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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.

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.

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.

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

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 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.

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.