Papers by Irina Kerelezova
Inženerni nauki, Jun 3, 2024
In this paper we present the results of an initial parametric study of the maximum moment in a si... more In this paper we present the results of an initial parametric study of the maximum moment in a simple beam loaded in bending. The investigated RC beam is three-point loaded with a rectangular cross-section. The area of the main flexural crack is modelled with fracture mechanics methods, allowing for crack propagation. Multiple numerical solutions were performed varying the reinforcement ratio, steel type and concrete strength. The aim is to investigate the maximum moment dependence on the present parameters in the assumed model. This analysis is the preliminary stage of a project to determine the maximum bending moment in a reinforced concrete beam in bending considering the concrete tensile strength.
It is well known fact that the bearing capacity of reinforced concrete beams depends on their cro... more It is well known fact that the bearing capacity of reinforced concrete beams depends on their cross section sizes, longitudinal reinforce ratio and the possibilities to develop shear cracks. The present article investigates the size effect concerning reinforced concrete shear beams. A shear strength comparison among such beams was made, according to design codes that are up to date and according some models that pay attention to size effect. Comparisons with real experimental data are given and some conclusions and deductions are made.
A special purpose 3D concrete finite element is employed in this research to model the complex no... more A special purpose 3D concrete finite element is employed in this research to model the complex nonlinear behaviour of reinforced concrete beams with no shear reinforcement. The theory is based on the 5 parameter plasticity failure surface due to Willam-Warnke and takes into account the tensile cracking in three orthogonal directions plus crushing status of certain Gaussian integration point. A comparison is made with experimental and numerical results taken from the literature. The load deflection curve analysis indicates a big sensitivity of the solution to small changes of the material parameters which shows that a further research for their adjustment is needed. Although in a smeared manner the shear cracking is available, the preliminary conclusions suggest that the typical big sliding accompanying the development of the critical shear crack is not fully handled by the present model.
The prediction of the ultimate shear strength of reinforced concrete (RC) beams is very important... more The prediction of the ultimate shear strength of reinforced concrete (RC) beams is very important especially when this value is used in the practical design. An unconservative value of the shear capacity may lead to an unexpected and at early stage brittle failure of the structural RC beam so, a great deal of research efforts have been put recently on the proper explanation, modeling and simulation of the shear crack phenomena [1],[5]. Although the current design codes for shear in RC beams rely almost entirely on the test results, a ...
Proc. of 10th Jubilee National Congress on TAM, Sep 1, 2005
The prediction of the ultimate shear strength of reinforced concrete (RC) beams is very important... more The prediction of the ultimate shear strength of reinforced concrete (RC) beams is very important especially when this value is used in the practical design. An unconservative value of the shear capacity may lead to an unexpected and early stage brittle failure of the structural RC beam, therefore a great deal of research efforts have been put recently on the proper explanation, modeling and simulation of the shear crack phenomena [1],[5]. Although the current design codes for shear in RC beams rely almost entirely on the test results, a ...
Proc. of SIC, VSU L. …, May 1, 2005
... Sonia L. Parvanova1, Konstantin S. Kazakov2, Irina G. Kerelezova1, Gospodin K. Gospodinov1 , ... more ... Sonia L. Parvanova1, Konstantin S. Kazakov2, Irina G. Kerelezova1, Gospodin K. Gospodinov1 , Mogens P. Nielsen3 ... The load deflection curve analysis indicates a big sensitivity of the solution to small changes of the material parameters which shows that a further research for ...
From experiments, it is a well-known fact that the shear crack path depends on the size of the be... more From experiments, it is a well-known fact that the shear crack path depends on the size of the beam and on the shear span ratio. The critical shear crack can be an almost straight line, a curved line, or in some cases beams collapse without forming a shear crack. In present paper is determined the shear crack path in RC beams using the principal stress criterion of LEFM. The numerical simulations are carried out using APDL (ANSYS Parameter Design Language) programming language of ANSYS. An investigation and analysis of crack path for different reinforcement percentages, is presented. Comparisons with experimental results, final analysis and conclusions are made.
A theoretical crack growth formula for the development of cracks in non-shear reinforced beams is... more A theoretical crack growth formula for the development of cracks in non-shear reinforced beams is presented and compared with experiments. The formula is based on a non linear two parameter fracture mechanics model and gives a possibility to investigate the full crack development. The shear crack path in longitudinally reinforced beams is determined using the principal stress criterion of linear elastic fracture mechanics. An investigation and analysis of the crack path, according to different reinforcement percentages, is made. The numerical simulations are carried out using APDL (ANSYS Parameter Design Language) programming language of the finite element package ANSYS. The calculations seem to indicate that the shear failure in the beam treated is not a fracture mechanics problem. If this is a general trend is not yet clear. More calculations have to be carried out.
