Dr. Michael Constantinou presented the 17th Annual Mueser Rutledge lecture to the Geotechnical Group at the General Society for Mechanics and Tradesmen in Manhattan on November 15, 2007. The lecture provided an overview of the various seismic protective systems and their application in mitigating the damaging effects of earthquakes on structures.

Dr. Constantinou began the lecture by describing seismic protective systems as technologies that reduce the inertial forces and/or absorb energy within the structural system. Addition of these systems to new or existing construction deflects earthquake-induced energy away from the structure. A key to this construction technique is limiting or eliminating damage to the gravity-load-resisting system of the structure.

Dr. Constantinou proceeded to describe the various types of seismic protection including passive systems of base isolation, and active or semi-active systems dampers. Passive systems “isolate” a structure from strong ground motions by increasing the structural natural period that results in lower accelerations and inertial forces. Principal forms include isolation bearings, typically elastomeric and sliding bearings, and viscous dampers. Elastomeric bearings such as lead-rubber (LR) bearings consist of alternate layers of steel and rubber bonded together with a lead core. The rubber layers allow the isolator to displace sideways reducing the earthquake loads felt by the building and its occupants. During an earthquake, the lead core is pushed sideways by the rubber and steel layers absorbing a portion of the earthquake energy. Sliding bearings such as friction pendulum (FP) bearings have a concave sliding surface that causes the supported structure to move with small inverted pendulum motions and thereby lengthen the natural period. The dynamic friction force generated provides a reduction to the force felt by the structure. In turn, the size of the structural members can be reduced and yield a savings in material costs.

Dr. Constantinou then presented several examples of seismic isolation systems used in the design of bridges, buildings, liquid storage tanks and offshore oil and gas platforms. For a 250-foot diameter liquid natural gas tank in Greece, 430 FP bearings were used. The isolation allowed construction of a more slender tank with a reduced footprint and smaller size foundation. Construction of offshore oil and gas platforms in 160 feet of water off Sakhalin Island in Russia used FP bearings to protect work platform and entire structure above massive concrete gravity base. The Woodrow Wilson Bridge spanning the Potomac River between Maryland and Virginia used LR bearings to redistribute loads to all elements of the bridge structure in a seismic event. The behavior of the LR bearings was important in both seismic and service conditions due to the cyclical loadings in the bridge structure from traffic and wind. Bearing performance was verified by cyclical wear testing of the bearings with dynamic testing performed before and after the wear tests.

Dr. Constantinou concluded the lecture with a discussion of some recent innovations in the use of damping systems and configurations to reduce structure displacements under seismic and service conditions. Following a number of questions from the audience, Dr. Constantinou was presented a Golden Apple from Geotechnical Group Chairman Terry Holman, Ph.D., P.E. in appreciation for his lecture.