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During a one-year period, several moderate intensity earthquakes occurred in the Balkan Peninsula, including four significant earthquakes, two of which had the same magnitude of Mw 6.4. The first earthquake took place on November 26, 2019, in Albania, and the second occurred on December 29, 2020, in Petrinja, Croatia. Following both events, the Serbian Association for Earthquake Engineering (SUZI-SAEE) dispatched expert teams to assess the earthquake impact on the built environment and assist in damage evaluation. Both events had devastating effects on for the building stock in the epicentral area. However, notable differences were observed between these two events and they are presented in this paper. This paper provides an overview of the most common types of failure, highlighting structural deficiencies, as well as examples of good behaviour in each earthquake. Additionally, recovery aspects of the earthquakes are compared, and the aim is to summarize key findings that could serve as a basis for lessons to help communities in the Balkan region prepare for and respond effectively to future earthquakes.

In the past few decades, demountable connectors have often been used for connections in composite and mixed steel-concrete structures to reduce construction time and costs. Furthermore, the application of demountable connectors enables the reuse of structural elements in these structures, which leads to sustainable design and a circular economy. In this paper, the demountable connector is made out of two parts: (1) mechanical coupler and rebar anchor placed in formwork before casting the concrete element, and (2) steel bolt used for connecting steel to the RC element. Although this connector is increasingly being used in contemporary building structures, its behaviour in composite connections is still insufficiently defined. The paper presents the results of experimental tests and numerical analysis of the connector with a mechanical coupler, focusing on the local behaviour of the tapered threaded connection between the mechanical coupler and rebar anchor.

The construction industry is one of the most important parts of economic development of society but it also has a very negative impact on the environment. Using the three concepts of circular economy: reuse, reduce and recycle, it is possible to decrease its negative impact. The steel-concrete composite structures and prefabricated structures enable, environmentally beneficial, circular life-cycle of buildings. For structural performance during the lifecycle, it is very important to have an adequate connection between the steel and reinforced concrete members. Different types of connectors have been widely used in composite structures. Demountable ones are advantageous in terms of reuse. In the last few years, the innovative demountable steel-concrete bolted connector with mechanical coupler has been proposed. There are two types of these bolted connectors depending on the type anchorage i.e., with the rebar anchor or with the second bolt. This paper gives an overview of previous research of bolted connectors with mechanical coupler capacity under static load. Influence of key parameters on the shear behaviour of the connector was observed: concrete compressive strength, connector dimensions and concrete edge distance. The shear and tension resistances of individual parts of the commercially available connectors were determined using recommendations of design codes and technical documentation. In case of the connector loaded in tension, it was concluded that the resistance is governed by the resistance of the rebar anchor. In case of the connector loaded in shear, design recommendations were also compared with the previous experimental tests. It was concluded that the shear resistance highly depends on the connection layout and concrete strength.

This paper documents performance of cast-in-place reinforced concrete (RC) buildings in the Durrës municipality during Albania earthquake of November 26, 2019 (MW 6.4). Both mid- and high-rise RC buildings were affected by the earthquake, experiencing structural and/or non-structural damage and even collapse in some cases. The authors performed a reconnaissance study after the earthquake and were involved in seismic assessment of buildings in the affected area. Besides the observations related to physical damage of RC buildings, the paper also presents results of a statistical analysis of damaged RC buildings in the Durrës municipality. The discussion in the paper is focused on damage patterns and failure mechanisms that are relevant for the seismic response of RC structures. Most common damage pattern observed after the earthquakes was related to masonry infill walls, which experienced damage and failure in some cases, and affected the performance of adjacent RC columns due to the infill/frame interaction. Taller RC framed buildings (10 storeys and higher) were expected to have RC shear walls; however, these walls were reportedly absent in the damaged buildings of this type. In some cases, masonry infill walls (instead of RC shear walls) were used in the elevator shaft areas, which resulted in inadequate seismic performance. A case study has been presented to illustrate seismic behaviour of mid-rise and high-rise cast-in-place RC buildings in the November 2019 earthquake, and is based on post-earthquake field observations and a detailed seismic assessment of two earthquake-damaged buildings. Finally, relevant lessons and recommendations are presented in light of the observed performance of RC buildings.

In the period of one year, several moderate intensity earthquakes occurred in the Balkan Peninsula. It is interesting that among four significant earthquakes in this period of time, two with the same magnitude (Mw 6.4) occurred. The first was on November 26, 2019 in Albania and second one on December 29, 2020 Petrinja (Croatia). Both events were quite devastating for the building stock in the epicentral area. Since most of the buildings in Balkan Peninsula are masonry buildings (single or multi-family apartments), this paper focuses on the performance of these buildings during the mentioned earthquakes. Quickly after both events, Serbian Association for Earthquake Engineering (SUZI-SAEE) organized an expert teams to visit affected areas. The goal was to document the consequences of the earthquakes on the built environment, as well as to provide support in damage assessment. Data collected during the visits is usded investigate the performance of masonry buildings. Most common types of failure are presented, pointing out the deficiencies in the behaviour of masonry structures. However, examples of good behaviour (mostly related to the well-constructed confined masonry buildings) are also presented.

Past earthquakes have affected millions of people whose lives changed within a minute, and caused damage or collapse of thousands of buildings and infrastructure systems. In many cases, earthquakes have long-term consequences. Therefore, it is very important to study the effects of damaging earthquakes and share the lessons and field experience with technical professionals and general public. The authors are members of Serbian Association for Earthquake Engineering (SUZI-SAEE), which organized reconnaissance visits to the areas affected by the November 26, 2019 Durrës, Albania earthquake (Mw 6.4) and the December 29, 2020 Petrinja Croatia earthquake (Mw 6.4). This paper presents findings on the performance of reinforced concrete buildings in these two events. Characteristic damage patterns are presented in the paper, along with the explanation of the causes of damage and recommendations for future engineering practice in the affected countries and the region.

