Behaviour of built-up stainless steel members subjected to axial compression

Iako je 2013. godine obeležena stogodišnjica pronalaska nerđajućeg čelika, njegova značajnija primena u građevinarstvu započinje tek početkom ovog veka. Austenitni nerđajući čelik odlikuje niz specifičnosti koje opravdavaju njegovu primenu u konstrukcijama posebne namene: postojanost i visoka otpornost na dejstvo korozije, značajan kapacitet plastifikacije i izražena duktilnost, poboljšanje svojstava materijala uticajem hladne deformacije, postojanost na visokim i niskim temperaturama, superiornost površinskog izgleda bez zaštitnih premaza, neškodljivost po okolinu. Najveći ograničavajući faktor za njegovu masovniju primenu je visoka jedinična cena, ali i nepotpunost tehničke regulative koja, još uvek, ne sagledava na odgovarajući način specifičnosti ovog materijala. Cilj istraživanja koje je prikazano u ovoj doktorskoj disertaciji je omogućavanje šire primene nerđajućeg čelika u konvencionalnim konstrukcijama kroz detaljnu analizu ponašanja centrično pritisnutih, hladnooblikovanih elemenata višedelnog preseka.Osnovni materijal primenjen u okviru istraživanja je nerđajući čelik austenitne mikrostrukture sa oznakom 1.4301. Predmet istraživanja su višedelni elementi formirani od dva C profila koji su međusobno direktno povezani šavovima ili zavrtnjevima. Eksperimentalnim ispitivanjem su obuhvaćene skoro sve osobenosti u ponašanju pritisnutih elemenata: ispitana su mehanička svojstva materijala, sagledan nivo asimetrije i anizotropije materijala, sagledan uticaj hladnog oblikovanja na poboljšanje mehaničkih svojstava materijala, utvrđen kapacitet nosivosti poprečnog preseka, izmerene početne geometrijske imperfekcije i određena nosivost elemenata na fleksiono izvijanje oko nematerijalne ose. Napredni numerički modeli na bazi metode konačnih elemenata su napravljeni da simuliraju ispitivanje pri fleksionom izvijanju a kalibrisani su na osnovu eksperimentalnih rezultata. Korištena je kvazi-statička analiza primenom eksplicitnog dinamičkog solvera softverskog paketa Abaqus. Ovako kalibrisani modeli na bazi MKE korišćeni su dalje za parametarsku analizu...Although the centenary of the invention of stainless steel was celebrated in 2013, its more significant implementation in construction industry was not established until the beginning of this century.Austenitic stainless steel is characterized by a number of features which justify its use in construction for special purposes: durability and corrosion endurance, high plastification capacity and ductility, improved characteristics of materials when subjected to deformation, resistance to high and low temperatures, superior surface appearance without protective coating, environmental safety. The main limiting factor for its wider application is the high unit price, as well as the incompleteness of technical regulations which are not taking into account properly all the specifics of this material. The purpose of the research presented in this doctoral dissertation is to enable wider application of stainless steel in conventional structures through detailed analysis of the behaviour of cold-formed built-up compression members.The base material used in this research is austenitic stainless steel grade 1.4301. Object research are built-up members composed of two C sections in contact, connected by weld or bolts. Experimental works included all the major behaviour characteristics of the compression member: mechanical properties of the material were measured, the level of asymmetry and material anisotropy was assessed, as well as the effects of the process of cold forming on improvement of the mechanical properties of the materials. Initial geometric imperfections, ultimate resistance of cross-section, ultimate resistance members to the flexural buckling around intangible axis, were also considered in experimental works. Advanced numerical models based on the finite element method were built to simulate behaviour under flexural buckling and they were calibrated with respect to the experiment data. Quasi-static analysis with the explicit dynamic solver software package Abaqus was engaged for the buckling analysis..

