8.3 Incremental dynamic analysis
3 min read•july 25, 2024
(IDA) is a powerful tool for assessing structural performance under earthquakes. It involves scaling ground motions and analyzing structural response across intensities, providing insights into behavior from elastic to collapse.
plot against , revealing key structural characteristics. This method enables , helping engineers understand building performance and make informed design decisions.
Fundamentals of Incremental Dynamic Analysis
Process of incremental dynamic analysis
Top images from around the web for Process of incremental dynamic analysis
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
1 of 2
Top images from around the web for Process of incremental dynamic analysis
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
Frontiers | Seismic Assessment of Non-conforming Infilled RC Buildings Using IDA Procedures View original
Is this image relevant?
1 of 2
- Select suite of representing seismic hazard at site
- Scale ground motions incrementally amplifying intensity
- Perform for each scaled record capturing structural behavior
- Record (drift, acceleration, base shear)
- Plot IDA curves graphing intensity measure vs. engineering demand parameter
- Evaluate structural performance across earthquake intensities from low to high
- Determine identifying point of dynamic instability
- Assess variability in structural response due to ground motion characteristics
- Provide data for probabilistic seismic performance assessment ()
Interpretation of IDA curves
- Components: Horizontal axis - Engineering Demand Parameter (EDP), Vertical axis - Intensity Measure (IM)
- shows linear relationship between IM and EDP (small deformations)
- marks transition from elastic to inelastic behavior (onset of damage)
- indicates increase in stiffness after yielding (strain hardening)
- reveals decrease in stiffness due to structural damage (strength degradation)
- signifies rapid increase in EDP for small increases in IM (dynamic instability)
- Quantify structural capacity across performance levels (, , )
- Identify critical intensity levels leading to specific damage states (, yielding, )
- Provide input for fragility curve development relating probability of exceedance to IM
- Enable probabilistic assessment of structural performance under various hazard levels
Application of IDA for seismic assessment
- Create structural model incorporating nonlinear material and geometric properties
- Select appropriate intensity measures (, )
- Choose relevant engineering demand parameters (, floor acceleration)
- Perform using scaled ground motions
- Generate IDA curves for multiple ground motions capturing record-to-record variability
- Determine representing central tendency of structural response
- Calculate dispersion of structural responses quantifying uncertainty
- Estimate probability of exceeding specific damage states (minor, moderate, severe)
- Evaluate assessing safety against collapse
- Combine IDA results with hazard curves for site-specific risk assessment
- Perform relating EDP to annual exceedance probability
- Develop for different limit states (serviceability, ultimate)
Advantages vs limitations of IDA
- Advantages:
- Provides comprehensive view of structural behavior across intensity levels
- Accounts for record-to-record variability capturing ground motion uncertainty
- Enables probabilistic performance assessment for risk-informed decision making
- Useful for calibrating simplified analysis methods ()
- Helps identify structural weaknesses and collapse mechanisms guiding retrofit strategies
- Limitations:
- Computationally intensive and time-consuming especially for complex structures
- Sensitive to ground motion selection and scaling affecting reliability of results
- May not capture cumulative damage effects from aftershocks or long-duration shaking
- Assumes first-mode dominated response potentially underestimating higher mode effects
- Difficulty in selecting appropriate intensity measures for some structures (base-isolated)
- Considerations:
- Balance between accuracy and computational effort through strategic sampling
- Need for careful interpretation of results considering uncertainties
- Importance of complementing IDA with other assessment methods (pushover analysis)
- Potential for standardization in building codes and guidelines for consistent application
Key Terms to Review (29)
Buckling: Buckling is a structural instability that occurs when a component, such as a column or beam, deforms under compressive loads, leading to a sudden change in shape. This phenomenon is critical in the context of structural engineering, as it can significantly affect the load-bearing capacity of structures and their overall safety during seismic events.
Collapse capacity: Collapse capacity refers to the maximum level of demand that a structure can withstand before experiencing a complete loss of structural integrity, leading to collapse. It is an essential concept in assessing a structure's ability to resist seismic forces, helping engineers determine how much energy a building can absorb during an earthquake before it fails. This concept plays a vital role in evaluating building performance and resilience against seismic events.
Collapse margin ratio: Collapse margin ratio is a measure used in structural engineering to evaluate the safety of a building against progressive collapse due to unexpected loads or events. It represents the ratio of the building's reserve strength to the load that could potentially cause failure. This term is crucial for understanding how structures respond during extreme loading conditions, such as earthquakes, and it helps engineers design buildings that can withstand such events without catastrophic failure.
