Ponašanje veze zavrtnja i armature ostvarene pomoću mehaničke spojnice pri dejstvu sile zatezanja

Primena montažno-demontažnih veza između čeličnih i AB elemenata omogućava ubrzani proces i smanjenje troškova izgradnje građevinskih konstrukcija ali i njihovu potencijalnu ponovnu upotrebu, što vodi ka održivom razvoju i cirkularnoj ekonomiji. Montažno-demontažni konektor koga čine: (1) mehanička spojnica i armaturni anker koji se postavljaju u oplatu pre betoniranja, i (2) zavrtanj kojim se čelični element povezuje za betonskim sve češće se koristi u savremenim montažno-demontažnim građevinskim konstrukcijama. Nosivost i ponašanje spregnute veze pri dejstvu sila smicanja, sila zatezanja ili njihove interakcije, za ove tipove konektora još uvek su nedovoljno istraženi. U radu su analizirani nosivost i lokalno ponašanje ovakvog konektora pri dejstvu sile zatezanja, na osnovu eksperimentalnih rezultata i numeričke analize u programu Abaqus

Sinteza mehatroničnog sistema za izradu specijalno oblikovanih žičanih profila

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

Demountable connections between steel and reinforced concrete elements with mechanical couplers under combined shear and tension loads

Primena spregnutih i mešovitih konstrukcija od čelika i betona u savremenoj građevinskoj praksi proistekla je iz težnje ka racionalnijoj upotrebi čelika i betona, kao i skraćenju vremena i smanjenju troškova izgradnje građevinskih objekata kao što su poslovne zgrade, garaže, mostovi i sl. Savremeni trendovi u građevinarstvu, koji su usmereni ka održivom razvoju i primeni principa cirkularne ekonomije, nameću mogućnost demontaže konstruktivnih elemenata kao dodatni projektni zahtev za spregnute i mešovite konstrukcije. Upotreba prefabrikovanih armiranobetonskih (AB) elemenata i demontažnih konektora sa mehaničkom spojnicom i armaturnim ankerom za vezu sa čeličnim elementom predstavljaju jedno od mogućih rešenja kojim se unapređuje održivost građevinskih konstrukcija. Spoj između čeličnog i armiranobetonskog elementa na gradilištu ostvaruje se pomoću kratkog demontažnog zavrtnja koji se vezuje za mehaničku spojnicu, prethodno ubetoniranu sa armaturnim ankerom u prefabrikovani AB element. Tom prilikom, površina AB elementa na mestu spoja je ravna pa primena ovakvog tipa konektora omogućava jednostavniju demontažu u poređenju sa primenom ostalih tipova demontažnih konektora. Takođe, pravilnim oblikovanjem spoja sa mehaničkim spojnicama omogućava se potencijalna ponovna upotreba svih komponenata spoja na kraju „prvog upotrebnog veka“. Iako je njihova primena u savremenoj građevinskoj praksi rasprostranjena, ponašanje konektora sa zavrtnjem, mehaničkom spojnicom i armaturnim ankerom pri dejstvu sile smicanja, sile zatezanja i njihove interakcije još uvek nije dovoljno istraženo. Adekvatna analiza ovakvog konektora treba da obuhvati sve moguće vidove loma pri proizvoljnom opterećenju, uključujući sve moguće vidove loma betona i vidove loma konektora. Pri tome, ponašanje konektora sa mehaničkom spojnicom je složenije od ponašanja ostalih tipova konektora jer se konektor sastoji od tri elementa koji imaju različite geometrijske karakteristike i mehaničke karakteristike materijala. U savremenim tehničkim normama i smernicama, nosivost konektora sa mehaničkom spojnicom određuje se na osnovu analogije sa tradicionalnim tipovima spojnih sredstava za beton, sa konstantnim poprečnim presekom duž konektora. Skorašnja istraživanja pokazala su da ovakva aproksimacija može rezultovati značajnim odstupanjima od realnog ponašanja ovakvog konektora. Istraživanje u ovoj doktorskoj disertaciji obuhvata eksperimentalnu i numeričku analizu spoja sa mehaničkim spojnicama pri dejstvu sile smicanja, pri dejstvu sile zatezanja i pri kombinovanom dejstvu sila smicanja i zatezanja. Analizirano je ponašanje samostalnih konektora u spoju, bez uticaja međusobnog rastojanja pojedinačnih konektora na nosivost i deformabilnost spoja. Posebna pažnja posvećena je ponašanju i nosivosti konektora sa mehaničkom spojnicom sa malim rastojanjem konektora od ivice AB elementa odnosno u uslovima koji odgovaraju spojevima čeličnih elemenata sa AB elementima ograničenih dimenzija na mestu spoja. Prvi deo eksperimentalnog istraživanja obuhvatio je ispitivanje ponašanja i nosivosti samostalnih konektora pri dejstvu sile smicanja. Ispitivanje je izvršeno primenom „push-out“ testa, u skladu sa preporukama standarda EN 1994-1-1 (CEN, 2004). U sopstvenom eksperimentalnom istraživanju varirana je srednja vrednost čvrstoće betona pri pritisku (f cm = 28-38 MPa), rastojanje konektora od ivice AB elementa (c = 75 mm i c = 150 mm) i tip oslonaca na koje su uzorci oslonjeni (pokretni oslonci i oslonci na sloju gipsa). Razmatrani su samo konektori sa M20 zavrtnjem. Rezultati ispitivanja dopunili su postojeću bazu podataka o nosivosti i ponašanju ovakvog spoja koja obuhvata, pored pomenutih parametara, i različite prečnike konektora sa zavrtnjem M16 i M20 (Milosavljević, 2014). Pri tome, uzorci sa rastojanjem konektora od ivice AB elementa c = 75 mm imalu su konektore sa M16 zavrtnjem (nije razmatran uticaj različitog