13.1 Analysis of structural failures in past earthquakes
3 min read•july 25, 2024
Earthquakes can wreak havoc on structures, causing devastating failures. Understanding why buildings collapse helps engineers design safer structures. From soft stories to , various factors contribute to structural damage during seismic events.
Historical failures reveal common vulnerabilities in building design and construction. Poor detailing, inadequate materials, and all play a role. By studying past earthquakes, engineers can improve codes and practices to create more resilient structures for the future.
Historical Earthquake Structural Failures
Causes of earthquake structural failures
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- shape structural response
- measures maximum force exerted on structures
- Duration of shaking influences (Mexico City 1985)
- affects with building periods
- Structural vulnerabilities increase collapse risk
- occurs in buildings with weak first floors (1994 Northridge)
- Pounding between adjacent buildings causes localized damage
- lead to twisting motions and stress concentration
- Failure modes determine collapse mechanisms
- in columns results from inadequate transverse reinforcement
- occur due to poor detailing and confinement
- stem from soil or excessive settlement
- compound structural damage
- Liquefaction causes loss of soil bearing capacity (1964 Niigata)
- trigger foundation failures and building collapses
- directly damages structures crossing fault lines
Design and construction in failures
- Design deficiencies compromise seismic performance
- Inadequate lead to excessive drift
- Poor detailing of reinforcement results in
- Lack of in structural elements limits energy dissipation
- weaken structural integrity
- Poor concrete mixing and placement reduces strength and durability
- Inadequate reinforcement anchorage leads to bond failures
- Improper material substitutions compromise design assumptions
- influence failure mechanisms
- increases vulnerability to shear failures
- limits plastic deformation capacity
- over time reduces load-bearing capacity
Soil-Structure Interaction and Failure Patterns
Soil-structure interaction effects
- Site effects amplify seismic forces on structures
- Amplification of ground motion occurs in
- enhances shaking at specific frequencies
- Foundation systems influence overall structural behavior
- Shallow vs affect load transfer mechanisms
- includes kinematic and inertial effects
- modifies input motion
- Foundation input motion differs from free-field ground motion
- Base slab averaging reduces high-frequency components
- alters dynamic properties
- occurs due to soil flexibility
- Increased damping results from soil-foundation energy dissipation
- Soil-foundation-structure system response involves complex mechanisms
- influence superstructure motion
- dissipates energy through wave propagation
Patterns in structural failures
- Building typology vulnerabilities persist across earthquakes
- exhibit poor
- lack adequate confinement
- face connection failures
- Failure mechanisms recurring in multiple events reveal
- Soft story collapses in multi-story buildings (1995 Kobe)
- Out-of-plane failures in unreinforced masonry walls (2011 Christchurch)
- Shear failures in short columns due to infill walls
- Geographical and shape damage patterns
- on ground motion amplification (Mexico City)
- cause pulse-like motions
- Evolution of building codes reflects lessons learned
- Lessons learned from past failures drive code improvements
- Implementation of enhances resilience
- Influence of local construction practices affects seismic performance
- Regional variations in building performance reflect local techniques
- Impact of informal construction methods increases vulnerability
Key Terms to Review (45)
Basin Effects: Basin effects refer to the amplification of seismic waves that occurs when they travel through sedimentary basins, leading to increased shaking intensity during an earthquake. These effects can significantly influence structural responses and damage patterns, as the geological characteristics of the basin can modify wave propagation, resulting in prolonged shaking and heightened ground motion in areas located within or near the basin.
Beam-column joint failures: Beam-column joint failures refer to the structural collapse or significant weakening of the connection points between beams and columns in a building, often observed during seismic events. These failures can lead to a loss of stability in structures, particularly in reinforced concrete frames, where the integrity of these joints is crucial for maintaining overall strength and load-bearing capacity. The analysis of past earthquakes highlights how deficiencies in design and construction practices can exacerbate these types of failures.
Brittle failures: Brittle failures occur when materials break suddenly without significant plastic deformation, typically under stress. This kind of failure is characterized by a rapid crack propagation, leading to an unexpected and catastrophic collapse of a structure, often seen in concrete and steel structures during seismic events.
Brittle reinforcement steel: Brittle reinforcement steel refers to a type of steel that exhibits little to no plastic deformation before failure, resulting in sudden and catastrophic breakage under stress. This behavior is particularly problematic in the context of seismic design, as it can lead to significant structural failures during earthquakes, where ductility and energy absorption are crucial for maintaining integrity under dynamic loads.
Construction quality issues: Construction quality issues refer to deficiencies or problems in the materials, workmanship, or overall execution of construction projects that can compromise the integrity and safety of structures. These issues are critical as they can lead to structural failures, particularly during seismic events, where the performance of a building is tested against extreme forces. Understanding these issues helps in identifying patterns from past structural failures in earthquakes and developing strategies for improving construction practices.
