Earthquake engineering is an
interdisciplinary
Interdisciplinarity or interdisciplinary studies involves the combination of multiple academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, anthropology, psychology, ec ...
branch of engineering that designs and analyzes structures, such as buildings and bridges, with
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
s 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
seismic risk
Seismic risk refers to the risk of damage from earthquake to a building, system, or other entity. Seismic risk has been defined, for most management purposes, as the potential economic, social and environmental consequences of hazardous events th ...
to
socio-economically
Socioeconomics (also known as social economics) is the social science that studies how economic activity affects and is shaped by social processes. In general it analyzes how modern societies progress, stagnate, or regress because of their loc ...
acceptable levels.
Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to
seismic loading
Seismic loading is one of the basic concepts of earthquake engineering which means application of an earthquake-generated agitation to a structure. It happens at contact surfaces of a structure either with the ground, or with adjacent structures, o ...
; it is considered as a subset of
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
,
geotechnical engineering
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
,
mechanical engineering
Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, and ...
,
chemical engineering
Chemical engineering is an engineering field which deals with the study of operation and design of chemical plants as well as methods of improving production. Chemical engineers develop economical commercial processes to convert raw materials int ...
,
applied physics
Applied physics is the application of physics to solve scientific or engineering problems. It is usually considered to be a bridge or a connection between physics and engineering.
"Applied" is distinguished from "pure" by a subtle combination ...
, 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
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...
,
mechanical engineering
Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, and ...
,
nuclear engineering
Nuclear engineering is the branch of engineering concerned with the application of breaking down atomic nuclei ( fission) or of combining atomic nuclei (fusion), or with the application of other sub-atomic processes based on the principles of n ...
, and from the
social sciences
Social science is one of the branches of science, devoted to the study of societies and the relationships among individuals within those societies. The term was formerly used to refer to the field of sociology, the original "science of soci ...
, especially
sociology
Sociology is a social science that focuses on society, human social behavior, patterns of Interpersonal ties, social relationships, social interaction, and aspects of culture associated with everyday life. It uses various methods of Empirical ...
,
political science
Political science is the scientific study of politics. It is a social science dealing with systems of governance and power, and the analysis of political activities, political thought, political behavior, and associated constitutions and la ...
,
economics
Economics () is the social science that studies the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods and services.
Economics focuses on the behaviour and intera ...
, and
finance
Finance is the study and discipline of money, currency and capital assets. It is related to, but not synonymous with economics, the study of production, distribution, and consumption of money, assets, goods and services (the discipline of fina ...
.
The main objectives of earthquake engineering are:
* Foresee the potential consequences of strong
earthquakes
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
on
urban areas
An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities, t ...
and civil infrastructure.
* Design, construct and maintain structures to
perform
PerForm and PerForm PRO were electronic form programs, initially designed to work under GEM in DOS. Later versions were designed to work in Windows 3.1, at which point it was succeeded by FormFlow.
The initial version of PerForm was created in 1 ...
at earthquake exposure up to the expectations and in compliance with
building code
A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...
s.
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.
Seismic loading
![Tokyo Sky Tree 2012](https://upload.wikimedia.org/wikipedia/commons/3/3e/Tokyo_Sky_Tree_2012.JPG)
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 wave
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere ...
s from
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...
. The loading that is expected at a given location on the Earth's surface is estimated by engineering
seismology
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
. It is related to the
seismic hazard
A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and includ ...
of the location.
Seismic performance
Earthquake or seismic performance defines a structure's ability to sustain its main functions, such as its
safety
Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to risk management, the control of recognized hazards in order to achieve an acceptable level of risk.
Meanings
There are ...
and
serviceability, ''at'' and ''after'' a particular earthquake exposure. A structure is normally considered ''safe'' if it does not endanger the lives and
well-being
Well-being, or wellbeing, also known as wellness, prudential value or quality of life, refers to what is intrinsically valuable relative ''to'' someone. So the well-being of a person is what is ultimately good ''for'' this person, what is in th ...
of those in or around it by partially or completely collapsing. A structure may be considered ''serviceable'' if it is able to fulfill its operational functions for which it was designed.
Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive a rare, very severe earthquake by sustaining significant damage but without globally collapsing.
On the other hand, it should remain operational for more frequent, but less severe seismic events.
Seismic performance assessment
Engineers need to know the quantified level of the actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking.
Such an assessment may be performed either experimentally or analytically.
Experimental assessment
Experimental evaluations are expensive tests that are typically done by placing a (scaled) model of the structure on a
shake-table that simulates the earth shaking and observing its behavior. Such kinds of experiments were first performed more than a century ago.
Only recently has it become possible to perform 1:1 scale testing on full structures.
Due to the costly nature of such tests, they tend to be used mainly for understanding the seismic behavior of structures, validating models and verifying analysis methods. Thus, once properly validated, computational models and numerical procedures tend to carry the major burden for the seismic performance assessment of structures.
Analytical/Numerical assessment
![Shaking NDC](https://upload.wikimedia.org/wikipedia/commons/8/8f/Shaking_NDC.jpg)
Seismic performance assessment or
seismic structural analysis 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
non-building structure
A nonbuilding structure, also referred to simply as a structure, refers to any body or system of connected parts used to support a load that was not designed for continuous human occupancy. The term is used by architects, structural engin ...
s. The technique as a formal concept is a relatively recent development.
In general, seismic structural analysis is based on the methods of
structural dynamics
Structural dynamics is a type of structural analysis which covers the behavior of a structure subjected to dynamic (actions having high acceleration) loading. Dynamic loads include people, wind, waves, traffic, earthquakes, and blasts. Any structur ...