This paper documents performance of cast-in-place reinforced concrete (RC) buildings in the Durrës municipality during Albania earthquake of November 26, 2019 (MW 6.4). Both mid- and high-rise RC buildings were affected by the earthquake, experiencing structural and/or non-structural damage and even collapse in some cases. The authors performed a reconnaissance study after the earthquake and were involved in seismic assessment of buildings in the affected area. Besides the observations related to physical damage of RC buildings, the paper also presents results of a statistical analysis of damaged RC buildings in the Durrës municipality. The discussion in the paper is focused on damage patterns and failure mechanisms that are relevant for the seismic response of RC structures. Most common damage pattern observed after the earthquakes was related to masonry infill walls, which experienced damage and failure in some cases, and affected the performance of adjacent RC columns due to the infill/frame interaction. Taller RC framed buildings (10 storeys and higher) were expected to have RC shear walls; however, these walls were reportedly absent in the damaged buildings of this type. In some cases, masonry infill walls (instead of RC shear walls) were used in the elevator shaft areas, which resulted in inadequate seismic performance. A case study has been presented to illustrate seismic behaviour of mid-rise and high-rise cast-in-place RC buildings in the November 2019 earthquake, and is based on post-earthquake field observations and a detailed seismic assessment of two earthquake-damaged buildings. Finally, relevant lessons and recommendations are presented in light of the observed performance of RC buildings.

The reliable operation of a mechanical system is dependent on the condition of installed rolling bearings. This paper presents a measuring system and equipment for analyzing the condition of rolling bearings. The developed system is a modular device (VibroLog) for measuring several diagnostic parameters for bearings, including vibration, number of revolutions, temperature and sound pressure. The device is a data collector and analyzer. Software in the Java programming language for the analysis and presentation of data obtained by VibroLog has also been developed. This paper is concerned with the development of a mathematical model for the evaluation and prediction of the qualitative state of rolling bearings in real operating conditions. It also presents results of measurement and mathematical modelling of the results. The model was formed by non-linear regression analysis as one of the most widely used statistical techniques. The analysis of the experimental data showed that the rate of change of a variable is proportional to its actual value. The model was tested on several rolling bearings having different degrees of damage. The developed model makes it possible to evaluate and predict the condition of the bearing by measuring the sound pressure level, which is simpler than vibration measurement in real operating conditions. During testing, the model generated results within the prediction error limits. The developed vibrodiagnostic system and the created model enable condition assessment and prediction for a wide range of rolling bearings.

The collapse and damage of large number of buildings during the November 26, 2019 (Mw 6,4) Albania earthquake caused 51 fatalities and injuries to at least 910 people. Most of collapsed or heavily damaged buildings were RC frame buildings. Although RC frame system is considered as very ductile seismic force-resisting system, its behaviour during earthquake highly depends on: (1) regularity in plan and elevation, and (2) global and local ductility. Based on the authors’ visit to the earthquake-affected area on behalf of the Serbian Association of Earthquake Engineering and observations of collapsed and damaged buildings, it was concluded that among main reasons for underperformance of these flexible systems were inadequate analysis of interaction between infill walls and RC frames and reinforcement detailing of RC members

Recent earthquakes in Balkan, including the September 21 and November 26, 2020 Albania earthquakes, March 22, 2020 Zagreb earthquake, and the December 29, 2020 Petrinja, Croatia earthquakes had devastating consequences for the affected population of these countries. Besides substantial structural damage of RC buildings as well as loadbearing masonry buildings, these earthquakes caused significant damage of non-structural masonry elements. This paper presents examples of the damage for loadbearing and non-structural masonry walls (infills and partitions) due to out-of-plane seismic effects, as observed by the authors during the reconnaissance visits to the affected areas. This type of damage can prevent the evacuation of people from the buildings during the earthquake, as the falling masonry elements block the evacuation routes, and hinder the reoccupancy and functional recovery of affected buildings after an earthquake. The authors recognize that both loadbearing and non-structural walls (infills and partitions) experienced out-of-plane collapse due to lack of connection to the floor/frame. Using the examples of the damage or failure of masonry walls during the recent earthquakes, their failure mechanisms were explained and the lessons learned were summarized in the paper.

Recent earthquakes in Balkan, including the September 21 and November 26, 2020 Albania earthquakes, March 22, 2020 Zagreb earthquake, and the December 29, 2020 Petrinja, Croatia earthquakes had devastating consequences for the affected population of these countries. Besides substantial structural damage of RC buildings as well as loadbearing masonry buildings, these earthquakes caused significant damage of non-structural masonry elements. This paper presents examples of the damage for loadbearing and non-structural masonry walls (infills and partitions) due to out-of-plane seismic effects, as observed by the authors during the reconnaissance visits to the affected areas. This type of damage can prevent the evacuation of people from the buildings during the earthquake, as the falling masonry elements block the evacuation routes, and hinder the reoccupancy and functional recovery of affected buildings after an earthquake. The authors recognize that both loadbearing and non-structural walls (infills and partitions) experienced out-of-plane collapse due to lack of connection to the floor/frame. Using the examples of the damage or failure of masonry walls during the recent earthquakes, their failure mechanisms were explained and the lessons learned were summarized in the paper.

