Hot-dip galvanizing of steel structures - possibilities and limitations

Hot-dip galvanizing is one of the most commonly used systems for the corrosion protection of steel structures. In cases where there are no restrictions for the application of hot-dip galvanizing, this procedure is the most economical solution because it offers permanent protection against corrosion that does not require maintenance during the structure’s exploitation. In this paper, we present the process of hot-dip galvanizing with an emphasis on its specificities, capabilities and limitations. Particular attention is paid to the process of preparing steel structures for hot-dip galvanizing as well as describing the acceptable quality of the finished product. The paper presents the possibilities and capacities of all hot-dip galvanizing companies in Serbia and in the region

Hot-dip galvanizing of steel structures - possibilities and limitations

Hot-dip galvanizing is one of the most commonly used systems for the corrosion protection of steel structures. In cases where there are no restrictions for the application of hot-dip galvanizing, this procedure is the most economical solution because it offers permanent protection against corrosion that does not require maintenance during the structure’s exploitation. In this paper, we present the process of hot-dip galvanizing with an emphasis on its specificities, capabilities and limitations. Particular attention is paid to the process of preparing steel structures for hot-dip galvanizing as well as describing the acceptable quality of the finished product. The paper presents the possibilities and capacities of all hot-dip galvanizing companies in Serbia and in the region

Steel structure corrosion protection systems according to the EN ISO 12944 standards

It is very important to protect steel structures against the influence of corrosion since it is one of the two biggest defects of steel structures. In addition to hot-dip galvanizing, coating is the most commonly used system for the protection of steel structures against corrosion. It is practically irreplaceable in cases where use of the hot-dip galvanizing is not possible. In this paper all relevant standards, with emphasis on SRPS EN ISO 12944 as most important for coatings usage, are shown. Terms of corrosivity categories, methods and preparation grades of steel surfaces, methods for coatings applying and measurement of their thickness, as well as which coatings type can be used for corrosion protection of steel structures are explaine

Steel structure corrosion protection systems according to the EN ISO 12944 standards

It is very important to protect steel structures against the influence of corrosion since it is one of the two biggest defects of steel structures. In addition to hot-dip galvanizing, coating is the most commonly used system for the protection of steel structures against corrosion. It is practically irreplaceable in cases where use of the hot-dip galvanizing is not possible. In this paper all relevant standards, with emphasis on SRPS EN ISO 12944 as most important for coatings usage, are shown. Terms of corrosivity categories, methods and preparation grades of steel surfaces, methods for coatings applying and measurement of their thickness, as well as which coatings type can be used for corrosion protection of steel structures are explaine

Theoretical and experimental research of losses of pretension force in high strength bolts