.
For decades, the most prominent instrument of seismic analysis has been the earthquake
response spectrum
A response spectrum is a plot of the peak or steady-state response (displacement, velocity or acceleration) of a series of oscillators of varying natural frequency, that are forced into motion by the same base vibration or shock. The resulting plo ...
method which also contributed to the proposed building code's concept of today.
However, such methods are good only for linear elastic systems, being largely unable to model the structural behavior when damage (i.e.,
non-linearity
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
) appears. Numerical ''step-by-step integration'' proved to be a more effective method of analysis for multi-degree-of-freedom
structural system
A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
s with significant
non-linearity
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
under a
transient
ECHELON, originally a secret government code name, is a surveillance program ( signals intelligence/SIGINT collection and analysis network) operated by the five signatory states to the UKUSA Security Agreement:Given the 5 dialects that ...
process of
ground motion
Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth a ...
excitation.
Use of the
finite element method
The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat ...
is one of the most common approaches for analyzing non-linear
soil structure interaction computer models.
Basically, numerical analysis is conducted in order to evaluate the seismic performance of buildings. Performance evaluations are generally carried out by using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate non-linear 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 non-linear deformations. The individual components are then assembled to create a full non-linear model of the structure. Thus created models are analyzed to evaluate the performance of buildings.
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
Abaqus FEA (formerly ABAQUS) is a software suite for finite element analysis and computer-aided engineering, originally released in 1978. The name and logo of this software are based on the abacus calculation tool.
The Abaqus product suite consis ...
, 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
OpenSees
OpenSees (the Open System for Earthquake Engineering Simulation) is an object-oriented software framework created during the National Science Foundation-sponsored era (1997-2007) of the Pacific Earthquake Engineering ResearchPEER Center. OpenSees ...
, MASTODON, which is based on the
MOOSE Framework, RUAUMOKO and the older DRAIN-2D/3D, several of which are now open source.
Research for earthquake engineering
![FPB testing-1](https://upload.wikimedia.org/wikipedia/commons/d/d0/FPB_testing-1.jpg)
Research for earthquake engineering means both field and analytical investigation or experimentation intended for discovery and scientific explanation of earthquake engineering related facts, revision of conventional concepts in the light of new findings, and practical application of the developed theories.
The
National Science Foundation
The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...
(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.
![E-Defense Shake Table](https://upload.wikimedia.org/wikipedia/commons/5/52/E-Defense_Shake_Table.jpg)
The
Earthquake Engineering Research Institute
The Earthquake Engineering Research Institute (EERI) is a leading technical society in dissemination of earthquake risk and earthquake engineering research both in the U.S. and globally. EERI members include researchers, geologists, geotechnical e ...
(EERI) is a leader in dissemination of
earthquake engineering research
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earth ...
related information both in the U.S. and globally.
A definitive list of earthquake engineering research related
shaking tables around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide. The most prominent of them is now E-Defense Shake Table in
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
.
Major U.S. research programs
NSF also supports the George E. Brown, Jr.
Network for Earthquake Engineering Simulation
The George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) was created by the National Science Foundation (NSF) to improve infrastructure design and construction practices to prevent or minimize damage during an earthquake or ts ...
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
analysis
Analysis ( : analyses) is the process of breaking a complex topic or substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (38 ...
and model based simulation of structural behaviour and response including soil-structure interaction; design concepts that improve
structure performance and flexibility; and application of new control techniques for structural systems.
(NEES) that advances knowledge discovery and innovation for
earthquakes
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
and
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...
loss reduction of the nation's civil infrastructure and new experimental simulation techniques and instrumentation.
The NEES network features 14 geographically-distributed, shared-use laboratories that support several types of experimental work:
geotechnical centrifuge research,
shake-table tests, large-scale structural testing, tsunami wave basin experiments, and field site research. Participating universities include:
Cornell University
Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
;
Lehigh University
Lehigh University (LU) is a private research university in Bethlehem, Pennsylvania in the Lehigh Valley region of eastern Pennsylvania. The university was established in 1865 by businessman Asa Packer and was originally affiliated with the Epis ...
;
Oregon State University
Oregon State University (OSU) is a public land-grant, research university in Corvallis, Oregon. OSU offers more than 200 undergraduate-degree programs along with a variety of graduate and doctoral degrees. It has the 10th largest engineering co ...
;
Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute () (RPI) is a private research university in Troy, New York, with an additional campus in Hartford, Connecticut. A third campus in Groton, Connecticut closed in 2018. RPI was established in 1824 by Stephen Van ...
;
University at Buffalo
The State University of New York at Buffalo, commonly called the University at Buffalo (UB) and sometimes called SUNY Buffalo, is a public research university with campuses in Buffalo and Amherst, New York. The university was founded in 1846 ...
,
State University of New York
The State University of New York (SUNY, , ) is a system of public colleges and universities in the State of New York. It is one of the largest comprehensive system of universities, colleges, and community colleges in the United States. Led by c ...
;
University of California, Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
;
University of California, Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The institut ...
;
University of California, Los Angeles
The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...
;
University of California, San Diego
The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public university, public Land-grant university, land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Insti ...
;
University of California, Santa Barbara
The University of California, Santa Barbara (UC Santa Barbara or UCSB) is a Public university, public Land-grant university, land-grant research university in Santa Barbara County, California, Santa Barbara, California with 23,196 undergraduate ...
;
University of Illinois, Urbana-Champaign
The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Universi ...