Resistance and serviceability analysis of steel footbridge structure according to Eurocode

This paper briefly presents resistance and serviceability analysis of steel footbridge structure. The main structural system consists of cold-formed members, which were designed according to EN 1993-1-3. Analysis of vibration of the footbridge structure was performed, including comparative study from the aspect of different criteria regarding the comfort according to Eurocode and SETRA/AFGC recommendations. Additionally, the paper compares behavior of steel footbridge with static and structural equivalent footbridge whose base material is aluminum alloy

Design of pedestrian bridge according to Eurocode 9

Aluminum alloys, due to its numerous advantages, is widely used in the construction of various types of structures in civil engineering. Design of pedestrian bridge, entirely constructed of extruded elements made of aluminum alloy EN-AW 6082 T6 with cross sections designed to enable the use of innovative joints, is presented in this paper. The design and construction of special bolted joints is presented using the recommendations given in standard for design of aluminum structures CNR-DT 208/2011. Also, calculation of pedestrian bridge vibrations through different design methods is given here. Results of numerical analysis are compared with the recommendations from different currently available standards and literature referring to the comfort criteria of pedestrian bridge vibrations

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

Behaviour of built-up stainless steel members subjected to axial compression

Iako je 2013. godine obeležena stogodišnjica pronalaska nerđajućeg čelika, njegova značajnija primena u građevinarstvu započinje tek početkom ovog veka. Austenitni nerđajući čelik odlikuje niz specifičnosti koje opravdavaju njegovu primenu u konstrukcijama posebne namene: postojanost i visoka otpornost na dejstvo korozije, značajan kapacitet plastifikacije i izražena duktilnost, poboljšanje svojstava materijala uticajem hladne deformacije, postojanost na visokim i niskim temperaturama, superiornost površinskog izgleda bez zaštitnih premaza, neškodljivost po okolinu. Najveći ograničavajući faktor za njegovu masovniju primenu je visoka jedinična cena, ali i nepotpunost tehničke regulative koja, još uvek, ne sagledava na odgovarajući način specifičnosti ovog materijala. Cilj istraživanja koje je prikazano u ovoj doktorskoj disertaciji je omogućavanje šire primene nerđajućeg čelika u konvencionalnim konstrukcijama kroz detaljnu analizu ponašanja centrično pritisnutih, hladnooblikovanih elemenata višedelnog preseka. Osnovni materijal primenjen u okviru istraživanja je nerđajući čelik austenitne mikrostrukture sa oznakom 1.4301. Predmet istraživanja su višedelni elementi formirani od dva C profila koji su međusobno direktno povezani šavovima ili zavrtnjevima. Eksperimentalnim ispitivanjem su obuhvaćene skoro sve osobenosti u ponašanju pritisnutih elemenata: ispitana su mehanička svojstva materijala, sagledan nivo asimetrije i anizotropije materijala, sagledan uticaj hladnog oblikovanja na poboljšanje mehaničkih svojstava materijala, utvrđen kapacitet nosivosti poprečnog preseka, izmerene početne geometrijske imperfekcije i određena nosivost elemenata na fleksiono izvijanje oko nematerijalne ose. Napredni numerički modeli na bazi metode konačnih elemenata su napravljeni da simuliraju ispitivanje pri fleksionom izvijanju a kalibrisani su na osnovu eksperimentalnih rezultata. Korištena je kvazi-statička analiza primenom eksplicitnog dinamičkog solvera softverskog paketa Abaqus. Ovako kalibrisani modeli na bazi MKE korišćeni su dalje za parametarsku analizu...Although the centenary of the invention of stainless steel was celebrated in 2013, its more significant implementation in construction industry was not established until the beginning of this century. Austenitic stainless steel is characterized by a number of features which justify its use in construction for special purposes: durability and corrosion endurance, high plastification capacity and ductility, improved characteristics of materials when subjected to deformation, resistance to high and low temperatures, superior surface appearance without protective coating, environmental safety. The main limiting factor for its wider application is the high unit price, as well as the incompleteness of technical regulations which are not taking into account properly all the specifics of this material. The purpose of the research presented in this doctoral dissertation is to enable wider application of stainless steel in conventional structures through detailed analysis of the behaviour of cold-formed built-up compression members. The base material used in this research is austenitic stainless steel grade 1.4301. Object research are built-up members composed of two C sections in contact, connected by weld or bolts. Experimental works included all the major behaviour characteristics of the compression member: mechanical properties of the material were measured, the level of asymmetry and material anisotropy was assessed, as well as the effects of the process of cold forming on improvement of the mechanical properties of the materials. Initial geometric imperfections, ultimate resistance of cross-section, ultimate resistance members to the flexural buckling around intangible axis, were also considered in experimental works. Advanced numerical models based on the finite element method were built to simulate behaviour under flexural buckling and they were calibrated with respect to the experiment data. Quasi-static analysis with the explicit dynamic solver software package Abaqus was engaged for the buckling analysis..

