ENGINEERING:
Engineering is the application of scientific and technical knowledge to solve human
problems. Engineers use imagination, judgment and reasoning to apply science, technology,
mathematics, and practical experience. The result is the engineering design, production, and
operation of useful objects or processes.
Engineering has several major fields, of which 19 major ones according to the National
Society of Professional Engineers are:
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Aerospace engineering
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Agricultural engineering
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Biomedical engineering
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Chemical engineering
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Civil engineering (general & structural)
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Computer engineering
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Control Systems
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Electrical & electronic engineering
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Environmental engineering
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Fire protection engineering
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Geotechnical engineering
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Industrial engineering
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Manufacturing engineering
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Mechanical engineering
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Mining engineering
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Nuclear engineering
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Petroleum engineering
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Sanitation engineering
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Traffic engineering
CIVIL ENGINEERING:
Civil Engineering is a broad field of engineering that deals with the planning, construction,
and maintenance of fixed structures, or public works, as they are related to earth, water, or
civilization and their processes. Most civil engineering today deals with roads, railways,
structures, water supply, sewer, flood control and traffic. In essence, civil engineering may be
regarded as the profession that makes the world a more agreeable place to live in.
STRUCTURAL ENGINEERING:
In the field of civil engineering, structural engineering is concerned with structural design
and structural analysis of structural components of buildings and non-building structures. This
involves calculating the stresses and forces that affect or arise within a structure, and designing
structural components that are able to withstand those forces. Major design concerns are building
seismic resistant structures and seismically retrofitting existing structures.
Structural engineers ensure that their designs satisfy a given design intent predicated on
safety (i.e. structures do not collapse without due warning) and on serviceability (i.e. floor
vibration and building sway are not uncomfortable to occupants). In addition, structural engineers
are responsible for making efficient use of funds and materials to achieve these over-arching
goals. Typically, entry-level structural engineers may design simple beams, columns, and floors
of a new building, including calculating the loads on each member and the load capacity of
various building materials (steel, timber, masonry, concrete). An experienced engineer would
tend to render more difficult structures, considering physics of moisture, heat and energy inside
the building components.
Structural loads on structures are generally classified as: live loads such as the weight of
occupants and furniture in a building, the forces of wind or weights of water, the forces due to
seismic activity such as an earthquake, dead loads including the weight of the structure itself and
all major architectural components and live roof loads such as material and manpower loading
the structure during construction. Structural engineers mainly fight against the forces of nature
like winds, earthquakes and Tsunamis. In recent years, however, reinforcing structures against
sabotage has taken on increased importance.
ENGINEERING DESIGN:
The task of the engineer is to identify, understand, and integrate the constraints on a
design in order to produce a successful result, which is called engineering design. It is usually not
enough to build a technically successful product; it must also meet further requirements.
Constraints may include available resources, physical or technical limitations, flexibility for future
modifications and additions, and other factors, such as requirements for cost, and the ability to
market, produce, and service. By understanding the constraints, engineers derive specifications
for the limits within which a viable structure may be produced and operated.
Engineers typically attempt to predict how well their designs will perform to their
specifications prior to full-scale production. They use, among other things: prototypes, scale
models, simulations, destructive tests, nondestructive tests, and stress tests. Creating an
appropriate mathematical model of a problem allows them to analyze it (sometimes definitively),
and to test potential solutions. Usually multiple reasonable solutions exist, so engineers must
evaluate the different design choices on their merits and choose the solution that best meets their
requirements.
Engineers as professionals take seriously their responsibility to produce designs that will
perform as expected and will not cause unintended harm to the public at large. Engineers
typically include a factor of safety in their designs to reduce the risk of unexpected failure.
However, the greater the safety factor, the less efficient the design may be.
As with all modern scientific and technological endeavors, computers and software play an
increasingly important role. Numerical methods and simulations can help predict design
performance more accurately than previous approximations. Computer models of designs can be
checked for flaws without having to make expensive and time-consuming prototypes. Of late, the
use of finite element method analysis (FEM analysis or FEA) software to study stress,
temperature, etc has gained importance. In addition, a variety of software is available to analyze
dynamic systems.
EARTHQUAKE:
Earthquakes are phenomena that result from the sudden release of stress in rocks that
radiate seismic waves. At the Earth's surface, earthquakes may manifest themselves by a
shaking or displacement of the ground and sometimes tsunamis, which may lead to loss of life
and destruction of property.
Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such
earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patch-work of plates in
slow but constant motion caused by the heat in the Earth's mantle and core. Plate boundaries
glide past each other, creating frictional stress. When the frictional stress exceeds a critical value,
called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure
occurs is called the fault plane. When the failure at the fault plane results in a violent
displacement of the Earth's crust, the elastic strain energy is released and elastic waves are
radiated, thus causing an earthquake.
Figure 1: Earth’s lithosphere tectonic plates.
Figure 2: Earth’s lithosphere tectonic plates’ boundaries.
The majority of tectonic earthquakes originate at depths not exceeding a few tens of miles.
Earthquakes occurring at boundaries of tectonic plates are called interplate earthquakes, while
the less frequent events that occur in the interior of the lithospheric plates are called intraplate
earthquakes.
Earthquakes occur on a daily basis around the world, most detected only by seismometers
and causing no damage. Large earthquakes however can cause serious destruction and massive
loss of life through a variety of agents of damage, including fault rupture, vibratory ground motion
(shaking), inundation (tsunami or dam failure), various kinds of permanent ground failure
(liquefaction, landslides), and fire or a release of hazardous materials.
Most large earthquakes are accompanied by other, smaller ones that can occur either
before or after the main shock; these are called foreshocks and aftershocks, respectively. While
almost all earthquakes have aftershocks, foreshocks occur in only about 10% of events.
EARTHQUAKES AND BUILDINGS:
In an earthquake, the building base experiences high-frequency movements, which results
in inertial forces on the building and its components. The force is created by the building's
tendency to remain at rest, and in its original position, even though the ground beneath it is
moving. This is in accordance with an important physical law known as D'Alembert's Principle,
which states that a mass acted upon by acceleration tends to oppose that acceleration in an
opposite direction and proportionally to the magnitude of the acceleration (See Figure 1). This
inertial force imposes strains upon the building's structural elements such as beams, columns,
walls and floors. If these strains are large enough, the building's structural elements suffer
damage of various kinds, which may lead to the collapse of the building.
Figure 3: Acceleration, Inertial Forces.
To illustrate the process of inertia generated strains within a structure, we can consider the
simplest kind of structure imaginable--a simple, perfectly rigid block of stone (See Figure 2).
During an earthquake, if this block is simply sitting on the ground without any attachment to it, the
block will move freely in a direction opposite to that of the ground motion, and with a force
proportional to the mass and acceleration of the block. If the same block, however, is solidly
founded in the ground and no longer able to move freely, it must in some way absorb the inertial
force internally. In Figure 2, this internal uptake of force is shown to result in cracking near the
base of the block.
Figure 4: Responses of a Simple Rigid Block.
Of course, real buildings do not respond as simply as described above. There are a
number of important characteristics common to all buildings which further affect and complicate a
building's response in terms of the accelerations it undergoes, and the deformations and
damages that it suffers.
The impact of an earthquake is determined by these factors:
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Earthquake details - magnitude, type, location, or depth
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Geologic conditions - distance from the epicenter, path of the seismic waves, types
of soil, water saturation of soil
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Social conditions - quality of construction, preparedness of the community, time of
day (e.g. rush hour)
Earthquakes can cause more damage and more deaths in some parts of the world
primarily because
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the buildings are poorly designed
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the buildings are poorly constructed
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seismic issues for the region have not been considered
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population density.
When engineers design a building, they consider a variety of important factors:
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Shape of the building: different shaped buildings behave differently. Geometric
shapes such as a square or rectangle usually perform better than buildings in the
shape of an L, T, U, H, +, O, or a combination of these.
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Various materials used to construct the building(s) can be used (alone or in
combination): steel, concrete, wood, brick. Concrete is the most widely used
construction material in the world. It is comprised of sand, gravel, and crushed
stone, held together with cement. Each material behaves differently. Ductile
materials perform better than brittle ones. Examples of ductile materials include
steel and aluminum. Examples of brittle materials include brick, stone and
unstrengthened concrete.
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Height of the building. Different heights shake at different frequencies.
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Soil beneath the building. Buildings constructed on soft soil force may suffer from a
stronger ground motion, and those on hard rocks are subject to high frequency
waves.
