The Dynamics of Rocking Isolation

Synopsis

The uplifting and rocking of slender, free-standing structures when subjected to ground shaking may limit appreciably the seismic moments and shears that develop at their base. While the high seismic performance of rocking isolation has been documented with the through-the-centuries survival of several free-standing ancient temples, it is only recently that rocking isolation starts to emerge as practical and attractive seismic design concept. Starting from the solitary free-standing column, the seminar uncovers the dynamics of the rocking frame – that is, an array of free-stranding columns capped with a freely supported rigid beam. Following a rigorous analysis, the seminar concludes with the remarkable result that the dynamic rocking response of the rocking frame is identical to the rocking response of a solitary free-standing column with the same slenderness yet with larger size – that is, a more stable configuration. Most importantly, the seminar shows that the heavier the freely supported cap beam is, the more stable is the rocking frame regardless of the rise of the centre of gravity of the cap beam, concluding that top-heavy rocking frames are more stable than when they are top-light. This ‘counter-intuitive’ finding renders rocking isolation a most attractive alternative for the seismic protection of bridges with tall piers; whereas, its potential implementation shall remove several of the concerns associated with the seismic connections of prefabricated bridges. The practice of increasing the lateral stiffness of the rocking frame with the use of unbonded vertical tendons is examined, and the seminar concludes that the concept of rocking isolation by intentionally designing a hinging mechanism is a unique seismic protection strategy for large, slender structures not just at the limit-state but also at the operational state.

About the speaker

Professor Nicos Makris received his Ph.D (1992) and his Master of Science (1990) from the State University of New York at Buffalo, USA; while he holds a Diploma in Civil Engineering from the National Technical University, Athens, Greece (1988). He has more than twenty-five (25) years of research, academic and professional experience in the areas of structural-earthquake engineering and applied mechanics-dynamics. He has served as: Assistant Professor at the University of Notre Dame (1992-1996) and at the University of California, Berkeley (1996-1998); Associate Professor at the University of California, Berkeley (1998-2002) and Professor at the University of California, Berkeley (2002-2005), the University of Patras (2003-2014) and the University of Central Florida (2014-present). He has published more than 95 papers in archival journals, while he has supervised ten Ph.D theses and more than forty MSc and 5th year Diploma theses. He has served as Associate Editor for the Journal of Engineering Mechanics, ASCE, and the Chair of the Dynamics Committee on the same Journal. He is a member of Academia Europaea “The Academy of Europe”, a member of the Congress Committee of IUTAM; while, he has been honoured with several international prizes and awards including the Walter L. Huber Civil Engineering Research Prize from the American Society of Civil Engineering (ASCE), the T. K. Hsieh Award from the Institution of Civil Engineers, U.K., the Shah Family Innovation Prize from the Earthquake Engineering Research Institute (EERI), USA and the CAREER Award from the National Science Foundation, USA. Upon returning to Greece from Berkeley, California in 2003, Professor Makris has also served for six consecutive years as the Director of Reconstruction of the Temple of Zeus in Ancient Nemea.

Further information

This seminar is jointly organised by SECED and RCCES (Research Centre for Civil Engineering Structures at City University London). Non-members of the society are welcome to attend. Attendance at this meeting is free. Seats are allocated on a first come, first served basis. For further information, please contact Greg James (tel. 020 7665 2229).