Troy A. Morgan

Performance of Seismic Protection Technologies during the 2011 Tohoku-Oki Earthquake

Many buildings in the Tohoku and Kanto area were strongly shaken during the Tohoku-oki earthquake on 11 March 2011. Soon after the earthquake, the Japan Society of Seismic Isolation (JSSI) established committees to investigate the performance of structures where modern seismic protection methods were used. Since response-control technologies are relatively new, few systems had been validated with actual earthquakes. Generally, the various buildings performed well, and there were no failures of superstructures of base-isolated or supplementally damped buildings. Failures of numerous expansion joints and lead dampers in base-isolated buildings are described. Acceleration records of both base-isolated and supplementally damped buildings are analyzed and their seismic performance characteristics are discussed.

Estimating the Storm Surge Recurrence Interval for Hurricane Sandy

Hurricane Sandy’s storm surge peaked at 2.87 m (9.40 ft) above mean sea level (MSL) (9.64 ft Manhattan Borough Datum [MBD]) at the southern tip of Manhattan in New York City on October 29, 2012 at 9:24 pm. The peak storm surge coincided with a tide of 0.64 m MSL (0.24 ft MBD), only 30 minutes after a high tide, contributing to catastrophic flooding of near-coastal areas. Traditional flood analysis fitting techniques using various probability distribution functions (normal, lognormal, Gumbel, and log-Pierson III) yielded return frequencies from 667 years to over 10,000 years. The more advanced Lin et al. (2010; 2012) analyses yielded recurrence intervals of between 559 and 650 years for the storm surge alone and 993 years for the surge plus tide. Considering the 2.77-mm/yr (0.11-in/yr) sea-level rise and using the analysis of Lin et al. (2012), future storms equal in magnitude to Hurricane Sandy will result in even greater flooding.

Collapse of Crossed Pendulum Ceiling Systems Due to Unstable Equilibrium

A failure analysis was conducted following the collapse of a 13,000 lbs., 165 ft by 16 ft rectangular steel suspended ceiling panel structure in a large public space. The ceiling framing structure was suspended from the roof structure with a unique system of stainless steel cables that cross one another between the ceiling structure attachment points and the anchorage to the supporting slab above. During construction, the entire ceiling panel structure rotated out of its installed horizontal position when the temporary cable bracing was removed, causing one edge of the ceiling structure to drop suddenly and the opposite edge to lift. No failure of the suspension cables or their attachments occurred. The collapse was caused by a design error that did not properly consider the stability of the suspended ceiling panel. The behavior of this particular ceiling panel structure is generalized to a wider class of crossed pendulum structures, and stability conditions based purely on system geometry are found using energy principles for a wide set of feasible parameters. Guidance is provided for the design of suspended systems involving crossed hangers, such as ceiling structures, bridges, and suspended walkways.

Independent Review of Siesmic Performance Assessments for the Plutonium Facility PF-4

The Plutonium Facility, designated PF-4, is located in Technical Area 55 at the Los Alamos National Laboratory (LANL). The facility is a one-story rectangular structure above a complete basement; the building was constructed of cast-in-place reinforced concrete, with small interior frames of structural steel. The plan dimensions of the building are 265’×284’. The overall height of the building varies between 39’-0” at the north and south ends, and 40’-6” at the center ridge. The programmatic work performed in the building is vital to our national security and its functions and storage purposes are not replicated elsewhere in the United States Department of Energy (DOE).

Risk Assessment of Emergency Diesel Generator Subject to Design-Basis Earthquake Shaking

A monitoring system intended to track vibrations associated with the operation of an emergency diesel generator (EDG) at a nuclear power plant was originally installed to trip generators during potential out-of-balance shaking. Years after original installation, plant engineers raised questions as to whether the monitoring system would have functioned properly in the event of excessive vibrations associated with earthquake ground shaking. As part of the plant’s examination of this issue, analytical models were developed for three vibration transducers via experimental characterization. A suite of ground motion records was selected and scaled such that their mean and dispersion were representative of the design-basis event (DBE) level of intensity at the plant site. The scaled suite of ground motions was used as an input for a three-dimensional (3D) analytical model representing the structure and soil-foundation interface, where the EDGs were installed. The voltage signal from the analytical transducer mod...

Risk Assessment of Emergency Diesel Generator Subject to Design Basis Earthquake Shaking

A monitoring system intended to track vibrations associated with the electric generation of an emergency diesel generator (EDG) at a nuclear power plant was originally installed to trip generators during potential out-of-balance shaking. Years after original installation, plant engineers raised questions as to whether the monitoring system would have functioned properly in the event of excessive vibrations associated with earthquake ground shaking. As part of the plant’s examination of this issue, analytical models were developed for three vibration transducers via experimental characterization. A suite of ground motion records were selected and scaled such that their mean and dispersion was representative of the design basis event (DBE) level of intensity at the plant site. The scaled suite of ground motions was used as an input for a three-dimensional analytical model representing the structure and soil-foundation interface where the EDGs were installed. The voltage signal from the analytical transducer model provided input to the physical vibration alarm monitor. This monitor filters the vibration transducer signal and generates an output to a time delay relay that will trip the EDG if the output from the vibration monitor is not reset within five seconds. The analysis and testing completed and described in this paper concluded that a DBE would not have caused the vibration monitoring circuit to spuriously trip the EDGs.Copyright

Satisfying Drift and Acceleration Criteria with Multi-Stage Friction Pendulum Isolation Systems

An objective in the design of seismically isolated structures is the selection of bearing properties so that optimal performance is achieved over a range of excitations and performance metrics. One dilemma in the design of isolation systems is that, to withstand very severe or near-fault motions, bearings often become so large, stiff and strong that they provide little isolation during moderate events. Experimental and numerical investigations are presented to characterize a new multi-stage isolation bearing, capable of progressively exhibiting different hysteretic properties at different stages of response and the feasibility of targeting these properties to achieve specific performance goals for a range of ground motion intensities and structural dynamic characteristics. This newly-developed triple pendulum isolator incorporates four concave surfaces and three independent pendulum mechanisms. Pendulum stages can be set to address specific response criteria for moderate, severe and very severe events. In particular, the tradeoff between limiting very rare isolator displacement demands and inducing high-frequency floor accelerations is examined for a range of levels of seismic hazard. Nonlinear dynamic analyses of realistic building systems are presented, including a thorough description of key structural demand parameters such as inter-story drift and floor acceleration spectra. Recommendations for design based on achieving target performance objectives under multiple seismic hazard levels are given.