Search

This paper investigates the bending resistance of an innovative lightweight composite floor system, LWT-FLOOR. The system consists of built-up cold- formed steel elements that are spot-welded and connected to the concrete slab using demountable shear connectors. As the system under investigation is new, the existing standards do not provide guidelines for calculating its bending resistance. This paper gives an overview of different analytical approaches and a comparison of calculated results using bending capacities from the numerical parametric study. Within the numerical parametric study, the influence of the height of the steel beam, the type and degree of shear connection, the connection between the steel elements, and the thickness of the corrugated web used for the bending capacity are investigated. Numerical results for the full shear connections resulted in lower bending capacities than the analytically calculated plastic bending resistances. However, numerically obtained bending capacities for partial shear connections were found to exceed the calculated characteristic non- linear bending resistances and bending resistances for partial shear connections. The obtained results will comprise the basis for further experimental tests, which will support the search for an optimal analytical approach for the bending resistance of the proposed composite system.

In some parts of the world, lightweight steel framed (LSF) construction systems have proven to be a fast, economical, and efficient method of constructing residential and non-residential buildings, offering significant advantages over concrete and masonry structures. Since thin steel lipped channel studs have high thermal conductivity, thermal insulation should be optimized to ensure the lowest possible thermal transmittance for an energy efficient building. In current practice, mineral wool (MW) placed in the cavity between at least two layers of gypsum plasterboard (GB) is the preferred choice of insulation. However, such LSF systems using MW do not take into account deficiencies such as the thermal bridging effect and potential moisture condensation, which can reduce the thermal performance of the assembly. It is known that polymer insulation materials have better thermal conductivity and resistance to water permeability than MW. Consequently, they can provide better thermal performance at ambient temperature for the same overall thickness of the assembly. However, the use of polymer insulation materials in LSF structures has not been explored due to the flammability of the material, which can negatively affect their fire resistance. Therefore, a new LSF composite structure is being studied in which steel studs and polymer foam are encapsulated in gypsum fiberboard (GFB). GFBs are believed to provide better fire performance than standard GFBs. Spacers are also used to separate the steel and lining boards to prevent thermal bridging. This paper presents the results of a fire test on such a LSF composite assembly and details of the preliminary finite element model developed to simulate the heat transfer mechanism through the specimen. The numerical analyzes were performed using the ABAQUS finite element program. The model is based on the preliminary thermal properties of the polymer foam and gypsum fiberboards tested by TGA and DSC methods, as well as data from the literature. The fire test showed that while the GFBs maintained their integrity the PUR foam did not ignite, and no significant temperature increases were observed at the steel structure or at the ambient side of panel. Numerical models showed good correlation with the fire test until ignition of the PUR foam.

The classical methods of joining aluminium structures have progressed in recent years, but the fundamental problems of degradation of mechanical properties are still present if welding is used as a joining technique. A different, more suitable, but not yet fully investigated, method for joining aluminium members is adhesive bonding. In this study, the application of adhesives in joining aluminium and steel components is investigated. The experimental study was carried out with the aim of characterising a bonded aluminium angle cleats connection in tension using four different types of adhesives. The laboratory tests included a tensile (Mode I) test of the pair of aluminium angle cleats adhesively bonded to a steel plate. A total of 12 pairs of angle cleats were tested, three specimens for each of the four different adhesive types. All specimens consist of two extruded aluminium angles L 100x100x10 mm (EN AW 6060-T66), 140 mm in length, with one leg bonded to a 30 mm thick steel plate. The other angle legs are bolted (6xM12, quality 8.8) to a steel plate mounted on the static testing machine with a capacity of 600 kN. The preparation of the surfaces and application of the adhesives was carried out by Sika Croatia staff, who provided all four types of adhesives. Two ductile (SikaFast 555 L10 – label A and SikaPower 4720 – label B) and two brittle (Sikadur 330 – label C and Sikadur 31 CF Normal – label D) adhesives were applied. In addition to conventional measurement techniques such as the LVDT sensors, the entire displacement field was measured using the non-contact stereophotogrammetric 3D measurement system. Due to the relatively small displacements, the non-contact measurement system proved to be very beneficial in capturing the realistic behaviour of these sensitive connections. All specimens failed over adhesives in different percentages of failure through the adhesive layer. The fracture surfaces varied for each specimen. The most consistent results were obtained for the specimens labelled B. The load-bearing capacity of the mentioned specimens was roughly 60 kN. The results of the specimens labelled C and D were quite scattered, mainly due to the different thickness of the adhesive layer, but also to the insufficient mechanical preparation of the cleat’s surface. The specimens labelled A showed the highest ductility, while the specimens labelled C were the most brittle.

