Earthquake engineering is the study of the behavior of buildings and structures subject to seismic loading. It is a subset of both structural and civil engineering.
The main objectives of earthquake engineering are:
- Understand the interaction between buildings or civil infrastructure and the ground.
- Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
- Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.
A properly engineered structure does not necessarily have to be extremely strong or expensive.
The most powerful and budgetary tools of earthquake engineering are vibration control technologies and, in particular, base isolation.
Seismic loading
Seismic loading means application of an earthquake-generated agitation to a structure. It happens at contact surfaces of a structure either with the ground , or with adjacent structures , or with gravity waves from tsunami. Seismic loading depends, primarily, on:
- Anticipated earthquake's parameters at the site
- Geotechnical parameters of the site
- Structure's parameters
- Characteristics of the anticipated gravity waves from tsunami (if applicable).
Ancient builders believed that earthquakes were a result of wrath of gods (in Greek mythology, e.g., the main "Earth-Shaker" was Poseidon) and, therefore, could not be resisted by humans. Nowadays, the people's attitude has changed dramatically though the seismic loads, sometimes, exceed ability of a structure to resist them without being broken, partially or completely.
Due to their mutual interaction, seismic loading and seismic performance of a structure are intimately related.
Seismic performance
Main article: Seismic analysisEarthquake or seismic performance is an execution of a building's or structure's ability to sustain their due functions, such as its safety and serviceability, at and after a particular earthquake exposure. A structure is, normally, considered safe if it does not endanger the lives and wellbeing of those in or around it by partially or completely collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed.
Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive The Big One (the most powerful anticipated earthquake) though with partial destruction .
Seismic performance evaluation
Engineers need to know the quantified level of an actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking.
The best way to do it is to put the structure on a shake-table that simulates the earth shaking and watch what may happen next . Such kinds of experiments were performed still more than a century ago
Another way is to evaluate the earthquake performance analytically.
Seismic performance analysis
Seismic performance analysis or, simply, seismic analysis is a major intellectual tool of earthquake engineering which breaks the complex topic into smaller parts to gain a better understanding of seismic performance of building and non-building structures. The technique as a formal concept is a relatively recent development.
In general, seismic analysis is based on the methods of structural dynamics. For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method which, also, contributed to the proposed building code's concept of today.
However, those spectra are good, mostly, for single-degree-of-freedom systems. Numerical step-by-step integration proved to be a more effective method of analysis for multi-degree-of-freedom structural systems with severe non-linearity under a substantially transient process of kinematic excitation.
Research for earthquake engineering
Research for earthquake engineering means both field and analytical investigation or experimentation intended for discovery and scientific explanation of earthquake engineering related facts, revision of conventional concepts in the light of new findings, and practical application of the developed theories. The National Science Foundation (NSF) is the main United States government agency that supports fundamental research and education in all fields of earthquake engineering. In particular, it focuses on experimental, analytical, and computational research on design and performance enhancement of structural systems.
The Earthquake Engineering Research Institute (EERI) is a leader in dissemination of earthquake engineering research related information both in the U.S. and globally.
A definitive list of earthquake engineering research related shaking tables around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide. The most prominent of them is now E-Defense Shake Table in Japan.
Major earthquake engineering research centers in the United States and worldwideAll earthquake engineering research activities worldwide are mostly associated with the following centers:
- Earthquake Engineering Research Institute (EERI)
- Earthquake Engineering Research Center
- Pacific Earthquake Engineering Research Center (PEER)
- John A. Blume Earthquake Engineering Center
- Consortium of Universities for Research in Earthquake Engineering (CUREE)
- Multidisciplinary Center for Earthquake Engineering Research (MCEER)
- Earthquake Engineering Research Projects of CSUN
- George E. Brown, Jr. Network for Earthquake Engineering Simulation
- USGS Earthquake Hazards Program
- Office of Earthquake Engineering at Caltrans
- Earthquake Engineering Research Centre of Iceland
- Earthquake Engineering New Zealand
- Canadian Research Centers and Research Groups on Earthquake Engineering
- Hyogo Earthquake Engineering Research Center
- Laboratory for Earthquake Engineering of NTUA
- Earthquakes and Earthquake Engineering in The Library of Congress
- International Institute of Earthquake Engineering and Seismology
- National Center for Research on Earthquake Engineering
Major U.S. research programs
The NSF Hazard Mitigation and Structural Engineering program (HMSE) supports research on new technologies for improving the behavior and response of structural systems subject to earthquake hazards; fundamental research on safety and reliability of constructed systems; innovative developments in analysis and model based simulation of structural behavior and response including soil-structure interaction; design concepts that improve structure performance and flexibility; and application of new control techniques for structural systems .
NSF also supports George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) that advances knowledge discovery and innovation for earthquakes and tsunami loss reduction of the nation's civil infrastructure, and new experimental simulation techniques and instrumentation.
NEES comprises a network of 15 earthquake engineering experimental equipment sites available for experimentation on-site or in the field and through telepresence. NEES equipment sites include shake-tables, geotechnical centrifuges, a tsunami wave basin, unique large-scale testing laboratory facilities, and mobile and permanently installed field equipment .
NEES Cyberinfrastructure Center (NEESit) connects, via Internet2, the equipment sites as well as provides telepresence, a curated central data repository, simulation tools, and collaborative tools for facilitating on-line planning, execution, and post-processing of experiments.
Earthquake simulation
The very first earthquake simulations were performed by statically applying some horizontal inertia forces based on scaled peak ground accelerations to a mathematical model of a building . With the further development of computational technologies, static approaches began to give way to dynamic
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