A New Visco-Plastic Device for Seismic Protection of structures

A New Visco-Plastic Device for Seismic Protection of Structures Yasser El-Husseini Ibrahim Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Civil and Environmental Engineering Dr. Finley A. Charney Dr. Thomas M. Murray Dr. Raymond H. Plaut Dr. Carin L. Roberts-Wollmann Dr. Mahendra P. Singh 02-07-2005 Blacksburg, VA Keywords: Visco-plastic, Viscoelastic, Dampers, Passive control, Seismic, Earthquakes. Copyright 2005, Yasser Ibrahim A New Visco-Plastic Device for Seismic Protection of Structures Yasser E. Ibrahim Abstract A new visco-plastic damper for seismic protection is introduced. This device combines and enhances many of the proven characteristics of both displacement-dependent and velocity-dependent devices. The device consists of a block of a high-damping viscoelastic material sandwiched between two steel shapes (plates or channels) bent in a certain configuration to amplify the deformations in the device in order to obtain large tensile and compressive strains in the viscoelastic material. Under low levels of vibrations, the device dissipates energy through amplified strains in the viscoelastic material only; however, under moderate to strong levels of vibrations, a new source of energy dissipation is added through the yielding of the steel elements. The inelastic behavior of the steel elements is controlled by the rigidity of the viscoelastic material. In addition to the energy dissipation, the device provides stiffness through the steel elements as well as the viscoelastic material. Moreover, one of the main advantages of the device is that its behavior is fully controlled through different parameters. First, a nonlinear time history analysis was conducted on structures with a preliminary model of the device using SAP2000 program to check the effectiveness of the device on the response of different structures under ground excitations. The device resulted in better improvement in the structural response compared to the existing viscoelastic dampers. A three-dimensional finite element model was developed for the device using the finite element package, ABAQUS. The hyperelastic and viscoelastic behavior of the block of the viscoelastic material were considered. The inelastic behavior of the steel elements was considered as well using the Von Mises yielding criterion. The device was analyzed under different dynamic loadings with different frequencies. Three simplified models were developed using SAP2000 program in order to facilitate the modeling of the device for structural engineers. These models were compared to the detailed finite element model to check their accuracy. The best model was used in the analysis of a multi-story steel frame with the visco-plastic devices under different ground excitations. Two different arrangements of the device were considered. The devices caused significant reduction in the story displacements, base shear and bending moment at column bases. Dedication TO: My parents My wife My kids: Mariam and Ahmed Acknowledgement I would like to take the opportunity to express my deepest appreciation and gratitude for all the people who helped me during my work in this research. First I would like to thank my advisor and committee chair, Dr. Finley Charney, for all of his support, guidance, and patience. I have learned a lot from his knowledge and practical experience in the area of Earthquake Engineering and structural Dynamics. It was really a privilege to work with him. I would also like to thank my committee members, Dr. Thomas Murray, Dr. Raymond Plaut, Dr. Carin Roberts-Wollmann and Dr. Mahendra Singh for taking the time to provide valuable insight for my thesis and for all the help they have offered me during the time I have spent at Virginia Tech. I would like to thank my wife for her love, encouragement and support during my work towards the PhD degree. Special thanks for my parents for all what they did for me throughout my life. I owe to them every success I have in my life. Finally, I would like to thank the Egyptian Government which supported me financially to pursue my research here in the United States. TABLE OF CONTENTS Chapter 1: Introduction.1 1.0 Introduction.1 1.1 Objective of the Research.2 1.2 Scope of the Research.3 1.3 Outli