Collapse point: The collapse point refers to the threshold at which a structure loses its ability to carry loads, resulting in a failure or complete collapse. This point is critical in understanding how structures behave under extreme conditions, particularly during seismic events. Knowing the collapse point helps engineers design buildings that can withstand such forces without catastrophic failure.
Collapse prevention: Collapse prevention refers to the design strategies and measures implemented in structures to ensure that they can withstand seismic forces without experiencing total failure during an earthquake. This involves creating a level of safety that allows a building to survive seismic events while minimizing the risk of collapse, thereby protecting occupants and preserving property.
Cracking: Cracking refers to the formation of cracks in materials, particularly concrete and other structural elements, due to stress, strain, or environmental factors. In the context of earthquake engineering, understanding cracking is essential for assessing the structural integrity and performance of buildings during seismic events, as it can lead to significant damage and compromise safety.
Elastic region: The elastic region refers to the portion of a material's stress-strain curve where the material deforms elastically, meaning that it will return to its original shape once the applied stress is removed. This region is crucial for understanding how structures behave under loading, as it indicates that the material can absorb energy without sustaining permanent damage.
Engineering Demand Parameters: Engineering Demand Parameters (EDPs) are quantitative measures that describe the expected response of a structure subjected to seismic events. They include metrics such as maximum displacement, interstory drift, and acceleration, which are critical in assessing the performance of structures during earthquakes. Understanding EDPs allows engineers to evaluate how a structure will behave under various ground motion scenarios and informs design decisions aimed at improving resilience against seismic hazards.
Fragility Curves: Fragility curves are graphical representations that show the probability of reaching or exceeding a specific level of damage to a structure given a certain level of seismic demand. These curves help in understanding how different structures respond to earthquakes, making them essential for assessing the vulnerability of buildings and infrastructure. By linking seismic hazard data with potential structural responses, fragility curves play a critical role in risk assessment, damage prediction, and informing retrofitting strategies.
Fragility Functions: Fragility functions are mathematical expressions that describe the probability of a structure or system reaching or exceeding a certain level of damage given specific earthquake ground motion intensities. These functions help engineers evaluate the performance of structures under seismic loads by quantifying uncertainty and establishing relationships between ground motion parameters and structural response. Understanding fragility functions is crucial for risk assessment and decision-making in earthquake engineering.
Ground Motion Records: Ground motion records are measurements of the movement of the ground during an earthquake, typically captured by seismographs. These records provide essential data for understanding how seismic waves propagate through the Earth and how structures respond to these forces. Analyzing these records helps in assessing the potential impact of future earthquakes on buildings and infrastructure.
Hardening: Hardening refers to the process of strengthening materials, particularly in the context of structural engineering, to improve their resistance to deformation and failure under stress. This concept is essential in evaluating the behavior of structures during seismic events, as it affects how a structure responds to dynamic loading and impacts its overall performance during earthquakes.
IDA Curves: IDA curves, or Incremental Dynamic Analysis curves, are graphical representations used in seismic risk assessment to illustrate how the response of a structure varies with increasing levels of ground motion intensity. These curves are essential for understanding the performance of structures under different seismic demands and are derived from the results of incremental dynamic analyses, which systematically increase seismic loading until the structural response reaches a predetermined limit state. IDA curves provide valuable insight into the capacity and vulnerability of structures, helping engineers design safer buildings.
Immediate Occupancy: Immediate occupancy refers to a performance objective in seismic design that ensures a structure can be occupied right after an earthquake with minimal repairs and without significant damage. This concept focuses on the safety and functionality of buildings, allowing them to be used for their intended purpose immediately after a seismic event, which is crucial for emergency response and community resilience.
Incremental dynamic analysis: Incremental dynamic analysis (IDA) is a procedure used in earthquake engineering to assess the performance of structures under varying levels of seismic demand by applying a series of increasing ground motion intensities. This method enables engineers to understand how a structure responds to different earthquake scenarios, providing detailed insights into its potential performance and failure mechanisms. The incremental nature of this analysis helps in establishing a clear relationship between seismic intensity and structural response, which is crucial for designing resilient buildings that can withstand seismic events.
Intensity Measures: Intensity measures are numerical values that quantify the severity of ground shaking during an earthquake. They are used to assess the impact of seismic events on structures and inform design decisions in earthquake engineering. Intensity measures help engineers evaluate how different buildings will respond to seismic forces, ensuring that structures are designed to withstand the specific conditions of potential earthquakes.
