Contenido

El comportamiento ante terremotos define la capacidad de una estructura para mantener sus funciones principales, como su seguridad y serviciabilidad&action=edit&redlink=1 "Capacidad de servicio (estructura) (aún no redactado)"), en y después de una exposición sísmica determinada. Normalmente, una estructura se considera segura si no pone en peligro la vida y el bienestar de las personas que se encuentran en ella o a su alrededor al derrumbarse parcial o totalmente. Una estructura puede considerarse útil si es capaz de cumplir las funciones operativas para las que fue diseñada.

Los conceptos básicos de la ingeniería sísmica, implementados en los principales códigos de construcción, asumen que un edificio debe sobrevivir a un terremoto muy severo y poco frecuente sufriendo daños significativos pero sin derrumbarse globalmente.[3]​ Por otro lado, debe permanecer operativo para eventos sísmicos más frecuentes pero menos severos.

Seismic performance evaluation

Engineers need to know the quantified level of actual or anticipated seismic behavior associated with direct damage to an individual building subjected to a specified ground shaking.

This evaluation can be carried out experimentally or analytically.

Experimental evaluations are expensive tests that are typically performed by placing a (scale) model of the structure on a shaking table that simulates ground shaking and observing its behavior.[4]​ These types of experiments were first performed over a century ago.[5]​ Only recently has it become possible to perform 1:1 scale tests on complete structures.

Due to the expensive nature of these tests, they tend to be used primarily to understand the seismic behavior of structures, validate models, and verify analysis methods. Thus, once properly validated, computational models and numerical procedures tend to bear most of the burden for the evaluation of the seismic behavior of structures.

Structural seismic analysis is a powerful seismic engineering tool that uses detailed modeling of the structure together with structural analysis methods to obtain a better understanding of the seismic behavior of building structures and non-built structures. The technique as a formal concept is a relatively recent development.

In general, seismic structural analysis is based on structural dynamics methods.[6]​ For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method, which also contributed to the concept of building code proposed today.[7]​.

However, such methods are only good for linear elastic systems, being largely incapable of modeling structural behavior when damage appears (i.e., nonlinearity). Numerical step-by-step integration proved to be a more effective analysis method for multi-degree-of-freedom structural systems with significant nonlinearity under a transient process&action=edit&redlink=1

Basically, numerical analysis is carried out in order to evaluate the seismic behavior of buildings. Behavioral evaluations are generally carried out using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate nonlinear modeling of structural components, such as beams, columns, beam-column joints, shear walls, etc. Thus, experimental results play an important role in determining the modeling parameters of individual components, especially those that are subject to significant nonlinear deformations. The individual components are then assembled to create a complete non-linear model of the structure. The models thus created are analyzed to evaluate the behavior of the buildings.

The capabilities of the structural analysis software are an important consideration in the above process as they constrain the possible component models, the available analysis methods and, most importantly, the numerical robustness. The latter becomes an important consideration for structures that venture into the nonlinear range and approach global or local collapse, as the numerical solution becomes increasingly unstable and therefore elusive. There are several commercial finite element analysis software programs, such as CSI-SAP2000 and CSI-PERFORM-3D, MTR/SASSI, Scia Engineer-ECtools, ABAQUS") and Ansys, which can be used to evaluate the seismic performance of buildings. In addition, there are research-based finite element analysis platforms, such as OpenSees"), MASTODON, which is based on MOOSE Framework&action=edit&redlink=1 "MOOSE (software) (not yet written)"), RUAUMOKO and the former DRAIN-2D/3D, several of which are now open source.

El diseño sismo resistente se basa en procedimientos, principios y criterios de ingeniería autorizados destinados a diseñar o readaptar estructuras sujetas a exposición sísmica. Esos criterios sólo son coherentes con el estado contemporáneo de los conocimientos sobre estructuras de ingeniería sísmica.[9]​ Por lo tanto, un diseño de edificio que siga exactamente las normas del código sísmico no garantiza la seguridad contra el colapso o daños graves.[10]​.

