Ingeniería Sísmica is an interdisciplinario branch of engineering that designs and analyzes structures, such as buildings and bridges, with terremotos in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake (or seismic) engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the riesgo sísmico to socio-económicamente acceptable levels.1 Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to carga sísmica; it is considered as a subset of Ingeniería estructural, Ingeniería geotécnica, Ingeniería Mecánica, Ingeniería Química, física Aplicada, 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 Ingeniería civil, Ingeniería Mecánica, Ingeniería Nuclear, and from the Ciencias Sociales, especially sociología, Ciencias Políticas, ciencias económicas, and Finanzas.2
Los principales objetivos de la ingeniería sísmica son:
Foresee the potential consequences of strong terremotos on Areas urbanas and civil infrastructure.
Design, construct and maintain structures to llevar a cabo at earthquake exposure up to the expectations and in compliance with construyendo códigos.3
A estructura adecuadamente diseñada 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.
carga sísmica
carga sísmica 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,5 with adjacent structures,6 or with ondas de gravedad from tsunami. The loading that is expected at a given location on the Earth's surface is estimated by engineering sismología. It is related to the peligro sísmico of the location.
Desempeño sísmico
Terremoto or desempeño sísmico defines a structure's ability to sustain its main functions, such as its la seguridad and utilidad, en and después a particular earthquake exposure. A structure is normally considered a salvo if it does not endanger the lives and bienestar-estando of those in or around it by partially or completely collapsing. A structure may be considered útil if it is able to fulfill its operational functions for which it was designed.
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 raro al sufrir daños significativos pero sin colapsar globalmente.7 On the other hand, it should remain operational for more frequent, but less severe seismic events.
Evaluación del desempeño sísmico
Los ingenieros necesitan saber el nivel cuantificado del desempeño sísmico real o anticipado asociado con el daño directo a un edificio individual sujeto a un movimiento del suelo específico. Tal evaluación puede realizarse de forma experimental o analítica.
Evaluación experimental
Experimental evaluations are expensive tests that are typically done by placing a (scaled) model of the structure on a agitar-la mesa that simulates the earth shaking and observing its behavior.8 Such kinds of experiments were first performed more than a century ago.9 Only recently has it become possible to perform 1:1 scale testing on full structures.
Debido a la naturaleza costosa de dichas pruebas, tienden a usarse principalmente para comprender el comportamiento sísmico de estructuras, validar modelos y verificar métodos de análisis. Por lo tanto, una vez debidamente validados, los modelos computacionales y los procedimientos numéricos tienden a soportar la mayor carga para la evaluación del comportamiento sísmico de las estructuras.
Evaluación analítica/numérica
Evaluación del desempeño sísmico or análisis estructural sísmico is a powerful tool of earthquake engineering which utilizes detailed modelling of the structure together with methods of structural analysis to gain a better understanding of seismic performance of building and estructuras no-edificiales. La técnica como concepto formal es un desarrollo relativamente reciente.
In general, seismic structural analysis is based on the methods of dinámica estructural.10 For decades, the most prominent instrument of seismic analysis has been the earthquake espectro de respuesta method which also contributed to the proposed building code's concept of today.11
However, such methods are good only for linear elastic systems, being largely unable to model the structural behavior when damage (i.e., no-linealidad) appears. Numerical integración paso-a-paso proved to be a more effective method of analysis for multi-degree-of-freedom sistemas estructurales with significant no-linealidad under a transitorio process of ground motion excitation.12 Use of the método de elementos finitos is one of the most common approaches for analyzing non-linear interacción suelo estructura computer models.
Básicamente, el análisis numérico se lleva a cabo para evaluar el comportamiento sísmico de los edificios. Las evaluaciones de rendimiento generalmente se llevan a cabo mediante el uso de análisis pushover estático no lineal o análisis de tiempo-histórico no lineal. En tales análisis, es esencial lograr un modelado no-lineal preciso de componentes estructurales como vigas, columnas, uniones de viga-columna, muros de corte, etc. Por lo tanto, los resultados experimentales juegan un papel importante en la determinación los parámetros de modelado de componentes individuales, especialmente aquellos que están sujetos a deformaciones no-lineales significativas. Luego, los componentes individuales se ensamblan para crear un modelo no-lineal completo de la estructura. Los modelos así creados se analizan para evaluar el desempeño de los edificios.