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Regional topography. Buildings on a hill are likely to slide down as the earthquake
strikes.
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Magnitude and duration of the earthquake.
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Direction and frequency of shaking.
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The number of earthquakes the building has previously had and the kinds of
damage suffered, if any. While the building may seem undamaged under weak to
moderate earthquakes, the resulting small damages and cracks make it more
vulnerable to future events.
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Intended function of the building (e.g. hospital, fire station, office building). If the
building is an important one, or the building’s performance is essential in case of
destructive earthquakes, the engineers should design a stronger building which, on
the other hand, will be more expensive.
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Proximity to other buildings.
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Financial limitations. Of course by spending a lot of money on a building, one can
have a very strong building, but it is the engineer’s task to make the most out of the
least resources.
Engineers’ standard approach to earthquake resistant design of buildings requires
providing the building with strength, stiffness and inelastic (unrecoverable or permanent)
deformation capacity, which are great enough to withstand a given level of earthquake-generated
force. This is generally accomplished by selecting an appropriate structural configuration and
carefully detailing the structural members, such as beams and columns, and the connections
between them.
In more advanced engineering approaches the engineers not only strengthen the building,
but try the amount of force transmitted to the main structural system. One of these methods is
base isolation, which directly reduces the effect of earthquake on the building. Another approach
can be putting advanced devices such as dampers in the building, which counter the effect of
earthquake, and reduce the amount of forces applied on the main structure.
Next, we briefly introduce some principles that should be considered in an earthquake
resistant building design.
LATERAL LOAD RESISTING SYSTEMS
When designing a building that will be capable of withstanding an earthquake, engineers
can choose various structural components, the earthquake resistance of which is now wellunderstood, and then combine them into what is known as a complete lateral load resisting
system. These structural components usually include:
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diaphragms
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shear walls
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braced frames
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moment resisting frames
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base isolation
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energy dissipation devices
These same elements are also basic parts of an architect's structural "vocabulary." The
choice of the appropriate lateral load resisting system for any particular building is thus highly
dependent upon the architectural concept of the building.
Of course, a building always possesses floors and a roof. But the earthquake resistant
characteristics of these basic elements are highly variable. Not only that, the building's horizontal
elements can be supported by a wide variety of wall and frame types or wall-frame combinations,
the choice of which is usually dictated by considerations other than earthquake resistance. For
instance, some buildings such as a warehouse or a parking garage must have a large open floor
space--which means that roof and floors of such structures will not be provided with as much
vertical support from beneath as they might be otherwise.
The engineer-designer in charge of making a building earthquake resistant must therefore
choose a combination of structural elements which will most favorably balance the demands of
earthquake resistance, building cost, building use, and architectural design.
DIAPHRAGMS
Diaphragms are horizontal resistance elements, generally floors and roofs that transfer the
lateral forces between the vertical resistance elements (shear walls or frames). Basically, a
diaphragm acts as a horizontal I-beam. That is, the diaphragm itself acts as the web of the beam
and its edges act as flanges.
Figure 5: Horizontal Diaphragm Action.
SHEAR WALLS
Shear walls are vertical walls that are designed to receive lateral forces from diaphragms
and transmit them to the ground. The forces in these walls are predominantly shear forces in
which the fibers within the wall try to slide past one another.
When you build a house of cards, you design a shear wall structure, and you soon learn
that sufficient card "walls" must be placed at right angles to one another or the house will
collapse.
Figure 6: Shear Walls.
If you were to connect your walls together with tape, it is easy to see that the strength of
this house of cards would immediately become greatly increased. This illustrates a very important
point: In general, the earthquake resistance of any building is highly dependent upon the
connections joining the building's larger structural members, such as walls, beams, columns and
floor-slabs.
Shear walls, in particular, must be strong in themselves and also strongly connected to
each other and to the horizontal diaphragms. In a simple building with shear walls at each end,
ground motion enters the building and creates inertial forces that move the floor diaphragms. This
movement is resisted by the shear walls and the forces are transmitted back down to the
foundation.
BRACED FRAMES
Braced frames act in the same manner as shear walls, but they may offer lower resistance
depending on their details of their design and construction. Bracing generally takes the form of
steel rolled sections, circular bar sections, or tubes. Vibration may cause the bracing to elongate
or compress, in which case it will lose its effectiveness and permit large deformations or collapse
of the vertical structure. Ductility therefore must be designed into the bracing to create a safe
assembly.