El precio de un mal diseño sísmico puede ser enorme. No obstante, el diseño sísmico siempre ha sido un proceso de ensayo y error tanto si se basaba en leyes físicas como en el conocimiento empírico del comportamiento estructural de diferentes formas y materiales.

Para poder llevar a cabo diseño de estructuras antisísmicas o evaluación sísmica de proyectos de ingeniería civil nuevos y existentes, un ingeniero debe, normalmente, aprobar un examen sobre Principios Sísmicos [11]​ que, en el Estado de California, incluyen:.

• - Datos sísmicos y criterios de diseño sísmico.

• - Características sísmicas de los sistemas de ingeniería.

• - Fuerzas sísmicas.

• - Procedimientos de análisis sísmico.

• - Detallado sísmico y control de calidad de la construcción.

Para construir sistemas estructurales complejos,[12]​ el diseño sísmico utiliza en gran medida el mismo número relativamente pequeño de elementos estructurales básicos (por no hablar de los dispositivos de control de vibraciones) que cualquier proyecto de diseño no sísmico.

Normalmente, de acuerdo con los códigos de construcción, las estructuras se diseñan para "resistir" el mayor terremoto de cierta probabilidad que es probable que se produzca en su ubicación. Esto significa que la pérdida de vidas humanas debe minimizarse evitando el colapso de los edificios.

El diseño sísmico se lleva a cabo mediante la comprensión de los posibles modos de falla") de una estructura y dotando a la estructura de la resistencia, rigidez, ductilidad adecuadas, y configuración de las estructuras[13]​ para garantizar que esos modos no se produzcan.

Seismic design requirements

Seismic design requirements depend on the type of structure, the location of the project and its authorities, which stipulate the applicable seismic design codes and criteria.[3]​ For example, the California Department of Transportation's requirements called The Seismic Design Criteria (SDC) and intended for the design of new bridges in California[14]​ incorporate an innovative approach based on seismic behavior.

The most significant feature of the SDC design philosophy is the shift from a force-based seismic demand assessment to a displacement-based demand and capacity assessment. Thus, the new displacement approach adopted is based on comparing the elastic displacement demand with the inelastic displacement capacity of the primary structural components, while guaranteeing a minimum level of inelastic capacity at all possible plastic articulation points.

In addition to the designed structure itself, seismic design requirements may include ground stabilization beneath the structure: sometimes, strongly shaken ground breaks, causing the structure sitting on it to collapse.[16]​

The following topics should be of primary interest: liquefaction; dynamic lateral earth pressures in retaining walls; seismic stability of slopes; earthquake-induced settlements.[17]​.

Nuclear Facilities must not jeopardize their safety in the event of earthquakes or other hostile external events. Therefore, their seismic design is based on much stricter criteria than those applied to non-nuclear facilities. "and have caused many other governments to reevaluate their nuclear programs"). Doubts have also been raised about the seismic evaluation and design of some other plants, including the Fessenheim Nuclear Power Plant) in France.

Failure modes

Failure mode is how an earthquake-induced failure is observed. In general, it describes how the failure occurs. Although costly and time-consuming, learning from each actual seismic failure remains a routine recipe for advancing seismic design methods. Below are some typical failure modes generated by earthquakes.

Lack of reinforcement") coupled with poor mortar&action=edit&redlink=1 "Mortar (masonry) (not yet drafted)") and inadequate ties between roof and wall can cause substantial damage to an unreinforced masonry building"). The most common damage caused by earthquakes is severe cracks or leaning walls. Damage that can occur between walls and ceiling or floor diaphragms is also dangerous. Separation between the frame and the walls can compromise the vertical support of the roof and floor systems.

Soft floor effect"). The absence of adequate rigidity at the floor level caused damage to this structure. Close examination of the image reveals that the rough board siding, once covered by a brick veneer"), has been completely removed from the stud wall. Only the rigidity of the upper floor, combined with the support on the two hidden sides of continuous walls, not penetrated with large doors as on the street sides, is preventing the total collapse of the structure.

