Seismic Performance
Until the early 1990s, seismic design was focused almost exclusively on the definition of design forces and moments based on Response Spectra Analysis (RSA). The Loma Prieta Earthquake in 1989, followed a few short years later by the Northridge and Kobe Earthquakes, vividly demonstrated the shortcomings of this approach, particularly for concrete structures.
ANATECH, working with the California Department of Transportation (Caltrans) and several University of California engineering schools, developed new performance-based methodologies to evaluate seismic vulnerabilities and retrofit strategies for key lifeline structures. This approach was based on accurate predictions of the actual behavior of concrete and steel structures subjected to ground motions beyond their design basis.
Nonlinear analysis, using ANATECH’s proven ANACAP-U concrete and steel-analysis-software system, was found effective and accurate in predicting the behavior of many complex cyclic tests performed at structural engineering laboratories at the University of California in San Diego, Berkeley and the University of Nevada at Reno. Such valuable collaboration furthered ANATECH’s ability to accurately predict, for the first time, the response, ductility capacity, and cyclic degradation of concrete and steel structures at loads well past design scenarios. Using these methodologies, ANATECH provided unparalleled, analytic support for the retrofit and replacement design efforts on many of California’s largest signature bridges, including the Golden Gate, East and West spans of the San Francisco/Oakland Bay Bridge, Richmond-San Rafael, San Mateo, Benicia Martinez, Vincent Thomas and Coronado Bridges. More recently ANATECH has used these methodologies in seismic vulnerability studies of the Brooklyn and Queensboro bridges for the New York Department of Transportation (NYDOT.)
ANATECH applies current research and knowledge learned from recent events such as the Tohoku Earthquake and Tsunami and the 2011 Virginia Earthquake to continually evolve our analytic software and to provide cutting-edge, structural-engineering support services.
Our seismic design team focuses on these areas:
Seismic Design Qualification
ANATECH performs analyses for the seismic design and qualification of nuclear-safety-related structural systems, such as overhead bridge or gantry cranes and their supporting structures. These analyses generally involve linear-response-spectra analyses, which conform to regulatory guidelines, to demonstrate that the structural sections meet the regulatory requirements for seismic demands. Nonlinear, time-history analyses are employed if the RSA indicates that a slack rope condition can develop.
Seismic Capacity, Ductility and Retrofitting
ANATECH has vast experience in determining the capacity and ductility of structures under seismic loading, particularly reinforced and prestressed containment systems and bridges. These analyses involve highly nonlinear, structural-response models that track progressive and extensive damage leading to structural failure. The extensive experience that ANATECH has developed allows us to provide incomparable support for new design and for any issues not adequately covered by current codes. Of equal importance is ANATECH’s ability to provide analytic support for seismic retrofitting of existing structures, particularly bridges, dams and intake structures. Many of these current structures are considerably, seismically deficient. ANATECH can and has provided structural analysis support to identify deficiencies, failure mechanisms, and evaluation of retrofit strategies to further the lifetime of key infrastructure elements.
Seismic Fragility
ANATECH offers analyses and engineering support to determine the seismic fragility of existing structural systems. Employing probabilistic methods with parameter variations, engineers perform a series of analyses and assess the results to evaluate the probability of failure for increasing seismic loading.