The collapse and damage of large number of buildings during the November 26, 2019 (Mw 6,4) Albania earthquake caused 51 fatalities and injuries to at least 910 people. Most of collapsed or heavily damaged buildings were RC frame buildings. Although RC frame system is considered as very ductile seismic force-resisting system, its behaviour during earthquake highly depends on: (1) regularity in plan and elevation, and (2) global and local ductility. Based on the authors’ visit to the earthquake-affected area on behalf of the Serbian Association of Earthquake Engineering and observations of collapsed and damaged buildings, it was concluded that among main reasons for underperformance of these flexible systems were inadequate analysis of interaction between infill walls and RC frames and reinforcement detailing of RC members

Pred Vama je publikacija kojom se otvara novo poglavlje u radu Srpskog udruženja za zemljotresno inženjerstvo (SUZI). Za posetu postradalim područjima u Albaniji, trebalo je: da se uopšte dogodi zemljotres, da SUZI shvati i odluči da treba ići kao i da, zahvaljujući Vašim članarinama SUZI bude u stanju da samostalno finansira ekspediciju. Obilazak je bio kratak, ali je obim informacija u ovoj publikaciji impresivan, zahvaljujući izuzetnom zalaganju članova tima, a i ostvarenoj saradnji sa albanskim kolegama čija pomoć je bila od neprocenjivog značaja za uspeh posete. Osim toga, članovi tima su imali prilike da sarađuju i sa kolegama iz Grčke, Velika Britanije, Nepala, Bugarske, i SAD, koji su posetili postradala područja, i sa kojima zajedno pripremaju izveštaj za Earthquake Engineering Research Institute (EERI), u kome SUZI učestvuje kao partner. Zemljotres ovakve magnitude (6.4) i posledica ne očekuje se na teritoriji Srbije, ali su prikupljena iskustva značajna i za našu praksu, sa stanovišta projektovanja, izvođenja i održavanja kao i pripreme društva kako da hitno reaguje, i potom obnovi život na postradalom području. Utisak je da pri toj jačini zemljotresa ipak nije trebalo, niti smelo da dođe do kolapsa objekata i ljudskih žrtava, da su poštovani propisi? S druge strane, puno je primera da su konstrukcije objekata dobro podnele zemljotres, ali su štete na nekonstruktivnim delovima objekata prevelike, što je teret za vlasnike i zajednicu. Dosadašnji koncept propisa, da treba sprečiti kolaps objekata i ljudske žrtve, bez obzira da li će objekat nakon zemljotresa uz sanaciju biti upotrebljiv, više nije dovoljan, nije društveno prihvatljiv. Dolazi vreme da struka sa investitorima i zajednicom dogovara koji je nivo eventualne štete prihvatljiv, da se procene rizici i nađe optimalan balans između troškova građenja i troškova eventualne sanacije jednog dana. Ovo treba imati u vidu u toku čitanja ove publikacije. Ovo je do sada najdetaljnija publikacija SUZI, i prva

Reinforced concrete (RC) frame structural system is widely used for housing and commercial construction in urban areas around the world. Exterior and interior partitions are in the form of masonry infills, which are usually constructed using solid clay bricks or multi-perforated clay blocks. Although masonry infills influence the strength and stiffness of a structure subjected to earthquake ground shaking, they are often disregarded in numerical models used for seismic analysis and design of these structures. Numerous RC frame structures with masonry infills experienced damage and/or collapse in past earthquakes, including the M 7.6 Izmit, Turkey (1999); M 7.7 Bhuj, India (2001); M 6.8 Boumerdes, Algeria (2003); and M 7.8 Gorkha, Nepal (2015). In most cases, RC buildings did not experience major structural damage but masonry infills experienced damage or failure.

Contemporary design and construction of steel-concrete composite structures employs the use of prefabricated concrete elements and demountable shear connectors in order to reduce the construction time and costs and enable dismantling of elements for their potential reuse at the end of life of buildings. Bolted shear connector with mechanical coupler is presented in this paper. The connector is assembled from mechanical coupler and rebar anchor, embedded in concrete, and steel bolt, used for connecting steel to concrete members. The behaviour and ultimate resistance of bolted connector with mechanical coupler in wide and narrow members were analysed based on push-out tests and FE analyses conducted in Abaqus software, with focus on concrete edge breakout and bolt shear failure modes. The effect of concrete strength, concrete edge distance and diameter and strength of bolts on failure modes and shear resistance was analysed. It was demonstrated that premature failure by breakout of concrete edge occurs when connectors are located 100 mm or closer from the edge in low-strength and normal-strength reinforced concrete. Furthermore, the paper presents a relatively simple model for hand calculation of concrete edge breakout resistance when bolted connectors with mechanical coupler are used. The model is based on the modification of prediction model used for cast-in and post-installed anchors loaded parallel to the edge, by implementing equivalent influence length of connector with variable diameter. Good agreement with test and FE results was obtained, thus confirming the validity of the proposed method.

Pred Vama je publikacija kojom se otvara novo poglavlje u radu Srpskog udruženja za zemljotresno inženjerstvo (SUZI). Za posetu postradalim područjima u Albaniji, trebalo je: da se uopšte dogodi zemljotres, da SUZI shvati i odluči da treba ići kao i da, zahvaljujući Vašim članarinama SUZI bude u stanju da samostalno finansira ekspediciju. Obilazak je bio kratak, ali je obim informacija u ovoj publikaciji impresivan, zahvaljujući izuzetnom zalaganju članova tima, a i ostvarenoj saradnji sa albanskim kolegama čija pomoć je bila od neprocenjivog značaja za uspeh posete. Osim toga, članovi tima su imali prilike da sarađuju i sa kolegama iz Grčke, Velika Britanije, Nepala, Bugarske, i SAD, koji su posetili postradala područja, i sa kojima zajedno pripremaju izveštaj za Earthquake Engineering Research Institute (EERI), u kome SUZI učestvuje kao partner. Zemljotres ovakve magnitude (6.4) i posledica ne očekuje se na teritoriji Srbije, ali su prikupljena iskustva značajna i za našu praksu, sa stanovišta projektovanja, izvođenja i održavanja kao i pripreme društva kako da hitno reaguje, i potom obnovi život na postradalom području. Utisak je da pri toj jačini zemljotresa ipak nije trebalo, niti smelo da dođe do kolapsa objekata i ljudskih žrtava, da su poštovani propisi? S druge strane, puno je primera da su konstrukcije objekata dobro podnele zemljotres, ali su štete na nekonstruktivnim delovima objekata prevelike, što je teret za vlasnike i zajednicu. Dosadašnji koncept propisa, da treba sprečiti kolaps objekata i ljudske žrtve, bez obzira da li će objekat nakon zemljotresa uz sanaciju biti upotrebljiv, više nije dovoljan, nije društveno prihvatljiv. Dolazi vreme da struka sa investitorima i zajednicom dogovara koji je nivo eventualne štete prihvatljiv, da se procene rizici i nađe optimalan balans između troškova građenja i troškova eventualne sanacije jednog dana. Ovo treba imati u vidu u toku čitanja ove publikacije. Ovo je do sada najdetaljnija publikacija SUZI, i prva