Cracks are present to some degree in all plain and reinforced concrete structures. They exist eit... more Cracks are present to some degree in all plain and reinforced concrete structures. They exist either as basic defects in materials or they may be induced in the construction during the time of the service. Cracks often act as stress concentrators, so in many cases they are the main reason for catastrophic crack propagation and structural failure under increasing load.
UACEG, 2014
Представената разработка представлява част от проект за определяне на носимоспособността на същес... more Представената разработка представлява част от проект за определяне на носимоспособността на съществуващ стоменен мост. В предходни изследвания са използвани нелинейни методи на механика на разрушението за определяне на носимоспособността на връзката главна-второстепенна греда на мостовата конструкция. В настоящата статия е предложено опростено определяне на тази носимоспособност. Целта на тези изчисления е да се проконтролират резултатите от нелинейните решения. Представени са някои сравнения и заключения.
UACEG, 2014
In the present article an analysis of the behavior of a steel bridge girder connection is made. T... more In the present article an analysis of the behavior of a steel bridge girder connection is made. The appearance of cracks in the links between different beams has led to a great interest to researchers to perform various tests, which examine the joints and the current carrying capacity of the structure. In this article a study of the nonlinear behavior of a beam connection is presented. It uses the methods of the nonlinear fracture mechanics. A comparison between the results from the different non-linear models and analysis are made, apart from that, conclusions of the obtained results are also made. Thus, the foundations for further future studies of the structure are laid.
Varna Free University, 2014
1. Abstract The cracks bridge is a steel riveted structure, which was built in 1937. Over the yea... more 1. Abstract The cracks bridge is a steel riveted structure, which was built in 1937. Over the years in the bridge's joints have appeared a number. In this report different numerical models of the joints are presented. Their aim is to describe the joint behaviour. The joints are modelled by using FEM in ANSYS. A linear and a nonlinear model have been created. A series of linear solutions have been performed in order to obtain the strain energy of the body, which corresponds to a specific crack length. Afterwards the energy is used to perform a nonlinear solution based on Nielsen's crack growth formula. Some comparisons and analysis of the results have been made. 2. Introduction The Storström bridge is a steel riveted structure. The bridge consists of a two narrow road lanes and a rail track, which suggests extremely heavy traffic through the whole year. The bridge has been put into service in 1937, which gives clarification to its small size and to the traffic for which it was designed. The facts, mentioned above, explain to some degree the appearance of the cracks, which are located in the joints. In a longitudinal direction the bridge is a cantilever beam, which indicates that if there is a deformation of an hinge caused by cracking, it will not lead to a complete destruction of the structure. The present research is directed specifically in performing numerical modelling and analysis using the methods of fracture mechanics for the beam connections. As an initial step in the study numerous FEM models, in the program ANSYS have been created and in addition multiple numerical experiments have been performed. Then the obtained strain energy of the body is incorporated in a nonlinear fracture mechanics model, thus performing a nonlinear solution for crack growth on an existing path. This is done by using Nielsen's crack growth formula, which is embedded in a VBA program in Excel. Further information concerning Nielsen's model can be seen in [1], [2]. On the one hand the study aims to consider the crack propagation in the beam joints with a known crack path and on the other hand it aims to examine the ability of Nielsen's crack growth formula to model the behaviour of a real steel structure. Comparisons of the results, obtained from the different models, are made and the frameworks for future research are outlined.
Varna Free University, 2014
The bridge Storströmsbroen is a steel riveted structure built in 1937. On the bridge joints appea... more The bridge Storströmsbroen is a steel riveted structure built in 1937. On the bridge joints appeared numerous cracks some years ago. In the present paper different numerical models of the joints aiming to describe their behaviour are presented. The beam joints of the bridge are modelled using FEM in ANSYS. The object of the present analysis is the beam joint strength of the existing cracked bridge. Different finite element models of the joint are developed. Various nonlinear fracture mechanics models are used to predict the joint strength. Plastic analysis model is performed with 3D finite element modelling. Comparisons and conclusions are made. 2. Introduction The present work is a part of research on the Storströmsbroen made by the authors. In the present paper nonlinear finite element modelling in ANSYS software is performed. To simulate crack growth the incorporated in ANSYS nonlinear fracture mechanics model is used. This model is developed for simulating crack opening in concrete structure. In this paper the model is used only as a first approximation of the bridge joint behaviour. Only static load is applied without any account of the dynamic behaviour. As an additional investigation a plastic model is implemented to investigate stress concentration. This research throws light on the possibilities of crack initiation at points different to the inner corner point. This information will give guidelines for future research by using more complicated finite element model. 3. Nonlinear fracture mechanics model of Xu and Needleman The cohesive zone model which is incorporated in the ANSYS program is model developed by Xu and Needleman (1994) [1] [2].This model is based on Hillerborg's idea of the cohesive stress distribution in a crack tip. The main theoretical base of the present model is as follows the cohesive zone laws can be uncoupled or coupled. In an uncoupled cohesive zone law the normal traction is independent of the tangential opening. In a coupled cohesive zone law, both normal and tangential tractions depend on both the normal and tangential opening displacement.
