Irregularidades estructurales y daño en los edificios

Name: Irregularidades estructurales y daño en los edificios
Uploaded: 2020-11-01T01:46:12.000Z
Duration: 3 h 10 min 39 s
Description: Transmisión en vivo Irregularidades estructurales y daño en los edificios

Welcome and Introduction

Opening Remarks by Yasmín Escobar

Yasmín Escobar welcomes attendees on behalf of the Colegio de Ingenieros de Guatemala and the Consejo de Educación Continua y Actualización Educativa. She expresses pride in concluding October with various engineering training sessions.

Acknowledgment is given to both central and regional connections that have participated in ongoing training, highlighting national and international engagement through social media platforms like YouTube and Facebook.

Conference Topic Announcement

Presentation of Structural Irregularities

The conference topic is introduced: "Irregularidades Estructurales y Daños en los Edificios," presented by engineer Gustavo Orozco, who will lead the session on structural irregularities. Instructions for attendance registration are provided.

Dayana Girón, representing Quetzaltenango, is introduced as a member of the education council, emphasizing her role in supporting the event. She hands over to Gildardo Martínez for further introductions.

Introduction of Speakers

Presenting Keynote Speakers

Gildardo Martínez introduces himself as a civil engineer from Universidad Rafael Landívar and founder of Ingenieros GT, emphasizing their focus on structural engineering in Guatemala's seismic context. He highlights the importance of addressing structural irregularities due to earthquake risks.

Engineer Gustavo Orozco is introduced as the main speaker; he holds a master's degree in structural engineering and has extensive experience both locally and internationally in this field. His expertise includes research on structural performance related to wood and masonry materials.

Understanding Structural Vulnerabilities

Importance of Addressing Structural Issues

Gildardo emphasizes that Ingenieros GT specializes in structural areas crucial for safety against seismic threats prevalent in Guatemala, urging attention to often overlooked issues regarding building integrity during earthquakes.

Gustavo Orozco's Presentation Begins

Focus on Earthquake Risks

Gustavo thanks attendees for their participation and begins his presentation on "Irregularidades Estructurales." He stresses Guatemala's vulnerability due to tectonic plate interactions leading to frequent earthquakes, referencing significant past events such as those from 2012 and 1976 that had devastating impacts on infrastructure.

He outlines his academic background again while preparing to discuss how these irregularities relate directly to damage caused by seismic activity, setting up an important discussion about mitigating risks associated with building structures under such conditions.

Understanding Earthquake Vulnerability and Structural Engineering

The Importance of Awareness in Seismic Zones

Engineers must adapt to the realities of living in seismic zones, such as the Pacific Ring of Fire, which accounts for over 90% of global earthquakes.

Many people lack awareness about seismic risks; thus, sharing knowledge is crucial for public safety.

Historical Context: The 1976 Guatemala Earthquake

The 7.5 magnitude earthquake in Guatemala caused significant trauma, leading to economic losses and loss of life. It marked a turning point in structural engineering practices within the country.

Long-term social consequences persist from this disaster, including displacement and poverty cycles due to vulnerable structures collapsing during the quake.

Structural Failures and Lessons Learned

Notable examples include buildings like the Hotel de la Terminal that suffered irregular collapses, highlighting vulnerabilities in design and construction practices.

High-rise buildings experienced non-structural damage that rendered them uninhabitable for extended periods, raising concerns about emergency services' functionality post-earthquake.

Advancements in Structural Design

Modern structural design now emphasizes performance-based criteria rather than merely preventing collapse; it focuses on maintaining operational functionality after an earthquake.

The concept of "design by performance" considers both structural integrity and non-structural damage to ensure buildings remain usable after seismic events.

Regulatory Framework and Standards

In Guatemala, the Association of Structural Engineering and Seismic Engineering (Hi) plays a vital role in promoting research and establishing safety standards for construction practices.