prečnika konektora). ii Drugi deo eksperimentalnog istraživanja usmeren je na ispitivanje ponašanja i nosivosti samostalnih konektora pri dejstvu sile zatezanja primenom „pull-out“ testa. U svim slučajevima, konektor se nalazio blizu ivice AB elementa (c = 75 mm) a variran je prečnik konektora (sa M16 i M20 zavrtnjem) i srednja vrednost čvrstoće betona (f cm = 28-38 MPa). Pored ispitivanja ponašanja spoja, ispitano je i ponašanje neubetoniranih konektora sa M16 i M20 zavrtnjem pri zatezanju kako bi se analiziralo lokalno ponašanje svih elemenata konektora i njihovih međusobnih veza. Treći, glavni, deo eksperimentalnog istraživanja obuhvatio je ispitivanje ponašanja i nosivosti samostalnih konektora pri interakciji sila smicanja i zatezanja. Ispitivanje je izvršeno primenom modifikovanog „push-out“ testa. U ovom delu istraživanja variran je prečnik konektora (sa zavrtnjem M16 i M20), rastojanje konektora od ivice AB elementa (c = 75 mm i c = 150 mm), čvrstoća betona (f cm = 28-38 MPa) i intenzitet aplicirane sile zatezanja (T = 0-100 kN). Na osnovu rezultata eksperimentalnog istraživanja formirani su numerički nelinearni modeli spoja sa konektorom koji ima M20 zavrtanj, odgovarajuću mehaničku spojnicu i armaturni anker u programskom paketu Abaqus/Explicit. Numerički modeli obuhvatili su plastifikaciju i oštećenje komponentalnih materijala. Validacijom numeričkih modela pokazano je dobro poklapanje sa rezultatima eksperimentalnog istraživanja. Ovi modeli iskorišćeni su za numeričku parametarsku analizu u kojoj su varirani: rastojanje konektora od ivice AB elementa (c = 75-200 mm), čvrstoća betona (f cm = 28-58 MPa), nosivost armaturnog ankera na zatezanje (Tu,a = 133-200 kN) i intenzitet aplicirane sile zatezanja (T = 0-134 kN). Rezultati eksperimentalne i numeričke analize pokazali su da ponašanje i nosivost konektora značajno zavisi od prečnika konektora, rastojanja konektora od ivice AB elementa i intenziteta aplicirane sile zatezanja. Lom spoja nastao je usled sledećih vidova loma: (i) loma demontažnog zavrtnja pri čistom smicanju i pri interakciji smicanja i zatezanja, (ii) loma i mehaničke spojnice pri smicanju i pri interakciji smicanja i zatezanja (iii) loma armaturnog ankera (veze ankera i spojnice) pri čistom zatezanju, i (iv) loma betona u blizini ivice AB elementa pri čistom smicanju i pri interakciji smicanja i zatezanja. Uporednom analizom pokazano je da trenutno važeće tehničke norme i smernice za projektovanje spojeva sa mehaničkim spojnicama u pojedinim slučajevima imaju značajna odstupanja od rezultata istraživanja sprovedenog u ovoj doktorskoj disertaciji. Ovo se pre svega odnosi na nosivost konektora pri lomu betona u blizini ivice AB elementa, nosivost mehaničke spojnice i nosivost demontažnog zavrtnja pri interakciji smicanja i zatezanja. Stoga, predloženi su novi predikcioni modeli za određivanje nosivosti ovih komponenata spoja. Rezultati analize ovih modela imaju dobra poklapanja sa rezultatima eksperimentalne i numeričke analize. Predloženi predikcioni modeli za određivanje nosivosti demontažnih konektora sa mehaničkom spojnicom i armaturnim ankerom, kao i preporuke za projektovanje formulisani su tako da su u saglasnosti sa, trenutno važećim, evropskim standardom za projektovanje spojnih sredstava za beton EN 1992-4 (CEN, 2018)The use of composite and mixed steel-concrete structures in contemporary structural building practice arose from the desire for optimal usage of steel and concrete, as well as to reduce the construction time and costs of building structures such as office buildings, garages, bridges, etc. Modern trends in construction industry, which are focused on sustainable design and circular economy, impose the possibility of disassembly of structural elements as an additional design objective for composite and mixed structures. The use of prefabricated reinforced concrete (RC) elements and demountable bolted connectors with mechanical coupler and rebar anchor represent one of the possible solutions towards more sustainable design of building structures. The connection between steel and reinforced concrete on site is achieved by connecting short demountable bolt to previously embedded mechanical coupler and rebar anchor in precast RC element. In this type of connection, the concrete surface is flat and, therefore, the use of demountable connectors enables easer disassembly compared to the use of other types demountable connectors. Furthermore, potential reuse of all connection components can be achieved after the “End-of-First-Use” by adequate design of the connection with mechanical couplers. Over the last 15 years, bolted connectors with mechanical coupler and rebar anchor are more widely used in contemporary structural practice. However, their behaviour under shear load, under tension load and under combined shear and tension loads is still insufficiently known. The adequate design of this type of connector needs to include all possible failure modes under arbitrary loads, including all possibly concrete failure modes and failure modes of connector components. In this regard, the behaviour of bolted connector with