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Earthquake Engineering: Theory and Implementation with the 2015 International Building Code, Third Edition - Google Books



Earthquake Engineering: Theory and Implementation with the 2015 International Building Code, Third Edition




Earthquakes are natural phenomena that can cause devastating impacts on human lives, properties, infrastructures, economies, and environments. To protect society from earthquakes, it is essential to understand how they affect buildings and structures, and how to design and construct them to resist seismic forces. This is the domain of earthquake engineering, an interdisciplinary branch of engineering that deals with the analysis, design, construction, maintenance, retrofitting, and risk management of structures subject to earthquakes.




Earthquake Engineering: Theory And Implementation With The 2015 International Building Code, Third E



In this article, we will introduce the basic concepts, principles, methods, techniques, tools, standards, and best practices of earthquake engineering theory and implementation. We will also discuss how the 2015 International Building Code (IBC), one of the most widely adopted building codes in the world, incorporates earthquake engineering provisions to ensure the safety and performance of structures in seismic regions. By reading this article, you will gain a comprehensive overview of earthquake engineering as a scientific field and a practical discipline.


Introduction




Earthquake engineering is a scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels. Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of structural engineering, geotechnical engineering, mechanical engineering, chemical engineering, applied physics, etc. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering, nuclear engineering, and from the social sciences, especially sociology, political science, economics, and finance.


The main objectives of earthquake engineering are:



  • 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. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.



The main challenges of earthquake engineering are:



  • Earthquakes are complex and unpredictable phenomena that involve multiple physical processes and uncertainties.



  • Earthquakes can generate different types and levels of seismic loading that can affect structures and geo-structures in various ways.



  • Structures and geo-structures have diverse geometries, materials, properties, functions, and interactions that can influence their seismic response and performance.



  • Earthquake engineering requires a multidisciplinary approach that integrates knowledge, data, models, methods, tools, standards, and best practices from different fields of engineering and science.



The 2015 International Building Code (IBC) is a model building code developed by the International Code Council (ICC) that provides minimum requirements for the design and construction of buildings and structures. It is intended to safeguard public health, safety, and welfare by regulating structural, fire, plumbing, mechanical, electrical, energy, accessibility, and other aspects of building performance. The IBC is adopted by many states and jurisdictions in the United States and other countries as the basis for their local building codes. The IBC is updated every three years to reflect the latest advances in technology, research, and practice.


The 2015 IBC addresses earthquake engineering in several chapters and sections that cover the following topics:



  • Seismic design categories and maps that classify the seismic hazard level of different regions based on the expected ground motion.



  • Seismic design criteria and procedures that specify the minimum requirements for the analysis, design, detailing, construction, inspection, testing, and quality assurance of structures subject to seismic loading.



  • Seismic design provisions for specific types of structures and materials, such as concrete, steel, wood, masonry, precast concrete, composite construction, etc.



  • Seismic design requirements for nonstructural components and systems, such as architectural elements, mechanical equipment, electrical fixtures, plumbing fixtures, etc.



  • Seismic design guidelines for special structures and facilities, such as hospitals, schools, essential facilities, high-rise buildings, etc.



Earthquake Engineering Theory




The theory of earthquake engineering is based on the fundamental concepts of mechanics, dynamics, materials science, soil mechanics, and structural analysis. It aims to understand how earthquakes generate seismic loading on structures and geo-structures, how they respond to seismic loading in terms of deformation, stress, strain, damage, and failure, and how they can be designed to achieve a desired level of seismic performance in terms of safety, serviceability, functionality, and resilience. The theory of earthquake engineering can be divided into three main topics: seismic loading, seismic performance, and seismic design.


Seismic Loading




Seismic loading means application of an earthquake-generated excitation on a structure (or geo-structure). It happens at contact surfaces of a structure either with the ground, with adjacent structures, or with gravity waves from tsunami. The loading that is expected at a given location on the Earth's surface is estimated by engineering seismology. It is related to the seismic hazard of the location.


There are two main types of seismic loading: ground motion and ground failure. Ground motion is the vibration or shaking of the ground caused by seismic waves that propagate from the earthquake source. Ground motion can be characterized by its amplitude, frequency, duration, direction, and spatial variation. Ground motion can cause inertial forces on structures that depend on their mass, stiffness, damping, and natural frequency. Ground failure is the deformation or rupture of the ground caused by seismic waves that exceed its strength or stability. Ground failure can include liquefaction, landslides, settlements, faulting, and surface fault rupture. Ground failure can cause kinematic forces on structures that depend on their geometry, foundation type, and soil-structure interaction.


