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Stability and geometrically nonlinear analysis of steel structures
Ondášová, Annamária ; Puklický, Libor (referee) ; Kala, Zdeněk (advisor)
The diploma thesis is dealing with the stability and geometrically nonlinear analysis of a steel structure, explanation of the principles and procedure of the steel structure calculations. The modeled structure is loaded with pressure forces and subsequently the bearing capacity of the structure is calculated using a stability and geometrically nonlinear analysis with initial imperfections. The solution of the frame structure using both approaches can provide slightly different results, which can have an impact on the assessment of the reliability of the structure, its over or under-dimensioning.
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Reliability Analysis of Steel Columns with Encased Web in High Strength Concrete under Compression
Puklický, Libor ; Krejsa,, Martin (referee) ; Melcher, Jindřich (referee) ; Kala, Zdeněk (advisor)
The presented paper deals with a theoretical analysis of the ultimate limit state. The results of experimental research carried out at the Institute of Metal and Timber Structures headed by Assoc. Prof. Karmazinová and Professor Melcher were applied. The geometrically and materially nonlinear solution based on the Timošenko’s solution is verified by the FEM model in the computer programme system ANSYS. The random influence of initial imperfections is taken into consideration. The FEM model also includes the influence of residual stress. In the parametric study, the influence of residual stress on the cross-section plastification is researched into, its influence on the load carrying capacity limit is, together with the influence of other imperfections, the subject of the stochastic analysis, applying the Latin Hypercube Sampling (LHS). Further on, the study proves a direct effect of the concrete part of the cross-section (combination of materials steel-concrete) on the decrease of load carrying capacity limit of the beam caused by influence of the residual stress of steel. With regard to the importance of time dependent phenomena of the concrete creep for the load carrying capacity, the studies given in the Ph.D. thesis are oriented in this respect. The parametric studies of the influence of the concrete creep having applied the Standard Eurocode 2 provide both a comparison of load carrying capacity limits when using common and high-strength concrete types, and also the variability of load carrying capacities. It follows from the comparison of the statistical analysis outputs according to the design reliability conditions of the Standard EN1990 and of the approach of Eurocode 4 that the Eurocode 4 can be recommended for dimensioning of this member type. According to the studies which we carried out, the design in compliance with Eurocode 4 can be evaluated as the reliable one. A larger set of experimental data is necessary to determine the economy.
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Problems of Reliability of Steel Members Sensitive to Imperfections
Nezbedová, Anna ; Lehký, David (referee) ; Kala, Zdeněk (advisor)
This thesis deals with the problems of reliability of steel members sensitive to imperfections. Formulas for nonlinear analysis of compressed and bended members are derived. For compressed elements, there is described the issue of buckling, for bended elements it is lateral-torsional buckling. Then a statistical analysis of reliability of these problems is performed and also comparison with the approach described in Eurocode 3.
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Sensitivity analysis of stability problems of steel structures
Valeš, Jan ; Vičan,, Josef (referee) ; Kučerová,, Anna (referee) ; Melcher, Jindřich (referee) ; Kala, Zdeněk (advisor)
The doctoral thesis is focused on evaluation of global sensitivity analysis of load-carrying capacity of steel hot-rolled beams. These beams are subjected to lateral-torsional buckling, weak axis buckling and strong axis buckling. Very comprehensive computational models which were both geometrically and materially nonlinear were created in Ansys software using solid finite elements to calculate the load-carrying capacity. The computational models allowed modelling of random initial imperfections such as initial curvature, deviations of cross-section dimensions and steel properties. Sensitivity analysis quantified their influence on the load-carrying capacity. Simulation runs of random imperfections were generated using the Latin Hypercube Sampling method. Since the evaluation of sensitivity analysis of load-carrying capacity of all finite element models would cost an extreme amount of computer time, the thesis aimed at developing a meta-model (also known as surrogate model) based on approximation of FEM model. The approximation polynomial then facilitated the evaluation of sensitivity indices using a high number of simulation runs. At the end, the relationships between the slenderness and the first and second-order sensitivity indices are plotted in graphs. Those random input imperfections that influence the variability of load-carrying capacity the most are pointed out.
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Nonlinear Response of Steel Structures on Statical Loading
Nezbedová, Anna ; Vlk, Zbyněk (referee) ; Kala, Zdeněk (advisor)
This paper deals with the nonlinear response of steel structures to static loads. There are formulas derived for nonlinear analysis compressed, bended and tension members. By compressed elements, there is described the issue of buckling, by the bended, it is lateral-torsional buckling and tension elements are cables. As an example there is an calculation of a suspension two spans pedestrian steel bridge under load action of asymetrical loads. As another possible calculation process, the finite elements method is described.