The capabilities of the structural analysis software are a major consideration in the above process as they restrict the possible component models, the analysis methods available and, most importantly, the numerical robustness. The latter becomes a major consideration for structures that venture into the non-linear range and approach global or local collapse as the numerical solution becomes increasingly unstable and thus difficult to reach. There are several commercially available Finite Element Analysis software's such as CSI-SAP2000 and CSI-PERFORM-3D, MTR/SASSI, Scia Engineer-ECtools, ABAQUS, and Ansys, all of which can be used for the seismic performance evaluation of buildings. Moreover, there is research-based finite element analysis platforms such as AbiertoVe, MASTODON, which is based on the Marco de alce, RUAUMOKO y el antiguo DRAIN-2D/3D, varios de los cuales ahora son de código abierto.
Investigación para la ingeniería sísmica
La investigación para la ingeniería sísmica significa investigación o experimentación analítica y de campo destinada al descubrimiento y la explicación científica de hechos relacionados con la ingeniería sísmica, la revisión de conceptos convencionales a la luz de nuevos hallazgos y la aplicación práctica de las teorías desarrolladas.
The Fundación Nacional de Ciencia (NSF) is the main United States government agency that supports fundamental research and education in all fields of earthquake engineering. In particular, it focuses on experimental, analytical and computational research on design and performance enhancement of structural systems.
The Instituto de Investigación de Ingeniería Sísmica (EERI) is a leader in dissemination of investigación en ingeniería sísmica related information both in the U.S. and globally.
A definitive list of earthquake engineering research related sacudiendo mesas around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide.14 The most prominent of them is now E-Defense Shake Table15 in Japón.
Principales programas de investigación de EE. UU.
NSF also supports the George E. Brown, Jr. Red para simulación de ingeniería sísmica
The NSF Hazard Mitigation and Structural Engineering program (HMSE) supports research on new technologies for improving the behaviour and response of structural systems subject to earthquake hazards; fundamental research on safety and reliability of constructed systems; innovative developments in análisis and model based simulation of structural behaviour and response including soil-structure interaction; design concepts that improve rendimiento de la estructura and flexibility; and application of new control techniques for structural systems.16
(NEES) that advances knowledge discovery and innovation for terremotos and tsunami loss reduction of the nation's civil infrastructure and new experimental simulation techniques and instrumentation.17
La red NEES cuenta con 14 laboratorios-distribuidos geográficamente y de uso compartido-que admiten varios tipos de trabajo experimental:17 geotechnical centrifuge research, agitar-la mesa tests, large-scale structural testing, tsunami wave basin experiments, and field site research.18 Participating universities include: Universidad de Cornell; Universidad de Lehigh; La Universidad Estatal de Oregon; Instituto Politécnico Rensselaer; universidad de búfalo, Universidad Estatal de Nueva York; Universidad de California, Berkeley; Universidad de California, Davis; Universidad de California, Los Angeles; Universidad de California, San Diego; Universidad de California, Santa Bárbara; Universidad de Illinois, Urbana-Champaña; Universidad de Minnesota; Universidad de Nevada, Reno; and the Universidad de Texas, Austin.17
The equipment sites (labs) and a central data repository are connected to the global earthquake engineering community via the NEEShub website. The NEES website is powered by HUBzero software developed at Universidad de Purdue for nanoHUB specifically to help the scientific community share resources and collaborate. The cyberinfrastructure, connected via Internet2, proporciona herramientas de simulación interactivas, un área de desarrollo de herramientas de simulación, un repositorio de datos central seleccionado, presentaciones animadas, asistencia al usuario, telepresencia, mecanismo para cargar y compartir recursos y estadísticas sobre usuarios y patrones de uso.
Esta ciberinfraestructura permite a los investigadores: almacenar, organizar y compartir datos de forma segura dentro de un marco estandarizado en una ubicación central; observar de forma remota y participar en experimentos mediante el uso de datos y videos sincronizados-en tiempo real; colaborar con colegas para facilitar la planificación, ejecución, análisis y publicación de experimentos de investigación; y realizar simulaciones informáticas e híbridas que pueden combinar los resultados de múltiples experimentos distribuidos y vincular experimentos físicos con simulaciones informáticas para permitir la investigación del rendimiento general del sistema.
