Our objective in earthquake engineering research is to improve the state of knowledge, through fundamental and applied research, to help decision-makers reduce seismic hazards.
Decision-makers are defined as all the individuals and agencies affecting the planning and design/construct process, such as planning or regulatory agencies, owners, investors and insurers — and the engineers who protect against seismic hazards through earthquake-resistant design.
Earthquake engineering is a multi-phased process that ranges from the description of earthquake sources, to characterization of site effects and structural response, and to description of measures of seismic protection. Our current research includes occurrence modeling, geophysical modeling, ground-motion modeling, stochastic and nonlinear dynamic analysis, and design and experimentation. Components of these studies pertain to the individual phases but also, and perhaps more importantly, to aspects that incorporate some or all of the phases of earthquake engineering.
Seismic hazard and risk analysis
For over 30 years, research at the John A. Blume Earthquake Engineering Center has focused on seismic hazard and risk analysis. Early work focused mainly on modeling sources, occurrence and attenuation, and developing probabilistic hazard analysis methodologies, using Poisson models and Bayesian models. In recent years, considerable efforts have been placed on introducing mechanistic models to occurrence and attenuation phenomena. Time- and space-dependent models have been introduced to represent the fault rupture mechanics and the stress accumulation and release cycles of large earthquakes. Most recently, advanced computational tools, such as geographic information systems (GIS) and database management systems (DBMS), have been used to capture, analyze, integrate and display the tectonic, seismological, geological and engineering information needed in seismic hazard assessment.
Working with various countries in Central America, North Africa, Asia and Europe, our researchers have developed seismic hazard maps and structural design criteria, while our faculty and graduate students have significantly contributed to the development of models and methods for earthquake vulnerability and risk assessment. Current research uses analytical models for damage and structural vulnerability assessment that are based on nonlinear structural response simulation. A key question currently being addressed is the assessment of losses resulting from structural damage. Damage and vulnerability models are developed for individual structures within the context of performance-based engineering and more generic vulnerability models are formulated for application over large regions to many different types of structures. These risk assessment tools have been implemented and utilized by the practicing engineering community as well as by government agencies, insurance/reinsurance companies and financial institutions.
Researchers in our department are also working on seismic risk assessment models for transportation systems. These models use GIS and transportation network analysis tools to estimate the losses from damage to components of the system as well as those due to traffic time delays or inaccessibility of particular locations. Tools for emergency response and resource allocation following disasters are key features currently under development. Significant components of this research are supported through the Pacific Earthquake Engineering Research Center (PEER).
Ground motion modeling
Prediction of strong ground motion continues to be a major research area in earthquake engineering, using simulation of ground motion models for seismic hazard analysis, stochastic-physical rupture process models for ground motion prediction, prediction of ground motion for engineering applications, and study of the nonstationary characteristics of simulated and recorded ground motions for nonlinear analysis of structures. Various geophysical models are being considered for simulating strong ground motion, and recorded motions from recent earthquakes are being studied for their characteristics and damage potential. Recent seismological studies have focused on the understanding and characterization of strong ground motion in the near field. The effect of near-field motions on structures has been observed from past earthquakes to be particularly important; however, systematic studies of these effects had not been conducted so they now are a focus of current research.
Damage potential of ground motion
Experience in past earthquakes has shown that the engineering profession has not yet succeeded in defining ground-motion parameters that correlate well with observed damage. From an engineering perspective, we are seeking representations of the seismic “demand” that can be used, through convolution with the structural “capacity,” to assess structural reliability. Thus, both demand and capacity need to be evaluated, the latter with due regard to structural characteristics and cumulative damage effects that depend on strong motion duration. If this can be achieved, seismic risk analysis can be based on reliability concepts, and design parameters can be derived that are consistent with the damage potential of the ground motions.
Research studies on seismic hazard analysis, input and response characterization, structural reliability, and design are treated as interrelated subjects through a consistent and coordinated approach. The major components of this research are development of damage models for structural response; characterization of ground motions based on damage potential; reliability evaluation; seismic risk analysis; and development of design parameters.
Design and experimentation
Considerable effort is being devoted to design research that can be implemented directly in engineering practice. This research, concerned with methods to evaluate and improve the behavior of new and existing structures in severe earthquakes, includes:
- Development of a deformation-based seismic design methodology.
- Dynamic stability considerations and P-delta effects.
- Evaluation of the effects of stiffness and strength irregularities in plan and elevation.
- Cumulative damage modeling.
- Retrofit measures for existing structures.
- Exploration of new materials and new structural systems for earthquake resistance.
Our research facilities include a laboratory with equipment for static and dynamic testing of structural materials, components and system models. Current structural testing is focusing on research to validate computational models to predict dynamic nonlinear response of structures and for developing health-monitoring technologies. This includes shaking table tests to examine structural collapse phenomena as affected by the complex interactions of degrading structural response and random earthquake input motions. Shake table testing is also an important component of the research to develop more robust wireless strong motion sensors. Other projects involve quasi-static testing of structural components and materials to evaluate fiber-optic sensors and to investigate the effect of localized failure mechanisms on structural performance.