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Stabilitní analýza ocelových konstrukcí s imperfekcemi
Kalina, Martin ; Krejsa, Martin (referee) ; Kala, Jiří (referee) ; Kala, Zdeněk (advisor)
The aim of this work is focused on soluti0on stability problem of planar bar structures. The calculation algorithms and methods used for analysis of behavior of these structures are described. The discrete computational model of steel of von Mises planar truss is presented. The structure deformation is evaluated by seeking the minimal potential energy. The effect of vertical displacement of top joint is determined by step-by-step method, and Newton iteration. Symmetric and asymmetric effects of initial shape of geometric imperfections of axes of struts are used in the model. The work is focused on another step in research of mapping of potential energy of elastic structures with aim at arch structures. For selected hinged arch loaded by displacement in the midpoint, the area of two concurrently existing postcritical statical equilibrium states is scanned using dynamical relaxation and applying of a set of designed mapping methods.
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Reliability analysis of thin-walled cylindrical tanks for crude oil storage
Serbousková, Kateřina ; Valeš, Jan (referee) ; Kala, Zdeněk (advisor)
This bachelor thesis is focused on the reliability of rotationally symmetric thin-walled cylindric tank for crude oil storage. The general form, membrane state, and balance equation of rotationally symmetric shell is described in the first part of the bachelor thesis. The second part of this bachelor thesis describes the probabilistic analysis of reliability of the tank by using Cornell's index of reliability. At the end the model of tank was created in ANSYS software, which indicates processes of stresses and deformations of the particular load.
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MATERIAL MODEL PARAMETER IDENTIFICATION OF STAINLESS STEEL (AISI 304L)
Jindra, D. ; Kala, Z. ; Seitl, Stanislav ; Kala, J.
Identification of Ramberg and Osgood nonlinear material model parameters for hot rolled stainless steel material grade 1.4307 (AISI 304L) was conducted. Reference data (stress-strain relation) were obtained from experimental program performed on normalized specimens. Parametrical numerical finite element model was created using commercially available software ANSYS classic APDL, and the subsequent optimization process was conducted in the environment of OptiSLang software.
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New methods of in vivo monitoring and management of colonic anastomoses leak in experimental study
Kalvach, Jaroslav ; Pohnán, Radek (advisor) ; Kala, Zdeněk (referee) ; Klos, Dušan (referee)
The primary aim of the project was to assess two different minimally invasive techniques (Transanal minimally invasive surgical approach - TAMIS and endoscopic closure) in the treatment of colorectal anastomosis dehiscence on an experimental model. The secondary aim was to evaluate microdialysis (MD), and confocal laser endomicroscopy (CLE) as novel methods potentially suitable for postoperative monitoring of colo-rectal anastomosis. In the first step, large animal model of dehiscent colo-rectal anastomosis was developed. Two novel techniques of dehiscence closure were then compared with conventional surgical repair and laparotomy with anastomotic diversion. Thus 4 intervention groups and one untreated control group were included. Transanal repair using TAMIS and endoscopic closure were technically feasible with high healing rate. Both techniques reduced the incidence of intra- abdominal septic complications compared to control. With regards to secondary aim, colorectal anastomosis was monitored using MD and CLE before and after the induction of ischaemia. Moreover, intramural and serosal positioning of MD sensors were compared. Both methods revealed hypoperfusion of anastomosis promptly and were proven as suitable for early detection of impaired healing. Based on the results of this project, a...
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Simulation of nonlinear response of construction materials and problem of identitifaction of material parameters
Hokeš, Filip ; Kala, Zdeněk (referee) ; Krejsa,, Martin (referee) ; Kala, Jiří (advisor)
The issue of parameter idenetification within numerical simulations can be considered a necessary step in the use of mathematical models, such as complex material models of building materials utilized in finite element method. The problem is particularly epmhasized in the case of anisothropic materials but also in the case of concrete, which behaves differently in tension and compression and which shows different response under rapid-dynamic and long-term loading. Correct capture of the concrete response in the computation requires usage of plasticity theory, damage theory, visco-elasticity and visco-plasticity or their mutual combinations. It results in development of material models and rheological schemes with large amount of parameters that are not commonly available in standards. The disseration presents application of meta-heuristic algorithm Particle Swarm for parameter identification. The success of the method is demonstrated in a pair of cases, first on the identification of elastoplastic material model parameters from stress strain diagram and then to identify the values of stiffness constants and viscosities of the rheological scheme from a creep curve.
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