doktorska disertacija
Franc Sinur (Author), Darko Beg (Mentor), Matjaž Mikoš (Thesis defence commission member), Ulrike Kuhlmann (Thesis defence commission member), Laszlo Dunai (Thesis defence commission member), Jože Korelc (Co-mentor)

Abstract

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.

Keywords

civil engineering;doctoral thesis;plated girders;bending-shear interaction;experimental tests;transverse stiffeners;numerical simulations;EN 1993-1-5;

Data

Language: English
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FGG - Faculty of Civil and Geodetic Engineering
Publisher: [F. Sinur]
UDC: 624.01:624.04:624.072.2(043.3)
COBISS: 5477729 Link will open in a new window
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Other data

Secondary language: Slovenian
Secondary title: Behaviour of longitudinally stiffened plate girders subjected to bending-shear interaction
Secondary abstract: 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.
Secondary keywords: gradbeništvo;disertacije;polnostenski nosilci;interakcija strg-upogib;eksperimentalni testi;prečne ojačitve;numerične simulacije;
File type: application/pdf
Type (COBISS): Dissertation
Thesis comment: Univ. Ljubljana, Fak. za gradbeništvo in geodezijo, Podiplomski študij gradbeništva, Doktorski študij
Pages: XVII, 205 str.
ID: 8710882