Aksijalna nosivost CFT stubova

This paper analyzes the axial load capacity of CFT columns according to the following standards and codes: EC 4, ACI, AS, AISC, AIJ, DL/T. The influence of the confinement concrete core by steel tube, ratio d/t i e/d, shrinkage and creep of concrete, local buckling, bond of steel tube and concrete core on the bearing capacity of composite section is considered. Diagrams of stress-strain for concrete and steel are shown, which are most commonly used in the literature for modeling CFT columns using finite element method. The influence of slenderness of the column, as one of the key factors to define the fracture of the girder. The numerical example was performed comparing the axial load capacity of circular CFT column to the aforementioned regulations and the values obtained are compared with experimental results available in the literature. Also, in case 2 the capacity calculation of slender column according to EC4 is shown, which is based on the effects of second-order and determining the interaction curve. In the attachment are given the coordinates of the characteristic points for constructing interaction curves for CFT columns of circular and rectangular cross-section.U radu je analizirana aksijalna nosivost CFT stubova prema sledećim standardima i kodovima: EC 4, ACI, AS, AISC, AIJ, DL/T. Razmatran je uticaj utezanja betona čeličnom cevi, odnosa d/t i e/d, skupljanja i tečenja betona, lokalnog izvijanja,veze čelične cevi i betonskog jezgra na nosivost spregnutog preseka. Prikazani su dijagrami veze napon-dilatacija za beton i čelik koji se u literaturi najčešće primenjuju za modeliranje CFT stubova primenom metode konačnih elemenata. Razmatran je uticaj vitkosti stuba, kao jedan od ključnih faktora za definisanje načina loma nosača. Na konkretnom brojnom primeru izvršeno je upoređivanje aksijalne nosivosti kružnog CFT stuba prema pomenutim pravilnicima i dobijene vrednosti upoređene su sa rezultatima eksperimenata dostupnih u literaturi. Takođe, u primeru 2 prikazan je proračun nosivosti vitkog stuba prema EC4 koji se zasniva na uticajima drugog reda i određivanju krive interakcije.U prilogu su date koordinate karakterističnih tačaka za crtanje krivih interakcije CFT stubova kružnog i pravougaonog poprečnog preseka

Collective Effects in Nuclear Collisions: Experimental Overview

These conferences proceedings summarize the experimental findings of collective effects in nuclear collisions, as presented at the Quark Matter 2018 conference.Comment: Final version of proceedings for an invited overview talk in XXVIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018), Venezia, Ital

Formulacija fiber elementa prilikom nelinearne analize ramova

The paper discusses two formulations for the fiber based distributed plasticity beam/column element. For force based and displacement based formulations, basic details and main differences are emphasized. The differences in results of analysis when elements with these two formulations are used are demonstrated on two numerical examples. The first example involves the nonlinear static pushover analysis of low-rise frame with distributed element loading. The second example is nonlinear time history analysis of two-story frame subjected to earthquake loading. The differences in global and local response depending on the used finite element discretization are shown. In conclusion, the advantages of force based formulation and directions for the use of the two elements are summarized.U radu su prikazane dve formulacije fiber konačnog elementa raspodeljene plastičnosti. Za metodu sila i metodu deformacija, ukazano je na osnovne razlike dve metode. Razlike u rezultatima analize koje se dobijaju primenom fiber elementa prema ove dve formulacije prikazane su putem dva numerička primera. Prvi primer obuhvata statičku pushover analizu rama s raspodeljenim opterećenjem duž greda. Drugi primer je nelinearna dinamička analiza dvospratnog rama izloženog zemljotresnom opterećenju. Prikazane su razlike kod dobijenog globalnog i lokalnog odgovora u zavisnosti od formulacije i diskretizacije rama. U zaključku, rezimirane su primene dve formulacije fiber elementa i date napomene u vezi s njihovim korišćenjem

Nosivost na savijanje spregnutih greda sa neduktilnim moždanicima

In this paper, the methods for determination of the bending resistance of composite beams with partial shear connection and nonductile shear connectors, according to Eurocode 4, are studied. The Eurocode 4 predicts the use of two calculation methods: the method based on the nonlinear theory and the simplified method that assume linear relation between elastic and plastic bending moment resistance. The algorithm for the nonlinear section analysis is explained in detail. Using the own computer program for nonlinear section analysis, for one composite beam cross section, the differences in results obtained by these two proposed methods are discussed.Zbornik radova Građevinskog fakultet

EXACT AND APPROXIMATE METHODS OF ANALYSIS OF STEEL-CONCRETE COMPOSITE BEAMS

The paper presents four different methods for viscoelastic analysis of steel-concrete composite structures: “exact” analysis method, simplified method, effective modulus method and method proposed by the European design code, Eurocode 4. The exact analysis method uses the mathematical theory of linear integral operators for presenting viscoelastic relations of the steel-concrete composite structures. The simplified analysis method is derived from the exact method. It adopts the assumption that generalized displacements change linearly with the concrete creep function. Due to this assumption, the problem equations transforms from nonhomogeneous integral equations to nonhomogeneous algebraic equations. The effective modulus method and the method proposed by the Eurocode 4 are algebraic methods where stress-strain relations for concrete are expressed through the effective modulus, which depend on time. On the numerical example of continuous steel-concrete beam, the results obtained using the mentioned approximate and the exact method are compare

Effects of Creep and Shrinkage on Deflections of Continuous Composite Beams

Creep and shrinkage of concrete affect the behavior of steel-concrete composite beams and should be taken into account in the analysis of these structures. A number of methods which have different level of accuracy are available for the time analysis of composite structures. Eurocode 4, the contemporary European code for design of steel- concrete composite structures, recommends simple methods for calculation of creep and shrinkage effects. In this paper, the deflections of continuous composite beams calculated with method proposed by Eurocode 4 and the more accurate Age Adjusted Effective Modulus Method (AAEM) are compared. Cracking of concrete is also considered. Through a set of numerical examples, accuracy of methods proposed by Eurocode 4 is discusse

Bearing capacity and stability of elastically fixed cft slender columns

CFT columns are one of the basic structural elements in "top-down" construction method. Because of the large depth of excavation the question of stability of these columns raises. This paper presents a procedure for calculation of critical buckling force of CFT columns which are on the upper side elastically fixed in the concrete ceiling and on the bottom side elastically fixed in the drilled pile. Using computer programs ABAQUS 6.12 and LPILE, as well as appropriate constitutive models the boundary conditions on the upper and lower end of the CFT columns are determined. For a building called "Cvijetni prolaz" in Zagreb, using program created in Excel the critical buckling force of elastically fixed CFT columns is determined. The dependence of the critical buckling force decreasing with increasing depth of excavation is presented. The impact of concrete class, diameter and wall thickness of the steel section, length and diameter of the pile, the thickness of the ceiling on the critical buckling force of CFT columns is analysed. The results are shown in diagrams and tables

Accuracy Evaluation of Creep and Shrinkage Calculation Methods According to EC4

In the paper, the creep and shrinkage calculation methods for composite steel-concrete beams are presented. The approximate methods AAEM, EM and methods according to Eurocode 4, as well as, the exact method based on the integral relation between stress and strain for concrete are used. For doubly-clamped composite beam, stresses at characteristic points of the cross-section for permanent loading and shrinkage effects are determined. Using the creep limit functions for concrete, the upper and lower limits for stresses are determined. According to these limits, the accuracy of the methods for creep and shrinkage calculation given in EC4 is evaluated