Estos recursos proporcionan conjuntamente los medios para la colaboración y el descubrimiento para mejorar el diseño sísmico y el rendimiento de los sistemas de infraestructura civil y mecánica.
Simulación de terremoto
The very first simulaciones de terremotos were performed by statically applying some fuerzas de inercia horizontales based on escamoso aceleraciones máximas del suelo to a mathematical model of a building.19 With the further development of computational technologies, estático approaches began to give way to dinámica ones.
Dynamic experiments on building and non-building structures may be physical, like Pruebas de-mesa agitada, or virtual ones. In both cases, to verify a structure's expected seismic performance, some researchers prefer to deal with so called "real time-histories" though the last cannot be "real" for a hypothetical earthquake specified by either a building code or by some particular research requirements. Therefore, there is a strong incentive to engage an earthquake simulation which is the seismic input that possesses only essential features of a real event.
A veces, la simulación de terremotos se entiende como una recreación-de los efectos locales de un fuerte temblor de tierra.
Simulación de estructuras
Theoretical or experimental evaluation of anticipated seismic performance mostly requires a simulación de estructura which is based on the concept of structural likeness or similarity. Semejanza is some degree of analogía or semejanza between two or more objects. The notion of similarity rests either on exact or approximate repetitions of patrones in the compared items.
In general, a building model is said to have similarity with the real object if the two share similitud geométrica, similitud cinemática and similitud dinámica. The most vivid and effective type of similarity is the cinemático one. Similitud cinemática exists when the paths and velocities of moving particles of a model and its prototype are similar.
The ultimate level of similitud cinemática is equivalencia cinemática when, in the case of earthquake engineering, time-histories of each story lateral displacements of the model and its prototype would be the same.
Control de vibraciones sísmicas
Control de vibraciones sísmicas is a set of technical means aimed to mitigate seismic impacts in building and no-edificio structures. All seismic vibration control devices may be classified as pasivo, activo or híbrido21 where:
dispositivos de control pasivo have no realimentación capability between them, structural elements and the ground;
dispositivos de control activo incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuadores within the structure;
dispositivos de control híbrido have combined features of active and passive control systems.22
When ground ondas sísmicas reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90 percent . However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.
After the seismic waves enter a superestructura, there are a number of ways to control them in order to soothe their damaging effect and improve the building's seismic performance, for instance:
to disipar the wave energy inside a superestructura with properly engineered amortiguadores;
dispersar la energía de las olas entre una gama más amplia de frecuencias;
to absorber the resonante portions of the whole wave frequencies band with the help of so-called amortiguadores de masa.23
Dispositivos de este último tipo, abreviados correspondientemente como TMD para el sintonizado (pasivo), as AMD for the activo, and as HMD for the amortiguadores de masa híbridos, have been studied and installed in edificios-altos, predominantemente en Japón, durante un cuarto de siglo.24
However, there is quite another approach: partial suppression of the seismic energy flow into the superestructura known as seismic or aislamiento básico.
For this, some pads are inserted into or under all major load-carrying elements in the base of the building which should substantially decouple a superestructura from its infraestructura resting on a shaking ground.
The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, una ciudad en la antigua Persia, ahora Irán, y data del siglo VI a. A continuación, hay algunos ejemplos de tecnologías de control de vibraciones sísmicas actuales.
Muros-de piedra seca en Perú
Perú is a highly sísmico land; for centuries the dry-stone construcción proved to be more earthquake-resistant than using mortar. People of civilizacion inca were masters of the polished 'dry-stone walls', called sillar, where blocks of stone were cut to fit together tightly without any mortero. Los incas estaban entre los mejores canteros que el mundo haya visto25 and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.
The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive control estructural technique employing both the principle of energy dissipation (coulomb damping) and that of suppressing resonante amplifications.26
Amortiguador de masa sintonizado
Typically the amortiguadores de masa sintonizados are huge concrete blocks mounted in rascacielos or other structures and move in opposition to the frecuencia de resonancia oscillations of the structures by means of some sort of spring mechanism.