Cumulative damage: Cumulative damage refers to the progressive deterioration of a structure due to repeated loading cycles, particularly in the context of dynamic forces such as earthquakes. This type of damage accumulates over time, as each loading event inflicts small amounts of harm that add up, ultimately compromising the structural integrity and performance. Understanding cumulative damage is vital for evaluating how structures respond during seismic events and for developing effective retrofitting strategies.
Deep foundations: Deep foundations are specialized structures that transfer building loads deep into the ground, reaching a more stable layer of soil or rock. They are essential in areas where surface soils are weak or prone to movement, ensuring that buildings remain stable during events like earthquakes. These foundations include piles and drilled shafts, and their design considers factors like soil properties and potential ground movement.
Degradation of materials: Degradation of materials refers to the process by which materials lose their properties and performance due to various factors, such as environmental exposure, mechanical stress, or chemical reactions. This degradation can significantly weaken structural integrity, making it a crucial factor in understanding failures in structures during earthquakes. Over time, materials like concrete, steel, and wood can deteriorate, leading to a loss of strength, stiffness, and durability, which can ultimately result in catastrophic structural failures.
Ductility: Ductility is the ability of a material to deform plastically before fracture, allowing structures to absorb and dissipate energy during seismic events. This property is crucial for maintaining structural integrity and safety, as it enables buildings to withstand the forces generated by earthquakes without collapsing instantly.
Foundation failures: Foundation failures occur when the structural support of a building or other construction loses its ability to carry loads due to soil movement, erosion, or other factors. These failures can lead to severe damage or collapse of structures, often highlighted during seismic events or extreme weather conditions, emphasizing the importance of proper foundation design and site analysis.
Frequency content: Frequency content refers to the range of frequencies present in a signal or a waveform, often analyzed to understand how different frequencies contribute to the overall behavior of a system. In the context of seismic activity and structural response, frequency content is crucial for assessing how vibrations affect structures and their interactions with soil. Understanding frequency content helps engineers design safer buildings that can withstand earthquakes by predicting how structures will respond to varying seismic waves.
Geographical influences: Geographical influences refer to the effects that physical location, terrain, and environmental conditions have on structures and their performance during seismic events. These factors include the type of soil, proximity to fault lines, elevation, and urban development patterns, all of which can affect how buildings respond to earthquakes. Understanding these influences is crucial for analyzing structural failures that occurred in past earthquakes and can inform better design practices for future construction.
Geological influences: Geological influences refer to the various natural factors related to the Earth's geology that can affect the behavior and response of structures during an earthquake. These influences include the type of soil, rock formations, fault lines, and the geological history of an area, all of which can significantly impact how seismic waves propagate and how buildings perform under stress.
Ground Motion Characteristics: Ground motion characteristics refer to the specific features and behaviors of seismic waves generated during an earthquake, influencing how structures respond to shaking. These characteristics include parameters such as amplitude, frequency content, duration, and the directional properties of ground motion, which collectively affect structural integrity and design requirements. Understanding these features is critical for analyzing structural failures observed in past earthquakes, as they reveal how various buildings reacted to different seismic events.
Inertial interaction: Inertial interaction refers to the forces and movements that occur between a structure and the seismic waves generated during an earthquake. This interaction is crucial in determining how a building responds to ground motion, as it dictates how forces are transmitted through the structure and how it deforms or fails under seismic loads. Understanding inertial interaction is essential for analyzing structural failures, evaluating the performance of seismically designed structures, and ensuring the effectiveness of isolation techniques that mitigate earthquake impacts.
Kinematic Interaction: Kinematic interaction refers to the influence that the movement and deformation of one structure can have on another nearby structure during seismic events. This phenomenon can lead to additional forces and displacements in structures that are not directly subjected to ground motion, which can exacerbate damage and affect overall performance during earthquakes. Understanding kinematic interaction is crucial for analyzing past structural failures, assessing the effectiveness of seismic designs, and considering isolation strategies in engineering.
Landslides: Landslides are geological phenomena that involve the downward movement of rock, soil, and debris on sloped terrain. They can occur due to various triggers such as heavy rainfall, earthquakes, volcanic activity, and human activities, resulting in significant structural damage and posing risks to life and property. Understanding landslides is crucial when analyzing the impact of earthquakes, as they often exacerbate the effects of seismic events on the surrounding environment and infrastructure.
Lateral force-resisting systems: Lateral force-resisting systems are structural elements designed to resist horizontal forces, such as those generated by wind or earthquakes. These systems play a crucial role in maintaining the stability and integrity of buildings during seismic events, ensuring they can withstand lateral loads without excessive deformation or failure. The effectiveness of these systems is often guided by specific design codes that vary internationally, influencing how structures are engineered to endure seismic forces.