Soil liquefaction'. In cases where the soil consists of loose granular materials deposited with a tendency to develop excessive hydrostatic pore water pressure of sufficient and compact magnitude, the liquefaction of such saturated loose deposits may result in non-uniform settling&action=edit&redlink=1 "Consolidation (soil) (not yet drafted)") and tilting of structures. This caused significant damage to thousands of buildings in Niigata, Japan, during the 1964 earthquake.[19]​.

Rockfall. A landslide is a geological phenomenon that includes a wide range of ground movements, including rockfalls. Normally, gravity is the main driving force for a landslide to occur, although in this case there was another contributing factor that affected the stability of the original slope: the landslide required a seismic trigger before being released.

Blows against the adjacent building. This is a photograph of the collapse of the five-story tower at San Jose Seminary, Los Altos, California, resulting in one fatality. During the Loma Prieta earthquake, the tower struck the adjacent building that was vibrating independently behind it. The possibility of slamming depends on the lateral displacements of both buildings, which must be accurately estimated and accounted for.

In the Northridge Earthquake), the Kaiser Permanente concrete frame office building had joints completely destroyed, revealing inadequate confining steel, which caused the second floor to collapse. In the transverse direction, the composite shear walls, consisting of two layers of brick and one layer of shotcrete supporting the lateral load, detached due to and failed.

In Spain, the areas of greatest seismic risk are found in Eastern Andalusia, Murcia and the Valencian Community, and in the Canary Islands because they are volcanic islands. For the construction of buildings in these regions, compliance with the NCSE-02 earthquake-resistant construction standard is mandatory.

• - Seismic isolation.

• - Medvedev-Sponheuer-Karnik scale.

• - Mercalli seismological scale.

• - Prestressed Structure.

• - Richter seismological scale.

• - Computer simulation.

• - Seismic vulnerability.

• - Seismic fitness (en).

• - UPM Seismic Engineering Research Group.

• - Engineering and Seismic Risk Group of the University of Alicante.

Contenido

El comportamiento ante terremotos define la capacidad de una estructura para mantener sus funciones principales, como su seguridad y serviciabilidad&action=edit&redlink=1 "Capacidad de servicio (estructura) (aún no redactado)"), en y después de una exposición sísmica determinada. Normalmente, una estructura se considera segura si no pone en peligro la vida y el bienestar de las personas que se encuentran en ella o a su alrededor al derrumbarse parcial o totalmente. Una estructura puede considerarse útil si es capaz de cumplir las funciones operativas para las que fue diseñada.

Los conceptos básicos de la ingeniería sísmica, implementados en los principales códigos de construcción, asumen que un edificio debe sobrevivir a un terremoto muy severo y poco frecuente sufriendo daños significativos pero sin derrumbarse globalmente.[3]​ Por otro lado, debe permanecer operativo para eventos sísmicos más frecuentes pero menos severos.

Seismic performance evaluation

Engineers need to know the quantified level of actual or anticipated seismic behavior associated with direct damage to an individual building subjected to a specified ground shaking.

This evaluation can be carried out experimentally or analytically.

Experimental evaluations are expensive tests that are typically performed by placing a (scale) model of the structure on a shaking table that simulates ground shaking and observing its behavior.[4]​ These types of experiments were first performed over a century ago.[5]​ Only recently has it become possible to perform 1:1 scale tests on complete structures.

Due to the expensive nature of these tests, they tend to be used primarily to understand the seismic behavior of structures, validate models, and verify analysis methods. Thus, once properly validated, computational models and numerical procedures tend to bear most of the burden for the evaluation of the seismic behavior of structures.

Structural seismic analysis is a powerful seismic engineering tool that uses detailed modeling of the structure together with structural analysis methods to obtain a better understanding of the seismic behavior of building structures and non-built structures. The technique as a formal concept is a relatively recent development.

In general, seismic structural analysis is based on structural dynamics methods.[6]​ For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method, which also contributed to the concept of building code proposed today.[7]​.