Reinforced concrete (RC) frame structural system is widely used for housing and commercial construction in urban areas around the world. Exterior and interior partitions are in the form of masonry infills, which are usually constructed using solid clay bricks or multi-perforated clay blocks. Although masonry infills influence the strength and stiffness of a structure subjected to earthquake ground shaking, they are often disregarded in numerical models used for seismic analysis and design of these structures. Numerous RC frame structures with masonry infills experienced damage and/or collapse in past earthquakes, including the M 7.6 Izmit, Turkey (1999); M 7.7 Bhuj, India (2001); M 6.8 Boumerdes, Algeria (2003); and M 7.8 Gorkha, Nepal (2015). In most cases, RC buildings did not experience major structural damage but masonry infills experienced damage or failure.

Contemporary design and construction of steel-concrete composite structures employs the use of prefabricated concrete elements and demountable shear connectors in order to reduce the construction time and costs and enable dismantling of elements for their potential reuse at the end of life of buildings. Bolted shear connector with mechanical coupler is presented in this paper. The connector is assembled from mechanical coupler and rebar anchor, embedded in concrete, and steel bolt, used for connecting steel to concrete members. The behaviour and ultimate resistance of bolted connector with mechanical coupler in wide and narrow members were analysed based on push-out tests and FE analyses conducted in Abaqus software, with focus on concrete edge breakout and bolt shear failure modes. The effect of concrete strength, concrete edge distance and diameter and strength of bolts on failure modes and shear resistance was analysed. It was demonstrated that premature failure by breakout of concrete edge occurs when connectors are located 100 mm or closer from the edge in low-strength and normal-strength reinforced concrete. Furthermore, the paper presents a relatively simple model for hand calculation of concrete edge breakout resistance when bolted connectors with mechanical coupler are used. The model is based on the modification of prediction model used for cast-in and post-installed anchors loaded parallel to the edge, by implementing equivalent influence length of connector with variable diameter. Good agreement with test and FE results was obtained, thus confirming the validity of the proposed method.

U disertaciji su predložene tri različite metode kojima se postiže uravnoteženje ravanskih mehanizama sa krutim članovima. Dodavanjem protivtegova, korišćenjem interpolacionih polinoma i primenom optimizacionih metoda izvršeno je smanjenje dinamičkih opterećenja, tj. uravnoteženje ravnih mehanizama. U cilju određivanja dinamičkih opterećenja, izvršena je kinematička i dinamička analiza mehanizama. Reakcije veza određene su primenom novog metoda koji se bazira na korišćenju Lagranževih jednačina sa množiteljima veza, metoda transformacije brzina i predstavljanjem članova manipulatora korišćenjem ekvivalentnog sistema sa koncentrisanim masama. Kroz odgovarajuće numeričke primere pokazana je efikasnost predloženih metoda za uravnoteženje mehanizama. Akcenat je na primeni savremenih biološki inspirisanih optimizacionih algoritama koji su se pojavili u poslednjih petnaestak godina. Ovim jednostavnim algoritmima, čiji se princip rada zasniva na oponašanju pojava i procesa u prirodi, moguće je rešiti kompleksne inženjerske optimizacione probleme. Problem uravnoteženja ravanskih mehanizama rešen je primenom dva optimizaciona algoritma: subpopulacijskog algoritma svica (SP-FA) koji predstavlja poboljšanu verziju standardnog algoritma svica i hibridnog algoritma svica i kukavičje pretrage (H-CS-FA) koji predstavlja kombinaciju dva biološki inspirisana algoritma. Postupak analize mehanizama proširen je zatim i na mehanizme sa elastičnim članovima. Predstavljen je nov pristup u dinamičkoj analizi mehanizama sa elastičnim članovima koji se temelji na mehanici sistema krutih tela. Detaljno je objašnjen postupak diskretizacije elastičnih članova u cilju dobijanja što tačnijeg dinamičkog modela. Takođe, prikazan je postupak određivanja reakcija veza kod manipulatora sa jednim elastičnim članom. Na kraju, proces projektovanja mehanizama zaokružen je procesom optimalne sinteze podesivih ravanskih mehanizama kao generatora putanje. Cilj je optimizovati putanju (koja je zadata istim sk, In the thesis, three different methods are proposed to achieve the balancing of planar mechanisms with rigid links. By adding counterweights, using interpolating polynomials and by applying optimization methods, dynamic load is reduced ie. balancing of mechanisms is achieved. In order to determine the dynamic load, it is necessary to perform the kinematic and dynamic analysis of the mechanisms first. Joint reaction forces were determined by using a new method based on the use of the Lagrange equations with the multipliers, velocity transformations and the equimomental system representation of the links of the mechanism. Through the corresponding numerical examples, the efficiency of the proposed methods for balancing the mechanisms was shown. The emphasis is on the application of modern biologically inspired optimization algorithms that have emerged in the last fifteen years. With these simple algorithms, whose work principle is based on mimicking phenomena and processes in nature, it is possible to solve complex engineering optimization problems. The problem of balancing of planar mechanisms was solved by using two optimization algorithms: a subpopulation firefly algorithm (SP-FA) that represents an improved version of the standard firefly algorithm and hybrid cuckoo search and firefly algorithm (H-CS-FA) which represents a combination of two biologically inspired algorithms. The analysis process of the mechanisms was then extended to mechanisms with flexible links. A new approach to the dynamic analysis of mechanisms with flexible links which is based on rigid multibody systems has been presented. The process of discretization of flexible links is explained in detail, in order to obtain a more accurate dynamic model. Also, the procedure for determining the joint reaction forces in the manipulator with one flexible link is shown. Finally, the process of designing the mechanisms is rounded up by the process of optimal synthesis of adjustable planar mechanisms as a p