Column Curves for Stainless Steel Lipped–Channel Sections

The strength of thin-walled stainless steel columns has been investigated extensively over the last few years. The present paper presents the results of an extensive computational study of the buckling strength of lipped–channel section columns made of austenitic, duplex, and ferritic grades. The numerically computed strengths together with the available experimental data collected in the literature are compared to the current European and Australian/New Zealand standard (AS/NZS) codified predictions over the whole slenderness range. Minor and major axis buckling as well as flexural-torsional buckling are considered. A reliability assessment in the sense of both standards is then performed. The safety factor γm and resistance factor ϕc are computed per family of stainless steel. In conclusion, we advise the use of different European buckling column curves rather than the one currently adopted in the code and to make a distinction between the families of stainless steel. Besides, seeing the very good agreement found against the AS/NZS guidance, we propose that the factor η, currently being a linear expression in the European standard, be replaced by the AS/NZS expression with the proposed parameters for each stainless steel family

Design recommendations of floor vibrations induced by human activities

Structural engineers are now facing with new demands towards long spans, lightweight floors in steelconcrete composite construction and big open interiors. Thеsе new design trends аrе leading to the extensive problems related to the serviceability limit state, especially problems with unwanted floor vibrations. Annoying vibrations caused by human activities are an important serviceability problem, which can significantly affect the comfort of people, quality of life and structures functionality. Over past years many design recommendations of floor vibrations induced by human activities have been published. This paper presents a short overview of dynamic loads modeling and design recommendations of floor vibrations induced by human activities

Mathematical interpretation of nonlinear relationship of stainless steel stress and strain

Basic distinctive characteristics of stainless steels are reflected in the nonlinear relationship of stress and strain, prominent ductility, strain hardening due to cold forming, asymmetry and anisotropy of material. These properties lead to a different behavior of structural elements of this material than the equivalent elements made of carbon steel. Implementation of a design concept based on an ideal elasto-plastic model of material such as carbon steel, often produces conservative results in case of stainless steel, which is already at a disadvantage due to its cost in construction engineering. Proper defining of recommendations for design and their implementation in technical codes requires a precise and accurate mathematical interpretation of nonlinearity of stainless steel. This paper presents the most important analytical models for description of the relationship of stress and strain of various alloys of stainless steel which have lately been developed worldwide. Most of these models are based on the original Ramberg-Osgood analytical expression

Classification of spherical tilings by congruent quadrangles over pseudo-double wheels (II)

We classify all edge-to-edge spherical isohedral 4-gonal tilings such that the skeletons are pseudo-double wheels. For this, we characterize these spherical tilings by a quadratic equation for the cosine of an edge-length. By the classification, we see: there are indeed two non-congruent, edge-to-edge spherical isohedral 4-gonal tilings such that the skeletons are the same pseudo-double wheel and the cyclic list of the four inner angles of the tiles are the same. This contrasts with that every edge-to-edge spherical tiling by congruent 3-gons is determined by the skeleton and the inner angles of the skeleton. We show that for a particular spherical isohedral tiling over the pseudo-double wheel of twelve faces, the quadratic equation has a double solution and the copies of the tile also organize a spherical non-isohedral tiling over the same skeleton.Comment: 28 pages, 14 figure