Compliance with updated norms (NSE) is essential for engineers designing new structures to mitigate irregularities effectively across various building types.

Understanding Geometric Irregularities

Geometric irregularities are categorized into horizontal (H1A-H5) and vertical types; these can significantly impact a building's seismic performance if not addressed properly.

Torsional irregularities (H1A & H1B) can lead to uneven deformation during an earthquake, necessitating careful analysis according to established norms like AS7 10 used in North America.

Implications of Torsional Irregularities

Buildings with torsional irregularity may experience differential movement between points, affecting overall stability during seismic activity; understanding these dynamics is critical for effective design strategies.

Specific penalties outlined in regulations address how to manage these irregularities through dynamic analysis methods such as modal spectral analysis to ensure compliance with safety standards.( t =853 s )

Analysis of Structural Irregularities in Buildings

Dynamic Analysis and Torsional Irregularities

The discussion begins with a clarification that dynamic analysis refers to spectral modal analysis, which is the most commonly used methodology in Guatemala for structural analysis.

According to restrictions 1.83 a and b, when torsional irregularities are present, there is a need to increase design forces by 25% for connections between diaphragms and vertical elements or collectors.

This increase is crucial because torsional irregularities can lead to the diaphragm separating from lateral resistance elements (beams, columns, walls), compromising the building's integrity.

Corner Irregularities and Their Implications

The second type of irregularity mentioned is corner irregularities, particularly in L-shaped buildings where stress concentration occurs at corners.

An example illustrates how damage can concentrate at critical points during an earthquake due to these corner irregularities.

To mitigate risks associated with such irregularities, seismic joints are often recommended; they help create two modules instead of one to reduce damage.

Design Considerations for Discontinuity

It’s advised that many modules incorporate seismic joints and use materials like aluminum sheets to connect both modules effectively.

The penalties outlined in sections 18.2a and 186 require dynamic modal spectral analysis and three-dimensional modeling for buildings taller than 9 meters; simplified analyses are insufficient.

Diaphragm Discontinuity Issues

Another common issue discussed is continuous diaphragms where discontinuity arises from architectural choices like mezzanines or double-height spaces on the first level.

Specific percentages define what constitutes a discontinuous diaphragm according to standards; if this occurs, similar penalties apply as previously mentioned.

Importance of Rigid Diaphragm Design

Emphasis is placed on ensuring proper attention towards diaphragm design; increasing design forces by 25% for connections remains critical.

In Guatemala, it has been noted that designing diaphragms isn't standard practice; however, recent updates in version 716 have adopted rigid diaphragm design methodologies.

Critical Lateral Offset Irregularities

The discussion transitions into lateral offset irregularities (H4), highlighting their critical nature where lateral resistance elements do not align vertically across levels.

This misalignment creates challenges in force transfer from upper elements downwards through lower resistance components.

Conclusion on Structural Integrity

A visual representation shows how misaligned walls can lead to significant structural issues; thus careful consideration must be given during design phases.

Structural Vulnerabilities in Corner Houses

Analysis of Structural Elements

The discussion begins with a typical case of a corner house where lateral resistance elements are placed at the perimeter, creating critical points during transitions.

A specific concern is raised regarding the size of a corner column, which may not meet minimum standards (30x30 cm), making it vulnerable to collapse during seismic events.

Reference is made to past issues observed in San Marcos, highlighting the importance of adhering to building codes to prevent structural failures.

Importance of Overstrength Factor

The Omega factor represents overstrength and is crucial for elements transferring loads that exceed design limits; it helps maintain elastic behavior and prevents plastic hinges from forming.

Engineers are advised to avoid irregularities that could lead to catastrophic failures, emphasizing prudence over merely applying the Omega factor.

Recommendations on Irregularities

While some engineers might push boundaries using the overstrength factor (up to three times design seismic forces), caution is recommended due to potential damage concentration at critical points.