The Taipei 101 skyscraper needs to withstand tifón winds and earthquake temblores common in this area of Asia/Pacific. For this purpose, a steel péndulo weighing 660 metric tonnes that serves as a tuned mass damper was designed and installed atop the structure. Suspended from the 92nd to the 88th floor, the pendulum sways to decrease resonant amplifications of lateral displacements in the building caused by earthquakes and strong ráfagas.
Amortiguadores histeréticos
A amortiguador histerético is intended to provide better and more reliable seismic performance than that of a conventional structure by increasing the dissipation of entrada sísmica energy.27 There are five major groups of hysteretic dampers used for the purpose, namely:
Amortiguadores viscosos fluidos (FVD)
Los amortiguadores viscosos tienen la ventaja de ser un sistema de amortiguación suplementario. Tienen un bucle histerético ovalado y la amortiguación depende de la velocidad. Si bien es posible que se requiera un mantenimiento menor, los amortiguadores viscosos generalmente no necesitan ser reemplazados después de un terremoto. Si bien son más costosos que otras tecnologías de amortiguación, se pueden usar tanto para cargas sísmicas como de viento y son los amortiguadores histeréticos más utilizados.28
Amortiguadores de fricción (FD)
Friction dampers tend to be available in two major types, linear and rotational and dissipate energy by heat. The damper operates on the principle of a amortiguador de culombio. Depending on the design, friction dampers can experience fenómeno de stick-slip and Soldadura en frio. La principal desventaja es que las superficies de fricción pueden desgastarse con el tiempo, por lo que no se recomiendan para disipar cargas de viento. Cuando se usa en aplicaciones sísmicas, el desgaste no es un problema y no requiere mantenimiento. Tienen un bucle histerético rectangular y, siempre que el edificio sea lo suficientemente elástico, tienden a volver a asentarse en sus posiciones originales después de un terremoto.
Amortiguadores de fluencia metálicos (MYD)
Metallic yielding dampers, as the name implies, yield in order to absorb the earthquake's energy. This type of damper absorbs a large amount of energy however they must be replaced after an earthquake and may prevent the building from settling back to its original position.
Amortiguadores viscoelásticos (VED)
Los amortiguadores viscoelásticos son útiles porque pueden usarse tanto para aplicaciones eólicas como sísmicas, generalmente están limitados a pequeños desplazamientos. Existe cierta preocupación en cuanto a la confiabilidad de la tecnología, ya que se prohibió el uso de algunas marcas en edificios en los Estados Unidos.
Amortiguadores de péndulo a horcajadas (oscilación)
Aislamiento de bases
El aislamiento de la base busca evitar que la energía cinética del sismo se transforme en energía elástica en el edificio. Estas tecnologías lo hacen aislando la estructura del suelo, lo que les permite moverse de forma algo independiente. El grado en que la energía se transfiere a la estructura y cómo se disipa la energía variará según la tecnología utilizada.
Cojinete de goma de plomo
Lead rubber bearing or LRB is a type of aislamiento básico employing a heavy mojadura. It was invented by bill robinson, un neozelandés.29
Heavy damping mechanism incorporated in control de vibraciones technologies and, particularly, in base isolation devices, is often considered a valuable source of suppressing vibrations thus enhancing a building's seismic performance. However, for the rather pliant systems such as base isolated structures, with a relatively low bearing stiffness but with a high damping, the so-called "damping force" may turn out the main pushing force at a strong earthquake. The video30 shows a Lead Rubber Bearing being tested at the UCSD Caltrans-SRMD facility. The bearing is made of rubber with a lead core. It was a uniaxial test in which the bearing was also under a full structure load. Many buildings and bridges, both in New Zealand and elsewhere, are protected with lead dampers and lead and rubber bearings. Te Papa Tongarewa, the national museum of New Zealand, and the New Zealand edificios del parlamento have been fitted with the bearings. Both are in Wellington which sits on an falla activa.29
Resortes-con-aislante de base de amortiguador
Springs-with-damper base isolator installed under a three-story town-house, Santa Mónica, California is shown on the photo taken prior to the 1994 Terremoto de Northridge exposure. It is a aislamiento básico device conceptually similar to Cojinete de goma de plomo.
