Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 12-2019 Reducing Thermal Bridging and Understanding Second-Order Effects in Concrete Sandwich Wall Panels Taylor J. Sorensen Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Civil and Environmental Engineering Commons Recommended Citation Sorensen, Taylor J., "Reducing Thermal Bridging and Understanding Second-Order Effects in Concrete Sandwich Wall Panels" (2019). All Graduate Theses and Dissertations. 7642. https://digitalcommons.usu.edu/etd/7642 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. REDUCING THERMAL BRIDGING AND UNDERSTANDING SECOND-ORDER EFFECTS IN CONCRETE SANDWICH WALL PANELS by Taylor J. Sorensen A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Civil Engineering (Structural Engineering) Approved: ______________________________ ______________________________ Marc Maguire, Ph.D. Nick Roberts, Ph.D. Major Professor Committee Member ______________________________ ______________________________ Marv Halling, Ph.D. Andrew Sorensen, Ph.D. Committee Member Committee Member ______________________________ ______________________________ Paul Barr, Ph.D. Richard S. Inouye, Ph.D. Committee Member Vice Provost for Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2019 ii Copyright © Taylor Sorensen 2019 All Rights Reserved ABSTRACT Reducing Thermal Bridging and Understanding Second-Order Effects in Concrete Sandwich Wall Panels by Taylor J. Sorensen, Doctor of Philosophy Utah State University, 2019 Major Professor: Dr. Marc Maguire Department: Civil and Environmental Engineering Recent advances in concrete sandwich wall panels (SWP) have sought to optimize structural efficiency by reducing wythe thickness. This is possible by utilizing increased composite action between wythes from improved SWP connectors. Partially-composite SWPs often achieve optimal structural efficiency, but at the expense of thermal efficiency. Conversely, some people strongly advocate non-composite SWP structures since these typically have higher thermal efficiency than partially-composite SWP structures, but do so at the expense of structural efficiency. This project sought to help allow SWPs to achieve optimal structural and thermal efficiency without sacrificing one or the other by increasing thermal efficiency of concrete SWP structures by identifying common locations of thermal bridging and developing alternate designs to eradicate (as much as possible) the use of solid sections in concrete sandwich wall panel design. iv This study performed infrared thermographic inspections of 79 SWP structures across the United States of America and analyzed heat transfer in SWP connections to identify details that can decrease thermal bridging in future SWP construction. Because corbel connections can be particularly difficult locations to avoid thermal bridging for partially-composite SWPs, 12 corbel connections were designed, created, and structurally tested to maintain a continuous thermal break and thereby eliminate thermal bridging. Nine successful alternative thermally efficient corbel connections were created, with GFRP grating providing the most promising results for application in SWP corbel construction. Use of SWP connectors to transfer loads between wythes locally at corbel connections was also found to be a feasible option. Corbel specimens were modeled using the Beam-Spring Method with good agreement with experimental results, with a predicted-to-measured ratio of 1.014 and a standard deviation of 0.286. Such validation led to completion of a parametric study to evaluate performance of the PCI Second-Order Analysis method, to quantify 2nd order effects in SWPs, and to investigate effects of length, panel stiffness, and wythe configuration on SWP behavior under combined axial and flexural loading. Findings of this dissertation will help reduce energy use and thermal bridging, increase sustainability, lessen environmental impact, and increase the safety of concrete sandwich wall panel structures. (472 pages) v PUBLIC ABSTRACT Reducing Thermal Bridging and Understanding Second-Order Effects in Concrete Sandwich Wall Panels Taylor J. Sorensen Structural engineers have traditionally detailed structures with structural and fabrication efficiency in mind, but often based on a limited understanding of thermal efficiency. Some connection designs can create significant thermal bridging, leading to unnecessary heat transfer and even premature degradation through condensation. Thermal bridging occurs when heat transfer is given a path through a more conductive material like concrete or steel rather than insulation. Concrete sandwich wall panels (SWP) tend to be highly efficient at preventing heat transfer in the middle of panels, with greatest heat transfer occurring at connections. This project identified thermally efficient details for future SWP construction to reduce heat transfer, lessen environmental impact, and increase sustainability of SWP structures. It can be particularly difficult to avoid thermal bridging at corbel connections, so 12 corbel specimens were created and tested to provide alternative corbel design options for engineers. Nine details were successfully created and are presented. Corbel specimens were modeled using the Beam-Spring Method with good agreement. After validating the Beam-Spring Model, a parametric study investigated effectiveness of the PCI Second Order Analysis and the effect of length, panel stiffness, and wythe configuration on SWP behavior under axial and flexural loads. vi ACKNOWLEDGMENTS I would like to express my deep appreciation to the Portland Cement Association Education Foundation for their continued support, guidance, sponsorship, and interest in this project. Appreciation should also be extended to the Precast/Prestressed Concrete Institute and the Tilt-Up Concrete Association for their willingness to help to identify and recommend precasters and contractors to assist me in identifying SWP buildings in cities across the United States to include in this study. These many precasters, contractors, and engineers also deserve recognition and thanks for their participation in this study in identifying SWP structures for us to visit to help us promote SWP structures as a whole in the industry. I am very grateful to the gracious owners of these structures that allowed us to visit and photograph their beautiful structures. Special thanks to Parker Syndergaard and Sattar Dorafshan for their help in taking many of the thermal images. Appreciation should also be extended to the various donors who contributed to the making of the concrete sandwich wall panels, including HK Composites for donating all HK SWP connectors used in this project, IconX LLC for donating the GFRP and CFRP IconX connectors, Owens Corning Infrastructure Solutions for the donation of the GFRP bars, and Fibergrate Composite Structures for donating the FRP grating used in this project. Special thanks to those graduate and undergraduate workers who assisted in preparing, casting, and testing the corbel specimens including Zachary Benson, Colby Bench, Tyler Daniels, Quinn Lythgoe, Ethan Schow, Reese Mikesell, Zack Hulsey, Nick Langford, and Jared McRory. I would also like to express my gratitude for Fray Pozo for vii his assistance in helping me create an API that allowed me to perform so many Beam- Spring Models in a most efficient manner. I am humbly grateful for all of the spectacular professors, teachers, and mentors I have had through my educational experience, both through my childhood and in my higher education, and would like to thank them all for the way they have touched my life through their teachings, friendship, and examples. I would like to express special thanks for my advisor, Dr. Marc Maguire, who has been a phenomenal mentor and friend. His continual guidance, supervision, constructive advice, and wise counsel has helped me arrive where I am now. I would not have pursued such a course of action if it were not for his intervention and his ability to see in me what I had not thought to imagine. Thank you for your influence, encouragement, and guidance. Finally, I wish to express the deepest and most profound love and gratitude to my family, and most particularly my wife. No one has been so supportive as she. Thank you for being patient and for sticking with me through the thick and thin. I wouldn’t have been able to do it without you! Taylor J. Sorensen viii CONTENTS ABSTRACT ....................................................................................................................... iii PUBLIC ABSTRACT .........................................................................................................v ACKNOWLEDGMENTS ................................................................................................. vi LIST OF FIGURES .............................................................................................................x LIST OF TABLES ........................................................................................................... xix LIST OF SYMBOLS AND NOTATION ..........................................................................xx