Time-Dependent Tensile Properties of ETFE Foils by Linda Charbonneau A thesis presented to the University of Waterloo in fulfilment of the thesis requirement for the degree of Master of Applied Science in Civil Engineering Waterloo, Ontario, Canada, 2011 © Linda Charbonneau 2011 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract The purpose of this thesis is to provide an overview of ETFE foil, as it applies to pneumatic cushion cladding, with a focus on creep behavior of the material. Characteristics of ETFE, including weight, optics, insulation, flexibility, environmental properties, fire performance, cushion span and other features are discussed, and, where possible, are compared to the characteristics of glass panels used in similar applications. Relevant chemical and mechanical properties of ETFE are given. Load carrying concepts of tension structures and inflated cushions are discussed, as well as structural design methods for ETFE cushions. Several prominent structures constructed using ETFE foil are introduced and benefits and design issues associated with these structures are reviewed. When used in cushion applications, ETFE films are placed in constant tension, and are therefore subject to creep. Quantifying this creep is desirable so that it can be predicted during the design phase. Therefore, this thesis summarizes the findings of other researchers in the area of creep of ETFE as well as the general mechanical behavior of the material, and presents the results of uniaxial creep tests done for the purpose of this study. These tests included 24 hour uniaxial creep tests done at four stress levels on both the transverse and longitudinal directions of three different brands of film. Two thicknesses of the third film were acquired and both were tested. The stress levels were chosen to coincide with typical design tensile stresses for ETFE film, and to be similar to the levels tested by other researchers. The effects of the different stresses, brands, directions and thicknesses are evaluated and discussed. Three seven day creep tests were also done on one of the films, each at a different stress level. Constitutive viscoelastic and viscoplastic models were developed to represent the 24-hour creep data. The viscoelastic models were based on a four-element Kelvin model and the viscoplastic models were based on a power- law model. The model parameters were determined from the data using linear least squares fitting. Models were also developed for the seven day creep data. Several of these models were based only upon the first 24 hours of data, and were used to determine the applicability of the 24-hour creep models to long-term behavior. It was found that while a viscoelastic model appears to fit long-term creep most closely, the 24-hour models are inadequate for modeling longer time frames. Another method is required for predicting long-term creep. Nonlinear fitting of the parameters is recommended as a possible alternative for creating more accurate models. Longer-term creep tests are also recommended. Tensile tests were also done on the films to confirm mechanical properties supplied by the film manufacturers. Good agreement to the given values was found in the test data. iii Acknowledgements I would like to acknowledge the guidance of Professor Maria Anna Polak, which made this thesis possible. Her knowledge and experience were extremely valuable during all the phases of researching, testing and writing. I would like to thank Professor Alexander Penlidis of Chemical Engineering for sharing his personal wealth of knowledge on polymers, guiding me to appropriate resources, and assisting me in procuring test samples. The work of past and present members of the “Creeps Group” at the University of Waterloo has also been an important resource for the writing of this thesis. The University of Waterloo Civil Engineering lab technicians were a great help in the testing phase of this research. I would particularly like to thank Richard Morrison for his extensive help with the planning, setting-up and conducting of experiments. I would also like to thank the individuals and companies that kindly provided samples of ETFE film to this research: Dr. Peter Scott of Dyneon USA, the late Dr. Tuyu Xie, and Drs. John Richards and John Congalidis of Dupont USA, Christian Hartz of the Technische Universität Berlin and Nowofol Germany. I greatly appreciate the support and care of my family over my entire academic career and especially over the last two years. I would like to thank Mum and Dad for always encouraging me to do my best, Paul, Jenny and Michael for helping me to relax when I need to, and all the Waddens, Chabonneaus and Sneddons for all their motivation, dedication and love. I would also like to thank my wonderful friends for their positivity and support during the past few years. Finally I would like to thank my husband Matt for his unfailing optimism and love and for always having time to listen. iv Table of Contents List of Figures ...............................................................................................................................................................ix List of Tables ............................................................................................................................................................. xiii Chapter 1 Introduction and Background ....................................................................................................................... 1 1.1 Overview of ETFE ....................................................................................................................................... 1 1.1.1 Weight ..................................................................................................................................................... 2 1.1.2 Optics ....................................................................................................................................................... 2 1.1.3 Insulation ................................................................................................................................................. 3 1.1.4 Flexibility ................................................................................................................................................. 3 1.1.5 Environmental Benefits ........................................................................................................................... 3 1.1.6 Fire Performance ..................................................................................................................................... 3 1.1.7 Span ......................................................................................................................................................... 3 1.1.8 Other Features .......................................................................................................................................... 4 1.1.9 Processing ................................................................................................................................................ 5 1.2 Load-Carrying Concepts of ETFE ............................................................................................................... 7 1.3 Structures using ETFE ................................................................................................................................. 9 1.3.1 DomAquarée, Berlin, Germany ............................................................................................................... 9 1.3.2 Allianz Arena, Munich, Germany .......................................................................................................... 10 1.3.3 Eden Project, Cornwall, England ........................................................................................................... 11 1.3.4 National Aquatics Centre, Beijing, China .............................................................................................. 12 1.3.5 Kingsdale School, London, England ..................................................................................................... 13 1.3.6 Khan Shatyry Entertainment Centre, Astana, Kazakhstan ..................................................................... 15 1.3.7 BC Place Stadium, Vancouver, Canada ................................................................................................. 16 1.4 Chemical Properties of ETFE .................................................................................................................... 18 1.5 Mechanical Properties of ETFE ................................................................................................................. 20 1.6 Structural Design Methods for ETFE Cushions ......................................................................................... 22 1.6.1 Huntington Method ................................................................................................................................ 22 1.6.2 Wagner Method ..................................................................................................................................... 23 v 1.6.3 Borgart Method ...................................................................................................................................... 26 1.6.4