One of two three-story town-houses like this, which was well instrumented for recording of both vertical and horizontal aceleraciones on its floors and the ground, has survived a severe shaking during the Terremoto de Northridge and left valuable recorded information for further study.
Cojinete de rodillos simples
Simple roller bearing is a aislamiento básico device which is intended for protection of various building and non-building structures against potentially damaging impactos laterales of strong earthquakes.
This metallic bearing support may be adapted, with certain precautions, as a seismic isolator to skyscrapers and buildings on soft ground. Recently, it has been employed under the name of cojinete de rodillos metalicos for a housing complex (17 stories) in Tokio, Japón.31
Cojinete de péndulo de fricción
Friction pendulum bearing (FPB) is another name of sistema de péndulo de fricción (FPS). It is based on three pillars:32
deslizador de fricción articulado;
superficie de deslizamiento cóncava esférica;
Cilindro envolvente para restricción de desplazamiento lateral.
Snapshot with the link to video clip of a agitar-la mesa testing of FPB system supporting a rigid building model is presented at the right.
diseño sísmico
diseño sísmico is based on authorized engineering procedures, principles and criteria meant to diseño or reacondicionar structures subject to earthquake exposure.19 Those criteria are only consistent with the contemporary state of the knowledge about estructuras de ingeniería sísmica.33 Therefore, a building design which exactly follows seismic code regulations does not guarantee safety against collapse or serious damage.34
The price of poor seismic design may be enormous. Nevertheless, seismic design has always been a prueba y error process whether it was based on physical laws or on empirical knowledge of the rendimiento estructural of different shapes and materials.
To practice diseño sísmico, seismic analysis or seismic evaluation of new and existing civil engineering projects, an ingeniero should, normally, pass examination on Principios sísmicos35 which, in the State of California, include:
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,36 seismic design largely uses the same relatively small number of basic structural elements (to say nothing of vibration control devices) as any non-seismic design project.
Normally, according to building codes, structures are designed to "withstand" the largest earthquake of a certain probability that is likely to occur at their location. This means the loss of life should be minimized by preventing collapse of the buildings.
Seismic design is carried out by understanding the possible modos de fallo of a structure and providing the structure with appropriate fuerza, rigidez, ductilidad, and configuración37 to ensure those modes cannot occur.
Requisitos de diseño sísmico
Requisitos de diseño sísmico depend on the type of the structure, locality of the project and its authorities which stipulate applicable seismic design codes and criteria.7 For instance, Departamento de Transporte de California's requirements called Los criterios de diseño sísmico (SDC) and aimed at the design of new bridges in California38 incorporate an innovative seismic performance-based approach.
The most significant feature in the SDC design philosophy is a shift from a evaluación basada-en la fuerza of seismic demand to a evaluación-basada en el desplazamiento of demand and capacity. Thus, the newly adopted displacement approach is based on comparing the desplazamiento elástico demand to the desplazamiento inelástico capacity of the primary structural components while ensuring a minimum level of inelastic capacity at all potential plastic hinge locations.
In addition to the designed structure itself, seismic design requirements may include a estabilización del suelo underneath the structure: sometimes, heavily shaken ground breaks up which leads to collapse of the structure sitting upon it.40 The following topics should be of primary concerns: liquefaction; dynamic lateral earth pressures on retaining walls; seismic slope stability; earthquake-induced settlement.41
Instalaciones nucleares should not jeopardise their safety in case of earthquakes or other hostile external events. Therefore, their seismic design is based on criteria far more stringent than those applying to non-nuclear facilities.42 The Accidentes nucleares de Fukushima I and daños a otras instalaciones nucleares that followed the 2011 Tōhoku earthquake and tsunami have, however, drawn attention to ongoing concerns over Estándares japoneses de diseño sísmico nuclear and caused many other governments to re-evaluar sus programas nucleares. Doubt has also been expressed over the seismic evaluation and design of certain other plants, including the Central nuclear de Fessenheim in France.
