Search

V prispevku je predstavljena študija potresne odpornosti polnonosilnih varjenih spojev prečka-steber. Izvedenih je bilo šestnajst laboratorijskih cikličnih testov na preizkušancih naravne velikosti. Za nedisipativne sovprežne stebre je bilo uporabljeno jeklo visoke trdnosti (HSS), za disipativne prečke pa mehko konstrukcijsko jeklo (MCS). V študijo sta vključeni dve konfiguraciji polnonosilnih varjenih ojačanih spojev: spoj, ojačan z rebri, in spoj, ojačan z veznima pločevinama. Poleg tega sta parametra študije še protokol cikličnega obremenjevanja in prisotnost visokega nivoja tlačne osne sile v stebru. Eksperimentalni rezultati so pokazali dobro obnašanje obravnavanih spojev pri doseženem odmiku plastifikacije proč od pasnice stebra v neojačani predel prečke. Ob praktično nepoškodovanem ojačanem spoju in sovprežnem stebru so vsi spoji izkazali veliko duktilnost in dobro odpornost proti nizkocikličnemu utrujanju.

Eurocode model, as all other existing theoretical models for the characterisation of angle in bending, is quite simple. However, when a little modification of angle is applied, e.g. adding a stiffener, behaviour becomes a bit complicated. Furthermore, when such modified connection component is going to be used in joint(s), the structural engineers do not know how to make quick and reliable design without support of advance FEM analysis. Therefore, the main goal of the present work is to give simple estimations which will provide reliable resistance and stiffness assessment of the above mentioned type of joints. After performed detail research of different typologies of the flange cleats in bending as components, the experimental work was extended to account for testing of the beam-to-column joints with the stiffened flange cleat(s) as the main connection component. Present paper gives insight into obtained experimental results, as well as, their comparison with the available theoretical models. In particular, depending on the stiffened flange cleat(s) location the four different (joint) configurations were tested. Detailed description of the laboratory testing and experimental results of the flange cleats joints in bending is presented. In addition, the experimental values of the resistance and stiffness for all tested (joint) specimens are obtained through characterization of the recorded moment-rotation curves. With an additional work related to the welding of a stiffener, the major effect on the behaviour of the mentioned type of the bolted joints was also recorded. Finally, according to the existing models for the standard angles in bending and modified models to suit behaviour of the stiffened angle, a modification of the lever arm is proposed. Through comparison with the experimental results (obtained in the present study) modified models and currently proposed lever arm are validated. Based on this the optimal models for different joint configurations are proposed.

Opisano je določevanje preostale uporabnosti kovičenega jeklenega železniškega mostu čez Dravo na Ptuju. Izračun temelji na metodah mehanike loma, na integraciji Parisove funkcije. Za začetno velikost napake vzamemo hipotetično razpoko, ki je skrita pod glavo kovice, kritično velikost razpoke pa določimo z merjenjem kritične vrednosti J-integrala ter z uporabo znane Sedlackekove odvisnosti J proti a, pri čemer je a velikost razpoke.

The problem of steel frames optimal design, when it is written in mathematical programming form, gives a moderate number of unknowns and a huge number of constraints. A typical frame has about 50 unknowns and 20000 constraints. The large number of constraints, which are complex functions of many parameters, represents a problem for most non-linear programming solvers. In order to reduce the number of constraints, we developed a method, which eliminates a large portion of constraints without their costly evaluation. The method is based on the problem specific constraints organization, where the constraints are organized into sets. It turns out that we can remove individual constraints from a set by simply comparing constraint parameters.

V diplomski nalogi je predstavljena statična analiza dvoetažne jeklene pravokotne poslovne stavbe. Konstrukcijo objekta sestavljajo momentni okvirji v obe smeri, ki so sestavljeni iz dvojnih HEB stebrov in IPE nosilcev. Notranje sile so določene z globalno elastično analizo z upoštevanjem teorije II. reda in globalnih začetnih nepopolnosti. Nosilnosti elementov, prerezov in spojev so dimenzionirani na mejno stanje nosilnosti, mejno stanje uporabnosti, potresno in požarno nezgodno stanje. Za določanje notranjih statičnih količin je uporabljen program SCIA Engineer. Največji poudarek diplomske naloge je na določanju požarne odpornosti jeklene stavbe po poenostavljeni metodi iz standarda SIST EN 1993-1-2. Nosilnost elementov je analizirana pri zahtevani odpornosti R30. S pomočjo nomogramov so določene temperature v jeklenem prerezu in nato odčitani redukcijski faktorji nosilnosti. Na koncu diplomske naloge so prikazani še načini požarne zaščite, ter postopki določitve požarne odpornosti pri požarno zaščitenih jeklenih elementih po poenostavljeni metodi. In this graduation thesis the static analysis of a duplex rectangle business building made of steel moment resisting frames in both directions is done. The columns are made of double HEB profiles and beams of IPE profiles. The global analysis was performed taking into account II. order analysis and initial geometric imperfections. For this purpose SCIA Engineer was used. The design of elements, cross-sections and joints was done for the ultimate limit state, serviceability limit state and for the earthquake and fire design situation. The main focus in this work was to determine fire resistance of the steel building through simplified method of standard SIST EN 1993-1-2. Capacity of elements was analysed for requested resistance R30. Using nomographic charts the temperatures in steel section and the reduction factor for capacity were determined. Finally, to resist the forces for the fire design situation, the fire protection of the steel elements was determined.