The NC3 code section 194 discusses how this factor varies based on structural systems like box or frame systems, necessitating thorough 3D modeling and dynamic analysis.

Horizontal and Vertical Irregularities

Horizontal Irregularities

An example of horizontal irregularity includes non-parallel lateral resistance systems, such as triangular buildings; these require careful analysis per reference section 185 for structures above 9 meters.

Vertical Irregularities Overview

Seven types of vertical irregularities are identified, ranging from flexible floors to stepped geometries and weak floor conditions.

Flexible Floors Concerns

Flexible floors can create extreme cases where upper levels are confined by stiffer elements below, distorting original design behavior—common in Guatemalan construction practices.

Effects of Floor Flexibility

A flexible floor tends to concentrate deformation rather than distribute it across levels. This can lead to increased moments in structural elements due to the P-delta effect, risking collapse under stress.

Examples and Implications

Visual examples illustrate how rigid upper levels restrict normal displacement in ductile frame systems while open lower levels (often designed for parking spaces) exacerbate flexibility issues.

Special Attention Required

Engineers must pay special attention to flexible or weak floors as they frequently occur in practice; calculations should consider variations in rigidity between different floor levels.

Understanding Structural Rigidity and Seismic Design

Evaluating Rigidity Levels

The model assesses the rigidity of each level in a building, applying penalties as necessary. Tools like SAP can provide rigidity percentages, particularly measured at the center of mass.

Displacement at the center of mass, influenced by base shear, helps determine rigidity per level. Comparing lower floors to upper ones reveals potential irregularities in the building's structure.

Seismic Protection Levels and Irregularities

For seismic protection levels D and E, certain irregularities (like B1B) are prohibited. Other irregularities incur penalties based on factors such as R values.

A redundancy factor is applied to account for additional seismic loads; for example, a 1.10 multiplier may be used depending on the seismic protection level being designed.

Importance of Checking Rigidity

It’s crucial to check rigidities at the center of mass when dealing with weak floor irregularities and apply extra design factors while considering effects like P-delta.

An example illustrates how buildings with braced systems distribute lateral forces evenly across floors compared to those with rigid systems that concentrate forces at lower levels.

Addressing Vertical Mass Concentration

Irregularity B2 refers to vertical mass concentration where heavy equipment on upper floors affects dynamic behavior; this must be factored into design considerations.

Regulations state if seismic weight on a floor exceeds 150% of adjacent floors' weights, lighter roofing must be considered due to irregularity B2 implications.

Geometric Considerations in Design

Irregularity B3 involves stepped vertical geometry where different levels have varying dimensions; this can lead to stress concentrations requiring additional design factors.

If horizontal dimensions exceed 130% compared to adjacent levels, it indicates an irregularity that necessitates further structural reinforcement.

Managing Design Complexity

Accumulating various irregularity factors can complicate designs leading to potentially unbuildable or excessively costly structures.

Engineers must communicate these complexities effectively with architects since not all designs are feasible without significant cost implications.

Recommendations for Seismic Areas

In seismically active regions like Guatemala, minimizing structural irregularities is essential for safety and cost-effectiveness in building design.

Irregularidades Estructurales y su Impacto en el Diseño

Irregularidades Verticales B4 y B5

Se discute la irregularidad B4 y B5, que se relaciona con discontinuidades en el plano vertical y condiciones de potencial debilidad. Estas irregularidades son similares a las horizontales (H4), pero desde una perspectiva vertical.

Se menciona un desfase crítico en los muros que transfieren carga a partes rígidas del edificio, lo cual es esencial para aplicar correctamente el factor Omega r.

Aplicación del Factor Omega R

El factor Omega r puede ser hasta tres veces la fuerza sísmica de diseño, lo que plantea preocupaciones sobre la economía del diseño estructural.

Para mantener elementos de transferencia dentro de un rango elástico, se sugiere un límite de 300% sobre la fuerza de diseño, lo cual no es práctico ni recomendable.

