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Lateral Torsional Buckling of Thin-Walled Steel Beams with Web Holes
Horáček, Martin ; Škaloud, Miroslav (referee) ; Juhás,, Pavol (referee) ; Melcher, Jindřich (advisor)
The current trend in the design of steel structures leads, due to the saving of the material, to the frequent use of thin-walled cold formed steel sections. Thin cold-formed steel profiles are often manufactured with web holes. A specific example of thin-walled steel profiles are Sigma beams used in additionally installed built-in floors systems in warehouses. The aim of doctoral thesis is the analysis, assessment and experimental verification of the technical solution of thin-walled steel beams with web openings loaded in bending with respect to lateral torsional buckling. The objective is to develop knowledge about the real properties of steel members of considered structural arrangement in order to specify the methods of analysis and design in industrial practice. The theoretical analysis describes the behavior of the beams by means of solving the differential equations of the equilibrium on deformed element of thin walled member under bending. In case of beams with web holes is used the solution in the form of introduction of substitute cross-section properties, which are defined as the weighted average of the properties of full and weakened section. The numerical analysis is focused on the use of commonly available software in order to predict the bending resistance of beams with web opening with respect to lateral torsional buckling. Since the software used in practice solves only the prismatic beams without option to model the web openings, it is in frame of numerical analysis verified the model of beam with reduced thickness of web constantly over the whole beam length in the zone of perforation. The experimental analysis is firstly focusing on the verification of real bending and torsion stiffness of the beams, based on which are being derived the values of basic cross-sectional properties. Subsequently the experimental verification of real bending resistance with respect to the lateral torsional buckling is being performed.
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"Breathing" of longitudinally stiffened steel webs subject to repeated partial edge loading
Kutmanová, I. ; Škaloud, Miroslav ; Januš, K.
The aim of the first part of the Prague experimental research on web "breathing" was to look into the effect of the repeated\ncharacter of patch loading on the ultimate limit state of steel plate girder webs fitted with longitudinal ribs. 80 experimental panels were tested to date, the flange size and the position and dimensions of the longitudinal ribs being varied. During the tests, the "breathing" of the girder webs under the action of a cyclic patch load, the initiation and propagation of cracks in the most heavily stressed areas of the webs, and their influence on the "erosion" of the plastic failure mechanisms of the test girders were carefully studied. Final analysis of the data obtained made it possible for the authors to establish the limit fatigue loads, longitudinally stiffened steel plate girders whose thin webs are subject to a repeated partial edge load.
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Ultimate load behaviour of longitudinally stiffened steel webs subject to partial edge loading
Kutmanová, I. ; Škaloud, Miroslav ; Januš, K. ; Löwitová, O.
The objective of the contribution is to describe the main results and conclusions of a several years' experimental investigation into the ultimate limit state of steel plate girders whose thin webs were loaded by a partial edge load. Altogether 184 experimental girders were tested, with the following geometrical characteristics of the test girders being varied from girder to girder: (i) the depth-to-thickness ratio of the webs, (ii) the flange size, (iii) the position of\nthe longitudinal rib, (iv) its dimensions and (v) the length of load. Special care was given to a study of (a) the\nstiffeners location and size and (b) the dimensions of the loaded flange upon the progression of plastification, the failure mechanisms and ultimate strengths of the girders tested.