Diplomska naloga v prvem delu zajema določitev zunanjih obtežb, ki poleg lastne teže konstrukcije delujejo nanjo. V izračunih so bili upoštevani vplivi stalne teže, vetra, snega in potresna obtežba. V nadaljevanju je narejen statični izračun in primerjava različnih konstrukcijskih zasnov okvirov jeklene industrijske skladiščne hale. Za nadaljnjo podrobnejšo obravnavo je bila izbrana konstrukcijska zasnova torčlenskega okvira, na katerem je bila narejena tudi natančnejša analiza in dimenzioniranje posameznih elementov. V izračunih tročlenskega okvira je upoštevana globalna geometrijska nepopolnost. Diplomsko delo zajema tudi izračune vseh podkonstrukcij in izračun potrebnih temeljev. The first part of my thesis determines the external loads that, in addition to its own weight, act on the structure. The calculations took into account self weight, wind, snow and earthquake loading. Hereinafter I made the static calculations and comparison of different structural concepts of frames for the steel industrial shed. For further detailed analysis I chose structural design of the frame with three hinges, and a detailed analysis and design of elements was conducted. In the calculations of the frame global geometrical imperfection was considered. The thesis also includes calculations of all secondary structures and foundations.

V diplomski nalogi sem projektiral tri-etažno poslovno stavbo s sovprežnimi stebri in nosilci. Nosilno konstrukcijo stavbe predstavlja sedem sovprežnih upogibnih okvirjev z razponom osem metrov na medosni razdalji sedem metrov. Horizontalna nosilnost v vzdolžni smeri je zagotovljena s centričnim povezjem. Etažne plošče so izvedene v sovprežni varianti. Globalna analiza je narejena v dveh ravninskih modelih, izračunana z elastično analizo po teoriji drugega reda, z upoštevanjem začetne geometrijske nepopolnosti. In this work three-storey office building with composite columns and beams is analysed and designed. The structure of the building consists of seven composite moment frames with spacing of eight meters. Horizontal capacity in longitudinal direction of the structure is provided with centric bracings. Floor slabs are designed as composite slabs. Global analysis has been made with two two-dimensional models. Second-order elastic analysis with geometric imperfections has been used to determine internal forces and displacements.