Irregularidades Verticales B6 y B7

Las irregularidades verticales incluyen el piso débil (B6) y el piso extremadamente débil (B7). La diferencia entre ambos radica en la resistencia de los elementos estructurales.

Un piso suave permite deformaciones sin daño significativo, mientras que un piso débil presenta déficit en resistencia, predisponiendo al colapso estructural.

Diseño Estructural Ideal

Se describe cómo un sistema estructural ideal debería tener una forma piramidal donde los niveles inferiores sean más resistentes. Invertir esta estructura aumenta vulnerabilidades críticas.

Ejemplos muestran pisos superiores rígidos con cerramientos inadecuados que pueden llevar a fallas alarmantes si no se corrigen adecuadamente.

Penalizaciones por Irregularidades

Las irregularidades B6 y B7 no están permitidas bajo normas sísmicas específicas como las aplicadas en Guatemala. Esto lleva a acumulaciones de penalizaciones que afectan negativamente al diseño final.

Es crucial evaluar si el porcentaje del corte basal es desproporcionado; si es así, se recomienda colaborar con arquitectos para mejorar la vulnerabilidad del edificio.

Aprendizajes Históricos Tras Terremotos

Las irregularidades no fueron consideradas seriamente hasta después de varios terremotos significativos; esto ha llevado a mejoras continuas basadas en lecciones aprendidas tras cada evento sísmico importante.

Ejemplos históricos como el sismo Northridge (1994), Kobe (1995), e Izmit (1999), han resaltado fenómenos críticos como la concentración de masa y su impacto negativo durante sismos.

Evaluación Post-Sismo 2012

En 2012, Guatemala experimentó un sismo significativo que afectó estructuras de mampostería. Este evento subraya la importancia continua de evaluar daños relacionados con las irregularidades discutidas anteriormente.

Impact of Earthquakes on Building Structures in Guatemala

Overview of Damage from the 2012 Earthquake

The earthquake primarily affected regions such as San Pedro San Marcos and Totonicapán, resulting in at least 50 fatalities and numerous building collapses, particularly adobe structures that had been standing for decades.

Personal accounts highlight the traumatic experience of witnessing destruction in San Marcos, emphasizing the need for engineers to learn from these events to prevent future tragedies.

Structural Changes Post-Earthquake

The 2012 earthquake prompted a shift in construction practices; it revealed vulnerabilities in adobe structures and led to an increased adoption of more resilient masonry systems.

Statistical trends indicate a significant decline in adobe buildings post-1976 earthquake, with masonry becoming the predominant construction method due to its improved resistance.

Current Construction Practices

By 2012, approximately 38% of buildings in San Marcos were still made of adobe, which contributed to high collapse rates during seismic events due to their inadequate lateral resistance.

In contrast, modern masonry has become the standard for new constructions across Guatemala, featuring reinforced concrete elements that enhance structural integrity.

Performance and Vulnerabilities of Masonry Structures

While masonry is widely used and generally performs well globally, issues arise when irregularities are present in design or height; this can compromise structural stability under load.

Specific vulnerabilities include poor ductility leading to shear failures at lower levels during earthquakes. This was evident in many buildings during the 2012 quake where insufficient wall density contributed to structural failure.

Observations on Structural Failures

Analysis reveals that common failure modes included diagonal cracking (shear failure), particularly noticeable at first levels where commercial spaces lacked adequate wall support.

The presence of weak walls relative to upper floors exacerbated vulnerability during seismic activity, highlighting critical design flaws that need addressing for future safety improvements.

Building Irregularities and Structural Failures

Overview of Structural Issues

The transcript discusses a building collapse due to irregularities, highlighting the complete failure of the first level, likely caused by inadequate structural support in lower elements.

A rigid upper structure failed to transfer lateral load effectively to the foundation, leading to a catastrophic collapse of the first level that compromised the entire building.

