Demontažni smičući spojevi ostvareni zavrtnjevima i moždanicima sa glavom kod spregnutih konstrukcija od čelika i betona

The reuse of constructional elements or entire structures is an important approach in the construction industry that follows the concept of sustainable development. Steel-concrete composite structures enable the efficient use of material and savings in material consumption. However, widespread steel-concrete composite beams with welded headed stud shear connectors do not have the demountability feature and therefore cannot be entirely reused. In the past few decades, much research in the field of steel-concrete composite structures has been focused on the development and investigations of demountable floor systems. A further contribution to that field is provided in this thesis. A novel demountable shear connection with bolts and welded headed studs is proposed. The suggested connection is applicable in composite concrete slabs cast in open trough profiled steel sheeting. Welded headed studs are installed in sheeting ribs, whereas bolts are placed between ribs. Implementation of the additional plate or angles between the beam flange and the concrete slab is required. During the building deconstruction, bolts are removed and the composite concrete slab is easily separated from the steel beam with the possibility of being installed again. Destruction methods are avoided and the entire floor structure including concrete slabs and steel beams may be reused in another location in the same configuration as during the first life cycle. The aim of the study is to promote the novel demountable connection with welded headed studs and bolts. The objectives of the research are to describe the demountable connection response to the shear load at the point of resistance and ductility, to identify failure mechanisms and propose instructions for the design. The developed demountable connection is examined by static push-out tests, conducting experimental and numerical investigations. The experimental work covers 20 push-out test specimens divided into eight series. Different configurations of the demountable steel-concrete connections are experimentally investigated: connections with continuous and discontinuous slabs over the supporting beam, connections with and without stirrup reinforcement around headed studs, connections with the angle between profiled sheeting ribs and the beam of 45°, 60° and 90°. The resistance, ductility and stiffness of demountable connections are compared with corresponding non-demountable connections with welded headed studs. According to the experimental research, the appropriate numerical finite element models are developed and used for a detailed analysis of the connection response and further parametric studies. A range of parameters that might influence the connection response is covered by parametric studies, including the headed stud diameter and height, bolt grade and diameter, concrete class, plate and angle thickness, the distance between the headed stud and slab edge, stirrup reinforcement diameter and position, the angle between sheeting ribs and the beam. The key influential parameters are identified and their effects on the connection performance are quantified. According to the wide set of the obtained data, conclusions regarding the connection response are drawn. Design recommendations for demountable shear connections with bolts and welded headed studs are proposed.Princip ponovne upotrebe konstruktivnih elemenata ili cele konstrukcije u građevinarstvu u skladu je sa konceptom održivog razvoja. Spregnute konstrukcije od čelika i betona omogućavaju efikasnu upotrebu materijala i uštede u potrošnji. Međutim, spregnute grede od čelika i betona sa zavarenim moždanicima sa glavom koje su u širokoj primeni, nisu demontažne i ne mogu se ponovo upotrebiti. U prethodnih nekoliko decenija, mnoga istraživanja u oblasti spregnutih konstrukcija bavila su se razvojem i ispitivanjem demontažnih međuspratnih konstrukcija. Doprinos navedenoj oblasti dat je kroz ovu disertaciju. Predložen je novi demontažni smičući spoj sa zavrtnjevima i moždanicima sa glavom, kao rešenje primenljivo u spregnutim pločama sa trapeznim profilisanim limom. Postavljanje moždanika predviđeno je u rebrima profilisanog lima, dok se zavrtnjevi postavljaju između, u prevojima lima. Neophodna je primena dodatnog čeličnog lima ili ugaonika na kontaktu između nožice čelične grede i betonske ploče. Tokom demontaže, zavrtnjevi se uklanjaju i spregnuta ploča se jednostavno razdvaja od čeličnog profila, uz mogućnost ponovnog korišćenja. Na ovaj način, destruktivne metode su izbegnute i kompletna međuspratna kontrukcija se može ponovo upotrebiti na drugoj lokaciji u istom obliku kao prilikom prvog životnog ciklusa. Cilj naučnog istraživanja je realizacija inovativnog demontažnog smičućeg spoja sa moždanicima sa glavom i zavrtnjevima. Cilj je opisati ponašanje demontažnog spoja pri dejstvu smičućeg opterećenja u pogledu nosivosti i deformabilnosti, identifikovati mehanizme loma i dati proračunske preporuke. Demontažni smičući spoj je ispitivan putem testova smicanja primenom eksperimentalnih i numeričkih metoda. Eksperimentalno ispitivanje obuhvata 20 testova smicanja podeljenih u osam serija. Ispitivane su različite konfiguracije demontažnog spoja: spojevi sa kontinualnom i diskontinualnom pločom iznad oslonačke grede, spojevi sa i bez uzengija postavljenih oko moždanika, spojevi sa uglovima između rebara profilisanog lima i ose nosača od 45°, 60° i 90°. Nosivost, duktilnost i krutost demontažnih spojeva upoređene su sa odgovarajućim standardnim spojevima sa zavarenim moždanicima sa glavom. Na osnovu eksperimentalnih rezultata, formirani su odgovarajući numerički modeli, koji su potom korišćeni za detaljnu analizu ponašanja spoja i dalju parametarsku analizu. Parametarskom analizom obuhvaćeni su različiti parametri koji bi mogli uticati na ponašanje spoja, uključujući: prečnik i visinu moždanika, prečnik i klasu čvrstoće zavrtnja, klasu betona, debljinu lima i ugaonika, rastojanje između moždanika i ivice betonske ploče, prečnik i poziciju uzengija, ugao između rebara profilisanog lima i ose nosača. Identifikovani su ključni uticajni parametri i njihov efekat je kvantifikovan. Na osnovu širokog skupa dobijenih rezultata, doneti su zaključci po pitanju ponašanja smičućeg spoja. Takođe, date su preporuke za projekotovanje demontažnog spoja sa zavrtnjevima i moždanicima sa glavom