Tarni spojevi sa prednapregnutim zavrtnjevima imaju veliki značaj u oblastičeličnih konstrukcija, posebno u slučajevima konstrukcija izloženenih dejstvudinamičkog opterećenja, kao što su mostovi, kranski nosači, stubovi vetro generatora,itd. Dva parametra koji imaju najveći uticaj na nosivost ovakvih spojeva su koeficijenttrenja na tarnim površima i ostvarena sila prednaprezanja u visokovrednimzavrtnjevima.Potreba da se prate savremeni trendovi u građevinarstvu, posebno sa aspektanovih materijala, rezultovala je ispitivanjem spojeva, u okviru ovog istraživanja, koji suantikoroziono zaštićeni savremenim cink-silikatnim premazima. Korišćen jekomercijalni premaz „Resist 86“, proizvođača „Jotun“ iz Norveške. Veze su ostvareneuz pomoć klasičnih HV visokovrednih zavrtnjeva, ali i uz pomoć, u građevinarstvu svečešće primenjivanih, zavrtnjeva sa zaključavanjem tipa „Huck BobTail (HBT)“,proizvođača „Alcoa Fastening Systems“ iz Engleske. Na ovaj način, klasičan postupakzaštite tarnih površina metalizacijom zamenjuje se jeftinijim, jednostavnijim i bržimpostupkom nanošenja premaza. Takođe, ispitivana je i opravdanost primene zavrtnjevasa zaključavanjem u poređenju sa klasičnim pregnapregnutim zavrtnjevima. Međutim,primena novog materijala kao antikoroziоne zaštite tarnih površina otvara pitanjegubitaka sile prednaprezanja u zavrtnjevima jer je opšte poznato da dominantan deoovih gubitaka potiče od promene debljine sloja antikorozione zaštite kroz vreme.Sprovedeno istraživanje ima dva osnovna cilja: da proveri opravdanost primenepredmetnog premaza u tarnim spojevima, sa stanovišta ostvarenog koeficijenta trenja isa stanovišta gubitaka sile prednaprezanja.Sprovedena su sopstvena eksperimentalna istraživanja i ispitano je 126 zavrtnjevau okviru 42 uzorka spojeva sa dvostrukim preklopom. Eksperimentalno istraživanje jezbog svog obima i raznolikosti podeljeno u nekoliko faza:- Određivanje fizičko-mehaničkih svojstava primenjenih materijala. Ova fazapodrazumeva određivanje koeficijenta trenja koji se ostvaruje primenompredmetnog cink silikatnog premaza kao i fizičko mehaničkih svojstava (granicerazvlačenja i zatezne čvrstoće) materijala od kog su izrađeni primenjeni HV iHBT zavrtnjevi;- Određivanje debljine nanetog premaza na svaku od čeličnih ploča od kojih suformirani uzorci;- Kalibracija sile u zavrtnjeva. Kao najracionalniji ali i najefikasniji način zamerenje sile u zavrtnju izabran je postupak ugradnje mernih traka u telozavrtnjeva. Nakon ugradnje mernih traka, a pre ugradnje zavrtnjeva u uzorke,izvršena je njihova kalibracija i tako uspostavljena veza između promene dužinezavrtnja (merne trake) i sile u zavrtnju. Neki dragoceni zaključci o raspodeli sileunutar zavrnjeva su izvedeni na bazi ovih rezultata.- Centralni deo istraživanja u kojem je izvršeno kontinuirano praćenje promenesile u zavrtnjevima i to 60 nedelja za prvo ugrađenih 36 zavrtnjeva, odnosno 24nedelje za preostalih 72 zavrtnja i- Ispitivanje 6 uzoraka (18 zavrtnjeva) na dejstvo dinamičkog opterećenja tokom2x106 ciklusa.Uzorci su formirani na način da se obezbedi variranje: vrste zavrtnja (HV i HBT),dužine zavrtnja preko različite debljine steznog paketa (18 mm, 35 mm i 55 mm),debljine premaza (uzorci sa i bez premaza) i vrste opterećenja uzorka (bez spoljašnjegopterećenja na uzorke i uzorci izloženi dejstvu dinamičkog opterećenja).Dobijeni rezultati potvrđuju opravdanost primene predmetnog premaza u tarnimspojevima, sa obzirom da su određeni koeficijenti trenja u intervalu 0,40-0,50. Takođe,za svaku grupu zavrtnjeva određeni su inicijalni, kratkoročni i dugoročni gubici sileprednaprezanja. Ekstrapolacijom rezultata sakupljenih u prve 24 nedelje na period od 20godina, za svaki tip i dužinu zavrtnja, definisana je kriva koja opisuje promenu sileprednaprezanja u zavrtnju u posmatranom periodu. Od svih ispitivanih zavrtnjeva jedinokod najkraćih HBT zavrtnjeva (dužine 55 mm) uočen je problem ostvarivanjaproračunske sile prednaprezanja. Kod zavrtnjeva ugrađenih u uzorke sa antikorozionomzaštitom gubici sile prednaprezanja značajno su veći od onih koji su ugrađeni u uzorkebez antikorozione zaštite. Uticaj dinamičkog opterećenja, definisanog tako da ne dovededo proklizavanja veze niti plastifikacije bilo kog njenog dela, može se zanemariti saaspekta gubitaka sile prednaprezanja. Takođe, može se zaključiti da je gubitak sileprednaprezanja najveći kod najkraćih zavrtnjeva i da opada sa povećanjem dužinezavrtnjeva. Primenom metode konačnih elemenata (MKE) modifikovani su postojećiizrazi za fleksibilnost HV zavrtnjeva i definisani novi za HBT zavrtnjeve. Takođe,primenom rezultata MKE i sopstvenog eksperimentalnog istraživanja, određena sureološka svojstva primenjenog cink-silikatnog premaza.Na osnovu rezultata sprovedenog istraživanja zaključuje se da je primenapredmetnih premaza kao i upotreba ispitivanih HBT zavrtnjeva u tarnim spojevimamoguća. Takođe, izvršena kvantifikacija gubitaka sile prednaprezanja omogućavaprojektantima da ih u postupku projektovanja uzmu u obzir i tako spreče gubitaknosivosti usled proklizavanja.Friction connections with high-strength pretension bolts are greatly important inthe field of steel structures, especially in structures imposed to dynamic loads, such asbridges, cranes and wind turbine towers. Two parameters mostly influencing the loadbearingcapacity of such connections are the friction coefficient on friction surfaces andthe achieved pretension force in high-strength bolts.In an effort to meet contemporary trends in the field of structural engineering,especially by usage of new materials, connections with state-of-the-art zinc-rich silicatebased coating as an anti-corrosive primer have been investigated in the scope of thisresearch. Such a commercial coating „Resist 86“, manufacturer by „Jotun“ in Norway,is used. Friction connections are formed using classical HV high-strength bolts but alsothe lock-bolts „Huck BobTail (HBT)“, manufactured by „Alcoa Fastening Systems“ inEngland, which are more and more frequently used in the field of structural engineering.In this way a classical procedure of providing metalized friction surfaces is replacedwith much cheaper, more simple and quicker coating process. At the same time lockboltsare analysed in terms of their applicability when compared to the classicalpretension bolts in use. On the other hand, application of the new material, which acts asanti-corrosion protection over friction surfaces, stirs debate with regards to pretensionforce loss in bolts as it is a commonly known fact that the dominant portion of theselosses stems from a change in anti-corrosion layer thickness which may emerge in time.The research in question strives at two principle goals: whether usage the coatingin question in tension connections is justified from the standpoint of achieved frictioncoefficient and from the standpoint of loss of the pretension force.Related experimental research has been conducted in which 126 bolts were testedwithin 42 double-lap joint specimens. The experimental works are divided into severalphases due to their large extent and variety:- Determination of physical and mechanical properties of the applied materials.This phase implies testing of friction coefficient which is achieved by applyingthe aforementioned zinc-based silicate coating, and the mechanical properties(yield strength and tensile strength) of the HV and HBT bolts materials;- Measuring the thickness of the coating applied to all the steel plates used to fromthe specimens;- Bolt force calibration. Bolt force measurement procedure relating to insertion ofstrain gauges into the bolts has been selected as the most rational and efficientone. After the strain gauges are fitted, and prior to assembling the bolts into thespecimens, bolt force is calibrated in means of determination of force-strainrelation for each bolt. Some significant conclusions about distribution of theforce in the bolt have been drawn relaying on these results.- The focal point of the research - continuous monitoring the changes in boltforces has been carried out over 60 weeks for the first batch of 36 bolts, and over24 weeks for the remaining 72 bolts;- Testing of 6 specimens (18 bolts) for dynamic loads in 2x106 cycles.Specimens have been formed in a way to allow variation of: bolt types (HV andHBT), bolt lengths for various clamping package thicknesses (18 mm, 35 mm and 55mm), coating thickness (with and without coating) and loading conditions (with noexternal load sustained by samples and samples exposed to dynamic loads).The obtained results justify the application of the investigated coating type infriction connections given that friction coefficients are in range of 0,40-0,50. Inaddition, initial short-term and long-term pretension force losses have been determinedfor each group of bolts. Results obtained within the first 24 weeks are extrapolated toperiod of 20 years where a curve which describes change in pretension force within timewas defined for each bolt type and bolt length separately. The shortest HBT bolts (55mm long) showed to be problematic with regards to achieving the design value ofpretension force. Pretension force losses are significant in bolts assembled to specimenswith the coating when compared to those without. Influence of the dynamic loads,which are below slip resistance of the connection, can be disregarded in means of lossof the pretension force. Additionally, the conclusion can be drawn that the pretensionforce loss is the largest in the case of shortest bolts and that it can be reduced byincreasing the bolt length. Using finite element method (FEM) for modelling theexperiments of calibration process of HV and HBT bolts, existing equations forflexibility of HV bolts are improved, and for the first time equations are defined forHBT bolts. Also, using the results of FEM and experimental research, rheologicalproperties of the applied zinc-silicate coating are determined.According to results obtained from the conducted research, application ofaforementioned coatings can be recommended, as well as the use of tested HBT bolts infriction connections. Quantification of pretension force loss allows for the engineers inpractice to take such data into consideration in the course of design development andprevention of overestimation of load-bearing capacity against slippage