However, such methods are only good for linear elastic systems, being largely incapable of modeling structural behavior when damage appears (i.e., nonlinearity). Numerical step-by-step integration proved to be a more effective analysis method for multi-degree-of-freedom structural systems with significant nonlinearity under a transient process&action=edit&redlink=1

Basically, numerical analysis is carried out in order to evaluate the seismic behavior of buildings. Behavioral evaluations are generally carried out using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate nonlinear modeling of structural components, such as beams, columns, beam-column joints, shear walls, etc. Thus, experimental results play an important role in determining the modeling parameters of individual components, especially those that are subject to significant nonlinear deformations. The individual components are then assembled to create a complete non-linear model of the structure. The models thus created are analyzed to evaluate the behavior of the buildings.

The capabilities of the structural analysis software are an important consideration in the above process as they constrain the possible component models, the available analysis methods and, most importantly, the numerical robustness. The latter becomes an important consideration for structures that venture into the nonlinear range and approach global or local collapse, as the numerical solution becomes increasingly unstable and therefore elusive. There are several commercial finite element analysis software programs, such as CSI-SAP2000 and CSI-PERFORM-3D, MTR/SASSI, Scia Engineer-ECtools, ABAQUS") and Ansys, which can be used to evaluate the seismic performance of buildings. In addition, there are research-based finite element analysis platforms, such as OpenSees"), MASTODON, which is based on MOOSE Framework&action=edit&redlink=1 "MOOSE (software) (not yet written)"), RUAUMOKO and the former DRAIN-2D/3D, several of which are now open source.

El diseño sismo resistente se basa en procedimientos, principios y criterios de ingeniería autorizados destinados a diseñar o readaptar estructuras sujetas a exposición sísmica. Esos criterios sólo son coherentes con el estado contemporáneo de los conocimientos sobre estructuras de ingeniería sísmica.[9]​ Por lo tanto, un diseño de edificio que siga exactamente las normas del código sísmico no garantiza la seguridad contra el colapso o daños graves.[10]​.

El precio de un mal diseño sísmico puede ser enorme. No obstante, el diseño sísmico siempre ha sido un proceso de ensayo y error tanto si se basaba en leyes físicas como en el conocimiento empírico del comportamiento estructural de diferentes formas y materiales.

Para poder llevar a cabo diseño de estructuras antisísmicas o evaluación sísmica de proyectos de ingeniería civil nuevos y existentes, un ingeniero debe, normalmente, aprobar un examen sobre Principios Sísmicos [11]​ que, en el Estado de California, incluyen:.

• - Datos sísmicos y criterios de diseño sísmico.

• - Características sísmicas de los sistemas de ingeniería.

• - Fuerzas sísmicas.

• - Procedimientos de análisis sísmico.

• - Detallado sísmico y control de calidad de la construcción.

Para construir sistemas estructurales complejos,[12]​ el diseño sísmico utiliza en gran medida el mismo número relativamente pequeño de elementos estructurales básicos (por no hablar de los dispositivos de control de vibraciones) que cualquier proyecto de diseño no sísmico.

Normalmente, de acuerdo con los códigos de construcción, las estructuras se diseñan para "resistir" el mayor terremoto de cierta probabilidad que es probable que se produzca en su ubicación. Esto significa que la pérdida de vidas humanas debe minimizarse evitando el colapso de los edificios.

El diseño sísmico se lleva a cabo mediante la comprensión de los posibles modos de falla") de una estructura y dotando a la estructura de la resistencia, rigidez, ductilidad adecuadas, y configuración de las estructuras[13]​ para garantizar que esos modos no se produzcan.

Seismic design requirements

Seismic design requirements depend on the type of structure, the location of the project and its authorities, which stipulate the applicable seismic design codes and criteria.[3]​ For example, the California Department of Transportation's requirements called The Seismic Design Criteria (SDC) and intended for the design of new bridges in California[14]​ incorporate an innovative approach based on seismic behavior.