Appropriate treatment of climatic loads on building structures is crucial from the structural reliability aspect. Since climatic loads are variable actions that are highly sensitive to regional conditions, they are covered by the National Annexes of each European member state. A huge work has been done in order to harmonize current rules for making maps for snow load, wind and thermal actions, as well as current procedures for calculation of loads on building structures. A few important issues regarding climatic loads on building structures are covered by this paper. Eurocode concept and current Eurocodes for snow load (EN 1991-1-3), wind (EN 1991-1-4) and thermal actions (EN 1991-1-5) have been represented in brief. An emphasis is given to the changes that the new generation of Eurocodes, considering climatic loads, brings. Tremendous work of the Project Teams related to the evolution of EN 1991 Parts 1-3, 1-4 and 1-5 was done in the framework of the project related to the second generation of Eurocodes. Important results of the update, harmonization and enhancing the ease of use of mentioned EN 1991 parts are summarized here. In addition, the second generation of Eurocodes will bring completely new parts related to climatic loads: EN 1991-1-8 (actions from waves and currents on coastal structures) and EN 1991-1-9 (atmospheric icing). Based on the recent studies, it can be concluded that the important step of future EN 1991 development will be related to changing climate. Predictions show drastic variation in the climatic loads on structures and its high impact on the long-term structural reliability of new and existing structures.

With the upcoming release of the second generation of European standards for the design of aluminium structures (Eurocode 9), significant changes in design guidelines are on horizon. The design of aluminium joints is a major component of the improvements and novelties that will be presented in the new generation of this standard. Therefore, this paper provides an up-to-date research overview on aluminium structural joints focusing on beam-to-colu- mn joints as well as identifying knowledge gaps and opportunities in this research field.

Thin-walled cold-formed steel (CFS) members have become increasingly popular over the last decades in the light-steel frame (LSF) construction industry as primary load-bearing members. Valuable properties of CFS arise from the manufacturing process, while the undesirable ones, such as cross-section and member instabilities, are especially pronounced at extreme temperatures. Considering present-day stringent fire safety regulations, which require that all buildings and their structural components perform safely in fire situations, structural designers have to make greater efforts to understand complex structural behaviour at elevated temperatures. Besides laboratory testing, numerical analyses provide adequate and economic solutions for better understanding and predicting such complex behaviour.

The use of aluminium lags behind other materials partially due to a lack of design standards in the past. That problem was solved with the development of new standards for the design of aluminium structures. The aluminium column design procedure implies flexural buckling verification, and Eurocode 9 provides design procedures for extruded and welded columns. Due to a lack of recent studies, the design procedure for longitudinally welded columns was based on experimental research conducted more than 40 years ago. An experimental study and detailed numerical analysis of longitudinally welded aluminium columns is required to assess the accuracy of the current design procedure.

Prikazan je proračun čelične konstrukcije Gornje postaje Nove žičare Sljeme na izvanredno djelovanje požara. Analizirani su kritični požarni scenariji realnog požara čiji je razvoj simuliran inženjerski (HRN EN 1991-1-2) u skladu s uvjetima iz elaborata zaštite od požara, a dimenzioniranje čeličnih elemenata provedeno je u skladu s normom HRN EN 1993-1-2. Primijenjeni inženjerski pristup proračuna požarnih scenarija omogućio je realnije vrednovanje požarnog opterećenja. Uvažavajući realnu namjenu i razvedenost prostora uzeta je u obzir diskontinuiranost požarnog opterećenja. Takav pristup je omogućio racionalnu procjenu razvoja požara u prostoru Gornje postaje Nove žičare Sljeme što je u konačnici rezultiralo pouzdanom i ekonomski opravdanom protupožarnom zaštitom čelične konstrukcije.