;
University of Minnesota
The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Tw ...
;
University of Nevada, Reno
The University of Nevada, Reno (Nevada, the University of Nevada, or UNR) is a public land-grant research university in Reno, Nevada. It is the state's flagship public university and primary land grant institution. It was founded on October 12, ...
; and the
University of Texas, Austin
The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,075 ...
.
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
Purdue University
Purdue University is a public land-grant research university in West Lafayette, Indiana, and the flagship campus of the Purdue University system. The university was founded in 1869 after Lafayette businessman John Purdue donated land and money ...
for
nanoHUB
nanoHUB.org is a science and engineering gateway comprising community-contributed resources and geared toward education, professional networking, and interactive simulation tools for nanotechnology. Funded by the United States National Science F ...
specifically to help the scientific community share resources and collaborate. The cyberinfrastructure, connected via
Internet2
Internet2 is a not-for-profit United States computer networking consortium led by members from the research and education communities, industry, and government. The Internet2 consortium administrative headquarters are located in Ann Arbor, Mi ...
, provides interactive simulation tools, a simulation tool development area, a curated central data repository, animated presentations, user support, telepresence, mechanism for uploading and sharing resources, and statistics about users and usage patterns.
This cyberinfrastructure allows researchers to: securely store, organize and share data within a standardized framework in a central location; remotely observe and participate in experiments through the use of synchronized real-time data and video; collaborate with colleagues to facilitate the planning, performance, analysis, and publication of research experiments; and conduct computational and hybrid simulations that may combine the results of multiple distributed experiments and link physical experiments with computer simulations to enable the investigation of overall system performance.
These resources jointly provide the means for collaboration and discovery to improve the seismic design and performance of civil and mechanical infrastructure systems.
Earthquake simulation
The very first earthquake simulations were performed by statically applying some ''horizontal inertia forces'' based on
scaled peak ground acceleration
Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an wikt:accelerogram, accelerogram at a ...
s to a mathematical model of a building.
With the further development of computational technologies,
static
Static may refer to:
Places
*Static Nunatak, a nunatak in Antarctica
United States
* Static, Kentucky and Tennessee
*Static Peak, a mountain in Wyoming
**Static Peak Divide, a mountain pass near the peak
Science and technology Physics
*Static el ...
approaches began to give way to
dynamic
Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' "power") or dynamic may refer to:
Physics and engineering
* Dynamics (mechanics)
** Aerodynamics, the study of the motion of air
** Analytical dynam ...
ones.
Dynamic experiments on building and non-building structures may be physical, like
shake-table testing, 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.
Sometimes earthquake simulation is understood as a re-creation of local effects of a strong earth shaking.
Structure simulation
![Kinematically equivalent building models on a shake-table](https://upload.wikimedia.org/wikipedia/commons/8/86/Kinematically_equivalent_building_models_on_a_shake-table.jpg)
Theoretical or experimental evaluation of anticipated seismic performance mostly requires a structure simulation which is based on the concept of structural likeness or similarity.
Similarity is some degree of
analogy
Analogy (from Greek ''analogia'', "proportion", from ''ana-'' "upon, according to" lso "against", "anew"+ ''logos'' "ratio" lso "word, speech, reckoning" is a cognitive process of transferring information or meaning from a particular subject ( ...
or
resemblance
Resemblance may refer to:
*Similarity (philosophy)
*Resemblance nominalism
*Family Resemblance (anthropology)
*Ludwig Wittgenstein's family resemblances
*In text mining, the degree to which two documents resemble each other, calculated using shingl ...
between two or more objects. The notion of similarity rests either on exact or approximate repetitions of
patterns
A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated l ...
in the compared items.
In general, a building model is said to have similarity with the real object if the two share ''geometric similarity'', ''kinematic similarity'' and ''dynamic similarity''. The most vivid and effective type of similarity is the ''kinematic'' one. ''Kinematic similarity'' exists when the paths and velocities of moving particles of a model and its prototype are similar.
The ultimate level of ''kinematic similarity'' is ''kinematic equivalence'' when, in the case of earthquake engineering, time-histories of each story lateral displacements of the model and its prototype would be the same.
Seismic vibration control
Seismic vibration control is a set of technical means aimed to mitigate seismic impacts in building and
non-building structures. All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybrid'' where:
* ''passive control devices'' have no
feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
capability between them, structural elements and the ground;
* ''
active control devices'' incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and
actuator
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
An actuator requires a control device (controlled by control signal) a ...
s within the structure;
* ''hybrid control devices'' have combined features of active and passive control systems.
When ground
seismic waves
A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. S ...
reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.
After the seismic waves enter a
superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships.
Aboard ships and large boats
On water craft, the superstruct ...
, 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
dissipate
In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to ...
the wave energy inside a
superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships.
Aboard ships and large boats
On water craft, the superstruct ...
with properly engineered
damper
A damper is a device that deadens, restrains, or depresses. It may refer to:
Music
* Damper pedal, a device that mutes musical tones, particularly in stringed instruments
* A mute for various brass instruments
Structure
* Damper (flow), a mechan ...
s;
* to disperse the wave energy between a wider range of frequencies;
* to
absorb the
resonant
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
portions of the whole wave frequencies band with the help of so-called ''
mass dampers''.