Inter-story drift: Inter-story drift is the relative displacement between two adjacent floors of a building during seismic events, which is a crucial factor in assessing the performance and safety of structures. This term is essential for understanding how buildings respond to earthquakes, particularly in terms of lateral stability and the potential for structural damage. Monitoring inter-story drift helps engineers evaluate if a building can withstand seismic forces without suffering excessive deformations or failure.
Life safety: Life safety refers to the measures and design strategies implemented to protect occupants during an emergency, particularly in the event of an earthquake. It focuses on ensuring that structures can withstand seismic forces while allowing for safe evacuation and minimizing the risk of injury or loss of life. This concept is crucial for establishing performance objectives and design criteria for buildings, as well as influencing the development of innovative materials and structural systems.
Median IDA Curve: The Median Incremental Dynamic Analysis (IDA) Curve is a graphical representation that illustrates the relationship between the maximum response of a structure and the corresponding intensity of ground motion during an incremental dynamic analysis. This curve serves as a crucial tool for assessing seismic performance, providing insights into how structures might behave under varying levels of earthquake loading and aiding in decision-making for design and retrofitting.
Nonlinear dynamic analysis: Nonlinear dynamic analysis refers to the evaluation of structural response under time-varying loads, particularly seismic forces, considering the inelastic behavior of materials and structural components. This approach captures the complex interactions between a structure and seismic waves, allowing engineers to assess performance beyond elastic limits. It connects to various essential concepts, such as the incremental dynamic analysis method, which systematically evaluates a structure's response over increasing ground motion intensities, and detailing requirements that ensure ductile behavior during extreme loading events.
Nonlinear time history analyses: Nonlinear time history analyses are a computational method used to assess the response of structures under dynamic loads, like earthquakes, by considering material and geometric nonlinearities. This approach allows engineers to simulate how a structure will behave throughout a seismic event, capturing complex interactions between loads and structural responses that simpler linear models might miss.
Peak Ground Acceleration: Peak Ground Acceleration (PGA) is a critical measure in earthquake engineering that represents the maximum acceleration experienced by the ground during an earthquake, typically expressed in units of g (gravity). It serves as a key parameter in assessing seismic hazards and designing structures to withstand ground motions, influencing various engineering practices and safety measures.
Probabilistic seismic assessment: Probabilistic seismic assessment is a methodology used to evaluate the performance and safety of structures under seismic loading by considering the uncertainty in earthquake ground motion and structural response. This approach employs statistical methods to estimate the likelihood of different levels of seismic hazard, allowing for a more comprehensive understanding of potential risks and performance outcomes. It integrates multiple factors, such as site characteristics, building design, and fault behavior, to provide a probabilistic measure of structural vulnerability during earthquakes.
Probabilistic Seismic Demand Analysis: Probabilistic seismic demand analysis is a method used to assess the expected seismic response of structures by considering uncertainties in ground motion and structural behavior. This approach incorporates probabilistic techniques to estimate the likelihood of various levels of demand on structures during earthquakes, which allows engineers to evaluate performance and design more resilient systems. It essentially provides a statistical framework for understanding how different factors affect a structure's response to seismic events.
Pushover analysis: Pushover analysis is a nonlinear static analysis method used to evaluate the seismic performance of structures by applying a gradual lateral load until failure occurs. This technique helps engineers understand how a structure will respond to seismic forces, identifying potential weaknesses and assessing ductility, which is essential for effective seismic design.
Softening: Softening refers to the reduction in stiffness or strength of a material, typically observed in structural systems under increasing loads or deformations. This phenomenon can lead to changes in the behavior of structures during seismic events, affecting how they absorb and dissipate energy, ultimately influencing their performance and safety.
Spectral Acceleration: Spectral acceleration is a key parameter in earthquake engineering that quantifies the maximum response of a structure to ground motion at a specific frequency. It serves as an important measure to assess how different structures will react during seismic events, linking ground motion characteristics to structural performance and safety.
Structural response parameters: Structural response parameters are quantitative measures that describe how a structure reacts to applied forces, especially during dynamic events like earthquakes. These parameters provide critical insights into the behavior of structures under seismic loading, including factors such as displacement, acceleration, and velocity. Understanding these parameters helps engineers assess performance and design buildings that can withstand seismic forces effectively.
Yielding point: The yielding point is the stress level at which a material begins to deform plastically and does not return to its original shape once the applied load is removed. This concept is crucial in understanding how materials behave under stress, especially in structural engineering and design, as it helps determine the limits of safety for structures under dynamic loads such as earthquakes.