U radu su prikazane analitičke metode proračuna požarne otpornosti aluminijskih konstrukcija koje su usvojene u (HRN) EN 1999-1-2. Budući da aluminij kao materijal više gubi mehanička svojstva pri nižim temperaturama nego li čelik, ispravan odabir aluminijske legure u smislu minimalnog smanjenja mehaničkih svojstava je bitan za zadovoljavanje požarnih uvjeta. Radi objašnjenja utjecaja odabira aluminijske legure s obzirom na dobivanje optimalne požarne otpornosti, prikazana je parametarska analiza u kojoj je demonstriran utjecaj aluminijske legure na proračunsku požarnu otpornost nosivog aluminijskog stupa., Analytical methods for calculating fire resistance of aluminium structures, specified in (HRN) EN 1999-1-2, are presented in the paper. Since aluminium as a material loses its mechanical properties at lower temperatures compared to steel, the correct selection of aluminium alloy in terms of minimal reduction of mechanical properties is essential for satisfying fire-related requirements. For clarifying the influence of selecting aluminium alloy for obtaining an optimum fire resistance, a parametric analysis is presented to demonstrate the influence of aluminium alloy on the design fire resistance of a load-bearing aluminium column.

Due to many comparative advantages of aluminium alloys, prefabricated aluminium halls represent one of the most common examples of their application in the field of Structural Engineering. They are mainly designed and built as temporary structures, but today, when economic and environmental resources are very important ; there is an evident need for their permanent usage and consequently their reliable design. For large spans, a typical structural system is made of aluminium frame with steel tension tie element. Aluminium joints of prefabricated halls are almost exclusively formed using bolts in combination with steel reinforcements (e.g. steel inserts embedded into the aluminium column and beam elements). In these joints, the transmission of forces is realized partially through bolts and partially through a complex contact mechanism between aluminium and steel insert. Since simple expressions for behaviour assessment of such joints do not exist, laboratory tests must be necessarily performed. Having that goal in mind, three different types of knee joints were tested under the application of static loading. The first type of specimens consisted of nominal steel joints with a tie element. The second type consisted of two analogical joints with beams made of specially shaped aluminium profiles that were plugged onto steel inserts. The last type consisted of single specimen, exactly the same as the second type, but only without the tie element. Structural properties of all three joint types (rotational stiffness, moment resistance and rotation capacity) as well as the recorded failure modes have been obtained and discussed.

Reliability issues in Eurocode 9 are shown through history review, state-of-the-art, and suggestions for the future development of Eurocode for the design of aluminium structures.

Analizirana je nosivost postojeće čelične servisne hale koja je bila izložena djelovanju realnog požara. Na temelju izjava očevidaca i provedenog vizualnog pregleda glavne nosive konstrukcije servisne hale nakon požara, utvrđen je mogući tijek razvoja požara i procijenjeno je realno požarno opterećenje. Dodatno, ispitana je tvrdoća konstrukcijskih elemenata kako bi se procijenile eventualne promjene mehaničkih svojstava čeličnog materijala. Za procjenu nosivosti opožarene konstrukcije provedene su simulacije nekoliko mogućih požarnih scenarija. Analiza djelovanja požara i izračun temperature u čeličnim nosivim elementima provedeni su prema HRN EN 1991-1-2 i HRN EN 1993-1-2. Potvrđeni su nalazi pregleda i utvrđeno je da postojeća čelična konstrukcija, bez dodatnih premaza ili bilo koje druge vrste zaštite od požara, nije doživjela trajne deformacije. S druge strane, provedena je konzervativna požarna analiza primjenom standardne ISO požarne krivulje. Dobivene temperature u čeličnim elementima uzrokovale bi rušenje konstrukcije. Dakle, konzervativnim pristupom bilo bi potrebno predvidjeti zaštitu od požara. Provedene analize potvrđuju zaključke pregleda i jasno upućuju na zaključak da je za ispravno i ekonomično projektiranje čeličnih konstrukcija nužno čim realnije procijeniti prirodu i razvoj požara.