MOMENT RESISTANT FRAMES
When seismic resistance is provided by moment resistant frames, lateral forces are
resisted primarily by the joints between columns and beams. These joints become highly stressed
and the details of their construction are very important. Moment frames use, as a last-resort
resistance strategy, the energy absorption obtained by permanent deformation of the structure
prior to ultimate failure. For this reason, moment resistant frames generally are steel structures
with bolts or welded joints in which the natural ductility of the material is of advantage. However,
properly reinforced concrete frames that contain a large amount of steel reinforcing are also
effective as ductile frames. They will distort and retain resistance capacity prior to failure and will
not fail in a brittle manner.
Figure 7: Beam-Column Joint, Moment-Resisting Frame.
Architecturally, moment resistant frames offer a certain advantage over shear walls or
braced frames because they tend to provide structures that are much more unobstructed
internally than shear wall structures, which facilitates the design of accompanying architectural
elements such as exterior walls, partitions, and ceilings and the placement of building contents
such as furniture and loose equipment. Nevertheless, moment resistant frames require special
construction and detailing and, therefore, are more expensive than shear walls or braced frames.
BASE ISOLATION
It is easiest to see this principle at work by referring directly to the most widely used of
these advanced techniques, which is known as base isolation. A base isolated structure is
supported by a series of bearing pads which are placed between the building and the building's
foundation (See Figure 6). A variety of different types of base isolation bearing pads have now
been developed.
Figure 8: Base-Isolated and Fixed-Base Buildings.
For our example, we'll discuss lead-rubber bearings. These are among the frequently-used
types of base isolation bearings (See Figure 7). A lead-rubber bearing is made from layers of
rubber sandwiched together with layers of steel. In the middle of the bearing is a solid lead "plug."
On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to
the building and foundation. The bearing is very stiff and strong in the vertical direction, but
flexible in the horizontal direction.
Figure 9: Lead-Rubber Bearing.
EARTHQUAKE GENERATED FORCES
To get a basic idea of how base isolation works, first examine Figure 8. This shows an
earthquake acting on both a base isolated building and a conventional, fixed-base, building. As a
result of an earthquake, the ground beneath each building begins to move. In Figure 8, it is
shown moving to the left. Each building responds with movement which tends toward the right.
We say that the building undergoes displacement toward the right. The building's displacement in
the direction opposite the ground motion is actually due to inertia. The inertial forces acting on a
building are the most important of all those generated during an earthquake.
Figure 10: Base-Isolated, Fixed-Base Buildings.
It is important to know that the inertial forces which the building undergoes are proportional
to the building's acceleration during ground motion. It is also important to realize that buildings
don't actually shift in only one direction. Because of the complex nature of earthquake ground
motion, the building actually tends to vibrate back and forth in varying directions. So, Figure 8 is
really a kind of "snapshot" of the building at only one particular point of its earthquake response.
DEFORMATION AND DAMAGES
In addition to displacing toward the right, the un-isolated building is also shown to be
changing its shape-from a rectangle to a parallelogram. We say that the building is deforming.
The primary cause of earthquake damage to buildings is the deformation which the building
undergoes as a result of the inertial forces acting upon it.
The different types of damage which buildings can suffer are quite varied and depend upon
a large number of complicated factors. But to take one simple example, one can easily imagine
what happens to two pieces of wood joined at a right angle by a few nails, when the very heavy
building containing them suddenly starts to move very quickly--the nails pull out and the
connection fails.
RESPONSE OF BASE ISOLATED BUILDING
By contrast, even though it too is displacing, the base-isolated building retains its original,
rectangular shape. It is the lead-rubber bearings supporting the building that are deformed. The
base-isolated building itself escapes the deformation and damage--which implies that the inertial
forces acting on the base-isolated building have been reduced. Experiments and observations of
base-isolated buildings in earthquakes have shown that base isolation systems reduce building
accelerations to as little as 1/4 of the acceleration of comparable fixed-base buildings. As we
noted above, inertial forces increase, and decrease, proportionally as acceleration increases or
decreases.
Acceleration is decreased because the base isolation system lengthens a building's period
of vibration, the time it takes for the building to rock back and forth and then back again. And in
general, structures with longer periods of vibration tend to reduce acceleration, while those with
shorter periods tend to increase or amplify acceleration.