Najnovije evropske preporuke za proračun širokih veza greda-stub sa čeonom pločom

Connections made by use of wide end plates, i.e., by means of four bolts in one row are widely used in steel structures, i.e., in building engineering. On the other hand, the applicable version of European standard EN 1993-1-8, does not provide recommendations for designing of such connections but rather limits itself to application of somewhat narrow bonds). Extensive research has been conducted in recent years throughout Europe in order to extend implementation of Eurocode with regards to connections made by wide end plates. This paper will show the latest research conducted in this engineering field, as well as key calculation points relating to resistance of a rigid joint made by use of four bolts in one row.Veze sa širokom čeonom pločom, odnosno sa četiri zavrtnja u redu imaju značajnu primenu u čeličnim konstrukcijama u zgradarstvu. Međutim, trenutna verzija evropskog standarda EN 1993-1-8, ne daje preporuke za projektovanje ovakvih veza, već se ograničava samo na primenu uskih veza. Proteklih godina širom Evrope su vršena istraživanja sa ciljem da se proširi primena evrokoda i na veze sa širokim čeonim pločama. U ovom radu su prikazana najnovija istraživanja u ovoj oblasti, kao i osnovne specifičnosti proračuna nosivosti momentne veze sa četiri zavrtnja u jednom redu

Wind towers - design of flange ring connection

Today, wind power is second largest available renewable resource of energy, with 870 TW (terawatts). Large wind farms, with hundreds of wind towers are big opportunity for steel production industry. Designers and manufacturers of wind towers pay special attention on every single detail, always looking for some new solutions, trying to reduce price of wind towers. Some of the most interesting design and manufacturing details are connections used to assemble sections of tubular steel towers supporting wind turbins. There is traditional and actually more used flange ring connection and on the other side, as a new proposal which is used more and more, friction connection. In this paper theoretic basis of design of flange ring connection of wind towers is give

Design of class 4 cross section in axial compression according to EUROCODE 3

In this paper theoretic basis of design of class 4 cross section in axial compression according to EN1993-1-5 is given. Design procedure is given as an flow chart and ilustrated with an worked example. Plate buckling is treated localy and globaly through the concept of effective cross sections. Interaction between plate-like and column-like behaviour of panels is carried out thought buckling reduction factors and final effective area of cross section