Influence of Column-Base Fixity On Lateral Drift of Gable Frames

In a typical light metal building, the structural members are designed for the forces and moments obtained from the wind drift analysis, which assumes pinned connections at the base. The pinned connections provide no moment at the base and have zero rotational stiffness. However, in reality every connection provides some restraint and has some rotational stiffness. Hence, by considering a modeling assumption of pinned condition, the actual behavior of the connection is not captured and this results in overestimation of lateral drifts and appearance of larger moments at the knee of the gable frames. Since the structural components are designed on the basis of these highly conservative results, the cost of the project increases. This thesis investigates the real behavior of the column base connection and tries to reduce the above stated conservatism by developing a computer program or “wizard” to calculate the initial rotational stiffness of any column base connection. To observe the actual behavior of a column base connection under different load cases, a number of finite element models were created in SAP2000. Each finite element model of the column base connection contained base plate, column stub, anchor bolts and in some cases grout as its components. The model was mainly subjected to three load cases, namely gravity, wind and gravity plus wind. After performing many analyses, the influence of flexibility of each component on the flexibility of the connection was observed and a list of parameters was created. These parameters are the properties of above mentioned components which characterizes any column base connection. These parameters were then used as inputs to model any configuration of the column base connection in the developed wizard. The wizard uses OpenSees and SAP2000 to analyze the modeled configuration of the connection and provides values of the initial rotational stiffness and maximum bearing pressure for the provided loads. These values can be further used in any structural analysis which is done to calculate the lateral drift of a frame under lateral loads. This will also help in getting results which are less conservative than the results which one gets on assuming pinned condition at the base. iii Acknowledgements I would like to thank Dr. Finley A Charney for being my advisor and committee chair. I really appreciate the fact that he provided a challenging work environment which made me work harder to complete this research successfully. I am really glad that I got an opportunity to work under his tutelage. I have learned lots of things from him as a student and person. I would like to thank Dr. Carin L. Roberts Wollmann for being one of my committee members and amazing teacher. I would also like to thank Dr. Matthew R. Eatherton for serving as one of my committee members and providing valuable information throughout my stay at Virginia Tech. I would like to thank the Metal Building Manufacturers Association for sponsoring this research project. I would like to express my sincere gratitude to Dr. Lee Shoemaker, who has served as the main contact person from MBMA and provided me valuable information time to time. I would like to thank Ms. Lindy Cranwell and Ms. Ann W. Crate for providing excellent support to the graduate students. The research reported in this thesis could not have been possible without the constant support and feedback from Ms. Jeena Rachel Jayamon, graduate student at Virginia Tech. Special thanks to Mr. David Padilla, doctoral student at Virginia Tech for his constant criticisms, which helped me improving the performance of the wizard. I would specially want to thank my parents, Mr. Dev Kumar Verma and Mrs. Amita Verma for being really supportive of my decisions and actions. Without their patience, sacrifices, love and blessings, I could not have completed this research. I would also like to thank my one and only sister, Ms. Avani Verma for her constant boost and support without which I would not have come this far.