![Cyrus tomb](https://upload.wikimedia.org/wikipedia/commons/a/a8/Cyrus_tomb.jpg)
Devices of the last kind, abbreviated correspondingly as TMD for the tuned (''passive''), as AMD for the ''active'', and as HMD for the ''hybrid mass dampers'', have been studied and installed in
high-rise building
A tower block, high-rise, apartment tower, residential tower, apartment block, block of flats, or office tower is a tall building, as opposed to a low-rise building and is defined differently in terms of height depending on the jurisdictio ...
s, predominantly in Japan, for a quarter of a century.
However, there is quite another approach: partial suppression of the seismic energy flow into the
superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships.
Aboard ships and large boats
On water craft, the superstruct ...
known as seismic or
base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoup ...
.
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
superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships.
Aboard ships and large boats
On water craft, the superstruct ...
from its
substructure resting on a shaking ground.
The first evidence of earthquake protection by using the principle of base isolation was discovered in
Pasargadae
Pasargadae (from Old Persian ''Pāθra-gadā'', "protective club" or "strong club"; Modern Persian: ''Pāsārgād'') was the capital of the Achaemenid Empire under Cyrus the Great (559–530 BC), who ordered its construction and the location of ...
, a city in ancient Persia, now Iran, and dates back to the 6th century BCE. Below, there are some samples of seismic vibration control technologies of today.
Dry-stone walls in Peru
Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
is a highly
seismic
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
land; for centuries the dry-stone
construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
proved to be more earthquake-resistant than using mortar.
People of
Inca civilization
The Incas were most notable for establishing the Inca Empire in Pre-Columbian America, which was centered in modern day South America in Peru and Chile. It was about 2,500 miles from the northern to southern tip. The civilization lasted from 14 ...
were masters of the polished 'dry-stone walls', called
ashlar
Ashlar () is finely dressed (cut, worked) stone, either an individual stone that has been worked until squared, or a structure built from such stones. Ashlar is the finest stone masonry unit, generally rectangular cuboid, mentioned by Vitruv ...
, where blocks of stone were cut to fit together tightly without any
mortar. The Incas were among the best stonemasons the world has ever seen 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
structural control technique employing both the principle of energy dissipation (coulomb damping) and that of suppressing
resonant
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
amplifications.
Tuned mass damper
![Taipei 101 Tuned Mass Damper](https://upload.wikimedia.org/wikipedia/commons/1/15/Taipei_101_Tuned_Mass_Damper.png)
Typically the
tuned mass damper
A tuned mass damper (TMD), also known as a harmonic absorber or seismic damper, is a device mounted in structures to reduce mechanical vibrations, consisting of a mass mounted on one or more damped springs. Its oscillation frequency is tuned ...
s are huge concrete blocks mounted in
skyscraper
A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ris ...
s or other structures and move in opposition to the
resonance frequency
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
oscillations of the structures by means of some sort of spring mechanism.
The
Taipei 101
Taipei 101 (; stylized as TAIPEI 101), formerly known as the Taipei World Financial Center, is a supertall skyscraper in Taipei, Taiwan. This building was officially classified as the world's tallest from its opening in 2004 until the 2009 ...
skyscraper needs to withstand
typhoon
A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for a ...
winds and earthquake
tremor
A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...
s common in this area of Asia/Pacific. For this purpose, a steel
pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the ...
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
gusts.
Hysteretic dampers
A hysteretic damper is intended to provide better and more reliable seismic performance than that of a conventional structure by increasing the dissipation of
seismic input energy. There are five major groups of hysteretic dampers used for the purpose, namely:
:* Fluid viscous dampers (FVDs)
Viscous Dampers have the benefit of being a supplemental damping system. They have an oval hysteretic loop and the damping is velocity dependent. While some minor maintenance is potentially required, viscous dampers generally do not need to be replaced after an earthquake. While more expensive than other damping technologies they can be used for both seismic and wind loads and are the most commonly used hysteretic damper.
:* Friction dampers (FDs)
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
coulomb damper. Depending on the design, friction dampers can experience
stick-slip phenomenon The stick–slip phenomenon, also known as the slip–stick phenomenon or simply stick–slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other.
Cause
Below is a simple, heuristic description of stick ...
and
Cold welding
Cold welding or contact welding is a solid-state welding process in which joining takes place without fusion or heating at the interface of the two parts to be welded. Unlike in fusion welding, no liquid or molten phase is present in the joint. ...
. The main disadvantage being that friction surfaces can wear over time and for this reason they are not recommended for dissipating wind loads. When used in seismic applications wear is not a problem and there is no required maintenance. They have a rectangular hysteretic loop and as long as the building is sufficiently elastic they tend to settle back to their original positions after an earthquake.
:* Metallic yielding dampers (MYDs)
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.
:* Viscoelastic dampers (VEDs)
Viscoelastic dampers are useful in that they can be used for both wind and seismic applications, they are usually limited to small displacements. There is some concern as to the reliability of the technology as some brands have been banned from use in buildings in the United States.
:* Straddling pendulum dampers (swing)
Base isolation
Base isolation seeks to prevent the kinetic energy of the earthquake from being transferred into elastic energy in the building. These technologies do so by isolating the structure from the ground, thus enabling them to move somewhat independently. The degree to which the energy is transferred into the structure and how the energy is dissipated will vary depending on the technology used.
:* Lead rubber bearing
![LRBtest](https://upload.wikimedia.org/wikipedia/commons/b/bc/LRBtest.jpg)
Lead rubber bearing or LRB is a type of
base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoup ...
employing a heavy
damping
Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples incl ...
. It was invented by
Bill Robinson
Bill Robinson, nicknamed Bojangles (born Luther Robinson; May 25, 1878 – November 25, 1949), was an American tap dancer, actor, and singer, the best known and the most highly paid African-American entertainer in the United States during the f ...