Buckling of plates and plate girders subjected to patch load

The determination of the elastic critical load (buckling load) is an important element of the assessment of the ultimate load of plate girders. An analysis of the critical load of a plate corresponding to the web of an I-girder for different boundary conditions and the critical load of the I-girder itself is given in the paper. Conclusions regarding their correspondence are given. Also, experimentally determined ultimate loads of I-girders are compared with values according to Eurocode for the models used in this analysis

Fleksiono izvijanje naknadno termički obrađenih i hladnooblikovanih stubova elipsastog poprečnog preseka: Numerička uporedna analiza

Even though structural elements of the elliptical hollow section (EHS) have been introduced to the construction market in the past years, the rules for their design were only partially introduced into the suitable codified procedures. The aim of this paper is to present a comparative numerical analysis of behaviour of cold-formed and hot-finished EHS columns exposed to flexural buckling under pure axial compression. Pin-ended columns of a various slenderness without lateral restrains and with incorporated geometrical imperfections are analysed. Material nonlinear behaviour is included through published experimental tensile test results, conducted in previous researches. In addition, numerical simulations of stub column behaviour are performed in order to obtain a cross-section compressive resistance. Results of the finite element analysis are compared to the design criteria defined in the draft version of Eurocode EN 1993-1-1:2015 and in North American specification for cold-formed member design AISI-S100. It is observed that North American standard provides more accurate predictions of both a cross-section resistance and a buckling column resistance. Equivalent diameter method described in Eurocode 3 led to more conservative results. According to the obtained numerical results, similar buckling behaviour is observed for both hot-finished and cold-formed columns of higher slenderness, while in the lower slenderness region, cold-formed compressed members tend to lower buckling curves. Underestimation of a column buckling resistance according to Eurocode regulations is noticed for cold-formed members of a higher slenderness.Iako se poslednjih godina šuplji profili elipsastog poprečnog preseka (EHS) mogu naći na tržištu, pravila za njihovo dimenzionisanje su tek delimično uvedena u odgovarajuće standarde za projektovanje. Cilj ovog rada jeste da prikaže komparativnu numeričku analizu ponašanja centrično pritisnutih hladnooblikovanih i naknadno termički obrađenih EHS stubova, usled fleksionog izvijanja. Analizirani su zglobno oslonjeni stubovi različitih vitkosti bez bočnog pridržanja duž elementa, uzimajući u obzir početne geometrijske imperfekcije. Nelinearno ponašanje materijala modelirano je na osnovu publikovanih eksperimentalnih rezultata testova pri zatezanju, sprovedenih u prethodnim ispitivanjima. Takođe, izvršene su numeričke simulacije ponašanja kratkih stubova kako bi se utvrdila nosivost poprečnog preseka na pritisak. Rezultati numeričke analize sprovedene metodom konačnih elemenata upoređeni su s računskim vrednostima graničnih nosivosti u skladu s revidiranom verzijom Evrokoda EN 1993-1-1:2015 i Severnoameričkom specifikacijom za projektovanje hladnooblikovanih čeličnih elemenata AISI-S100. Uočeno je da Severnoamerički standard daje preciznije predikcije – i za nosivosti poprečnog preseka i za nosivosti stuba na fleksiono izvijanje. Metoda ekvivalentnog prečnika, opisana u Evrokodu 3, daje konzervativnije rezultate. Prema dobijenim numeričkim rezultatima, slično ponašanje pri fleksionom izvijanju uočeno je kod naknadno termički obrađenih i hladnooblikovanih stubova veće vitkosti, dok u oblasti manje vitkosti, hladnooblikovani pritisnuti elementi teže nepovoljnijim krivama izvijanja. Primećeno je da Evrokod potcenjuje nosivosti na izvijanje hladnooblikovanih stubova veće vitkosti