V nalogi je bila, na osnovi eksperimentalnih cikličnih testov, opravljena študija potresne odpornosti varjenih polnonosilnih spojev prečka-steber ojačanih z rebroma in veznima pločevinama. Pri tem so bili uporabljeni različni protokoli obremenjevanja. Za dosego večje robustnosti koncepta močan steber/šibka prečka so bili uporabljeni sovprežni stebri. Upoštevana je hibridna zasnova momentnih okvirov, pri čemer je jeklo visoke trdnosti uporabljeno v stebrih, nedisipativnih elementih, mehko konstrukcijsko jeklo pa v disipativnih prečkah. Dodatni parameter študije je bil visok nivo osne sile v stebru. Vsi preizkušanci so izkazali obnašanje skladno s konceptom načrtovane nosilnosti: varovan neduktilen varjeni stik ob pasnici stebra je ostal nepoškodovan, vse plastične deformacije so bile skoncentrirane v prečki za ojačanim delom. Vsi spoji testirani s spremenljivo amplitudo rotacije so zadostili prekvalifikacijskim pogojem iz EN 1998-1 in ANSI/AISC 341-10. Rezultati testov skupaj z eksperimentalnimi podatki iz literature so služili za verifikacijo numeričnega modela, ki je bil uporabljen v nadaljni parametrični študiji obeh konfiguracij ojačanih spojev pri monotoni in ciklični obremenitvi. Pomemben del študije obsega razvoj krivulje poškodb za analizo nizkocikličnega utrujanja spojev. Namen numerične parametrične študije je podkrepitev predlaganih priporočil za detajliranje in dimenzioniranje obeh obravnavanih tipov ojačanih spojev predvsem v smislu zajema morebitnih neugodnih vplivov iz naslova različnih velikosti in geometrije I in H prečnih prerezov prečk, ki se pogosto uporabljajo v Evropi. Vsi analizirani polnonosilni spoji izpostavljeni monotoni in ciklični obremenitvi so izkazali polno plastično kapaciteto priključene prečke. Parametrična študija je potrdila rezultate testov: spoj z veznima pločevinama se obnaša bolje kot spoj ojačan z rebroma tlačna osna sila v stebru do vrednosti 60 % njegove tlačne nosilnosti ne vpliva na obnašanje varjenega stika prečkasteber za analiziran nabor prerezov prečk predlagan koncept dimenzioniranja daje povsem sprejemljive dimenzije ojačilnih pločevin. Študija predstavlja pomemben doprinos tudi v smislu mejne upogibne nosilnosti jeklenih prečk in potrjuje potrebo po uporabi dvojne klasifikacije jeklenih elementov pri potresno odpornem projektiranju: glede na njihovo duktilnost in dodatno upogibno nosilnost. Pri tem je bila posebej obravnavana večja možna nosilnost prečke zaradi pričakovane vrednosti tečenja materiala γov in dodatna nosilnost s zaradi plastičnega utrjevanja jekla, kar še vedno ostaja nejasno obravnavano v EN 1998-1. Največja vrednost skupnega faktorja dodatne nosilnosti v skladu z EN 1998-1 znaša 1.1× γov = 1.375. V študiji je jasno pokazano, da ta vrednost v določenih primerih ne zagotavlja dovolj velike dodatne nosilnosti spoja za razvoj polnoplastične kapacitete priključene prečke. Predlagani vrednosti γov = 1.25 in s = 1.2 dajeta vrednost skupnega faktorja dodatne nosilnosti γov' = s·γov = 1.5, kar se je izkazalo zadovoljivo. Cyclic tests with different loading protocols were carried out on full-strength welded ribstiffened and cover-plate beam-to-column joints to study their seismic performance. Composite columns were used to increase the robustness of the applied strong column/weak beam design concept. Hybrid-steel approach for moment-resisting and braced frames was implemented with high strength steel used for columns as non-dissipative elastic members and mild carbon steel for beams acting as dissipative members. Additional parameter of the study was axial force of high level compression in the column. All rib-stiffened and coverplate beam-to-column joints fulfilled the objective of the applied capacity design concept: the whole inelastic action was transferred away from the face of the beam-to-column connection into the beam section behind the stiffened region. All the joints subjected to variable amplitude loading met prequalification requirements from EN 1998-1 and ANSI/AISC 341-10. The test results with additional experimental data from literature were used to verify numerical model, which was employed for further parametric studies on both types of stiffened connection subjected to monotonic and cyclic loading. An important part of the study was also dedicated to the development of damage curve for low-cycle fatigue resistance evaluation of joints. Numerical parametric study was performed to support the proposed joint detailing and design guidelines for the two stiffened joint types against possibly adverse beam member size effects within the selected range of practically applicable I and H beam profiles typically used in Europe. All designed stiffened beam-to-column joints developed full plastic capacity of the connected beam under monotonic and cyclic loading. Parametric study confirmed the outcomes from experimental tests: cover-plate is superior to rib-stiffened connection column axial compressive load up to 60 % of its capacity should not undermine welded beam-to-column connection the applied joint design concept results in reasonable stiffening plate dimensions for the considered range of beam profiles. The study presents an important contribution also in terms of flexural ultimate behaviour of steel beams and confirms the need for a twofold classification of steel members according to their ductility and overstrength as the most appropriate approach for seismic design applications. Clear distinction is made between overstrength due to random material variability γov and overstrength due to strain-hardening s, which is still not clearly addressed in the current European seismic design code. Maximum value of the complete overstrength factor 1.1× γov = 1.375 as exists in EN 1998-1 was shown to be too small to guarantee a sufficient overstrength of a connection in order to assure the development of the full plastic capacity of the connected beam. Proposed values for both γov = 1.25 and s = 1.2 result in overall overstrength factor γov' = s·γov = 1.5, which proved to be satisfactory.