Case Study: San Pedro Fire Station

The San Pedro fire station, inaugurated in 2012, exemplifies poor design with significant irregularities; it features a soft story at the bottom and a rigid upper section which created vulnerabilities.

Building codes categorize structures based on their importance; essential buildings must withstand seismic events without failure due to their critical role in public safety.

Importance Levels in Building Design

Ordinary buildings (e.g., warehouses) have lower seismic protection requirements compared to important buildings (e.g., convention centers), which accommodate larger crowds.

Essential facilities like hospitals must remain operational post-earthquake as they serve critical functions during emergencies; failures can lead to severe consequences for public health.

Consequences of Structural Failures

The fire station's near-collapse illustrates systemic issues where inadequate design leads to potential loss of life and property; public investment is jeopardized by such failures.

Observations reveal excessive lateral deformation due to rigidity differences between levels, resulting in shear cracks at 45 degrees—common indicators of structural distress.

Patterns of Damage and Regulatory Gaps

Many recent constructions exhibit similar crack patterns indicating widespread design flaws; regulatory measures are insufficiently enforced, allowing dangerous practices.

The lack of balance between wall density above and below contributes significantly to structural instability; there is no specific criterion guiding necessary wall densities for safety.

Economic Impact Assessment

Visual evidence shows extensive damage from collapses affecting large investments and endangering lives; this highlights urgent needs for stricter regulations on construction practices.

Statistics indicate that residential buildings accounted for 43% of earthquake damage in San Marcos, emphasizing vulnerability within densely populated areas.

Impact of Earthquakes on Local Economy and Infrastructure

Economic Consequences Post-Earthquake

The earthquake left many local businesses inoperable, significantly impacting the local economy. Many establishments were unable to reopen for an extended period due to damage.

There is a lack of statistical data in Guatemala regarding the impact of seismic events on society, which complicates understanding and addressing these issues.

Need for Improved Data Collection

Emphasizes the importance of collecting more statistics and data from each seismic event to better prepare for future earthquakes. This information can enhance response strategies and infrastructure resilience.

During research for a master's thesis, it was noted that there was minimal information available about structural evaluations post-earthquake, highlighting a significant gap in municipal record-keeping practices.

Structural Vulnerability Assessment

Research Focus on Masonry Behavior

The speaker dedicated their thesis to studying non-linear behavior in masonry structures within Guatemala, aiming to provide insights into vulnerability assessments following seismic events.

A table presented during the discussion illustrates how different levels of building height correlate with compression capacity in masonry blocks commonly used in the region. It indicates that buildings exceeding three stories may exceed safe compression limits.

Material Quality Concerns

Discusses the poor quality of masonry blocks produced by unregulated factories, which often have low compressive strength (e.g., porous blocks). These materials are still widely used despite their inadequacy for construction purposes.

Highlights that measuring wall density is crucial; walls must be greater than 1 meter thick to avoid shear failure risks during seismic activity. The contribution of each wall's area relative to its height is essential for assessing overall structural integrity.

Damage Probability Analysis

Critical Damage Scenarios

An example is provided where a three-story building constructed with low-density materials could face up to 100% damage at ground level during an earthquake due to combined compression and shear failures. Conversely, using higher-quality materials could reduce expected damage significantly (to around 42%).

Recommendations for New Structures

It is recommended that new structures maintain a wall density factor of at least 2% as per guidelines from organizations like Build Change, although this standard isn't yet formally regulated in Guatemala's building codes.

Performance-Based Design Methodology

Understanding Structural Behavior Over Time

Introduces performance-based design methodology focusing on how buildings behave under stress over time; initially linear behavior transitions into non-linear as damage accumulates leading towards potential collapse scenarios if not properly managed.

Seismic Demand vs Capacity Curves

Discusses methodologies such as ASCE 41 and FEMA 440 developed in the U.S., which help assess building performance against seismic demands by comparing capacity curves with actual demand levels experienced during earthquakes.