The effects of seismic loading on structures and geo-structures can be classified into three categories: global effects, local effects, and secondary effects. Global effects are the overall response of the structure or geo-structure as a whole to seismic loading. They include displacement, rotation, Seismic Design




Seismic design is the process of creating structures that can withstand seismic loading without significant loss of functionality or collapse. Seismic design aims to achieve a desired level of seismic performance that meets the expectations and requirements of the owners, users, regulators, and society. Seismic design is based on the principles of mechanics, dynamics, materials science, structural analysis, and engineering judgment.


There are three main methods of seismic design: force-based design, displacement-based design, and performance-based design.



  • Force-based design (FBD) is the traditional method of seismic design that uses forces as the main design parameters. FBD assumes that structures can resist seismic loading by developing adequate strength and ductility. FBD involves two steps: first, determining the design seismic forces based on the seismic hazard level, the structural characteristics, and the importance factor; second, checking the strength and detailing of structural elements and connections to ensure they can resist the design seismic forces without exceeding their capacity.



  • Displacement-based design (DBD) is an alternative method of seismic design that uses displacements as the main design parameters. DBD assumes that structures can resist seismic loading by controlling their deformations and displacements. DBD involves two steps: first, determining the target displacement based on the seismic hazard level, the structural characteristics, and the performance objective; second, designing structural elements and connections to ensure they can accommodate the target displacement without exceeding their deformation limits.



  • Performance-based design (PBD) is an advanced method of seismic design that uses performance as the main design parameter. PBD assumes that structures can resist seismic loading by achieving a specified level of performance that reflects the expectations and requirements of different stakeholders. PBD involves three steps: first, defining performance objectives and criteria for different levels of seismic intensity and different structural components; second, conducting nonlinear dynamic analysis to evaluate the expected performance of the structure under different earthquake scenarios; third, designing or modifying structural elements and connections to ensure they can satisfy the performance objectives and criteria.



The 2015 IBC adopts a modified version of FBD as its main method of seismic design for structures. However, it also allows the use of DBD or PBD for special cases where FBD may not be adequate or appropriate. For example, DBD or PBD can be used for structures with irregularities, complex geometries, innovative materials, or high-performance demands. The 2015 IBC also provides some guidance and references for applying DBD or PBD in seismic design.


Earthquake Engineering Implementation




The implementation of earthquake engineering is based on the application of the theory of earthquake engineering to practical problems and projects. It involves the use of various techniques, tools, standards, and best practices to analyze, design, construct, maintain, retrofit, and manage structures subject to earthquakes. The implementation of earthquake engineering can be divided into three main topics: seismic analysis, seismic retrofitting, and seismic risk management.


Seismic Analysis




Seismic analysis is the process of evaluating the response of structures and geo-structures to seismic loading using various methods and techniques. Seismic analysis can be used for different purposes, such as seismic design, seismic assessment, seismic retrofitting, seismic monitoring, and seismic risk management. Seismic analysis can provide useful information about the dynamic characteristics, deformation modes, stress distribution, damage patterns, and failure mechanisms of structures and geo-structures under earthquake excitation.


There are two main types of seismic analysis: linear and nonlinear. Linear seismic analysis assumes that the structure or geo-structure behaves elastically under seismic loading, meaning that there is no permanent deformation or damage. Nonlinear seismic analysis accounts for the inelastic behavior of the structure or geo-structure under seismic loading, meaning that there is some permanent deformation or damage. Nonlinear seismic analysis can capture more realistic and accurate response of structures and geo-structures, especially for large earthquakes that exceed their elastic capacity.


There are also two main techniques of seismic analysis: static and dynamic. Static seismic analysis applies a set of equivalent static forces to the structure or geo-structure to represent the effect of earthquake ground motion. Static seismic analysis is simpler and faster than dynamic seismic analysis, but it may not capture the true dynamic response of the structure or geo-structure. Dynamic seismic analysis applies a time-varying ground motion to the structure or geo-structure and calculates its response at each time step. Dynamic seismic analysis can capture the true dynamic response of the structure or geo-structure, but it is more complex and time-consuming than static seismic analysis.


There are several methods of seismic analysis that can be used depending on the type and technique of analysis. Some of the common methods are:



  • Equivalent static analysis: This method uses a set of equivalent static forces based on a percentage of the structure or geo-structure weight and a lateral force distribution factor. This method is simple and conservative, but it may not capture higher modes of vibration and irregularities.



  • Response spectrum analysis: This method uses a response spectrum curve that represents the maximum response of a single-degree-of-freedom system with different natural frequencies under a given ground motion. This method can capture higher modes of vibration and irregularities, but it may not capture nonlinear behavior and phase information.



  • Time history analysis: This method uses a time history record that represents the actual or synthetic ground motion at a given location. This method can capture nonlinear behavior and phase information, but it may require a large number of time steps and ground motion records.