Liquefaction: Liquefaction is a phenomenon where saturated soil substantially loses its strength and stiffness in response to applied stress, typically during an earthquake. This process can lead to ground failure, causing structures to settle, tilt, or even collapse, as the soil behaves more like a liquid than a solid. Understanding liquefaction is crucial for assessing seismic risks and for designing structures that can withstand such ground behavior.
Low-strength concrete: Low-strength concrete is a type of concrete that has a compressive strength lower than standard concrete mixes, typically defined as having a compressive strength of less than 17 MPa (2,500 psi). This material is often used in non-structural applications where high strength is not critical, but its performance during seismic events can be questionable, leading to structural failures in past earthquakes.
Material Properties: Material properties refer to the physical and mechanical characteristics of materials that define their behavior under various conditions, especially when subjected to forces like seismic activity. These properties influence how materials respond to stress, strain, and deformation, which is crucial when assessing the stability and safety of structures during earthquakes. Understanding these properties is essential for engineers to design buildings and infrastructure that can withstand seismic waves and mitigate structural failures.
Near-fault directivity effects: Near-fault directivity effects refer to the phenomena where ground motion characteristics are influenced by the relative location of an earthquake source to a site, particularly when that site is near the fault line. This effect can lead to intensified ground shaking and modified waveforms, significantly affecting the structural response and behavior of buildings during seismic events. The understanding of these effects is crucial for analyzing how structures failed in past earthquakes, as they can lead to unexpected damage patterns that might not be predicted by standard seismic analysis.
Non-ductile concrete frame buildings: Non-ductile concrete frame buildings are structures that utilize reinforced concrete frames but lack the necessary design features to absorb and dissipate energy during seismic events. These buildings tend to have rigid connections and insufficient reinforcement, making them vulnerable to collapse under the stress of an earthquake. This vulnerability has been observed in past seismic events, highlighting the need for improved design standards.
Out-of-plane stability: Out-of-plane stability refers to the ability of structural elements, such as walls and frames, to resist lateral forces acting perpendicular to their plane. This concept is crucial in understanding how buildings respond to seismic events, as the out-of-plane forces can lead to catastrophic failures if not properly addressed in design and analysis. The analysis of structural failures during past earthquakes has shown that inadequate out-of-plane stability often results in significant damage or collapse.
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.
Period Elongation: Period elongation refers to the increase in the natural vibration period of a structure when it is subjected to dynamic loads, such as seismic activity. This phenomenon is significant because it can affect how structures respond during earthquakes, influencing their displacement and acceleration. Understanding period elongation is crucial for designing effective seismic isolators and ensuring that structures maintain their integrity during seismic events.
Pile foundation behavior: Pile foundation behavior refers to how pile foundations perform under various loads, particularly during seismic events. These foundations transfer the load of a structure to deeper, more stable soil layers, enhancing stability and reducing settlement. Understanding their behavior is crucial for evaluating structural integrity during earthquakes, as inadequately designed piles can lead to significant structural failures.
Pounding effects: Pounding effects refer to the impact that occurs when two or more adjacent structures, typically during an earthquake, collide due to their differing dynamic responses. These interactions can lead to severe structural damage, as the energy from the shaking causes one building to push against another, compromising their integrity. The assessment of pounding effects is crucial for understanding structural failures in previous earthquakes and improving design practices to mitigate such issues.
Precast concrete structures: Precast concrete structures are components made by casting concrete in a reusable mold or form and then curing it in a controlled environment. This method allows for higher quality control, faster construction times, and reduced labor costs compared to traditional on-site pouring methods. They are commonly used in various applications including buildings, bridges, and other infrastructural elements, making them a significant aspect of modern construction techniques.
Radiation damping: Radiation damping refers to the phenomenon where the energy from a vibrating or oscillating system is lost to the surrounding medium, typically through the emission of waves or vibrations. This process plays a crucial role in understanding how structures respond to dynamic loads, particularly during earthquakes, by influencing the overall behavior and stability of soil-structure systems, assessing structural failures, and determining the effectiveness of isolation techniques.
Resonance: Resonance is the phenomenon that occurs when a system or object vibrates at its natural frequency due to external forces, resulting in amplified oscillations. In the context of seismic events, buildings and structures can experience resonance when seismic waves match their natural frequencies, leading to potentially catastrophic results. Understanding resonance is crucial in various engineering applications, especially in mitigating structural damage during earthquakes and ensuring safety in design.
Rocking and sliding of foundations: Rocking and sliding of foundations refer to the two primary modes of instability that can occur in structures during seismic events. Rocking involves the tilting or rotational motion of a foundation about a pivot point, while sliding refers to the lateral movement of a foundation across its base. Both phenomena can significantly affect a building's stability and integrity during earthquakes, leading to structural failures that have been observed in past seismic events.