Modos de fallo
Modo de fallo is the manner by which an earthquake induced failure is observed. It, generally, describes the way the failure occurs. Though costly and time consuming, learning from each real earthquake failure remains a routine recipe for advancement in diseño sísmico methods. Below, some typical modes of earthquake-generated failures are presented.
The lack of reforzamiento coupled with poor mortero and inadequate roof-to-wall ties can result in substantial damage to an edificio de mampostería no reforzada. Las paredes severamente agrietadas o inclinadas son algunos de los daños de terremotos más comunes. También es peligroso el daño que puede ocurrir entre las paredes y los diafragmas del techo o del piso. La separación entre la estructura y las paredes puede poner en peligro el soporte vertical de los sistemas de techo y piso.
Efecto de historia suave. Absence of adequate stiffness on the ground level caused damage to this structure. A close examination of the image reveals that the rough board siding, once covered by a revestimiento de ladrillos, has been completely dismantled from the studwall. Only the rigidez of the floor above combined with the support on the two hidden sides by continuous walls, not penetrated with large doors as on the street sides, is preventing full collapse of the structure.
licuefacción del suelo. In the cases where the soil consists of loose granular deposited materials with the tendency to develop excessive hydrostatic pore water pressure of sufficient magnitude and compact, licuefacción of those loose saturated deposits may result in non-uniform asentamientos and tilting of structures. This caused major damage to thousands of buildings in Niigata, Japan during the terremoto de 1964.43
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Deslizamiento de rocas. A deslizamiento de tierra is a geological phenomenon which includes a wide range of ground movement, including desprendimientos de rocas. Typically, the action of gravedad is the primary driving force for a landslide to occur though in this case there was another contributing factor which affected the original estabilidad de taludes: the landslide required an disparador de terremoto before being released.
Golpeando contra el edificio adyacente. This is a photograph of the collapsed five-story tower, St. Joseph's Seminary, Los Altos, California which resulted in one fatality. During terremoto de loma prieta, the tower pounded against the independently vibrating adjacent building behind. A possibility of pounding depends on both buildings' lateral displacements which should be accurately estimated and accounted for.
At Terremoto de Northridge, the Kaiser Permanente concrete frame office building had joints completely shattered, revealing acero de confinamiento inadecuado, which resulted in the second story collapse. In the transverse direction, composite end muros de corte, consisting of two wythes of brick and a layer of hormigón proyectado that carried the lateral load, peeled apart because of inadecuada a través-lazos and failed.
Improper sitio de construcción on a estribaciones.
Poor detailing of the reforzamiento (lack of concrete confinement in the columns and at the beam-column joints, inadequate splice length).
Seismically weak historia suave at the first floor.
Long voladizos with heavy peso muerto.
Efecto deslizamiento de las bases of a relatively rigid residential building structure during Terremoto de Whittier Narrows de 1987. The magnitude 5.9 earthquake pounded the Garvey West Apartment building in Monterey Park, California and shifted its superestructura about 10 inches to the east on its foundation.
If a superstructure is not mounted on a aislamiento básico system, its shifting on the basement should be prevented.
Concreto reforzado column burst at Terremoto de Northridge due to modo de refuerzo de cortante insuficiente which allows main reinforcement to hebilla outwards. The deck unseated at the bisagra and failed in shear. As a result, the La Cienega-Venice paso inferior section of the 10 Freeway collapsed.
terremoto de loma prieta: side view of reinforced concrete fallo de-columnas de soporte which triggered el piso superior colapsa sobre el piso inferior of the two-level Cypress viaduct of Interstate Highway 880, Oakland, CA.
Falla del muro de contención at terremoto de loma prieta in Santa Cruz Mountains area: prominent northwest-trending extensional cracks up to 12 cm (4.7 in) wide in the concrete aliviadero to Austrian Dam, the north contrafuerte.
