen Vergleichen zwischen den experimentellen Tests und den Analyseergebnissen festgestellt, einschließlich Spitzenverschiebung, Rissmuster, Schadensgrad und Fehlerarten bei Stahlbetonträ gern.
Proceedings of the VII European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016), 2016
Acta Mechanica, 2016
This paper proposes a numerical procedure that can predict the minimum duration of a rectangular,... more This paper proposes a numerical procedure that can predict the minimum duration of a rectangular, half-cycle sine wave, linearly increasing and triangular single-pulse excitation required to overturn the rigid block resting on a moving base. Since the linearization assumption in the derivation of an analytical solution, which has already been used by Housner and other researchers, cannot be valid for a block with various slenderness ratios and dimensions, a derivation of numerical solutions which would be valid for all types of block is necessary. The proposed numerical procedure takes into account the possibility of sliding and uplifting of the block from the base. The numerical algorithm for the proposed numerical procedure in a commercial code C++ is given in the "Appendix."
International Journal of Architectural Heritage
Engineering Computations, 2013
Purpose – The purpose of this paper is to present a new numerical model based on a combined finit... more Purpose – The purpose of this paper is to present a new numerical model based on a combined finite-discrete element method, capable of predicting the behaviour of reinforced concrete structures under dynamic load up to failure. Design/methodology/approach – An embedded model of reinforcing bars is implemented in combined finite-discrete element code. Cracking of the structure was enabled by a combined single and smeared crack model. The model for reinforcing bars was based on an approximation of the experimental curves for the bar strain in the crack. The developed numerical model includes interaction effects between reinforcement and concrete and cyclic behaviour of concrete and steel during dynamic loading. Findings – The findings provide a realistic description of cracking in the concrete structure, where all non-linear effects are realized in joint elements of the concrete and reinforcing bars. This leads to a robust and precise model for non-linear analysis of reinforced concre...
III European Conference on Computational Mechanics
Method for defining appropriate form of prestressed, tensile cable structures and for calculating... more Method for defining appropriate form of prestressed, tensile cable structures and for calculating stress and displacements for such structures is presented. The developed numerical model is taking into account the material and geometric nonlinearity. The described model represents a practical way of implementing the large displacements theory in the analysis of finding appropriate form of prestressed cable structures. The behavior
2nd Croatian Conference on Earthquake Engineering ‒ 2CroCEE
In this paper, numerical analysis of several historical masonry towers located in Italy was condu... more In this paper, numerical analysis of several historical masonry towers located in Italy was conducted. The towers differ in their geometric characteristics in terms of slenderness, thickness of the outer walls, the proportion of openings, while the material properties of all towers are similar. The purpose of this paper was to analyse the influence of various geometries, soil properties and types of earthquakes on the seismic resistance of masonry structures. The geometries of the towers were taken from the available literature. The analysis was carried out with the planar numerical model Y-2D, which is based on the finite-discrete element method (FDEM). The towers were discretized at the macro level using triangular three-node finite elements between which contact elements were implemented that take into account material nonlinearity. The discretization of the towers was carried out at the macro level, taking into account the averaged properties of the mortar and blocks. This is mo...
Proceedings - ECOMAS MSF 2021 - 5th International Conference on Multi-scale Computational Methods for Solids and Fluids, 2021
The application of the finite-discrete element method (FEM/DEM) in the analysis of reinforced con... more The application of the finite-discrete element method (FEM/DEM) in the analysis of reinforced concrete (RC) structures is still in its early stages. Therefore, in this paper, sensitivity of the numerical model for analysis of RC structures based on the FEM/DEM method to the numerical parameters is presented. The accuracy of the solution, depending on the mesh refinement, crack spacing and penalty term, was analysed. The performed numerical analyses are useful in predicting the penalty parameter and mesh density in order to minimize numerical errors in analysis of RC structures with the FEM/DEM method. Validation of the numerical model for adopted numerical parameters was also shown by comparing numerical and experimental results
International Journal of Masonry Research and Innovation, 2016
This paper presents numerical model based on the finite discrete element method for the analysis ... more This paper presents numerical model based on the finite discrete element method for the analysis and prediction of the collapse of masonry structures with mortar joints and dry stone masonry structures. The model consists of a numerical model in a finite element, contact interaction algorithm which simulates the interaction between stone blocks in dry joint and numerical model in an interface element which simulate the behavior of the mortar joints and unit-mortar interface. The verification of the model was performed on examples by comparing it with the results obtained with the known numerical and experimental results from literature.