Continuing development of aluminium alloys highlights the problem of choosing adequate constitutive stress-strain relationships, especially as aluminium has no pronounced yield strength and a significant degree of nonlinearity before reaching the 0.2% proof strength. Thus, for the sake of a more realistic approximation of the stress-strain relation more complex models are required. These complex models are continuous, defined either as a function of stress or strain. Unfortunately, basic mechanical properties available to engineers are often not adequate for material behaviour modelling in nonlinear numerical analysis, which are required for intricate design problems. Moreover, studies regarding suitability of various models are scarce. Since any deviations from experimental stress-strain behaviour consequently introduces errors in simulation results, it is necessary to quantify errors, and to enable a reliable choice among available models, depending on type of modelled phenomena. To gain insight on these problems, own experimental stress- strain data of coupons from alloys EN AW-6082-T6 and EN AW-6060-T66 was utilized. Alloys were selected as being representative of a group of commonly used alloys in structural engineering (T5, T6, and T66), due to their similar shape of the stress-strain curve. Experimental curves were divided into two zones, the dominantly elastic and plastic, and relative errors between six constitutive laws and experimental data by zone and in total behaviour were established. Descriptive and dispersion statistics of determined relative errors allowed for quantitative indicators of suitability, which then allowed for conclusions regarding choice of tested constitutive relationships.

In the present study, the behavior of steel plate shear walls (SPSW) with variable column flexural stiffness is experimentally and numerically investigated. Altogether six one-bay one-story specimens, three moment resisting frames (MRFs) and three SPSWs, were designed, fabricated and tested. Column flexural stiffness of the first specimen pair (one MRF and one SPSW) corresponded to the value required by the design codes, while for the second and third pair it was reduced by 18% and 36%, respectively. The quasi-static cyclic test result indicate that SPSW with reduced column flexural stiffness have satisfactory performance up to 4% story drift ratio, allow development of the tension field over the entire infill panel, and cause negligible column “pull-in” deformation which indicates that prescribed minimal column flexural stiffness value, according to AISC 341-10, might be conservative. In addition, finite element (FE) pushover simulations using shell elements were developed. Such FE models can predict SPSW cyclic behavior reasonably well and can be used to conduct numerical parametric analyses. It should be mentioned that these FE models were not able to reproduce column “pull-in” deformation indicating the need for further development of FE simulations with cyclic load introduction which will be part of another paper.

Prikazan je kratak rezime najvažnijih izmjena i dopuna koje će postati sastavni dio nove generacije europskih normi za projektiranje aluminijskih konstrukcija (EN 1999). Trenutni razvoj 2. generacije EN 1999 odvija se pod mandatom M/515, kojeg za CEN (European Committee for Standardization) provodi NEN (Netherlands Standardization Institute). U tu svrhu osnovana su tri međunarodna projektna tima eksperata ; SC9.PT1-PT3. Prva dva projektna tima (SC9.PT1 i PT2) su lani završila s trogodišnjim radom, a SC9.PT3 djeluje do 2020. godine kada će biti završene sve planirane aktivnosti za unapređenje aktualne generacije EN 1999. SC9.PT1 se bavio ažuriranjem i pojednostavljenje svih dijelova EN 1999, dok je SC9.PT2 donosio smjernice za projektiranje novih tipova aluminijskih spojeva. Osnovni dio, EN 1999-1-1, je doživio toliki obim izmjena da se može smatrati apsolutno novim dokumentom. SC9.PT3 se bavi konstrukcijama velikih raspona a obrađuje krovne konstrukcije i mostove. Dopune koje donosi SC9.PT3 biti će uvrštene u EN 1999-1-1 kao novi dodaci koji ne postoje u niti jednom standardu na svijetu. Iako još u začetnoj fazi, istraživanja koja se provode u području potresne otpornosti, sugeriraju da će i ovo područje uskoro biti obrađeno. Štoviše, u reviziji EN 1998 već se implementiraju opća pravila za aluminijske konstrukcije.

Since welding of aluminium alloys results in significant resistance reductions, the aluminium joints of prefabricated halls are almost exclusively formed using bolts. Therefore, it is common to apply steel reinforcements at joints through which the action effects are transmitted between the aluminium elements (e.g. steel inserts embedded into the aluminium column and beam elements). The results of ongoing experimental investigations of bolted aluminium beam-to- column joint reinforced by steel are presented. Moreover, the participants of SC9 meeting participated in the test of one joint specimen up to the failure.