mechanical coupler is more complex than the behaviour of other types of connectors. The reason lies in the fact that this type of connector is comprised of three components with different geometrical characteristics and mechanical characteristics of steel. In contemporary design codes and recommendations, the resistance of bolted connectors with mechanical coupler is determined by using the analogy with the traditional type of connectors, with constant diameter over the connector length. Recent studies have shown that this approximation can result in large deviations from the real behaviour of bolted connectors with mechanical coupler. The research presented in this doctoral dissertation covers experimental and numerical analysis of the connection with mechanical couplers under shear load, under tension load and under combined shear and tension loads. The behaviour of single connector is analysed, without the influence of spacing of the connectors within the connection on the resistance, stiffness and ductility. The research is mainly focused on the behaviour and resistance of bolted connectors with mechanical couplers located close to the concrete edge i.e., in situations where RC elements have limited dimensions at the location of the connection. The first part of experimental research focuses on the analysis of the behaviour and resistance of single connectors under shear load. Experimental tests were conducted using “push-out” tests according to recommendations given in EN 1994-1-1 (CEN, 2004). Mean concrete strength (f cm = 28-38 MPa), concrete edge distance (c = 75 mm and c = 150 mm) and support type (roller and gypsum supports) were varied. Only the connectors with M20 bolts were analysed. Research results have extended the existing database of resistance and behaviour this type of the connector (Milosavljević, 2014). Apart from the above-mentioned parameters, the existing database covers the results for different connector diameters with M16 and M20 bolts. In this regard, only specimens with concrete edge distance c = 75 mm and M16 bolts were analysed. iv The second part of experimental research focuses on the testing of the behaviour and resistance of single connectors under tension load in “pull-out” tests. In all tests, the connector was located close to the concrete edge (c = 75 mm), while the connector diameter (with M16 and M20 bolts) and mean concrete strength (f cm = 28-38 MPa) were varied. In addition, tensile behaviour of “in-air” specimens with M16 and M20 bolts was analysed, in order to closely establish the local behaviour of connector components as well as component connections. The third and the main part of experimental research focuses on the analysis of the behaviour and resistance of single connectors under combined shear and tension loads. Tests were conducted using the modified “push-out” test. In this part of research, the connector diameter (with M16 and M20 bolts), concrete edge distance (c = 75 mm and c = 150 mm), mean concrete strength (f cm = 28- 38 MPa) and the level of the applied tension force were varied. Based on the experimental test results, the nonlinear finite element models with M20 bolts and corresponding coupler and rebar anchor were constructed and calibrated using software Abaqus/Explicit, which included plasticity and damage of component materials. The validation of numerical models showed good agreement with experimental test results. These models were used for numerical parametric study which included the variation of concrete edge distance (c = 75-200 mm), mean concrete strength (f cm = 28-58 MPa), tensile resistance of rebar anchor (Tu,a = 133-200 kN) and the level of applied tension force (T = 0-134 kN). The results of experimental and numerical research have shown that the behaviour and resistance of the connector highly depends on the connector diameter, concrete edge distance and the level of the applied tension force. Different failure modes of the connection were detected: (i) bolt failure under shear load and under combined loads, (ii) mechanical coupler failure under shear load and under combined loads, (iii) rebar anchor failure (anchor-coupler connection) under tension load, and (iv) concrete edge failure under shear load and under combined loads. The comparative analysis has shown that, in most cases, the prediction equations for resistance of the connector from technical codes and guidelines give significant deviations from the resistance determined in tests and numerical analysis. This conclusion mostly applies for the concrete edge resistance, mechanical coupler resistance and bolt resistance under combined shear and tension loads. Therefore, a new prediction models for calculating the resistance of these components were developed. These models have good agreements with experimental and numerical results. The calculation models for resistance of bolted connector with mechanical coupler and rebar anchor as well as the design recommendations are formulated in form which is suitable for inclusion in current European design codes for design of fastenings for use in concrete EN 1992-4 (CEN, 2018

