Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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1. INTRODUCTION imposes precise constructional and performance guidelines; however it does not furnish adequate information on the use of the various structural schemes, or on the associated constructional solutions and design methodologies, for which it often refers designers to codes and regulations regarding non-earthquake-resistant structures. Thus, it is necessary to conduct systematic studies of structural schemes by analysing their constructional requirements as well as their performance in terms of ductility and dissipative capacity. Such analysis must provide designers with precise rules regarding the constructional solutions suitable to each scheme and to the associated design methodologies necessary for evaluating their performances. 1.2 Organization of the work On the basis of the aforementioned developments in earthquake design, in this thesis the attention will be focused on new solutions assuring the necessary ductility, which can be obtained not only through careful study of building morphology, structural schemes, and construction details, but also through a rational use of materials. The attention will be focused on detailed analyses, design and tests of beam-to-column joints that can ensure the necessary ductility by their plastic deformations, and then the necessary energy dissipation under earthquake strong motion. Three main topics are analyzed and briefly introduced below. 1.2.1 Seismic behaviour of bolted end plate beam-to-column steel joints The study conducted in the first year of the research activity is part of a research programme which has a two-fold purpose: (i) to analyse the seismic performance of partial strength bolted extended end plate joints with fillet welds, which represent an alternative to fully welded connections for use in seismic force resisting moment frames; (ii) to verify the feasibility of the mechanical approach adopted for joints undergoing monotonic loading in a low-cycle fatigue regime, whereby the properties of a complete joint are understood and obtained by assembling the properties of its component parts. The experimental investigation clearly showed that failure of connections and components always happened due to initiation and stable growth of microcracks at the weld toe. These issues represent fundamental aspects of research and code developments on the seismic design of beam-to- column extended end plate joints, and they are the issues explored by this the 3
1. INTRODUCTION research: (i) mechanical and metallurgic characterization of the connection material in order to estimate fracture toughness parameters like the inelastic crack tip opening displacement (CTOD); (ii) development of adequate numerical models taking into account the initiation and subsequent crack growth as well as the cyclically stable stress-strain curve; (iii) parametric study on some design parameters which influence the fracture resistance of steel bolted extended plate connections. More specifically, the effects of the weld-to-base metal yield strength ratio, the residual stress influence, and the end plate yield-to-ultimate strength ratio have been determined through detailed two- and three-dimensional non-linear finite element analyses of isolated Tee stub connections and complete joints. 1.2.2 Seismic response of partial-strength composite joints This research activity is part of a ECOLEADER Project (3D Full-Scale Seismic Testing of a Steel-Concrete Composite Building at Elsa, 2004), in which the University of Trento plays the role of technical coordination. The project was partially conducted jointly with an ECCS Project (Applicability of Composite Structures to Sway Frames - 7210-PR-250 Project). In order to evaluate the feasibility and effectiveness of the composite constructions with partial-strength beam-to-column joints and partially encased columns in earthquake-prone regions, the study aims at calibrating design rules affecting the aforementioned components and the participation of the concrete slab in the relevant transfer mechanisms. The results of this project led to improved design procedures for composite constructions (Section 7, Part 1 of Eurocode 8, 2002). On the basis of constructional considerations and of the favourable seismic behaviour of both the column web panel and the end plate connection of the previous activity, the composite solution adopted in the tested structure relies on plain steel columns. Cyclic and Pseudo-Dynamic (PsD) tests have been conducted on a virtually full- scale steel-concrete composite 3D structure with two-storey two-bay layout. Pseudo-dynamic tests were performed in order to evaluate the performance of the structure in terms of complex hysteretic behaviour under earthquake-like loading. Moreover, new performance-based seismic design guidelines require that steel- concrete composite buildings be analysed by using non-linear static pushover analyses or non-linear dynamic analyses in order to control local and global performances. For this reason, experimental data of beam-to-column joints performed with the ECCS Project were then used to validate 3D model assembled with the ABAQUS code and 1D composite frame set up with the IDARC-2D code. The 3D model is used to analyse the local behaviour of composite members and 4
Page 1 and 2: Dipartimento di Ingegneria Meccanic
Page 3 and 4: UNIVERSITÀ DEGLI STUDI DI TRENTO D
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Page 10 and 11: INDEX 1 INTRODUCTION...............
Page 12 and 13: INDEX iii 4.10.3 Results of the PsD
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3. SEISMIC BEHAVIOUR OF BOLTED END
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4. SEISMIC RESPONSE OF PARTIAL-STRE
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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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6. SUMMARY, CONCLUSIONS AND FUTURE
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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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