Analysis of Vulnerability in Masonry Structures

Understanding Vulnerabilities in Non-Confining Buildings

The discussion highlights that buildings lacking confinement exhibit the highest vulnerability, necessitating appropriate retrofitting to ensure operational safety.

Research by Maximiliano Astrosa is mentioned, focusing on the deformation capacity of confined masonry walls across various performance levels.

Importance of Experimental Research

Emphasizes the need for investment in research to assess performance levels through lateral push tests on typical masonry walls, measuring deformation and applied force.

Advocates for bridging theoretical knowledge with laboratory research to keep pace with advancements made by other countries like Chile and Mexico.

Development of Fragility Curves

Structural engineers in Guatemala aim to generate fragility curves specific to lateral resistance systems, particularly for masonry structures.

Discusses the significance of understanding damage probability related to lateral deformation and how it applies to various structural systems.

Gaps in Knowledge Regarding Probabilistic Behavior

Highlights a lack of understanding regarding the probabilistic behavior of older structural systems, such as poorly confined frames from previous decades.

References a 2007 study focused on creating a backbone model for nonlinear behavior in masonry based on data from Latin America.

Application of Experimental Data

The importance of applying experimental findings to develop equations that describe typical wall behavior is emphasized, aiding in structural improvement efforts.

Stresses that without this information, it becomes challenging to enhance existing structures effectively.

Advances in Seismic Design Methodologies

Introduces seismic design based on displacements for low-rise masonry buildings, referencing work done at UNAM involving scaled models and SAP 2000 simulations.

Describes how equivalent frame methods are used within software simulations to analyze plastic hinge formation under shear stress conditions.

Observations from Structural Failures

Notes that initial levels often sustain the most damage during seismic events, corroborated by historical examples such as those observed in San Marcos.

Transitioning Design Approaches

Calls for a shift from force-based design methodologies towards displacement-based approaches as they better reflect actual damage mechanisms during seismic activity.

Reiterates that understanding elastic displacement is crucial for assessing potential damage within masonry systems.

Vulnerability in Structural Engineering: Insights and Solutions

Understanding Structural Vulnerability

The concept of structural vulnerability extends beyond buildings to various systems, including frames. Irregularities must be considered across all structural types.

Historical wooden buildings in San Francisco exhibit weak floor irregularities due to their design from the 19th and early 20th centuries, impacting their seismic resilience.

The 1989 Loma Prieta earthquake highlighted vulnerabilities in these structures, particularly at lower levels designed for parking rather than habitation.

Research on Building Reinforcement

Current research focuses on assessing and reinforcing vulnerable buildings in San Francisco to prevent future collapses due to weak floors.

Torsional irregularities can lead to critical failure points; ensuring the center of mass aligns with the center of rigidity is crucial for stability.

Design Considerations for Steel Frames

Steel frame designs often face challenges when lower levels lack wall density, leading to increased risk during seismic events.

A proposed reinforcement system by Dr. Barbara Simpson aims to address soft story behavior by redistributing damage across higher levels.

Effective Structural Systems

Implementing strong back systems can enhance the performance of steel frames by distributing forces more evenly throughout the structure.

Proper modeling techniques like pushover analysis help identify where damage concentrates, allowing for better design strategies that utilize full frame capacity.

Addressing Soft Story Issues

Vulnerabilities are not limited to one type of structural system; they vary based on material properties and joint configurations.

Q&A Session Highlights

Participants were encouraged to ask questions regarding structural engineering practices and research findings presented during the session.

Accessing academic resources such as Gustavo Orosco's thesis is facilitated through platforms like ResearchGate for further reading on these topics.

Design Challenges and Solutions

The discussion included how lateral loads impact design requirements, emphasizing diaphragm integrity during seismic events.

Strategies exist to limit soft story conditions through penalties or nonlinear analyses that assess specific building vulnerabilities.