Finally, since they are highly elastic, the rubber isolation bearings don't suffer any damage.
But what about that lead plug in the middle of our example bearing? It experiences the same
deformation as the rubber. However, it also generates heat as it does so. In other words, the lead
plug reduces, or dissipates, the energy of motion -i.e. kinetic energy - by converting that energy
into heat. And by reducing the energy entering the building, it helps to slow and eventually stop
the building's vibrations sooner than would otherwise be the case - in other words, it damps the
building's vibrations. Damping is the fundamental property of all vibrating bodies which tends to
absorb the body's energy of motion, and thus reduce the amplitude of vibrations until the body's
motion eventually ceases.
A SECOND TYPE OF BASE ISOLATION: SPHERICAL SLIDING ISOLATION SYSTEMS
As we said earlier, lead-rubber bearings are just one of a number of different types of base
isolation bearings which have now been developed. Spherical Sliding Isolation Systems are
another type of base isolation. The building is supported by bearing pads that have a curved
surface and low friction. During an earthquake, the building is free to slide on the bearings. Since
the bearings have a curved surface, the building slides both horizontally and vertically (See
Figure 9). The force needed to move the building upwards limits the horizontal or lateral forces
which would otherwise cause building deformations. Also, by adjusting the radius of the bearing's
curved surface, this property can be used to design bearings that also lengthen the building's
period of vibration.
Figure 11: Spherical Sliding Isolation Bearing.
ENERGY DISSIPATION DEVICES
The second of the major new techniques for improving the earthquake resistance of
buildings also relies upon damping and energy dissipation, but it greatly extends the damping and
energy dissipation provided by lead-rubber bearings.
As we've said, a certain amount of vibrational energy is transferred to the building by
earthquake ground motion. Buildings themselves do possess an inherent ability to dissipate, or
damp, this energy. However, the capacity of buildings to dissipate energy before they begin to
suffer deformation and damage is quite limited. The building will dissipate energy either by
undergoing large scale movement or sustaining increased internal strains in elements such as the
building's columns and beams. Both of these eventually result in varying degrees of damage.
So, by equipping a building with additional devices which have high damping capacity, we
can greatly decrease the seismic energy entering the building, and thus decrease building
damage.
Accordingly, a wide range of energy dissipation devices have been developed and are now
being installed in real buildings. Energy dissipation devices are also often called damping
devices. The large number of damping devices that have been developed can be grouped into
three broad categories:
•
Friction Dampers: these utilize frictional forces to dissipate energy
•
Metallic Dampers: utilize the deformation of metal elements within the damper
•
Viscoelastic Dampers: are devices that show both stiffness and damping, and
utilize the controlled shearing of solids
•
Viscous Dampers: are devices that show only damping, and utilize the forced
movement of fluids within the damper
FLUID VISCOUS DAMPERS
To try to illustrate some of the general principles of damping devices, we'll look more
closely at one particular type of damping device, the Fluid Viscous Damper, which is one variety
of viscous dampers that has been widely utilized and has proven to be very effective in a wide
range of applications.
DAMPING DEVICES AND BRACING SYSTEMS
Damping devices are usually installed as part of bracing systems. Figure 10 shows one
type of damper-brace arrangement, with one end attached to a column and one end attached to a
floor beam. Primarily, this arrangement provides the column with additional support. Most
earthquake ground motion is in a horizontal direction; so, it is a building's columns which normally
undergo the most displacement relative to the motion of the ground. Figure 10 also shows the
damping device installed as part of the bracing system and gives some idea of its action.
Figure 12: Damping Device Installed with Brace.
STRUCTURAL MODEL PROPERTIES:
Understanding the requirements and limitations is one of the primary steps in engineering
design of a building. The engineer needs to know the level of performance required by the
building, the available material for construction, and of course, the overall cost that he/she is
allowed to allocate for that building. Next, we list some basic properties of the materials and
components that are allowed to be used in the building.