, a New Zealander.
Heavy damping mechanism incorporated in
vibration control
In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures.
All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybrid' ...
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 video shows a Lead Rubber Bearing being tested at the
UCSD
The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public university, public Land-grant university, land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Insti ...
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 Museum of New Zealand Te Papa Tongarewa is New Zealand's national museum and is located in Wellington. ''Te Papa Tongarewa'' translates literally to "container of treasures" or in full "container of treasured things and people that spring fr ...
, the national museum of New Zealand, and the New Zealand
Parliament Buildings have been fitted with the bearings. Both are in
Wellington
Wellington ( mi, Te Whanganui-a-Tara or ) is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the second-largest city in New Zealand by me ...
which sits on an
active fault
An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...
.
:* Springs-with-damper base isolator
![GERB spring with damper](https://upload.wikimedia.org/wikipedia/commons/0/03/GERB_spring_with_damper.jpg)
Springs-with-damper base isolator installed under a three-story town-house,
Santa Monica
Santa Monica (; Spanish: ''Santa Mónica'') is a city in Los Angeles County, situated along Santa Monica Bay on California's South Coast. Santa Monica's 2020 U.S. Census population was 93,076. Santa Monica is a popular resort town, owing to ...
, California is shown on the photo taken prior to the 1994
Northridge earthquake
The 1994 Northridge earthquake was a moment 6.7 (), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the City of Los Angeles.
The quake had a duration of approximately ...
exposure. It is a
base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoup ...
device conceptually similar to ''Lead Rubber Bearing''.
One of two three-story town-houses like this, which was well instrumented for recording of both vertical and horizontal
acceleration
In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the ...
s on its floors and the ground, has survived a severe shaking during the
Northridge earthquake
The 1994 Northridge earthquake was a moment 6.7 (), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the City of Los Angeles.
The quake had a duration of approximately ...
and left valuable recorded information for further study.
:* Simple roller bearing
Simple roller bearing is a
base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoup ...
device which is intended for protection of various building and non-building structures against potentially damaging
lateral impacts 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 ''
metallic roller bearing
A metallic roller bearing is a base isolation device which is intended for protection of various building and non-building structures against potentially damaging lateral impacts of strong earthquakes.
This bearing support may be adapted, with ce ...
'' for a housing complex (17 stories) in
Tokyo, Japan
Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...
.
:*
Friction pendulum bearing (FPB) is another name of friction pendulum system (FPS). It is based on three pillars:
* articulated friction slider;
* spherical concave sliding surface;
* enclosing cylinder for lateral displacement restraint.
Snapshot with the link to video clip of a
shake-table testing of FPB system supporting a rigid building model is presented at the right.
Seismic design
Seismic design is based on authorized engineering procedures, principles and criteria meant to
design
A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process or the result of that plan or specification in the form of a prototype, product, or process. The verb ''to design'' ...
or
retrofit
Retrofitting is the addition of new technology or features to older systems. Retrofits can happen for a number of reasons, for example with big capital expenditures like naval vessels, military equipment or manufacturing plants, businesses or go ...
structures subject to earthquake exposure.
[ Those criteria are only consistent with the contemporary state of the knowledge about ]earthquake engineering structures
Earthquake-resistant or aseismic structures are designed to protect buildings to some or greater extent from earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to ...
. Therefore, a building design which exactly follows seismic code regulations does not guarantee safety against collapse or serious damage.
The price of poor seismic design may be enormous. Nevertheless, seismic design has always been a trial and error
Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying.
According to W.H. Thorpe, the term was devised by C. Lloyd Morgan (1 ...
process whether it was based on physical laws or on empirical knowledge of the structural performance of different shapes and materials.
To practice seismic design
Seismic analysis is a subset of structural analysis and is the calculation of the response of a building (or nonbuilding) structure to earthquakes. It is part of the process of structural design, earthquake engineering or structural assessment ...
, seismic analysis or seismic evaluation of new and existing civil engineering projects, an engineer
Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considering the l ...
should, normally, pass examination on ''Seismic Principles'' which, in the State of California, include:
* Seismic Data and Seismic Design Criteria
* Seismic Characteristics of Engineered Systems
* Seismic Forces
* Seismic Analysis Procedures
* Seismic Detailing and Construction Quality Control
To build up complex structural systems, 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 failure mode
Failure causes are defects in design, process, quality, or part application, which are the underlying cause of a failure or which initiate a process which leads to failure. Where failure depends on the user of the product or process, then human er ...
s of a structure and providing the structure with appropriate strength
Strength may refer to:
Physical strength
*Physical strength, as in people or animals
*Hysterical strength, extreme strength occurring when people are in life-and-death situations
*Superhuman strength, great physical strength far above human ca ...
, stiffness
Stiffness is the extent to which an object resists deformation in response to an applied force.
The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.
Calculations
The stiffness, k, of a b ...
, ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, and configuration
Configuration or configurations may refer to:
Computing
* Computer configuration or system configuration
* Configuration file, a software file used to configure the initial settings for a computer program
* Configurator, also known as choice board ...
to ensure those modes cannot occur.
Seismic design requirements
Seismic design requirements depend on the type of the structure, locality of the project and its authorities which stipulate applicable seismic design codes and criteria. For instance, California Department of Transportation
The California Department of Transportation (Caltrans) is an executive department of the U.S. state of California. The department is part of the cabinet-level California State Transportation Agency (CalSTA). Caltrans is headquartered in Sacrame ...