UACEG, 2013
Множество изследвания показват участието на различни фактори, влияещи върху носимоспособността на... more Множество изследвания показват участието на различни фактори, влияещи върху носимоспособността на стоманобетоновите греди, работещи на срязване. Моделите, които целят създаването на формули за ефект на размера се опитват да изследват влиянието на всички фактори, влияещи върху носимоспособността на срязване. Реално, отчитането им в затворен вид е невъзможно, което води до множество емпирични зависимости. В настоящото изследване е направен параметричен анализ на един от моделите, отчитащ ефекта на размера при стоманобетонови греди. Извършен е анализ на влиянието на отделните параметри върху носимоспособността на срязване.
International Conference VSU, 2013
The modelling of RC beams depending on their size is a serious problem established by many scient... more The modelling of RC beams depending on their size is a serious problem established by many scientists in the world. The presence of so many models provokes making a classification of them.
списание "Строителство", 2012
В настоящата статия е направена ретроспекция на механика на разрушението като клон на строителнат... more В настоящата статия е направена ретроспекция на механика на разрушението като клон на строителната механика. Направен е кратък исторически преглед и са пояснени основните параметри и модели. Придставена е основната концепция на линейната механика на разрушението, след което са описани на кратко някои нелинейни модели за квазикрехки материали като бетон. В залючение се набяга на важността за инженера на този бързоразвиващ се клон от механиката и се дават препоръки за включването на елементи от нея в Еврокод.
UACEG, 2010
С навлизането на ново поколение мощна изчислителна техника се забелязва развитие на нови изчислит... more С навлизането на ново поколение мощна изчислителна техника се забелязва развитие на нови изчислителни алгоритми и числени методи, насочени към решаване на задачи с голям брой неизвестни. Това касае най-вече метода на крайните елементи а също така и метода на граничните елементи (МГЕ). Типичен пример е задачата за статическо изследване на конструктивни елементи, направени от композитни материа-ли. Обикновено този тип материали са нехомогенни и се състоят от най-малко две фази: матрица и усилвания във вид на еластични включвания – най-често това са някакъв вид нишки. Коректното изследване на такъв материал изисква определянето на т.нар. ефективни еластични материални характеристики, за получаването на които се отделя специална подобласт от елемента, обикновено това е квадрат с малки размери, наречен представителен обем (ПО). Този обем се изследва с подхода на микромеханиката, като за решението се прилага някой от числените методи. При моделирането се вземат предвид всички реални компоненти на композитния материал, като ще допълним, че нехомогенността на материала може да се получи и при наличие на отвори или система от пукнатини, свободни от напрежения.
UACEG, 2006
В настоящата статия са представени два подхода, от гледна точка на механика на разрушението, за о... more В настоящата статия са представени два подхода, от гледна точка на механика на разрушението, за определяне на пътя на развитие на пукнатина в бетонови и стоманобетонови греди. За числената реализация на процеса са използвани два различни числени метода: метод на крайните елементи (МКЕ) и метод на граничните елементи (МГЕ). За приложението на МКЕ е използван програмния пакет ANSYS, в който са разработени отделни макроси. За приложението на МГЕ е използвана програмата BEPLANE, в която е разработен модул за осъществяване на процедурата. Направени са сравнения на резултатите между различните подходи и методи. Извършена е съпоставка на числените резултатите с експерименталните данни за бетонови и стоманобетонови греди.
International Conference VSU’ 2005, 2005
A Visual Basic for Application’s program for calculating crack growth in concrete and reinforced ... more A Visual Basic for Application’s program for calculating crack growth in concrete and reinforced concrete beams is presented in this paper. This program is useful for obtaining quick results for initial analysis and parametric study. In the present program Nielsen’s crack growth formula is incorporated which is a new and original effective crack model. Some results are presented and comparisons with experiments are performed.
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Papers by Irina Kerelezova