Polnostenske nosilce običajno sestavljajo vitke stojine in kompaktne pasnice. Za povečanje nosilnosti se stojina ojača s prečnimi in vzdolžnimi ojačitvami razlicnih oblik. Posebnost polnostenskih nosilcev, ki se uporabljajo za premostitev večjih razponov, je izkazovanje velike postkritične nosilnosti, ki je dosežena potem, ko se pločevina že izboči. Za boljše razumevanje obnašanja vzdolžno ojačanih polnostenskih nosilcev, obremenjenih z velikimi upogibnimi momenti in strižnimi silami, smo izvedli štiri eksperimente na nosilcih naravnih dimenzij. Rezultati eksperimentalnih testov so bili uporabljeni za verifikacijo numeričnega modela, uporabljenega za nadaljnje študije vpliva različnih parametrov. Na verificiranem numeričnem modelu smo opravili študijo vpliva začetnih geometrijskih nepopolnosti in zaostalih napetosti na nosilnost. Upoštevane so bile naslednje začetne geometrijske nepopolnosti: dejanske izmerjene, lastne oblike uklonske analize in deformirane oblike nosilca, določene s predhodno nelinearno analizo idealnega nosilca. Vpliv zaostalih napetosti smo upoštevali s poenostavljenim modelom razporeditve napetosti po prerezu, pri čemer smo spreminjali nivo tlačnih napetosti v pločevini. Končno vrednost vpliva zaostalih napetosti smo določili na podlagi nivoja zaostalih napetosti, ki smo jih izmerili v prerezu testnega nosilca. S poenostavljenim verificiranim numeričnim modelom smo z namenom določitve nosilnosti vzdolžno ojačanih nosilcev sistematično opravili parametrično nelinearno analizo. Na podlagi 630 numeričnih simulacij smo določili novo interakcijsko enačbo za območje velikih strižnih in upogibnih obremenitev ter določili prerez v panelu, kjer naj se kontrola interakcije izvede. Sledila je obširna analiza zanesljivosti petih modelov odpornosti, in sicer modela odpornosti iz EN 1993-1-5, novo določene enačbe, modela, ki določa bruto upogibno nosilnost prereza, ter dveh modelov, ki sta kombinacija prvih treh. Namen analize zanesljivosti je bil določitev delnih varnostnih faktorjev in kontrola ustreznosti modelov, ki jih določa EN 1993-1-5. Na podlagi obsežnih analiz smo pokazali, da se nosilnost vzdolžno ojačanih polnostenskih nosilcev lahko določi po EN 1993-1-5 pri pogojih, da se interakcija izvede na oddaljenosti hwi,max/2 in da se pri bruto upogibni nosilnosti prereza upošteva varnostni faktor M1 = 1,1. V zadnjem delu naloge smo se dotaknili tudi določitve vplivov diagonalnega nateznega polja na vmesne prečne ojačitve. V ta namen smo opravili dva eksperimentalna testa na nosilcih naravne velikosti ter tako določili velikost osnih sil v prečnih ojačitvah. Sledila je sistematična parametrična študija, na podlagi katere smo raziskali vpliv togosti ojačitev na mejno nosilnost nosilca. Pokazali smo, da je določanje velikosti osnih sil po EN 1993-1-5 konzervativno, in predlagali nov način projektiranja togih prečnih ojačitev, ki temelji le na upogibni togosti teh ojačitev. Slender plated girders are usually composed of slender webs and compact flanges. In order to increase their capacity, they are stiffened with transverse and longitudinal stiffeners of different shapes. Thin plated girders used to support loads over long spans develop significant post-critical resistance after the plate buckling occurs. To achieve better understanding of longitudinally stiffened plated girders subjected to high bending moments and shear forces, four experimental tests on large scale test specimens were performed. The results of these tests were used to verify the numerical model, which was employed for further parametric studies. With numerical simulations the influence of initial imperfections and residual stresses on the capacity of girders was investigated. Initial imperfections were considered as actual measured initial imperfections, as positive buckling modes and as deformed shapes, based on preliminary nonlinear calculations of perfect girders. Residual stresses were considered with a simplified stress pattern where the level of compression stresses was varied. The final residual stresses were determined on the basis of residual stresses measured in the tested girder. With a verified simplified numerical model a parametric nonlinear analysis was systematically carried out to determine the resistance of longitudinally stiffened plated girders. Based on 630 numerical simulations a new equation for interaction at high bending moments and shear forces, as well as the section, where the check should be performed is proposed. An extensive reliability analysis of five different design models was made, i.e., the EN 1993-1-5 interaction model, the proposed new model, the gross cross-section bending resistance model and two models, which are a combination of the first three. The purpose of this reliability analysis is to determine partial safety factors and study the adequacy of the EN 1993-1-5 resistance model. The studies have shown, that the capacity of longitudinally stiffened plated girders can satisfactory be determined according to EN 1993-1-5 under the condition, that the check is made at a distance hwi,max/2 and that the gross cross-section bending capacity includes safety factor �M1 = 1,1. Finally, the influence of the tension field action on intermediate transverse stiffeners was studied. Two tests on a full scale girder were performed to determine the axial forces in transverse stiffeners. Parametric study, where the influence of stiffener’s stiffnesses on the girders limit capacity was investigated, followed. The EN design rule for axial forces in transverse stiffeners, proved to be conservative, thereby a new design rule for rigid intermediate transverse stiffeners, based on the minimum flexural stiffness of a stiffener is proposed.