This paper is focused on the effects of confinement of the reinforcement reinforced concrete sections, i.e. in the way that the transverse reinforcement affects the improvement of the characteristics of both the material and the affected zone of the element. The practical meaning of the confinement effectiveness factor from the expression of Eurocode 8 was explained. Size of the part of element that is effectively confined by the stirrups is estimated on examples of differently reinforced circular and square sections of the column by analysis of the three-dimensional presentation of effectively confined concrete sections. The connection between confinement effectiveness factor by Eurocode 8 and real effective concrete core is established.

This paper is focused on the effects of confinement of the reinforcement reinforced concrete sections, i.e. in the way that the transverse reinforcement affects the improvement of the characteristics of both the material and the affected zone of the element. The practical meaning of the confinement effectiveness factor from the expression of Eurocode 8 was explained. Size of the part of element that is effectively confined by the stirrups is estimated on examples of differently reinforced circular and square sections of the column by analysis of the three-dimensional presentation of effectively confined concrete sections. The connection between confinement effectiveness factor by Eurocode 8 and real effective concrete core is established.

U ovom radu posebna pažnja je usmerena na efekte utezanja preseka, tj. na način na koji transverzalna armatura utiče na ojačavanje, kako materijala, tako i utegnute zone elementa. Da bi se pojasnilo praktično značenje koeficijenta utezanja iz izraza Evrokoda 8 i procenili koji deo elementa je stvarno efektivno utegnut uzengijama, analizirani su različito armirani kružni i kvadratni preseci stubova trodimenzionalnim modeliranjem. Uspostavljena je relacija između koeficijenta utezanja prema izrazima Evrokoda 8 i efektivno utegnutog dela betonskog elementa.

U radu je opisan koncept proračuna za procenu stanja i oštećenja armiranobetonskih zgrada prema odredbama Evrokoda 8-3. Kako je pomenuti dokument prvi pokušaj standardizacije procene seizmičke otpornosti konstrukcija u Evropskim normama, cilj ovog rada je da se komentarima i smernicama približi koncept standarda inženjerima i olakša njegova primena u praksi. U radu je prikazan i numerički primer određivanja seizmičkog kapaciteta konstrukcije prema odredbama Evrokoda 8-3, za objekat koji je izvorno projektovan na osnovu odredbi još uvek aktuelnih domaćih pravilnika. Utvrđeno da je seizmički kapacitet konstrukcije iscprljen duktilnim mehanizmom loma za ubrzanje tla ag/g=0.197, što iznosi čak 98.5% najvećeg očekivanog ubrzanja tla za seizmičku zonu za koju je konstrukcija projektovana.

The majority of older existing RC buildings in regions of moderate and high seismicity are vulnerable to earthquake effects. They often do not meet current seismic codes requirements which are more stringent compared to the older codes. Addition of new RC shear walls is an effective retrofit strategy for the reduction of seismic demands on the existing members, especially in case of RC frame structures. The paper presents a case study of an existing school building located in high seismic hazard zone in Central Asia. The building is a bare RC frame structure, designed and constructed in 1960s. The seismic assessment via linear elastic and pushover analysis showed that the structure is deficient for code-prescribed earthquake intensity. A feasible retrofit scheme in the form of new RC shear walls has been developed and its effectivness was verified via linear elastic and pushover analysis.

Rezime: Globalizacija savremenog tržišta zahteva proizvodnju sve složenijih proizvoda, sa velikim brojem varijanti projektnih rešenja, radi prilagođavanja specifičnim zahtevima krajnjeg potrošača. Konkurencija na svetskom tržištu, posebno izražena u mašinogradnji, vazduhoplovnoj industriji, industriji motornih vozila, elektronskoj i sličnim industrijama, zahteva stalno povećanje kvaliteta proizvoda, smanjenje cena, smanjenje vremena izlaska proizvoda na tržište i fleksibilnu proizvodnju. Posmatrano sa tehničko-tehnološkog aspekta, uslov opstanka na tržištu je stalno uvođenje novih tehnologija, kao što su: programabilna i fleksibilna automatizacija, kompjuterski integrisana proizvodnja i novi koncepti, kao što su agilni proizvodni sistemi, inteligentni proizvodni sistemi i slično. Parametarsko projektovanje ima mogućnost kontrole modela parametarski definisanim „vodećim” dimenzijama, kao i uvođenja nedimenzionih geometrijskih i drugih ograničenja. Parametar kao informacija koja u potpunosti određuje model proteže se kroz sve nivoe sistema, a savremeni CAD/CAM sistemi imaju dvosmernu asocijativnost (izmena parametra na nekom nivou – modelu izaziva promenu na svim ostalim nivoima – modelima). Promenom vrednosti parametara koji definišu geometriju, automatski se menja i putanja alata, što znači da se na ovaj način može ostvariti brza izmena CNC programa – za delove, koji su geometrijski i tehnološki slični, ili – za nove varijante prizvoda. Na osnovu referentnog modela predstavnika grupe realizuju se eksplicitni modeli pojedinih članove grupe promenom vrednosti parametara modela., The globalization of today’s market requires the production of increasingly more complex products, with a large number of variants of design solutions, in order to accommodate the specific requirments of the end customer. Competition in the global market, especially strongly expressed in mechanical engineering, aviation industry, industry of motor vehicles, electronics and related industries requires steadily increasing product quality, reducing prices, reducing the time – to market and flexible production. Being seen from the point of technical and technological aspect, condition of survival on the market is: constantly introducing new technologies as programmable and flexible automatization, computer integrated manufacturing and new concepts such as agile production systems, intelligent production systems and similarly. Parametric designing has the ability to control the model parametrically defined as "major" dimensions, as well as introducing no-dimensional geometric and other restrictions. Parameter as information which fully defines model, is extending through all levels of the system and advanced CAD/CAM systems have bidirectional associativity (changing parameter art some level causes a change in the model for all other levels – models). By chaning the values of parametres that define the geometry, automatically is, changing the tool path, which means that in this way is possible to achieve rapid shift of CNC programs, for the parts that are geomtry and technologically similar or for new variants of products. Based on the reference model as representative of the group, we can see that an explicit models of individual members of the group are realising by changing the values parameters of model.