Zbog mnogih komparativnih prednosti aluminijskih legura (omjer težine i otpornosti, mogućnost oblikovanja različitih poprečnih presjeka, trajnost i jeftina montaža) montažne aluminijske hale predstavljaju jedan od najčešćih primjera njihove upotrebe u građevinskim konstrukcijama. Budući da zavarivanje kod aluminijskih legura uzrokuje značajne redukcije otpornosti, priključci aluminijskih elemenata montažnih hala izvode se isključivo vijcima. Uobičajeno se na mjestima priključaka izvode čelična ojačanja preko kojih se učinci djelovanja prenose između aluminijskih elementa (primjerice čelični ulošci koji ulaze u aluminijske elemente stupa i prečke). U predavanju je dan pregled uobičajenih rješenja priključaka portalnih montažnih aluminijskih hala, a naglasak je stavljen na čelikom ojačan priključak između prečke i stupa. Kod takvog priključka prijenos sila ostvaruje se djelomično vijcima, a djelomično složenim kontaktnim mehanizmom između aluminijskih i čeličnih dijelova. Kako ne postoje jednostavni izrazi za procjenu ponašanja ovakvog priključka izrađena je preliminarna numerička simulacija. To je ujedno i podloga za laboratorijsko ispitivanje koje će dati još realniji odgovor.

Prema iskustvu, procjena požarne otpornosti čeličnih elemenata prema europskim normama je konzervativna, a napredne metode proračuna su složene i dugotrajne. U sklopu međunarodne Round Robin studije, procjena postojećih metoda analizirana je za ispitani čelični nosač izložen savijanju i standardnom ISO požaru. Usporedba rezultata pokazuje da napredne metode daju neujednačene procjene. Svejedno, napredne su metode proračuna potrebne za poboljšanje normiranih metoda koje precjenjuju požarnu otpornost ovog "trivijalnog" problema., Experience shows that the assessment of fire resistance of steel elements based on European standards is conservative, while advanced methods are complex and time consuming. The analysis of existing methods for the tested steel beam exposed to bending and standard ISO fire was conducted in the scope of the international Round Robin study. The comparison of results shows that advanced methods provide non-uniform assessments. Nevertheless, advanced methods are necessary for improving standard methods that overestimate fire resistance of this "trivial" problem.

Čelična konstrukcija mehaničarske radionice bila je izložena požaru. Kako bi se utvrdilo stanje nosive konstrukcije nakon gašenja požara kao i mogućnost njene daljne uporabe proveden je vizualni pregled opožarenih elemenata. Kako bi se provjerilo da nije došlo do promjene mehaničkih svojstava čeličnog materijala na ključnim mjestima provedena su ispitivanja tvrdoće materijala postupkom bez razaranja primjenom tvrdomjera.

Prikazan je proračun čeličnih konstrukcija Osnovne škole Ivanja Reka na izvanredno djelovanje požara. Proračun je izrađen za dvije odvojene čelične konstrukcije - trodijelnu dvoranu s pripadnim prostorima i polivalentnu dvoranu s knjižnicom. Analizirani su kritični požarni scenariji realnog - lokaliziranog požara čiji je razvoj simuliran inženjerski (HRN EN 1991-1-2) u skladu s uvjetima iz elaborata zaštite od požara. Dimenzioniranje čeličnih elemenata provedeno je u skladu s normom HRN EN 1993-1-2. Dokazano je da je samo mali dio (2% ukupne težine) čelične konstrukcije potrebno štititi. Za tu svrhu, kao optimalno rješenje iz aspekta trajanja realnog požara odabrana je zaštita protupožarnim premazom za R30. Na primjeru je pokazano da je, uz racionalnu procjenu razvoja požara i kritičko razmatranje požarnih situacija, moguće pouzdano i relativno jednostavno procijeniti ponašanje konstrukcije pri povišenim temperaturama. Nadalje, kvantitativna i kvalitativna optimizacija možebitne protupožarne zaštite nužno vodi k ekonomski opravdanom projektantskom rješenju.