's requirements called ''The Seismic Design Criteria'' (SDC) and aimed at the design of new bridges in California incorporate an innovative seismic performance-based approach.
The most significant feature in the SDC design philosophy is a shift from a ''force-based assessment'' of seismic demand to a ''displacement-based assessment'' of demand and capacity. Thus, the newly adopted displacement approach is based on comparing the ''elastic displacement'' demand to the ''inelastic displacement'' 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 ''ground stabilization'' underneath the structure: sometimes, heavily shaken ground breaks up which leads to collapse of the structure sitting upon it.
The following topics should be of primary concerns: liquefaction; dynamic lateral earth pressures on retaining walls; seismic slope stability; earthquake-induced settlement.
Nuclear facilities
Nuclear may refer to:
Physics
Relating to the Atomic nucleus, nucleus of the atom:
*Nuclear engineering
*Nuclear physics
*Nuclear power
*Nuclear reactor
*Nuclear weapon
*Nuclear medicine
*Radiation therapy
*Nuclear warfare
Mathematics
*Nuclear ...
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. The Fukushima I nuclear accidents
The was a nuclear accident in 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. The proximate cause of the disaster was the 2011 Tōhoku earthquake and tsunami, which occurred on the afternoon of 11 March 2011 and ...
and damage to other nuclear facilities that followed the 2011 Tōhoku earthquake and tsunami
The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude 9.0–9.1 (M) undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region, and lasted approximately six minutes ...
have, however, drawn attention to ongoing concerns over Japanese nuclear seismic design standards and caused many other governments to re-evaluate their nuclear programs. Doubt has also been expressed over the seismic evaluation and design of certain other plants, including the Fessenheim Nuclear Power Plant
The Fessenheim Nuclear Power Plant is located in the Fessenheim commune in the Haut-Rhin department in Grand Est in north-eastern France, north east of the Mulhouse urban area, within of the border with Germany, and approximately from Switzerla ...
in France.
Failure modes
Failure mode 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 ''seismic design'' methods. Below, some typical modes of earthquake-generated failures are presented.
The lack of reinforcement
In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher freq ...
coupled with poor mortar and inadequate roof-to-wall ties can result in substantial damage to an unreinforced masonry building. Severely cracked or leaning walls are some of the most common earthquake damage. Also hazardous is the damage that may occur between the walls and roof or floor diaphragms. Separation between the framing and the walls can jeopardize the vertical support of roof and floor systems.
Soft story effect. 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 brick veneer
Masonry veneer walls consist of a single non-structural external layer of masonry, typically made of brick, stone or manufactured stone. Masonry veneer can have an air space behind it and is technically called "anchored veneer". A masonry veneer ...
, has been completely dismantled from the studwall. Only the rigidity 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.
Soil liquefaction
Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in ...
. 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, liquefaction
In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics.
It occurs both naturally and artificially. As an example of the ...
of those loose saturated deposits may result in non-uniform settlements and tilting of structures. This caused major damage to thousands of buildings in Niigata, Japan during the 1964 earthquake.
Landslide rock fall. A landslide
Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...
is a geological phenomenon which includes a wide range of ground movement, including rock falls. Typically, the action of gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
is the primary driving force for a landslide to occur though in this case there was another contributing factor which affected the original slope stability
Slope stability analysis is a static or dynamic, analytical or empirical method to evaluate the stability of earth and rock-fill dams, embankments, excavated slopes, and natural slopes in soil and rock. Slope stability refers to the condition of i ...
: the landslide required an ''earthquake trigger'' before being released.
Pounding against adjacent building. This is a photograph of the collapsed five-story tower, St. Joseph's Seminary, Los Altos, California
Los Altos (; Spanish for "The Heights") is a city in Santa Clara County, California, in the San Francisco Bay Area. The population was 31,625 according to the 2020 census.
Most of the city's growth occurred between 1950 and 1980. Originally a ...
which resulted in one fatality. During Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred on California's Central Coast on October 17 at local time. The shock was centered in The Forest of Nisene Marks State Park in Santa Cruz County, approximately northeast of Santa Cruz on a section of t ...
, 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 Northridge earthquake
The 1994 Northridge earthquake was a moment 6.7 (), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the City of Los Angeles.
The quake had a duration of approximately ...
, the Kaiser Permanente concrete frame office building had joints completely shattered, revealing inadequate confinement steel, which resulted in the second story collapse. In the transverse direction, composite end shear wall
In structural engineering, a shear wall is a vertical element of a system that is designed to resist in-plane lateral forces, typically wind and seismic loads. In many jurisdictions, the International Building Code and International Residential Co ...
s, consisting of two wythe
A wythe is a continuous vertical section of masonry one unit in thickness. A wythe may be independent of, or interlocked with, the adjoining wythe(s). A single wythe of brick that is not structural in nature is referred to as a masonry veneer
...
s of brick and a layer of shotcrete
Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically r ...
that carried the lateral load, peeled apart because of inadequate through-ties and failed.
* Improper construction site
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
on a foothill
Foothills or piedmont are geographically defined as gradual increases in elevation at the base of a mountain range, higher hill range or an upland area. They are a transition zone between plains and low relief hills and the adjacent topograp ...
.
* Poor detailing of the reinforcement
In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher freq ...
(lack of concrete confinement in the columns and at the beam-column joints, inadequate splice length).
* Seismically weak soft story at the first floor.
* Long cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
s with heavy dead load
A structural load or structural action is a force, deformation, or acceleration applied to structural elements. A load causes stress, deformation, and displacement in a structure. Structural analysis, a discipline in engineering, analyzes the e ...