The influence of a roof mounted small-scale HAWT on headed studs fatigue resistance

Installation of small-scale wind turbines in urban regions can gain higher energy efficiency, considering that energy production takes place at the place of its consumption. The aim of this work is to investigate effects of installation of a small-scale horizontal axis wind turbine (HAWT) on a roof structure of an existing building. This paper is focused on fatigue resistance of headed studs that are preinstalled in the building roof composite steel-concrete deck to ensure shear connection and that are indirectly dynamically loaded during wind turbine operation. Turbulent wind profiles with mean wind speeds from 3 m/s up to 15 m/s are generated and applied on the model of HAWT with 5 m rotor diameter using Ashes software package. Time-dependent forces and bending moments induced by wind turbine operation are applied on the composite roof deck model. Based on the time-history of transverse force in the composite steel-concrete beam and wind speed records during a year, fatigue cumulative damage of headed studs is calculated according to Eurocode. It is obtained that installation of HAWT do not significantly affect residual life of headed studs with reference to fatigue

The influence of a roof mounted small-scale HAWT on headed studs fatigue resistance

Installation of small-scale wind turbines in urban regions can gain higher energy efficiency, considering that energy production takes place at the place of its consumption. The aim of this work is to investigate effects of installation of a small-scale horizontal axis wind turbine (HAWT) on a roof structure of an existing building. This paper is focused on fatigue resistance of headed studs that are preinstalled in the building roof composite steel-concrete deck to ensure shear connection and that are indirectly dynamically loaded during wind turbine operation. Turbulent wind profiles with mean wind speeds from 3 m/s up to 15 m/s are generated and applied on the model of HAWT with 5 m rotor diameter using Ashes software package. Time-dependent forces and bending moments induced by wind turbine operation are applied on the composite roof deck model. Based on the time-history of transverse force in the composite steel-concrete beam and wind speed records during a year, fatigue cumulative damage of headed studs is calculated according to Eurocode. It is obtained that installation of HAWT do not significantly affect residual life of headed studs with reference to fatigue

Numerical evaluation of flexural buckling of hot-finished and cold-formed EHS columns

Elliptical hollow sections (EHS) have been recently introduced to the construction market. However, in the current Eurocode standard for steel structures EN 1993-1-1, there are no design criteria defined for EHS. The aim of this paper is to present a comparative numerical analysis of behaviour of cold-formed and hot-finished EHS columns exposed to flexural buckling under pure axial compression. Pin-ended columns of various slendernesses without lateral restrains and with incorporated geometrical imperfections are analysed. Material nonlinear behaviour is included through experimental tensile test results adopted from previous researches. According to obtained numerical results, similar buckling behaviour is observed for both hot-finished and cold-formed columns of higher slenderness, while in the lower slenderness region, cold-formed compressed members tend to lower buckling curves

Numerical study on bending behaviour of hot-finished and cold-formed elliptical hollow sections

