ISSN: 1402-1544 ISBN 978-91-86233-XX-X Se i listan och fyll i siffror där kryssen är DOCTORAL T H E SIS Elzbieta Lukaszewska Timber-Concrete Composite of FloorsPrefabricatedDevelopment DOCTORAL THESIS Department of Civil, Mining and Environmental Engineering Division of Structural Engineering DevelopmentDevelopment ofof PrefabricatedPrefabricated ISSN: 1402-1544 ISBN 978-91-86233-85-3 Timber-Concrete Timber-Concrete CompositeComposite Floors Floors Luleå University of Technology 2009 ElzbietaElzbieta LukaszewskaLukaszewska Luleå University of Technology DOCTORAL THESIS Development of Prefabricated Timber-Concrete Composite Floors Elzbieta Lukaszewska Luleå University of Technology Department of Civil, Mining and Environmental Engineering Division of Structural Engineering SE-971 87 Luleå Sweden www://www.ltu.se/shb © Elzbieta Lukaszewska Printed by Universitetstryckeriet, Luleå 2009 ISSN: 1402-1544 ISBN 978-91-86233-85-3 Luleå www.ltu.se A new star has been discovered, which doesn’t mean that things have gotten brighter or that something we’ve been missing has appeared… (fragment from Surplus by W. Szymborska) Development of Prefabricated Timber-Concrete Composite Floors Elzbieta Lukaszewska Avdelning för byggkonstruktion Institutionen för Samhällsbyggnad Luleå Tekniska Universitet Akademisk avhandling som med vederbörligt tillstånd av Tekniska fakultetsnämnden vid Luleå tekniska universitet för avläggande av teknologie doktorsexamen, kommer att offentligt försvaras i universitetssal F531, onsdagen den 30 september 2009, klockan 10.00. Fakultetsopponent är Prof. Hans Joachim Blass, Ingenieurholzbau und Baukonstruktionen, Universität Karlsruhe (TH), Karlsruhe, Tyskland. Betygsnämndsledamöter är: Docent Ulf Arne Girhammar, Tillämpad fysik och elektronik, Umeå universitet, Umeå, Sverige. Prof. Robert Kliger, Konstruktionsteknik, Stål- och träbyggnad, Chalmers tekniska högskola, Göteborg, Sverige. Prof. Erik Serrano, Institutionen för teknik och design, Träbyggnadsteknik, Växjö universitet, Växjö, Sverige. Huvudhandledare: Prof. Lars Stehn, Samhällsbyggnad, Byggkonstruktion, Träbyggnad, Luleå tekniska universitet Biträdande handledare: Tekn. Dr. Helena Johnsson, Byggkonstruktion, Träbyggnad, Luleå tekniska universitet Luleå September 2009 Front page: The illustration shows a prefabricated timber-concrete composite floor element with SST+S* type connector before assembly. Photo by E. Lukaszewska (2006). Preface Preface Working as a PhD student and writing this thesis has been a rich and fantastic journey for me. It begun six years ago and has taken me to many heights, through many valleys and storms. The work described in this thesis was carried out at the Department of Civil, Mining and Environmental Engineering, Division of Structural Engineering, Luleå University of Technology, between August 2003 and September 2009. This work has been supported by Lars Erik Lundberg Scholarship Fund, J. Gust. Richert Memorial Found and Luleå University of Technology. The research has been presented at several international conferences and it was possible due to the scholarships from Åke and Greta Lissheds, Seth M Kempes, Wallenberg, Ångpanneföreningens Foundations. The Foundations are greatly acknowledged. I learnt much during the course of several visits during this time to institutions in New Zealand, USA and Italy. I am grateful to my sponsors for providing these opportunities, and for the host institutions for welcoming me. I took one year maternity leave from September 2007 to September 2008. I would like to thank my main supervisor, Professor Lars Stehn at Luleå University of Technology, for his support over the last six years. His encouragement, insight and advice have been invaluable to the success of this research project. Lars, thank you for letting me travel around the world in search of contacts and ideas that could assist my work. I am grateful to Dr Helena Johnsson at Luleå University of Technology, my deputy supervisor whose guidelines, explanations and judgement helped me not only to identify boundaries of my project and kept me focus but also enabled me to find a clear path through the research jungle. From the depth of my heart I would like to thank Dr Massimo Fragiacomo at the University of Sassari, Italy, who has been engaged in this research project from spring 2006 as a dedicated and enthusiastic external co-supervisor, who has followed every line of my work from a distance over the last three years. Massimo, thank you for abundant offer of ideas and constructive suggestions, without your wholehearted support this project would not have been such a success. I also would like to thank Paola for her patience and great time we spent in Christchurch and Alghero. My gratitude goes to Professor Richard Gutkowski, at