The most significant feature of the SDC design philosophy is the shift from a force-based seismic demand assessment to a displacement-based demand and capacity assessment. Thus, the new displacement approach adopted is based on comparing the elastic displacement demand with the inelastic displacement capacity of the primary structural components, while guaranteeing a minimum level of inelastic capacity at all possible plastic articulation points.

In addition to the designed structure itself, seismic design requirements may include ground stabilization beneath the structure: sometimes, strongly shaken ground breaks, causing the structure sitting on it to collapse.[16]​

The following topics should be of primary interest: liquefaction; dynamic lateral earth pressures in retaining walls; seismic stability of slopes; earthquake-induced settlements.[17]​.

Nuclear Facilities must not jeopardize their safety in the event of earthquakes or other hostile external events. Therefore, their seismic design is based on much stricter criteria than those applied to non-nuclear facilities. "and have caused many other governments to reevaluate their nuclear programs"). Doubts have also been raised about the seismic evaluation and design of some other plants, including the Fessenheim Nuclear Power Plant) in France.

Failure modes

Failure mode is how an earthquake-induced failure is observed. In general, it describes how the failure occurs. Although costly and time-consuming, learning from each actual seismic failure remains a routine recipe for advancing seismic design methods. Below are some typical failure modes generated by earthquakes.

Lack of reinforcement") coupled with poor mortar&action=edit&redlink=1 "Mortar (masonry) (not yet drafted)") and inadequate ties between roof and wall can cause substantial damage to an unreinforced masonry building"). The most common damage caused by earthquakes is severe cracks or leaning walls. Damage that can occur between walls and ceiling or floor diaphragms is also dangerous. Separation between the frame and the walls can compromise the vertical support of the roof and floor systems.

Soft floor effect"). The absence of adequate rigidity at the floor level caused damage to this structure. Close examination of the image reveals that the rough board siding, once covered by a brick veneer"), has been completely removed from the stud wall. Only the rigidity of the upper floor, combined with the support on the two hidden sides of continuous walls, not penetrated with large doors as on the street sides, is preventing the total collapse of the structure.

Soil liquefaction'. In cases where the soil consists of loose granular materials deposited with a tendency to develop excessive hydrostatic pore water pressure of sufficient and compact magnitude, the liquefaction of such saturated loose deposits may result in non-uniform settling&action=edit&redlink=1 "Consolidation (soil) (not yet drafted)") and tilting of structures. This caused significant damage to thousands of buildings in Niigata, Japan, during the 1964 earthquake.[19]​.

Rockfall. A landslide is a geological phenomenon that includes a wide range of ground movements, including rockfalls. Normally, gravity is the main driving force for a landslide to occur, although in this case there was another contributing factor that affected the stability of the original slope: the landslide required a seismic trigger before being released.

Blows against the adjacent building. This is a photograph of the collapse of the five-story tower at San Jose Seminary, Los Altos, California, resulting in one fatality. During the Loma Prieta earthquake, the tower struck the adjacent building that was vibrating independently behind it. The possibility of slamming depends on the lateral displacements of both buildings, which must be accurately estimated and accounted for.

In the Northridge Earthquake), the Kaiser Permanente concrete frame office building had joints completely destroyed, revealing inadequate confining steel, which caused the second floor to collapse. In the transverse direction, the composite shear walls, consisting of two layers of brick and one layer of shotcrete supporting the lateral load, detached due to and failed.

In Spain, the areas of greatest seismic risk are found in Eastern Andalusia, Murcia and the Valencian Community, and in the Canary Islands because they are volcanic islands. For the construction of buildings in these regions, compliance with the NCSE-02 earthquake-resistant construction standard is mandatory.

• - Seismic isolation.

• - Medvedev-Sponheuer-Karnik scale.

• - Mercalli seismological scale.

• - Prestressed Structure.

• - Richter seismological scale.

• - Computer simulation.

• - Seismic vulnerability.

• - Seismic fitness (en).

• - UPM Seismic Engineering Research Group.

• - Engineering and Seismic Risk Group of the University of Alicante.