Incremental Dynamic Analysis
Encyclopedia
Incremental Dynamic Analysis (IDA) is a computational analysis method of Earthquake Engineering
for performing a comprehensive assessment of the behavior of structures under seismic loads. It has been developed to build upon the results of probabilistic seismic hazard analysis
in order to estimate the seismic risk
faced by a given structure. It can be considered to be the dynamic equivalent of the static pushover analysis.
, each scaled to several levels of seismic intensity. The scaling levels are appropriately selected to force the structure through the entire range of behavior, from elastic to inelastic and finally to global dynamic instability, where the structure essentially experiences collapse. Appropriate postprocessing can present the results in terms of IDA curves, one for each ground motion record, of the seismic intensity, typically represented by a scalar Intensity Measure (IM), versus the structural response, as measured by an Engineering Demand Parameter (EDP).
Possible choices for the IM are scalar (or rarely vector) quantities that relate to the severity of the recorded ground motion and scale linearly or nonlinearly with its amplitude. The IM is properly chosen well so that appropriate hazard maps (hazard curves) can be produced for them by probabilistic seismic hazard analysis. Possible choices are the peak ground acceleration
, peak ground velocity or Arias intensity
, but the most widely used is the 5%-damped spectral acceleration
at the first-mode period of the structure.
The EDP can be any structural response quantity that relates to structural, non-structural or contents' damage. Typical choices are the maximum (over all stories and time) interstory drift, the individual peak story drifts and the peak floor accelerations.
In the wake of the damage wrought by the 1994 Northridge earthquake
, the SAC/FEMA
project was launched to resolve the issue of poor performance of steel moment-resisting frames due to the fracturing beam-column connections. Within the creative environment of research cooperation, the idea of subjecting a structure to a wider range of scaling emerged. Initially, the method was called Dynamic Pushover and it was conceived as a way to estimate a proxy for the global collapse of the structure. It was later recognized that such a method would also enable checking for multiple limit-states, e.g. for life-safety, as is the standard for most seismic design methods, but also for lower and higher levels of intensity that represent different threat levels, such as immediate-occupancy and collapse-prevention. Thus, the idea for Incremental Dynamic Analysis was born, which was mainly adopted and later popularized by researchers at the John A. Blume Earthquake Research Center of Stanford University
. This has now met with wider recognition in the earthquake research community and has spawned several different methods and concepts for estimating structural performance.
Earthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
for performing a comprehensive assessment of the behavior of structures under seismic loads. It has been developed to build upon the results of probabilistic seismic hazard analysis
Seismic hazard
Seismic hazard refers to the study of expected earthquake ground motions at the earth's surface, and its likely effects on existing natural conditions and man-made structures for public safety considerations; the results of such studies are published as seismic hazard maps, which identify the...
in order to estimate the seismic risk
Seismic risk
Seismic risk uses the results of a seismic hazard analysis, and includes both consequence and probability. Seismic risk has been defined, for most management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified period of time...
faced by a given structure. It can be considered to be the dynamic equivalent of the static pushover analysis.
Description
IDA involves performing multiple nonlinear dynamic analyses of a structural model under a suite of ground motion recordsStrong ground motion
"Peak ground velocity" redirects here.Seismologists usually define strong ground motion as the strong earthquake shaking that occurs close to a causative fault...
, each scaled to several levels of seismic intensity. The scaling levels are appropriately selected to force the structure through the entire range of behavior, from elastic to inelastic and finally to global dynamic instability, where the structure essentially experiences collapse. Appropriate postprocessing can present the results in terms of IDA curves, one for each ground motion record, of the seismic intensity, typically represented by a scalar Intensity Measure (IM), versus the structural response, as measured by an Engineering Demand Parameter (EDP).
Possible choices for the IM are scalar (or rarely vector) quantities that relate to the severity of the recorded ground motion and scale linearly or nonlinearly with its amplitude. The IM is properly chosen well so that appropriate hazard maps (hazard curves) can be produced for them by probabilistic seismic hazard analysis. Possible choices are the peak ground acceleration
Peak ground acceleration
Peak ground acceleration is a measure of earthquake acceleration on the ground and an important input parameter for earthquake engineering, also known as the design basis earthquake ground motion...
, peak ground velocity or Arias intensity
Arias Intensity
The Arias Intensity is a measure of the strength of a ground motion. It determines the intensity of shaking by measuring the acceleration of transient seismic waves. It has been found to be a fairly reliable parameter to describe earthquake shaking necessary to trigger landslides...
, but the most widely used is the 5%-damped spectral acceleration
Spectral acceleration
Spectral acceleration is a unit measured in g that describes the maximum acceleration in an earthquake on an object – specifically a damped, harmonic oscillator moving in one physical dimension...
at the first-mode period of the structure.
The EDP can be any structural response quantity that relates to structural, non-structural or contents' damage. Typical choices are the maximum (over all stories and time) interstory drift, the individual peak story drifts and the peak floor accelerations.
Development History
IDA grew out of the typical practice of scaling accelerograms by multiplying with a constant factor to represent more or less severe ground motions than the ones that were recorded at a site. Since the natural recordings available are never enough to cover all possible needs, scaling is a simple, yet potentially problematic method (if misused) to "fill-in" gaps in the current catalog of events. Still, in most cases, researchers would scale only a small set of three to seven records and typically only once, just to get an estimate of response in the area of interest.In the wake of the damage wrought by the 1994 Northridge earthquake
Northridge earthquake
The Northridge earthquake was a massive earthquake that occurred on January 17, 1994, at 04:31 Pacific Standard Time in Reseda, a neighborhood in the city of Los Angeles, California, lasting for about 10–20 seconds...
, the SAC/FEMA
Federal Emergency Management Agency
The Federal Emergency Management Agency is an agency of the United States Department of Homeland Security, initially created by Presidential Reorganization Plan No. 1 of 1978 and implemented by two Executive Orders...
project was launched to resolve the issue of poor performance of steel moment-resisting frames due to the fracturing beam-column connections. Within the creative environment of research cooperation, the idea of subjecting a structure to a wider range of scaling emerged. Initially, the method was called Dynamic Pushover and it was conceived as a way to estimate a proxy for the global collapse of the structure. It was later recognized that such a method would also enable checking for multiple limit-states, e.g. for life-safety, as is the standard for most seismic design methods, but also for lower and higher levels of intensity that represent different threat levels, such as immediate-occupancy and collapse-prevention. Thus, the idea for Incremental Dynamic Analysis was born, which was mainly adopted and later popularized by researchers at the John A. Blume Earthquake Research Center of Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
. This has now met with wider recognition in the earthquake research community and has spawned several different methods and concepts for estimating structural performance.
External links
- http://www.fema.gov/library/viewRecord.do?id=1538 SAC/FEMA 350 Report
- http://www.fema.gov/library/viewRecord.do?id=1751 SAC/FEMA 351 Report
- http://users.ntua.gr/divamva/publications.html IDA-related publications from D. Vamvatsikos at the National Technical University of AthensNational Technical University of AthensThe National Technical University of Athens , sometimes simply known as Athens Polytechnic, is among the oldest and most prestigious higher education institutions of Greece....