.
Sliding off foundations effect of a relatively rigid residential building structure during 1987 Whittier Narrows earthquake
The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of Southern California, United States, at on October 1. The moderate magnitude 5.9 blind thrust earthquake was centered several miles no ...
. The magnitude 5.9 earthquake pounded the Garvey West Apartment building in Monterey Park, California and shifted its superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships.
Aboard ships and large boats
On water craft, the superstruct ...
about 10 inches to the east on its foundation.
If a superstructure is not mounted on a base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoup ...
system, its shifting on the basement should be prevented.
Reinforced concrete
Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
column burst at Northridge earthquake
The 1994 Northridge earthquake was a moment 6.7 (), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the City of Los Angeles.
The quake had a duration of approximately ...
due to insufficient shear reinforcement mode which allows main reinforcement to buckle
The buckle or clasp is a device used for fastening two loose ends, with one end attached to it and the other held by a catch in a secure but adjustable manner. Often taken for granted, the invention of the buckle was indispensable in securing tw ...
outwards. The deck unseated at the hinge
A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...
and failed in shear. As a result, the La Cienega-Venice underpass
A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube constr ...
section of the 10 Freeway collapsed.
Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred on California's Central Coast on October 17 at local time. The shock was centered in The Forest of Nisene Marks State Park in Santa Cruz County, approximately northeast of Santa Cruz on a section of t ...
: side view of reinforced concrete support-columns failure which triggered the upper deck collapse onto the lower deck of the two-level Cypress viaduct of Interstate Highway 880, Oakland, CA.
Retaining wall failure at Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred on California's Central Coast on October 17 at local time. The shock was centered in The Forest of Nisene Marks State Park in Santa Cruz County, approximately northeast of Santa Cruz on a section of t ...
in Santa Cruz Mountains area: prominent northwest-trending extensional cracks up to 12 cm (4.7 in) wide in the concrete spillway
A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...
to Austrian Dam, the north abutment
An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end which provide vertical and lateral support for the span, as well as acting as retaining walls ...
.
Ground shaking triggered soil liquefaction
Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in ...
in a subsurface layer of sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
, producing differential lateral and vertical movement in an overlying carapace
A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
of unliquefied sand and silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
. This mode of ground failure, termed lateral spreading, is a principal cause of liquefaction-related earthquake damage.
Severely damaged building of Agriculture Development Bank of China after 2008 Sichuan earthquake: most of the beams and pier columns are sheared. Large diagonal cracks in masonry and veneer are due to in-plane loads while abrupt settlement
Settlement may refer to:
*Human settlement, a community where people live
*Settlement (structural), the distortion or disruption of parts of a building
* Closing (real estate), the final step in executing a real estate transaction
*Settlement (fin ...
of the right end of the building should be attributed to a landfill
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
which may be hazardous even without any earthquake.
Twofold tsunami impact: sea wave
In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction o ...
s hydraulic pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
and inundation
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...
. Thus, the Indian Ocean earthquake of December 26, 2004, with the epicenter
The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.
Surface damage
Before the instrumental pe ...
off the west coast of Sumatra
Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...
, Indonesia, triggered a series of devastating tsunamis, killing more than 230,000 people in eleven countries by inundating surrounding coastal communities with huge waves up to 30 meters (100 feet) high.
Earthquake-resistant construction
Earthquake construction means implementation of seismic design to enable building and non-building structures to live through the anticipated earthquake exposure up to the expectations and in compliance with the applicable building code
A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...
s.
Design and construction are intimately related. To achieve a good workmanship, detailing of the members and their connections should be as simple as possible. As any construction in general, earthquake construction is a process that consists of the building, retrofitting or assembling of infrastructure given the construction materials available.
The destabilizing action of an earthquake on constructions may be ''direct'' (seismic motion of the ground) or ''indirect'' (earthquake-induced landslides, soil liquefaction
Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in ...
and waves of tsunami).
A structure might have all the appearances of stability, yet offer nothing but danger when an earthquake occurs. The crucial fact is that, for safety, earthquake-resistant construction techniques are as important as quality control
Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements".
This approach places ...
and using correct materials. ''Earthquake contractor'' should be registered in the state/province/country of the project location (depending on local regulations), bonded and insured
Insurance is a means of protection from financial loss in which, in exchange for a fee, a party agrees to compensate another party in the event of a certain loss, damage, or injury. It is a form of risk management, primarily used to hedge ...
.
To minimize possible losses, construction process should be organized with keeping in mind that earthquake may strike any time prior to the end of construction.
Each construction project
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and come ...
requires a qualified team of professionals who understand the basic features of seismic performance of different structures as well as construction management
Construction management (CM) is a professional service that uses specialized, project management techniques and software to oversee the planning, design, construction and closeout of a project. The purpose of Construction management is to control ...
.
Adobe structures
Around thirty percent of the world's population lives or works in earth-made construction. Adobe
Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of e ...
type of mud brick
A mudbrick or mud-brick is an air-dried brick, made of a mixture of loam, mud, sand and water mixed with a binding material such as rice husks or straw. Mudbricks are known from 9000 BCE, though since 4000 BCE, bricks have also been fi ...
s is one of the oldest and most widely used building materials. The use of adobe
Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of e ...
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.
Adobe buildings are considered very vulnerable at strong quakes. However, multiple ways of seismic strengthening of new and existing adobe buildings are available.
Key factors for the improved seismic performance of
adobe construction are:
* Quality of construction.
* Compact, box-type layout.