Analiza primene sekundarnih seizmičkih elemenata u proračunu prema Evrokodu 8

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

The analysis of application of secondary seismic elements in design according to Eurocode 8

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

Advanced rule-based energy management for better fuel economy of hybrid electric tracked vehicle

Sva nedavna tehnološka dostignuća na polju raspodele snage između pogonskih agregata u hibridnim guseničnim vozilima su uglavnom teško primenjiva i teška za izračunavanje što ih čini nepraktičnim za primenu u stvarnom vremenu. U ovom radu predložena je nova strategija upravljanja paralelnim hibridnim električnim guseničnim vozilima zasnovana na robusnoj i jednostavnoj termostatskoj strategiji sa dodatkom nekih karakteristika power-follower strategije (PFCS). Cilj strategije upravljanja je smanjenje potrošnje goriva. Kao referentno vozilo izabrano je borbeno vozilo pešadije BVP M80-A domaće proizvodnje. U svrhu validacije, u Simulink okruženju je kreiran (backward-looking) model realnog vozila. Analiza rezultata pokazuje da predložena strategija upravljanja omogućava uštedu goriva od 12,8%, a istovremeno efikasno održava stanje napunjenosti baterije (SOC). Još bolji rezultati (23,2%) postignuti su primenom predložene strategije na modelu sa dodatim generatorom za dopunu baterije. Zaključeno je da se dodatna poboljšanja mogu postići kombinovanom optimizacijom konstrukcionih parametara vozila i parametara modela upravljanja.All recent technological developments in the field of power distribution in hybrid electric tracked vehicles are often hard to apply and carry high computational burden which makes them impractical for real-time applications. In this paper, a novel control strategy is proposed for parallel hybrid electric tracked vehicle based on robust and easy to implement thermostat strategy with added merits of power follower control strategy (PFCS). The goal of the control strategy is enhanced fuel economy. Serbian infantry fighting vehicle BVP M80-A is chosen as the reference vehicle. For the purpose of validation, a backward-looking, high fidelity model is created in Simulink environment. Investigation of the results indicates that the proposed control strategy offers 12.8% better fuel economy while effectively maintaining battery state of charge (SOC). Even better results (23.2%) were achieved applying the proposed strategy to a model with an additional generator. It is concluded that further improvements can be made with combined sizing and control optimization