Tehnički Vjesnik, 2019
This paper presents a three-dimensional numerical model based on finite-discrete element method f... more This paper presents a three-dimensional numerical model based on finite-discrete element method for simulating cracking and predicting failure in reinforced concrete (RC) structures. Discrete representation of concrete cracks is coupled with a non-linear reinforcement model where reinforcing bars interact with concrete and slip due to crack opening and steel plastic deformation. Hence, it enables a simulation of complex material behaviour of concrete and steel in cracked zones and its influence on global structural behaviour. Several numerical examples are used to study the sensitivity of the model to different numerical and physical parameters and its capabilities in the analysis of RC structures.
Building construction using stone or clay bricks which are held together by mortar is one of the ... more Building construction using stone or clay bricks which are held together by mortar is one of the oldest building techniques which is still in use today. In spite of the simplicity which is manifested during the construction of masonry structures, understanding and describing mechanical behaviour of those structures, especially in conditions of seismic loading, represents a true challenge. The reason is the nature of masonry structures which might or might not be filled in with mortar in joints among the blocks. Such structures show a complex and particular nonlinear behaviour. Many masonry structures are located in seismically active zones in which earthquakes exposed their vulnerability. Among these, number of buildings and monuments are classified as cultural heritage. However some of them, which were originally built with mortar joints, have experienced a significant loss of mortar during the long period of time and the behaviour of these structures becomes similar to those made ...
In this paper the resonant spectra of wind and earthquake action obtained by a windows-wavelet tr... more In this paper the resonant spectra of wind and earthquake action obtained by a windows-wavelet transformation on the single degree of freedom system (SDOF) are shown. The earthquake load was taken from the literature, while the wind load was obtained from the measuring experiments. The analyses show that the averaging interval is extremely important for the wind loading of the structure. A good approach is usage of the averaging interval equal to the duration of the period T of the analysed system. The significant increase of the intensity of the constant component by de-creasing the period T of analysed system can be observed. The part of the fluctuating component presented as sinusoidal function of the duration of one wave is quantified. Its intensity is on an av-erage one half of the intensity of the constant component. The total action, presented by the ex-treme elastic force, is quantified by the dynamic factor of the elastic force in relation to the force magnitude of the cons...
One of very interesting problem in civil engineering applications is reinforced concrete structur... more One of very interesting problem in civil engineering applications is reinforced concrete structures subjected to impact load which are often used in protective purpose. Frag- mentation that may occur during impact cannot be modelled by the continuum methods. Predicting of the behaviour of reinforced concrete structures under impact imposes the need to develop numerical model which will be able to include effects of the behaviour of concrete structures due to dynamic action in linear elastic stage, crack initiation and propagation, en-ergy dissipation mechanisms due to non linear effects, inertial effects due to motion, contact impact and finally to attain state of the rest that is a consequence of energy dissipation mechanisms in the system. It is possible to include all previously mentioned effects with the finite - discrete element method (FEM/DEM).
International Journal of Engineering, 2017
This paper presents a numerical model for confined masonry structures under seismic load. The mod... more This paper presents a numerical model for confined masonry structures under seismic load. The model is based on a combination of the finite discrete element models for reinforced concrete confining elements and a masonry infill. Material non-linearity, including fracture and fragmentation of discrete elements, is considered through contact elements, which are implemented within a finite element mesh. The model includes the following phenomena: nonlinear cyclic behaviour of concrete, reinforcement and masonry during the seismic event, interaction between the reinforcement and concrete, cracking of the reinforced concrete confining elements and masonry units, as well as failure and softening in tension and shear for mortar joints. The application of the developed numerical model is exemplified on a confined masonry wall exposed to seismic excitation.
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Papers by Nikolina Živaljić