* Seismic reinforcement.
Limestone and sandstone structures
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
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 limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
and sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
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 and County Building
The Salt Lake City and County Building, usually called the "City-County Building", is the seat of government for Salt Lake City, Utah. The historic landmark formerly housed offices for Salt Lake County government as well, hence the name.
History ...
in Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
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.
Timber frame structures
Timber framing 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 timber framing in buildings provides their complete skeletal framing which offers some structural benefits as the timber frame, if properly engineered, lends itself to better ''seismic survivability''.
Light-frame structures
Light-frame construction, Light-frame structures usually gain seismic resistance from rigid plywood shear walls and wood structural panel diaphragm (structural system), diaphragms. Special provisions for seismic load-resisting systems for all engineered wood structures requires consideration of diaphragm ratios, horizontal and vertical diaphragm shears, and Gender of connectors and fasteners, connector/fastener values. In addition, collectors, or drag struts, to distribute shear along a diaphragm length are required.
Reinforced masonry structures
A construction system where steel reinforcement is embedded in the mortar joints of masonry or placed in holes and that are filled with concrete or grout is called reinforced masonry. There are various practices and techniques to reinforce masonry. The most common type is the reinforced ''hollow unit masonry''.
To achieve a ductile behavior in masonry, it is necessary that the shear strength of the wall is greater than the flexural strength. The effectiveness of both vertical and horizontal reinforcements depends on the type and quality of the masonry units and mortar.
The devastating 1933 Long Beach earthquake revealed that masonry is prone to earthquake damage, which led to the California Codes, California State Code making masonry reinforcement mandatory across California.
Reinforced concrete structures
Reinforced concrete
Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
is concrete in which steel reinforcement bars (rebars) or fibers have been incorporated to strengthen a material that would otherwise be brittle. It can be used to produce Beam (structure), beams, columns, floors or bridges.
Prestressed concrete is a kind of reinforced concrete used for overcoming concrete's natural weakness in tension. It can be applied to Beam (structure), beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member 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 ductile 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.
Prestressed structures
Prestressed structure is the one whose overall integrity, Structural stability, stability and security depend, primarily, on a ''prestressing''. ''Prestressing'' means the intentional creation of permanent stresses in a structure for the purpose of improving its performance under various service conditions.
There are the following basic types of prestressing:
* Pre-compression (mostly, with the own weight of a structure)
* Prestressed concrete, Pretensioning with high-strength embedded tendons
* Prestressed concrete, Post-tensioning with high-strength bonded or unbonded tendons
Today, the concept of prestressed structure is widely engaged in design of buildings, underground structures, TV towers, power stations, floating storage and offshore facilities, nuclear reactor vessels, and numerous kinds of bridge systems.
A beneficial idea of ''prestressing'' was, apparently, familiar to the ancient Rome architects; look, e.g., at the tall attic wall of Colosseum working as a stabilizing device for the wall piers beneath.
Steel structures
Steel structures are considered mostly earthquake resistant but some failures have occurred. A great number of welded steel moment-resisting frame buildings, which looked earthquake-proof, surprisingly experienced brittle behavior and were hazardously damaged in the 1994 Northridge earthquake. After that, the Federal Emergency Management Agency (FEMA) initiated development of repair techniques and new design approaches to minimize damage to steel moment frame buildings in future earthquakes.
For structural steel seismic design based on Load and Resistance Factor Design (LRFD) approach, it is very important to assess ability of a structure to develop and maintain its bearing resistance in the inelastic range. A measure of this ability is ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, which may be observed in a ''material itself'', in a ''structural element'', or to a ''whole structure''.
As a consequence of Northridge earthquake
The 1994 Northridge earthquake was a moment 6.7 (), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the City of Los Angeles.
The quake had a duration of approximately ...
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 Steel Moment Resisting Frames employ either connections contained in AISC 358, or the use of connections that have been subjected to pre-qualifying cyclic testing.
Prediction of earthquake losses
Earthquake loss estimation is usually defined as a ''Damage Ratio'' (DR) which is a ratio of the earthquake damage repair cost to the Total Economic Value, total value of a building. ''Probable Maximum Loss'' (PML) 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.
Earthquake loss estimations are also referred to as ''Seismic Risk Assessments''. The risk assessment process generally involves determining the probability of various ground motions coupled with the vulnerability or damage of the building under those ground motions. The results are defined as a percent of building replacement value.
See also
* Anchor plate
* Earthquake Engineering Research Institute
The Earthquake Engineering Research Institute (EERI) is a leading technical society in dissemination of earthquake risk and earthquake engineering research both in the U.S. and globally. EERI members include researchers, geologists, geotechnical e ...
* Earthquake resistant structures
* Emergency management
* Facade
* Geotechnical engineering
* International Institute of Earthquake Engineering and Seismology
* List of international earthquake acceleration coefficients
* National Center for Research on Earthquake Engineering
* Probabilistic risk assessment
* Seismic intensity scales
* Seismic magnitude scales
* Seismic response of landfill
* Seismic retrofit
* Seismic site response
* Soil structure interaction
* Spectral acceleration
References
External links
*
Earthquake Engineering Research Institute
Consortium of Universities for Research in Earthquake Engineering (CUREE)
NHERI: A natural hazards engineering research infrastructure
* [http://www.inrisk.ubc.ca/ Infrastructure Risk Research Project at The University of British Columbia, Vancouver, Canada]
{{Authority control
Earthquake engineering,
Civil engineering
Structural engineering
Seismic vibration control
Engineering disciplines
Seismology