Advanced rule-based energy management for better fuel economy of hybrid electric tracked vehicle

Sva nedavna tehnološka dostignuća na polju raspodele snage između pogonskih agregata u hibridnim guseničnim vozilima su uglavnom teško primenjiva i teška za izračunavanje što ih čini nepraktičnim za primenu u stvarnom vremenu. U ovom radu predložena je nova strategija upravljanja paralelnim hibridnim električnim guseničnim vozilima zasnovana na robusnoj i jednostavnoj termostatskoj strategiji sa dodatkom nekih karakteristika power-follower strategije (PFCS). Cilj strategije upravljanja je smanjenje potrošnje goriva. Kao referentno vozilo izabrano je borbeno vozilo pešadije BVP M80-A domaće proizvodnje. U svrhu validacije, u Simulink okruženju je kreiran (backward-looking) model realnog vozila. Analiza rezultata pokazuje da predložena strategija upravljanja omogućava uštedu goriva od 12,8%, a istovremeno efikasno održava stanje napunjenosti baterije (SOC). Još bolji rezultati (23,2%) postignuti su primenom predložene strategije na modelu sa dodatim generatorom za dopunu baterije. Zaključeno je da se dodatna poboljšanja mogu postići kombinovanom optimizacijom konstrukcionih parametara vozila i parametara modela upravljanja.All recent technological developments in the field of power distribution in hybrid electric tracked vehicles are often hard to apply and carry high computational burden which makes them impractical for real-time applications. In this paper, a novel control strategy is proposed for parallel hybrid electric tracked vehicle based on robust and easy to implement thermostat strategy with added merits of power follower control strategy (PFCS). The goal of the control strategy is enhanced fuel economy. Serbian infantry fighting vehicle BVP M80-A is chosen as the reference vehicle. For the purpose of validation, a backward-looking, high fidelity model is created in Simulink environment. Investigation of the results indicates that the proposed control strategy offers 12.8% better fuel economy while effectively maintaining battery state of charge (SOC). Even better results (23.2%) were achieved applying the proposed strategy to a model with an additional generator. It is concluded that further improvements can be made with combined sizing and control optimization

Geodata management by developing of national data infrastructure in the republic of Serbia

Sharing of spatial information between the state establishments and private sector, based on standards for technical infrastructure of spatial data and services, is the strategic objective of the Mid-Term Program of Works of the Republic of Serbia, covering the National Spatial Data Infrastructure (NSDI) Instigation and the maintenance for the period from 2011 to 2015. With the objective to achieve the goals set, the research was performed, with the results published in the present paper. The paper shows the status in the Spatial Data Infrastructure instigation; with the evaluation of development level achieved and recommendations for the future INSPIRE Directive implementation in Serbia. Geodata status analysis was performed over the sample of 78 local government organisations, state administration bodies, public enterprises and educational institutions. Overview was given for use, the types and availability conditions for spatial data. The issues of NSDI concept implementation were particularly noted, referring to the pricing policy for spatial data use, for the legislation and issues in spatial data coordination in the Republic of Serbia

The design of local ductility for reinforced concrete elements by eurocode 8 - confinement effectiveness factor

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