Ground shaking triggered licuefacción del suelo in a subsurface layer of arena, producing differential lateral and vertical movement in an overlying carapacho of unliquified sand and limo. This modo de falla a tierra, termed extensión lateral, es una de las principales causas de daños por terremotos relacionados con la licuefacción-.44
Severely damaged building of Agriculture Development Bank of China after Terremoto de Sichuan de 2008: most of the las vigas y las columnas del muelle se cortan. Large diagonal cracks in masonry and veneer are due to in-plane loads while abrupt asentamiento of the right end of the building should be attributed to a vertedero which may be hazardous even without any earthquake.45
Doble impacto del tsunami: las olas del mar hydraulic presión and inundación. Thus, el terremoto del océano Índico of December 26, 2004, with the epicentro off the west coast of Sumatra, Indonesia, triggered a series of devastating tsunamis, killing more than 230,000 people in eleven countries by inundando las comunidades costeras circundantes con enormes olas up to 30 meters (100 feet) high.47
Construcción-resistente a terremotos
Construcción de terremotos means implementation of diseño sísmico to enable building and non-building structures to live through the anticipated earthquake exposure up to the expectations and in compliance with the applicable construyendo códigos.
El diseño y la construcción están íntimamente relacionados. Para lograr una buena mano de obra, el detalle de los miembros y sus conexiones debe ser lo más simple posible. Como toda construcción en general, la construcción sísmica es un proceso que consiste en la construcción, reforzamiento o montaje de infraestructura dados los materiales de construcción disponibles.48
The destabilizing action of an earthquake on constructions may be directo (seismic motion of the ground) or indirecto (earthquake-induced landslides, licuefacción del suelo and waves of tsunami).
Una estructura puede tener todas las apariencias de estabilidad y, sin embargo, ofrecer nada más que peligro cuando ocurre un terremoto.49 The crucial fact is that, for safety, earthquake-resistant construction techniques are as important as control de calidad and using correct materials. contratista de terremotos should be registrado in the state/province/country of the project location (depending on local regulations), garantizado and aseguradocita necesaria.
To minimize possible pérdidas, el proceso de construcción debe organizarse teniendo en cuenta que un terremoto puede ocurrir en cualquier momento antes del final de la construcción.
Each proyecto de construccion requires a qualified team of professionals who understand the basic features of seismic performance of different structures as well as gestión de la construcción.
estructuras de adobe
Around thirty percent of the world's population lives or works in earth-made construction.50 Adobe type of ladrillos de barro is one of the oldest and most widely used building materials. The use of adobe is very common in some of the world's most hazard-prone regions, traditionally across Latin America, Africa, Indian subcontinent and other parts of Asia, Middle East and Southern Europe.
Los edificios de adobe se consideran muy vulnerables a los terremotos fuertes.51 However, multiple ways of seismic strengthening of new and existing adobe buildings are available.52
Los factores clave para el desempeño sísmico mejorado de la construcción de adobe son:
Calidad de construcción.
Diseño compacto tipo caja-.
Refuerzo sísmico.53
Estructuras de piedra caliza y arenisca
Caliza is very common in architecture, especially in North America and Europe. Many landmarks across the world are made of limestone. Many medieval churches and castles in Europe are made of caliza and arenisca masonry. They are the long-lasting materials but their rather heavy weight is not beneficial for adequate seismic performance.
Application of modern technology to seismic retrofitting can enhance the survivability of unreinforced masonry structures. As an example, from 1973 to 1989, the Salt Lake City y edificio del condado in Utah was exhaustively renovated and repaired with an emphasis on preserving historical accuracy in appearance. This was done in concert with a seismic upgrade that placed the weak sandstone structure on base isolation foundation to better protect it from earthquake damage.
Estructuras de entramado de madera
entramado de madera dates back thousands of years, and has been used in many parts of the world during various periods such as ancient Japan, Europe and medieval England in localities where timber was in good supply and building stone and the skills to work it were not.
The use of entramado de madera in buildings provides their complete skeletal framing which offers some structural benefits as the timber frame, if properly engineered, lends itself to better supervivencia sísmica.54
Estructuras-estructuras ligeras
Estructuras-estructuras ligeras usually gain seismic resistance from rigid madera contrachapada shear walls and wood structural panel diafragmas.55 Special provisions for seismic load-resisting systems for all madera de ingeniería structures requires consideration of diaphragm ratios, horizontal and vertical diaphragm shears, and conector/cierre values. In addition, collectors, or drag struts, to distribute shear along a diaphragm length are required.