  • Pushover analysis: This method uses a series of incremental static forces that increase until the structure or geo-structure reaches its ultimate capacity. This method can capture nonlinear behavior and damage accumulation, but it may not capture dynamic effects and multiple load patterns.



The 2015 IBC requires dynamic seismic analysis for structures that are classified as Seismic Design Category D, E, or F, or that have irregularities in plan or elevation. The 2015 IBC also allows static seismic analysis for structures that are classified as Seismic Design Category A, B, or C, or that have regularity in plan and elevation. The 2015 IBC provides some guidance and references for applying different methods of seismic analysis in accordance with ASCE 7-10.


Seismic Retrofitting




Seismic retrofitting is the process of modifying existing structures and geo-structures to improve their seismic performance and reduce their seismic risk. Seismic retrofitting is usually done for structures and geo-structures that are either damaged by previous earthquakes, vulnerable to future earthquakes, or important for post-earthquake recovery and functionality. Seismic retrofitting can extend the service life, enhance the safety and functionality, and increase the value and resilience of structures and geo-structures.


There are several techniques available for seismic retrofitting. Some of the common techniques are:



  • Concrete jacketing: This technique involves adding a layer of reinforced concrete around the existing structural elements (such as columns, beams, walls) to increase their cross-sectional area, strength, stiffness, and ductility. Concrete jacketing can also improve the bond and confinement of existing reinforcement.



  • Steel jacketing: This technique involves wrapping steel plates or angles around the existing structural elements (such as columns, beams, walls) to increase their cross-sectional area, strength, stiffness, and ductility. Steel jacketing can also provide additional reinforcement and confinement.



  • Fiber-reinforced polymer (FRP) wrapping: This technique involves wrapping FRP sheets or strips around the existing structural elements (such as columns, beams, walls) to increase their strength, stiffness, and ductility. FRP wrapping can also provide additional reinforcement and confinement.



  • Base isolation: This technique involves installing isolators (such as rubber bearings, sliding devices, friction pendulums) between the structure or geo-structure and its foundation to reduce the transmission of seismic forces from the ground to the superstructure. Base isolation can also reduce the deformation and damage of the structure or geo-structure.



  • Supplemental damping: This technique involves installing dampers (such as viscous dampers, friction dampers, metallic dampers) within or between the structural elements (such as beams, columns, braces) to dissipate seismic energy and reduce the response of the structure or geo-structure. Supplemental damping can also reduce the deformation and damage of the structure or geo-structure.



The 2015 IBC encourages seismic retrofitting for existing structures and geo-structures that do not meet the current seismic design requirements or that have a substantial seismic risk. The 2015 IBC provides some guidance and references for applying different techniques of seismic retrofitting in accordance with ASCE 41-13.


Seismic Risk Management




Seismic risk management is the process of identifying, assessing, reducing, and controlling the seismic risk of structures and geo-structures. Seismic risk management aims to minimize the expected losses and maximize the expected benefits from earthquakes. Seismic risk management involves the participation and collaboration of various stakeholders, such as owners, users, engineers, planners, regulators, insurers, and society.


There are several methods of seismic risk management that can be used depending on the type and scope of the problem. Some of the common methods are:



  • Seismic risk assessment: This method involves estimating the seismic hazard, vulnerability, and consequences for a given structure or geo-structure, or a group of structures or geo-structures. Seismic risk assessment can provide useful information about the probability and magnitude of potential losses and benefits from earthquakes.



  • Seismic risk mitigation: This method involves implementing various measures to reduce the seismic risk of structures and geo-structures. Seismic risk mitigation can include structural and nonstructural retrofitting, relocation, demolition, land use planning, building codes enforcement, insurance policies, etc.



  • Seismic risk optimization: This method involves finding the optimal combination of seismic risk mitigation measures that maximizes the net benefit or minimizes the net cost of seismic risk management. Seismic risk optimization can consider various criteria and constraints, such as technical feasibility, economic efficiency, social acceptability, environmental sustainability, etc.



The 2015 IBC promotes seismic risk management for existing and new structures and geo-structures that are exposed to significant seismic hazard or that have a high value or importance for society. The 2015 IBC provides some guidance and references for applying different methods of seismic risk management in accordance with FEMA P-58.


Conclusion




In this article, we have introduced the basic concepts, principles, methods, techniques, tools, standards, and best practices of earthquake engineering theory and implementation. We have also discussed how the 2015 International Building Code (IBC) incorporates earthquake engineering provisions to ensure the safety and performance of structures in seismic regions.


We have learned that earthquake engineering is an interdisciplinary field that deals with the analysis, design, construction, maintenance, retrofitting, and risk management of structures subject to earthquakes. We have also learned that earthquake engineering can be divided into three main topics: seismic loading, seismic performanc


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