Rocking Isolation for New and Existing Retrofitted Structures

Synopsis

According to current seismic codes, the foundation soil is not allowed to fully mobilize its strength, and plastic deformation is restricted to above-ground structural members. Capacity design is applied to the foundation guiding failure to the superstructure, thus prohibiting mobilization of soil bearing capacity. However, a significant body of evidence suggests that allowing strongly nonlinear foundation response may be advantageous. The lecture will introduce an alternative seismic design philosophy termed rocking isolation, in which soil yielding is used as a “fuse”. According to such a scheme, the foundation is intentionally under-designed to uplift and fully mobilize its bearing capacity, limiting the inertia transmitted onto the superstructure. To unravel the effectiveness of rocking isolation, an idealized bridge pier is used as an illustrative example. A conventionally designed system is compared with a rocking–isolated alternative. Their seismic performance is explored analytically, through nonlinear finite element analyses, and experimentally, through shaking table and centrifuge model testing. A similar comparison is performed for an existing 3-storey building, designed and constructed according to obsolete seismic codes, and retrofitted by adding shear walls. Emphasis is placed on the foundation of the shear walls, comparing conventional design with rocking isolation. The physical model encompasses the structural system, along with the foundations, and the soil. The nonlinearity of structural members is simulated through specially designed and carefully calibrated artificial plastic hinges. The vulnerability of the original structure is confirmed, as it is found to collapse with a soft-storey mechanism when subjected to moderate intensity seismic shaking. The conventionally retrofitted structure is proven capable of sustaining larger intensity shaking, and the rocking–isolated structure is shown to offer increased safety margins. Finally two novel concepts are introduced, aiming to reduce the permanent rotations and settlements: (a) variable-geometry foundations; and (b) hybrid hinged tie beams.

About the speaker

Professor Ioannis Anastasopoulos, Chair of Civil Engineering at the University of Dundee, specializes in geotechnical earthquake engineering and soil–structure interaction, combining numerical with experimental methods. His academic degrees include a PhD from the National Technical University of Athens (NTUA), an MSc from Purdue University, and a Civil Engineering Diploma from NTUA. His publication record includes over 60 publications in refereed journals, and 100 more in books and conference proceedings. Ioannis also has extensive professional experience, as he has worked in a variety of projects of significance in Greece, but also in the US (Queensboro bridge), and the Middle East (over 70 Technical Reports). His consulting work ranges from special seismic design of bridges, buildings, retaining walls, metro stations and tunnels, to harbor quay walls (all major ports of Greece), and special design against faulting-induced deformation applying the methods he developed during and after his PhD. He serves as an Editorial Board Member of Géotechnique and ICE Geotechnical Engineering, and has given several Keynote and Invited talks at International Conferences and academic institutions. Ioannis is the inaugural recipient of the Young Researcher Award of the ISSMGE in Geotechnical Earthquake Engineering, and winner of the 2012 Shamsher Prakash Research Award.

Further information

This evening meeting is organised by SECED and chaired by Mark Scorer (Atkins). 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. Tea and biscuits will be served from 5.30pm - 6pm. For further information, please contact Greg James (tel. 020 7665 2229).