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Managing Wind Risk on Long Span Roofs

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Managing Wind Risk on Long Span Roofs Managing Wind Risk on Long Span Roofs Dissertation submitted to and approved by the Faculty of Architecture, Civil Engineering and Environmental Sciences University of Braunschweig ‐ Institute of Technology and the Faculty of Engineering University of Florence in candidacy for the degree of a Doktor‐Ingenieur (Dr.‐Ing.) / Dottore di Ricerca in "Riduzione del Rischio da Catastrofi Naturali su Strutture ed Infrastrutture" *) by Giuseppe Olivato born 10 November 1981 from Selvazzano Dentro (PD), Italy Submitted on 18 March 2010 Oral examination on 06 May 2010 Professorial advisors Prof. A. Saetta Prof. D. Dinkler 2010 *) Either the German or the Italian form of the title may be used. “The man who can smile when things go wrong has thought of someone he can blame it on” Jones' law Risk transfer on the Murphy's Law Abstract ABSTRACT A number of modern structures characterized by a relevant impact and elegance often coupled with lightness and irregular shapes are dramatically exposed to the wind aerody‐ namic action, which becomes a key factor in their safety assessment. These structures are involved into a global and complex design process in which players like the environment and social sciences join engineering in order to guarantee an optimal result under several aspects, not the last the economical aspect. In this background, it is not possible trusting into unreliable deterministic considerations, where the over‐engineering would assure the result. The attention is now shifted to overall frameworks of Performance‐Based Design aimed to specific performance targets and their optimization. In particular, the criteria to ensure the achievement of the results are expressed in terms of risk of failure. This work of thesis presents a general framework for calculating all the possible structural damages and subsequently economic losses after a natural catastrophic event. The framework is adjusted and applied to the specific case study of the covering of the Sta‐ dium of Braga in Portugal, where the hazard of a windstorm, the loads that the latter en‐ forces on the covering, the structural response, the resulting damages and other conse‐ quences are hierarchically calculated. Particular emphasis, and original contribution of the work, is paid on the evaluation of the dynamic response of the structure. Pressure fluctua‐ tions on buildings produced by storms have a complex temporal and spatial organization and their study, keeping under control the whole physical phenomena, is quite difficult. Accordingly, some suitable tools like the orthogonal decomposition are adopted in order to handle the huge amount of data. Moreover a consistent and operative procedure aimed at enhancing the assessment of the aerodynamic wind pressure on the covering is provided. This work addresses a fundamental topic for the risk assessment; the results achieved by the duly application of the framework can be successfully transferred to other actors in‐ volved in the management and the governmental processes devoted to natural hazards. 6 Abstract Acknowledgments ACKNOWLEDGMENTS In a very funny comic strip on graduate students, a brave girl ventures on a perilous jour‐ ney looking for the legendary lost dissertation, just to find out that it was only a white parchment paper. Suddenly the voice of her advisor explains her that the treasure she was looking for lies not into the dissertation but in the journey itself. During the last three years I have focussed all my energies on the drawing up of this study, but only now that I have finished and I am going to write these words, I recognize myself in completely agreement with the comics. I have spent a lot of time and a lot of efforts to reach this goal and now I realize what I have really gained during my journey: the great many people who have helped me, who have worked with me, who have simply talked to me, all of them have left something I will bring with me independently from my research, from the dissertation. For this precious treasure I found, I would like to thank my two tutors, Prof. Anna Saetta and Prof. Dieter Dinkler; they supervised my work and supported me during these years of academic research. I owe my thanks to Dr. Lazzari and Dr. Pontow, with whom I shared stimulating and profitable discussions on the field of wind engineering and finite ele‐ ments. I would also like to express my sincere gratitude to the two coordinators of the Doctoral School, Prof. Borri and Prof. Peil, as they give me the opportunity to live this en‐ riching experience within the international doctoral course. Now the list starts growing fast because all my colleagues and friends, all the people from whom I had the opportunity to learn a lot, both form scientific and personal point of view, all the people that have shared experiences with me in these three years are integral part of my treasure and I beg all of them to feel included in my huge thank I devote to them. Thank you. 8 Acknowledgments Contents CONTENTS Abstract .......................................................................................................................... 5 Acknowledgments .................................................................................................................. 7 Contents .......................................................................................................................... 9 List of Figures .......................................................................................................................13 List of Tables ........................................................................................................................19 Chapter 1: Risk assessment framework ...........................................................................21 1.1 Introduction ...........................................................................................................21 1.2 Natural disasters ....................................................................................................23 1.2.1 Windstorms ....................................................................................................25 1.3 Risk Framework ......................................................................................................26 1.3.1 Catastrophe modelling ...................................................................................26 1.3.2 Decision process criteria ................................................................................28 1.3.3 Proposed risk assessment chain .....................................................................31 1.3.4 Computation of risk ........................................................................................33 Chapter 2: Hazard on the stadium of Braga .....................................................................35 2.1 Stadium description ...............................................................................................36 2.1.1 Construction process ......................................................................................37 2.2 Dynamic characterization ......................................................................................39 10 Contents 2.2.1 Full scale tests ................................................................................................39 2.2.2 Natural frequencies and vibration modes ......................................................41 2.2.3 Modal damping ratios ....................................................................................43 2.3 Wind speed profile .................................................................................................44 2.3.1 Meteorological data .......................................................................................45 2.3.2 Topographic model ........................................................................................46 2.3.3 Characterization of the wind speed profile ....................................................49 2.4 Wind speed annual exceedance probability ..........................................................53 Chapter 3: Wind pressure load ........................................................................................57 3.1 Principal Component Analysis ................................................................................58 3.1.1 Proper Orthogonal Decomposition ................................................................59 3.2 Pressure loads on the stadium roof .......................................................................63 Chapter 4: Numerical Model of the Stadium ...................................................................75 4.1 Corotational truss element ....................................................................................75 4.1.1 Truss implementation ....................................................................................75 4.1.2 Non‐linear static and dynamic validation .......................................................78 4.2 DKT plate element ..................................................................................................82 4.2.1 Plate element implementation ......................................................................82 4.2.2 Experimental results for the plate element ...................................................85 4.3 OPT membrane triangle .........................................................................................86 4.3.1 ANDES template .............................................................................................86
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