Elliptical hollow sections (EHS) are new products on the construction market. Their growing implementation in steel structures led to complementing design rules in the draft version of Eurocode EN 1993-1-1:2015. In this paper bending strength of elliptical hollow sections is being discussed, analysing cold-formed and hot-finished EHS profiles under pure bending. Numerical models include short members of diverse section slenderness with applied concentrated moments at the ends about either the major or the minor axis of inertia. Material nonlinear behaviour is included through experimental tensile test results adopted from previous researches. Influence of geometrical imperfections is incorporated in the analysis, however, imperfection amplitude variation has shown an insignificant effect on bending strength. For all analysed members, it is shown that numerically obtained ultimate moments are higher than bending strengths prescribed in EN 1993-1-1:2015. Differences in responses of hot-finished and cold-formed EHS are discussed. Comments on elliptical cross-section classification according to the design standard are made, as well as comments on the defined effective cross-sectional geometrical properties. Review of the set limiting slenderness for class 3 is suggested

Elastična kritična sila ploča i limenih nosača pod dejstvom lokalizovanog opterećenja

The determination of the elastic critical load (buckling load) is an important element of the assessment of the ultimate load of plate girders according to Eurocode 3 for design of steel structures. An analysis of the critical load of a plate corresponding to the web of an I-girder for different boundary conditions and the critical load of the I-girder itself subjected to patch load is given in the paper. Conclusions regarding their correspondence are given. Also, experimentally determined ultimate loads of I-girders are compared with predictive values according to Eurocode 3 for the models used in this analysis. A modified procedure for the ultimate load determination is proposed by following the Eurocode 3 algorithm and changing only buckling coefficient. In order to improve the ultimate load prediction, it is suggested to calculate the buckling coefficient also as a function of patch load length.Određivanje elastične kritične sile (sile izbočavanja) predstavlja važan element u određivanju granične nosivosti limenih nosača prema Evrokodu 3 za proračun čeličnih konstrukcija. U radu se daje analiza kritične sile izbočavanja izolovane ploče koja odgovara rebru Inosača s variranim uslovima oslanjanja i kritične sile koja odgovara samom I-nosaču, usled dejstva lokalizovanog opterećenja. Dati su zaključci o njihovoj vezi. Takođe, upoređena su eksperimentalno određena granična opterećenja I-nosača s vrednostima prema Evrokodu 3, za modele korišćene u ovoj analizi. Predložena je izmenjena procedura za određivanje granične nosivosti, koja sledi algoritam dat u Evrokodu 3, a prema kojoj se modifikuje izraz za određivanje koeficijenta izbočavanja. Kako bi se poboljšalo određivanje granične nosivosti, predloženo je računanje koeficijenata izbočavanja i u funkciji dužine lokalizovanog opterećenja

Demontažni smičući spoj sa zavrtnjevima i moždanicima sa glavom [Novo tehničko rešenje (nije komercijalizovano)]

M85 - Novo tehničko rešenje (nije komercijalizovano

Uticaj sredine na trajnost čelične konstrukcije – Studija slučaja stubova reklamnih medija

The steel structures of canopies, public garage columns, street lighting, power lines and other street furniture are constantly exposed to weather effects in their service life. The steel structure of street furniture is often exposed to the effects of de-icing salts from the roads. The paper analyses the effects of the urban environment on the durability of steel structures. The macroscopic visual inspection included 181 steel billboard poles on the territory of the City of Belgrade. The analysis of the surface treatment, the condition of the structure and its location provided conclusions regarding the durability of steel structures in urban environments. The environmental corrosivity on the territory of the City of Belgrade has been analysed. The analysis included the bearing steel structure of poles and the joint between the steel structure and foundations.Čeličnu konstrukciju nadstrešnica, stubova javnih garaža, ulične rasvete, dalekovoda i drugog urbanog mobilijara karakteriše stalna izloženost atmosferskim uticajima tokom životnog veka. Čelična konstrukcija urbanog mobilijara je neretko izložena i uticaju soli za održavanje saobraćajnica. U radu je analiziran uticaj gradske sredine na trajnost čelične konstrukcije. Stručnim vizuelno-makroskopskim pregledom obuhvaćen je 181 stub čelične konstrukcije za nošenje reklamnih medija na teritoriji grada Beograda. Analizirajući vrstu antikorozione zaštite, stanje konstrukcije i lokaciju konstrukcije izvedeni su zaključci o trajnosti čelične konstrukcije u urbanoj sredini. Analiziran je i stepen korozivnosti sredine na teritoriji grada Beograda. Analiza je obuhvatila noseću čeličnu konstrukciju stubova i detalj veze čelične konstrukcije i temelja