Estructuras de mampostería reforzada
A construction system where refuerzo de acero is embedded in the juntas de mortero of albañilería or placed in holes and that are filled with hormigón or lechada is called mampostería reforzada.56 There are various practices and techniques to reinforce masonry. The most common type is the reinforced mampostería de unidad hueca.
To achieve a dúctil behavior in masonry, it is necessary that the resistencia a la cizalladura of the wall is greater than the fuerza flexible.57 The effectiveness of both vertical and horizontal reinforcements depends on the type and quality of the masonry units and mortero.
The devastating Terremoto de Long Beach de 1933 revealed that masonry is prone to earthquake damage, which led to the Código del Estado de California making masonry reinforcement mandatory across California.
Estructuras de hormigón armado
Concreto reforzado is concrete in which steel reinforcement bars (barras de refuerzo) or fibras have been incorporated to strengthen a material that would otherwise be frágil. It can be used to produce vigas, columnas, pisos o puentes.
Hormigón pretensado is a kind of concreto reforzado used for overcoming concrete's natural weakness in tension. It can be applied to vigas, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendones (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a estrés compresivo that offsets the esfuerzo de tracción that the concrete miembro de compresión would, otherwise, experience due to a bending load.
To prevent catastrophic collapse in response earth shaking (in the interest of life safety), a traditional reinforced concrete frame should have dúctil joints. Depending upon the methods used and the imposed seismic forces, such buildings may be immediately usable, require extensive repair, or may have to be demolished.
Estructuras pretensadas
Estructura pretensada is the one whose overall integridad, estabilidad and seguridad depend, primarily, on a pretensado. pretensado means the intentional creation of permanent stresses in a structure for the purpose of improving its performance under various service conditions.58
Existen los siguientes tipos básicos de pretensado:
Pre-compresión (principalmente, con el propio peso de una estructura)
pretensado with high-strength embedded tendons
Post-tensado with high-strength bonded or unbonded tendons
Today, the concept of estructura pretensada is widely engaged in design of edificios, underground structures, TV towers, power stations, floating storage and offshore facilities, reactor nuclear vessels, and numerous kinds of puente systems.59
A beneficial idea of pretensado was, apparently, familiar to the ancient Rome architects; look, e.g., at the tall ático wall of Coliseo working as a stabilizing device for the wall muelles beneath.
Estructuras de acero
Estructuras de acero are considered mostly earthquake resistant but some failures have occurred. A great number of welded momento de acero-marco resistente buildings, which looked earthquake-proof, surprisingly experienced brittle behavior and were hazardously damaged in the Terremoto de Northridge de 1994.60 After that, the Agencia Federal para el Manejo de Emergencias (FEMA) initiated development of repair techniques and new design approaches to minimize damage to steel moment frame buildings in future earthquakes.61
For acero estructural seismic design based on Diseño de factor de carga y resistencia (LRFD) approach, it is very important to assess ability of a structure to develop and maintain its bearing resistance in the no elástico range. A measure of this ability is ductilidad, which may be observed in a material en sí, in a elemento estructural, or to a toda la estructura.
As a consequence of Terremoto de Northridge experience, the American Institute of Steel Construction has introduced AISC 358 "Pre-Qualified Connections for Special and intermediate Steel Moment Frames." The AISC Seismic Design Provisions require that all Marcos resistentes a momentos de acero employ either connections contained in AISC 358, or the use of connections that have been subjected to pre-qualifying cyclic testing.62
Predicción de pérdidas por terremoto
Estimación de pérdidas por terremoto is usually defined as a Relación de daño (DR) which is a ratio of the earthquake damage repair cost to the valor total of a building.63 Pérdida Máxima Probable (LMP) is a common term used for earthquake loss estimation, but it lacks a precise definition. In 1999, ASTM E2026 'Standard Guide for the Estimation of Building Damageability in Earthquakes' was produced in order to standardize the nomenclature for seismic loss estimation, as well as establish guidelines as to the review process and qualifications of the reviewer.64
Earthquake loss estimations are also referred to as Evaluaciones de riesgo sísmico. El proceso de evaluación de riesgos generalmente implica determinar la probabilidad de varios movimientos del suelo junto con la vulnerabilidad o el daño del edificio bajo esos movimientos del suelo. Los resultados se definen como un porcentaje del valor de reemplazo del edificio.65