The research of shear connectors composed from mechanical couplers with rebar anchors, embedded in concrete, and steel bolts, as a mean of shear transfer in composite connections is presented in the paper. Specific issues related to this type of connections are local concrete pressure in the connector vicinity as well as the shear flow along the connector axis. The experimental research included 18 specimens, arranged in 5 series. Nonlinear numerical analyses using Abaqus software was conducted on corresponding FE models. Different failure modes were analysed, with emphasis on concrete edge failure and bolt shear failure. The influence of key parameters on the behaviour of shear connector was examined: (1) concrete compression strength, (2) bolt tensile strength and diameter and (3) concrete edge distance. It is concluded that bolted shear connectors with mechanical couplers have sufficient capacity to be used as shear connectors in composite structures and that their behaviour is similar to the behaviour of post installed anchors as well as other types of connectors anchored without the head.

The thermal electromotive force (TEMF) and the thermal electromotive force coefficient (TEMFC) of the thermocouple consisting of a copper wire and an (X5CrNi1810) steel wire plastically deformed under tension or bending conditions were found to increase with increasing degree of plastic deformation. The increase in the degree of deformation disturbs the microstructure of steel due to increases in the density of chaotically distributed dislocations and internal microstress, resulting in a decrease in the electron density of states near the Fermi level. Through the effect of thermal energy, annealing at elevated temperatures up to 300°C leads to microstructural ordering along with simultaneous increases in the free electron density of states, TEMF and TEMFC. Based on the temporal change of the TEMF, the kinetics of microstructural ordering was determined. During the initial time interval, the process is a kinetically controlled first-order reaction. In the second time interval, the process is controlled by the diffusion of reactant species.

The thermal electromotive force (TEMF) and the thermal electromotive force coefficient (TEMFC) of the thermocouple consisting of a copper wire and an (X5CrNi1810) steel wire plastically deformed under tension or bending conditions were found to increase with increasing degree of plastic deformation. The increase in the degree of deformation disturbs the microstructure of steel due to increases in the density of chaotically distributed dislocations and internal microstress, resulting in a decrease in the electron density of states near the Fermi level. Through the effect of thermal energy, annealing at elevated temperatures up to 300°C leads to microstructural ordering along with simultaneous increases in the free electron density of states, TEMF and TEMFC. Based on the temporal change of the TEMF, the kinetics of microstructural ordering was determined. During the initial time interval, the process is a kinetically controlled first-order reaction. In the second time interval, the process is controlled by the diffusion of reactant species.

The research of shear connectors composed from mechanical couplers with rebar anchors, embedded in concrete, and steel bolts, as a mean of shear transfer in composite connections is presented in the paper. Specific issues related to this type of connections are local concrete pressure in the connector vicinity as well as the shear flow along the connector axis. The experimental research included 18 specimens, arranged in 5 series. Nonlinear numerical analyses using Abaqus software was conducted on corresponding FE models. Different failure modes were analysed, with emphasis on concrete edge failure and bolt shear failure. The influence of key parameters on the behaviour of shear connector was examined: (1) concrete compression strength, (2) bolt tensile strength and diameter and (3) concrete edge distance. It is concluded that bolted shear connectors with mechanical couplers have sufficient capacity to be used as shear connectors in composite structures and that their behaviour is similar to the behaviour of post installed anchors as well as other types of connectors anchored without the head.

Analysis of conceptual design of reinforced concrete (RC) structure with secondary seismic elements in compliance with Eurocode 8 is presented in this paper. The application of this concept is complex due to the requirements regarding the classification and calculation of design internal forces, although the contribution of these elements in the total structural stiffness is neglected. The basic calculations of 8-story RC structure are performed with the main goal to emphasize and explain the problems of utilization of this concept. Its advantages are clearly presented and critical analysis of application in aseismic structural design is performed. The results of comparative analysis of structural design in which some structural elements are treated as a primary or as a secondary are presented., U radu je analiziran koncept proračuna armirano-betonske konstrukcije sa sekundarnim seizmičkim elementima prema zahtevima Evrokoda 8. Iako se doprinos krutosti ovih elemenata zanemaruje prilikom seizmičkog odgovora konstrukcije, primena ovog koncepta je kompleksna zbog niza zahteva u pogledu klasifikacije i načina proračuna statičkih uticaja. S ciljem da se istaknu i objasne specifičnosti primene, pokažu prednosti, ali i kritički razmotri upotreba opcije sekundarnih elemenata, izvršen je proračun osmoetažne armiranobetonske konstrukcije. Prikazane su dve metode za klasifikaciju sekundarnih elemenata, način proračuna uticaja u njima, kao i rezultati uporedne analize u kojoj su određeni elementi konstrukcije razmatrani kao primarni i kao sekundarni.