FLOORS:
2 mm Lauan Plywood – 30 cm ×30 cm - The structure has 5 stories
Mass: 275 g (0.6 lb )
Additional Mass: 490 g (1.08 lb )
COLUMNS:
5 mm -Diameter Hardwood Dowels – At least 4, up to 16 columns are allowed
Area: 17.81 mm
2
Area Moment of Inertia: 25.25 mm
4
Modulus of Elasticity: 3440 N / mm
2
CONNECTIONS:
Wood Glue or Hot Melt Glue
ESTIMATED STRUCTURAL SYSTEM PROPERTIES:
Damping Ratio: 16%
Natural Frequency: Ranges from 0.78 s to 1.57 s .
EXPLANATION OF PROPERTIES:
Now, we briefly introduce the properties listed above, to point out their performance to the
engineer, who is responsible in the selection of appropriate components and configurations.
MASS: is a property of a physical object that quantifies the amount of matter and energy it
contains. Unlike weight, the mass of something stays the same regardless of location. During an
earthquake, the ground acceleration results in inertial forces to be produced in masses present in
the structure. The more the mass, the more the force will be, and hence, stronger elements are
required to handle it during an earthquake.
AREA: is a physical quantity expressing the size of a part of a surface. Larger areas of the
same material normally produce more resistance to loads, but the shape of the part is also
important in determination of its stiffness.
AREA MOMENT OF INERTIA: is a property of a shape that is used to predict its
resistance to bending and deflection. Shapes of the same areas and materials may have different
moments of inertia, implying different resistance to external forces.
MODULUS OF ELASTICITY: is the mathematical description of an object or substance's
tendency to be deformed when a force is applied to it. Theoretically, it can be defined as the
amount of force required to reduce the length of an object with unit area and length to zero. As
this definition suggests, stiffer materials exhibit higher values elasticity modulus.
DAMPING: is any effect that tends to reduce the amplitude of oscillations of an oscillatory
system. All structures demonstrate damping in a variety of ways, as no oscillation will last forever
in any system. Damping ratio is a numerical quantity showing the damping as a percentage of a
critical damping, which is enough to prevent any oscillation in the system. Real values of damping
in civil engineering structures range from 2% to 10% of the critical value, depending on the
material and geometric properties, as well as excitation severity. Supplemental damping for
reduction of oscillation is possible through installation of special devices called dampers in the
building.
NATURAL FREQUENCY: is the oscillation rate at which the structure tends to oscillate.
This property depends on the material and geometric properties of the elements, as well as the
overall configuration of structure, connection properties, and the amount of mass present in the
building. A specific structure demonstrates several natural frequencies and their corresponding
mode shapes (oscillation form). When the natural frequency of the excitation gets closer to the
natural frequency of the building, resonance occurs, which results in increased drifts and
accelerations of the structure.
EARTHQUAKE RECORDS:
The earthquakes that are selected to be applied to the building are the 1940 El Centro,
1994 Northridge, and 1995 Kobe records. These data are actually recorded during the abovementioned earthquakes. The first one happened in Imperial Valley, CA, and was one of the first
earthquakes to be accurately recorded by the pre-installed instruments. The other two are
stronger than El Centro, but they happen less frequently. Each earthquake has specific properties
that make it different from others, and may affect the building in a very different way.
The problem is now to design a building, using the material whose properties were
mentioned above, to suffer the least damage under these earthquakes. As the El Centro record is
weaker than the others and its probability of occurrence is more, the building should be designed
to remain undamaged. The other two earthquakes, however, are too strong for a building to
remain undamaged, as it is too expensive to design a building that survives any earthquake. So
standards generally require the buildings to be designed in such a way that they don’t collapse
under strong earthquakes, but they may have some damage at the end. This shows the
importance of the inelastic deformation capacity of a building that allows it to deform, but not
collapse.
TESTING BUILDINGS:
A variety of experimental methods exist for testing buildings or building components under
the effect of earthquakes. These methods range from application of forces by actuators to largescale shake table tests.
In a shake table test, a reduced-scale model of building will be placed on a platform that
can simulate a pre-recorded earthquake by moving in horizontal and vertical directions. Simplified
versions of these shake tables are able to move in one direction only, and have limited force and
displacement capacity. As Figure 11 shows, there are some additional masses attached to each
floor, to represent the effect of entities present in any building, such as walls, appliances and
furniture. The deformations and accelerations of test structures are measured by the instruments
that are mounted on the system. These measurements give valuable information to the engineer,
that helps predict the structural behavior under a real earthquake.
Figure 13: An instrumented building model on a shake table.