Colorado State University, USA, who encouraged me to start a fantastic research journey around the world. Richard and Irene, thank you for being my family during my stay in Fort Collins. Thanks are also expressed to the staff at Complab Laboratory for their help with preparations and running all my experimental tests. I thank my colleagues at the Division of Timber Structures for their support throughout the course of this project. In particular, I thank Gabi, Ylva, Susanne and John for their understanding and putting up with me during the downs of the last few months. I would like to extend my gratitude to all my friends and family, Ania and Wiesia thank you for being there, when I needed support. Heartfelt thanks go to my mother and my sister, whose unconditioned acceptance and continued support has helped me become the person I am. I thank my mom for being an example of selfless giving. I could not imagine having a better mom. I would like to thank my sister for being my best friend over the years. v Development of Prefabricated Timber-Concrete Composite Floors No words can express my love for my son, Kacper Leonard who brings so much joy into my life and who makes every day worthwhile. Finally, I would like to thank Andreas, for his patience, understanding and continued love. Elzbieta Lukaszewska Luleå, September 2009 vi Abstract Abstract Timber-concrete composite structures were originally developed for bridges and upgrading existing timber floors, but today they have new applications in multi-storey buildings. Most of the research performed to date on these structures has focused on systems in which “wet” concrete is cast on top of timber beams with mounted connectors. A novel composite system, in which the concrete slab is prefabricated off-site with the connectors embedded and then connected on-site to the timber joists is presented in this thesis. A notable benefit of prefabricating the concrete slab is that most of the concrete shrinkage will occur before the slab is connected to the timber beam, markedly reducing the correlated increases in deflection and flexural stresses in the composite beam. Another advantage of the prefabrication is that moving work from the building site to the workshop reduces construction costs. In the research presented here special attention has been paid to the development and use of connection systems that are easy to produce and mount in order to speed up the construction process. Diverse types of shear connectors suitable for prefabrication were investigated: coach screws (alone or combined with a timber joist notch), metal plates (glued or nailed), dowels, and toothed metal plates embedded in the concrete slab. The experimental test programme included: (i) direct shear tests to failure of seven different connection systems, (ii) full-scale bending tests to failure followed by a numerical analysis, (iii) long-term tests under sustained load of full-scale composite beams and a following numerical analysis. The outcomes of the experimental tests show that it is possible to achieve good structural performance with a prefabricated system, particularly using the connection with coach screws and timber notches. The mechanical properties of the prefabricated connections can be used in the design method described in Eurocode 5. The experimental-numerical investigations indicate that the new shear connections are suitable for prefabricated timber-concrete composite structures and perform equally well as “wet” systems. It is possible to achieve high load-carrying capacity and stiffness (with up to 98% composite efficiency) using the new shear connectors, and it is feasible to manufacture timber- concrete composite structures as prefabricated elements. An additional benefit is that some of the systems are fully demountable, allowing the owner to disassemble the timber beams and concrete panels at the end of their service life. From the numerical analysis it was found that at the end of service life (50 years) the prefabricated timber-concrete composite floors behave adequately, with a mid-span deflection within the acceptable limit of l/250. Numerical studies show that prefabrication off-site of the concrete slab results in a reduction of the long-term deflection if the slab is cured for at least 56 days before it is connected to the timber beam. Furthermore, although propping is required during the manufacture of both traditional and prefabricated timber-concrete systems, the props should be left in place for at least seven days using cast-in-situ concrete, while for prefabricated concrete slabs the props need to be left in place only for one day, leading to a significant economic advantage. Lastly, the long-term deflection of the proposed prefabricated system is hardly affected