This paper presents the procedure for calculation of creep coefficient and shrinkage strain according to Eurocode 2 (SRPS EN 1992-1-1:2004). The calculated values of final creep coefficient and shrinkage strain, for the usual design conditions, are given in Annexes. The influence of key parameters on final creep coefficient and shrinkage strain is analyzed and the comparison between their final values calculated according to Eurocode 2 and BAB 87 is presented., U tekstu je prikazan postupak izračunanja vrednosti koeficijenta tečenja i dilatacije skupljanja prema Evrokodu 2 (SRPS EN 1992-1-1:2004). Izračunate vrednosti, za uobičajene proračunske uslove, su date u priloženim tabelama. Analiziran je uticaj pojedinih parametara na konačne vrednosti i urađeno poređenje vrednosti određenih prema Evrokodu 2 i PBAB 87.

Eurocode 2 (EN 1992-1-1:2004) instructions for deflection control are discussed in the paper. Several problems arise with application of the span-to-depth limits. This procedure is not always applicable due to adopted pre-defined inputs and calculation of the deflections is necessary. The simplest procedure is to interpolate between deflections calculated using stiffness of the uncracked and the cracked member. This is an equivalent to the CEB bilinear method, but without explicit instruction for the interpolation coefficient. The most rigorous method of assessing deflections is based on the integration of the mean curvatures calculated at a number of cross sections along the member. This procedure may require additional adjustments in case of statically indeterminate structures.

Analysis of conceptual design of reinforced concrete (RC) structure with secondary seismic elements in compliance with Eurocode 8 is presented in this paper. The application of this concept is complex due to the requirements regarding the classification and calculation of design internal forces, although the contribution of these elements in the total structural stiffness is neglected. The basic calculations of 8-story RC structure are performed with the main goal to emphasize and explain the problems of utilization of this concept. Its advantages are clearly presented and critical analysis of application in aseismic structural design is performed. The results of comparative analysis of structural design in which some structural elements are treated as a primary or as a secondary are presented., U radu je analiziran koncept proračuna armirano-betonske konstrukcije sa sekundarnim seizmičkim elementima prema zahtevima Evrokoda 8. Iako se doprinos krutosti ovih elemenata zanemaruje prilikom seizmičkog odgovora konstrukcije, primena ovog koncepta je kompleksna zbog niza zahteva u pogledu klasifikacije i načina proračuna statičkih uticaja. S ciljem da se istaknu i objasne specifičnosti primene, pokažu prednosti, ali i kritički razmotri upotreba opcije sekundarnih elemenata, izvršen je proračun osmoetažne armiranobetonske konstrukcije. Prikazane su dve metode za klasifikaciju sekundarnih elemenata, način proračuna uticaja u njima, kao i rezultati uporedne analize u kojoj su određeni elementi konstrukcije razmatrani kao primarni i kao sekundarni.

This paper presents the procedure for calculation of creep coefficient and shrinkage strain according to Eurocode 2 (SRPS EN 1992-1-1:2004). The calculated values of final creep coefficient and shrinkage strain, for the usual design conditions, are given in Annexes. The influence of key parameters on final creep coefficient and shrinkage strain is analyzed and the comparison between their final values calculated according to Eurocode 2 and BAB 87 is presented., U tekstu je prikazan postupak izračunanja vrednosti koeficijenta tečenja i dilatacije skupljanja prema Evrokodu 2 (SRPS EN 1992-1-1:2004). Izračunate vrednosti, za uobičajene proračunske uslove, su date u priloženim tabelama. Analiziran je uticaj pojedinih parametara na konačne vrednosti i urađeno poređenje vrednosti određenih prema Evrokodu 2 i PBAB 87.

U radu je analiziran koncept proračuna armiranobetonske konstrukcije sa sekundarnim seizmičkim elementima prema zahtevima Evrokoda 8. Iako se doprinos krutosti ovih elemenata zanemaruje prilikom seizmičkog odgovora konstrukcije, primena ovog koncepta usložnjena je nizom zahteva po pitanju klasifikacije i načina proračuna statičkih uticaja. Sa ciljem da se istaknu i objasne specifičnosti primene, pokažu prednosti, ali i kritički razmotri upotreba opcije sekundarnih elemenata, izvršen je proračun osmoetažne armiranobetonske konstrukcije. Prikazane su dve metode za klasifikaciju sekundarnih elemenata, način proračuna uticaja u njima, kao i rezultati uporedne analize u kojoj su određeni elementi konstrukcije razmatrani kao primarni i kao sekundarni.