Seismic design provisions: Seismic design provisions are regulations and guidelines that dictate how structures should be designed and constructed to withstand the forces generated by earthquakes. These provisions are based on research and analysis of past seismic events, aiming to improve the resilience of buildings and infrastructure against seismic hazards. They encompass a range of strategies, including material specifications, structural configurations, and performance criteria that engineers must follow to ensure safety and minimize damage during an earthquake.
Seismic hazards: Seismic hazards refer to the potential risks and impacts associated with earthquakes, including ground shaking, surface rupture, landslides, liquefaction, and tsunamis. Understanding seismic hazards is crucial for assessing the vulnerability of structures and populations in earthquake-prone regions. By analyzing these hazards, engineers and planners can develop effective strategies to mitigate damage and enhance safety during seismic events.
Shallow foundations: Shallow foundations are structural elements that transfer building loads to the ground at a depth that is relatively close to the surface, typically less than 3 meters. They are commonly used for lighter structures and on sites where soil conditions are favorable, providing stability while minimizing excavation costs. Their design and performance can greatly influence structural integrity, especially in areas prone to seismic activity.
Shear failure: Shear failure refers to the failure of a structural element due to shear stress exceeding the material's shear strength. This type of failure is often critical in the context of structural integrity during seismic events, where lateral forces can cause significant displacement and stress in materials. Understanding shear failure is essential for analyzing past structural failures and for implementing effective design strategies, particularly in nonlinear static analysis methods like pushover analysis.
Site effects: Site effects refer to the influence that local geological and soil conditions have on the intensity and characteristics of ground shaking during an earthquake. These effects can lead to variations in ground motion, which significantly affect the performance of structures in different locations. Understanding site effects is crucial for accurately predicting ground motion and analyzing how structures might fail in past earthquakes.
Soft soil deposits: Soft soil deposits are geological formations consisting of loose, unconsolidated materials like clay, silt, or organic matter that have low shear strength and can easily deform under stress. These types of soils are often found near bodies of water and are significant because their mechanical properties can greatly influence how structures behave during seismic events. Understanding soft soil deposits is crucial for predicting potential structural failures in earthquakes as they amplify ground motion and can lead to increased settlement and lateral spreading.
Soft story collapse: Soft story collapse refers to the failure of a building's structure due to a weaker lower floor, often designed with large openings such as garages or storefronts, which compromises its ability to support the upper stories during seismic events. This structural vulnerability can lead to catastrophic results, particularly in earthquakes where the lateral forces exerted on the building exceed its capacity to withstand them. The lack of stiffness in the soft story can cause a disproportionate transfer of loads, resulting in a severe risk of collapse.
Soil liquefaction: Soil liquefaction is a phenomenon where saturated soil substantially loses strength and stiffness in response to applied stress, often caused by seismic shaking or excessive loading. During an earthquake, the shaking can increase pore water pressure within the soil, reducing the effective stress and causing the ground to behave like a liquid. This can lead to significant structural failures, as buildings and other structures may settle unevenly or topple over.
Soil resonance: Soil resonance refers to the phenomenon where seismic waves interact with the soil's natural frequency, amplifying ground motion during an earthquake. This amplification can lead to significant structural damage, especially when the frequency of the seismic waves matches the natural frequency of the soil, causing buildings and other structures to experience excessive vibrations.
Surface fault rupture: Surface fault rupture is the visible expression of fault movement at the Earth's surface during an earthquake. It occurs when accumulated stress along a fault line is released, resulting in the ground breaking and displacing horizontally or vertically. This phenomenon can lead to significant damage to structures and infrastructure located near the fault line, highlighting the importance of understanding fault behavior in earthquake engineering.
Systemic issues: Systemic issues refer to deep-rooted problems within a system that affect its overall performance and stability. These issues often arise from interconnected factors and can lead to widespread failures or inefficiencies, particularly in complex environments like construction and engineering where various components must work together seamlessly.
Torsional irregularities: Torsional irregularities refer to an imbalance in the distribution of mass or stiffness in a building, which can cause it to twist or rotate unevenly during seismic activity. This phenomenon often leads to increased vulnerability of structures during earthquakes, as it can amplify the effects of ground motion and lead to significant structural damage. Understanding these irregularities is essential for improving the design and resilience of buildings against seismic forces.
Unreinforced masonry structures: Unreinforced masonry structures are buildings constructed from brick, stone, or concrete blocks without the inclusion of steel reinforcement bars to enhance tensile strength. These structures are particularly vulnerable during seismic events, as their inability to flex or absorb energy leads to increased risk of failure under earthquake loading conditions.