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Lateral Torsional Buckling of Thin-Walled Steel Beams with Web Holes
Horáček, Martin ; Škaloud, Miroslav (referee) ; Juhás,, Pavol (referee) ; Melcher, Jindřich (advisor)
The current trend in the design of steel structures leads, due to the saving of the material, to the frequent use of thin-walled cold formed steel sections. Thin cold-formed steel profiles are often manufactured with web holes. A specific example of thin-walled steel profiles are Sigma beams used in additionally installed built-in floors systems in warehouses. The aim of doctoral thesis is the analysis, assessment and experimental verification of the technical solution of thin-walled steel beams with web openings loaded in bending with respect to lateral torsional buckling. The objective is to develop knowledge about the real properties of steel members of considered structural arrangement in order to specify the methods of analysis and design in industrial practice. The theoretical analysis describes the behavior of the beams by means of solving the differential equations of the equilibrium on deformed element of thin walled member under bending. In case of beams with web holes is used the solution in the form of introduction of substitute cross-section properties, which are defined as the weighted average of the properties of full and weakened section. The numerical analysis is focused on the use of commonly available software in order to predict the bending resistance of beams with web opening with respect to lateral torsional buckling. Since the software used in practice solves only the prismatic beams without option to model the web openings, it is in frame of numerical analysis verified the model of beam with reduced thickness of web constantly over the whole beam length in the zone of perforation. The experimental analysis is firstly focusing on the verification of real bending and torsion stiffness of the beams, based on which are being derived the values of basic cross-sectional properties. Subsequently the experimental verification of real bending resistance with respect to the lateral torsional buckling is being performed.
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Problems connected with the application of lamella flanges in steel bridge construction
Křístek, V. ; Kunrt, J. ; Škaloud, Miroslav ; Urushadze, Shota
Lamella flanges have lately grown very popular with the designers of steel bridges, because - in their belief - they provide us with the possibility of avoiding very thick flange plates in steel bridge structures. This belief is based on the assumption that the lamellas are perfectly plane and therefore, in perfect contact everywhere, so that the loading from one lamela is transmitted into other via pure compression, and that the perfect interaction of both lamellas is materialized by means of boundary fillet welds connecting both of the two lamellas. This simple assumption is, however, far from reality: it is not the means of steel fabricators, not even in the means of those which are very progressively equipped, to produce perfectly plane lamellas. Then both lamellass exhibit unavoidable initial curvatures, which in combination form a gap between the lamellas, and consequently the directly loaded lamela are pressed into this gap. As the loading acting on every bridge is many times repeated, the aforsaid phenomenon is also many times repeated, (we can say that the lamellas "breathe"), and then an unavoidable cumulative damage proces in the lamellas comes to being. The results of investigation will be described in the paper and thereby will demonstrate that the fatigue phenomenon accompanying the breathing of the lamellas can considerably limit the lifetime of the structure.
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The "miracle" of post-buckled behaviour in thin-walled steel construction and some limitations to its full exploitation
Škaloud, Miroslav ; Zörnerová, Marie
Thin-walled steel structures, i.e. structural systems made of thin (usually plate) elements, represent a powerful tool for increasing the competitiveness of steel construction. Then, on the other side, it is in the nature of things that the limit state of the systém is in the danger of being substantially reduced by stability phenomena. Fortunately, the situation is remedied by the beneficial effect of post-buckled (post-critical) behaviour, which is in detail described and "mapped" in the contribution. However, attention is also turned to some limitations which in some cases hinder a full exploitation of the phenomenon, one of them, viz. the unavoidable reduction of the post-buckled reserve of strength due to breathing-induced fatigue, being described in detail in the paper
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The breathing of the lamella flanges of the Lochkov Bridge on SOKP
Kunrt, J. ; Křístek, V. ; Škaloud, Miroslav
The main results obtained by an extended test on the fatigue behaviour generated by changes in the relative distance of the plate elements of the lamella flanges of the Lochkov Bridge, which occur under the passages of heavy vehicles are presented. The plate elements exhibit unavoidable out-of-plane imperfections, which results in them not being in perfect contact. The lamellas are then subjected to many times repeated bending, which generates cumulative damage in the welds that connect the two lamellas.
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Breathing-induced fatigue in thin-walled steel bridge construction
Škaloud, Miroslav ; Zörnerová, Marie ; Urushadze, Shota
Several years ago, the authors started an experimental investigation into the breathing phenomenon of the webs of thin-walled steel girders , which to date comprised more than two hundred tests. The cumulative damage behaviour generated by web breathing was analysed, the process of the initiation and propagation of fatigue cracks induced thereby was studied, and their impact on the failure mechanism and the fatigue limit state of the girders was determined. And, to conclude, a recommendation for design, taking account of the aforesaid, was established.
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