The paper analyzes the results of reinforced concrete flat slabs, using different methods based on the theory of elasticity and theory of plasticity. Were considered three methods: stripe method, method according to Hillerborg and Wiesinger and Yield Line theory. The stripe method based on the theory of elasticity and is one of the most commonly used methods for calculation flat slabs, which are recommended by many regulations for calculation reinforced concrete structures. This paper also presents two methods based on the theory of plasticity, the method according to Hillerborg and Wiesinger - lower bound and Yield Line theory - upper bound, which uses a solutions of Johansen. Solutions obtained by these methods define limits interval of critical load. Review the basic theoretical hypothesis of all these methods and their application to flat slabs. Conducted calculation according to Eurocode 2 with a regular arrangement of pillars, analyzed the results and commented differences that occur as a result of the adoption of various hypothesis., U radu su analizirani rezultati proračuna armiranobetonskih ploča direktno oslonjenih na stubove, koristeći različite metode koje se zasnivaju na teoriji elastičnosti i teoriji plastičnosti. Razmatrane su tri metode: metoda ekvivalentnih traka, metoda prema Hillerborg-u i Wiesinger-u i metoda linija loma. Metoda ekvivalentnih traka zasniva se na teoriji elastičnosti i jedna je od najčešće primenjivanih metoda za proračun ploča direktno oslonjenih na stubove, koju preporučuju mnogi propisi za proračun armiranobetonskih konstrukcija. U radu su predstavljene i dve metode koje se zasnivaju na teoriji plastičnosti, metoda prema Hillerborg-u i Wiesinger-u teorija donje granice i metoda linija loma (Yield Line theory) teorija gornje granice, koja koristi rešenja Johansen-a. Rešenja dobijena ovim metodama definišu granice intervala kritičnog opterećenja. Prikazane su osnovne teorijske pretpostavke svih navedenih metoda kao i njihova primena na ploče direktno oslonjene na stubove. Sproveden je proračun ploče prema Evrokodu 2 sa pravilnim rasporedom stubova, analizirani su rezultati i komentarisane razlike koje se javljaju kao posledica usvajanja različitih pretpostavki.

The paper analyzes the results of reinforced concrete flat slabs, using different methods based on the theory of elasticity and theory of plasticity. Were considered three methods: stripe method, method according to Hillerborg and Wiesinger and Yield Line theory. The stripe method based on the theory of elasticity and is one of the most commonly used methods for calculation flat slabs, which are recommended by many regulations for calculation reinforced concrete structures. This paper also presents two methods based on the theory of plasticity, the method according to Hillerborg and Wiesinger - lower bound and Yield Line theory - upper bound, which uses a solutions of Johansen. Solutions obtained by these methods define limits interval of critical load. Review the basic theoretical hypothesis of all these methods and their application to flat slabs. Conducted calculation according to Eurocode 2 with a regular arrangement of pillars, analyzed the results and commented differences that occur as a result of the adoption of various hypothesis., U radu su analizirani rezultati proračuna armiranobetonskih ploča direktno oslonjenih na stubove, koristeći različite metode koje se zasnivaju na teoriji elastičnosti i teoriji plastičnosti. Razmatrane su tri metode: metoda ekvivalentnih traka, metoda prema Hillerborg-u i Wiesinger-u i metoda linija loma. Metoda ekvivalentnih traka zasniva se na teoriji elastičnosti i jedna je od najčešće primenjivanih metoda za proračun ploča direktno oslonjenih na stubove, koju preporučuju mnogi propisi za proračun armiranobetonskih konstrukcija. U radu su predstavljene i dve metode koje se zasnivaju na teoriji plastičnosti, metoda prema Hillerborg-u i Wiesinger-u teorija donje granice i metoda linija loma (Yield Line theory) teorija gornje granice, koja koristi rešenja Johansen-a. Rešenja dobijena ovim metodama definišu granice intervala kritičnog opterećenja. Prikazane su osnovne teorijske pretpostavke svih navedenih metoda kao i njihova primena na ploče direktno oslonjene na stubove. Sproveden je proračun ploče prema Evrokodu 2 sa pravilnim rasporedom stubova, analizirani su rezultati i komentarisane razlike koje se javljaju kao posledica usvajanja različitih pretpostavki.

Predmet ovog rada su teorijsko-eksperimentalna istraživanja projektovanja složenih tehničkih sistema na primeru realizacije mehatroničkog sistema za izradu specijalno oblikovanih žičanih profila (skraćeno, linija MSŽ). Proizvodi koji se dobijaju na liniji MSŽ su specijalni žičani profili poprečnog preseka trapeznog oblika, prstenasto savijeni na određenom koraku radi dalje montaže u finalni proizvod, strogih zahteva kvaliteta (potrebna tvrdoća, uske tolerancije mera oblika i dimenzija, itd). Profili se izrađuju od žice kružnog poprečnog preseka, prečnika Ø2÷5 mm, uglavnom od kvalitetnih nerđajućih čelika u normalizovanom stanju. Dobijeni žičani profili koriste se za formiranje tzv. pukotinastih sita (u svetu poznata kao Looped Wedge Wire Screens)., The paper is focusing theoretical and experimental research of design of complex technical systems on the example of realization of mechatronic system for production of specially-designed wire profile (abbreviated MSZ). Products obtained on the MSZ are specially designed wire profiles wedge shaped and looped on a certain step for further assembly into final products having strict quality requirements (high hardness, tight tolerances of the dimensions shape and size, etc.). Profiles are fabricated from circular cross section wire with diameter of Ø2-5 mm, mainly high-quality stainless steel in the normalized condition. Obtained wire profiles are used for production of socalled Looped Wedge Wire Screens. System complexity enables all challenges of the mechatronic systems design to be shown, to perform all the necessary analysis both analytical and experimental, and to define mechatronic system with best characteristics by the synthesis of relevant data. Along with prototype realization an integrated design methodology of complex technical systems has been developed. Specific requirements are defined and many problems of theoretical and practical character have been solved. Certain experimental measurements were performed to verify obtained analytical results. Process parameters and particular solutions for specific segments of the system are defined by a modeling, simulation and analysis.

This paper considers the problem of defining and solving problems in robot mechanics that is fundamental for successful design and performance of robot control system. It considers a few different approaches for describing dynamics of robots and forming of dynamics models with purpose to get a set of mathematical equations describing activity of torques and forces on robot arm in form of motion equations describing the dynamic behavior of the manipulator. It describes the formulation, characteristics and properties of dynamics equations of motion, which are suitable for control purposes, through three different formulations, whereby advantages and disadvantages of each are described separately. To realize practical application of dynamics calculation and solving them using the PC computer, the method use 3×3 rotation matrices and 4×4 homogeneous transformation matrices.