Essay: APPLICATION OF ENERGY DISSIPATION DEVICES AS EARTHQUAKE RESISTANT TECHNIQUES ON STRUCTURE

1. INTRODUCTION
1.1 INTRODUCTION
‘Momentary shaking of the ground or vibrations or oscillations of the ground caused by the slip or bye volcanic or magnetic activity or other sudden stress changes in the earth are called earthquake’.
To protect the structure from significant damages and response reduction of structure under such severe earthquakes has become an important in structural engineering.
FIG 1.1 HOW EARTHQUAKE EFFECT ON STRUCTURE
The study of new technology option for the improvement of the earthquake resistant techniques in the construction sector should be based on the actual needs of the existent structure.
Now a days to protect the structure from earthquakes using advance earthquake techniques such like as shear wall, seismic isolation devices and seismic damping devices.
From the above techniques, we will present here seismic damping devices as earthquake resistant devices for protect the structure from earthquake effect. Seismic damping devices known as energy dissipation devices, which are absorb the dynamic energy come from ground.
Conventionally, structures are designed to resist dynamic forces through a combination of strength, deformability and energy absorption. These structures may deform well beyond the elastic limit, for example, in a severe earthquake. It indicates that structures designed with these methods are sometimes vulnerable to strong earthquake motions.
In order to avoid such critical damages, structural engineers are working to figure out different types of structural systems that are robust and can withstand strong motions. Alternatively, some types of structural protective systems may be implemented to mitigate the damaging effects of these dynamic forces. These systems work by absorbing or reflecting a portion of the input energy that would otherwise be transmitted to the structure itself.
In such a scenario, structural control techniques are believed to be one of the promising technologies for earthquake resistance design. The concept of structural control is to absorb vibration energy of the structure by introducing supplemental devices.
Various types of structural control theories and devices have been recently developed and introduced to large-scale civil engineering structures.
1.2 A BRIEF HISTROY OF ENERGY DISSIPATION DEVICES
Energy dissipation devices have been used in mechanical systems for over one hundred years. Of relevance to this presentation is the first use of fluid viscous dampers by the French army in the 1890s to dampen the shock loadings from artillery pieces. Many of the components in those dampers can be found in the most modern of fluid viscous dampers today.
The use of discrete energy dissipation devices for earthquake engineering applications is somewhat recent with the first applications in New Zealand in the 1970s.Yielding steel devices were used in these applications
The first applications of seismic energy dissipation devices in North America date to the late 1980s where use was made of yielding steel and fluid viscous dampers. However, the use of fluid damping devices for shock and vibration isolation dates back to the beginning of the 20th century.
The use of energy dissipation devices for buildings, bridges and infrastructure was spurred by the publication in the late 1980s of a draft guideline for the implementation of damping devices in buildings (Whittaker et al., 1993), which provided regulators with a means by which to judge the efficacy of a design using dampers. The draft guideline was superseded in mid 1990s with the publication of FEMA 273 and FEMA 274 (ATC, 1997) and lately with the publication of the 2003 NEHRP (BSSC, 2003) and Standard ASCE/SEI 7-05 (ASCE, 2005).
1.3 THE CONCEPT OF SEISMIC DAMPING DEVICES
FIG 1.2 CONCEPT OF DEMPING DEVICES
Damper is devices which dissipate to energy coming from ground due to occurring earthquake. As show in fig 1.3 Damper is provided in the structure at the wall, and also in foundation.
It is operated when either the wind load or seismic are work on structure at that time damper is providing ductility, stiffness to structure which is resist to access displacement or acceleration in structure, thus main concept to provide in structure is protect or resist the effect which occurring due to earthquake.
1.3.1 CONCEPT OF INTRINSIC DAMPING IN REINFORCED CONCRETE STRUCTURES
RCC structures are considered to possess 5% inherent damping whereas steel structures are believed to have 2% damping. However actual site measurements have shown that intrinsic damping of buildings is far more complicated and variable than the generic figures of 1.3 and 5%. Damping reduces as height increases and also the damping levels greatly differ from one building to another. For building up to 50 meters in height the measured intrinsic damping was seen to vary from 1 to 5% whereas for very tall structures greater than 200 meters in height the intrinsic damping was just 0.5 to 1%. What is of greater concern is that this intrinsic damping cannot be accurately known or calculated at the design stage.
Fig. 1.3 Concept of intrinsic damping structure
The only way to tell the correct damping is by physical testing and measurements after the building is constructed. This uncertainty in the damping levels can prove fatal under seismic conditions.
To prove the case in point if in actual the damping is 1%, where as the designer has designed the building assuming 5% damping then the structure so designed will not be able to perform to the expected standards in the event of an earthquake.
This emphasizes the thought process that the designers should assume a conservative damping value while designing else it is almost certain that even with computer aided analysis and design the buildings designed would be unsafe.
1.3.2 CONCEPT OF SUPPLEMENTARY DAMPIND IN STRUCTUR
(a)
(b)
Fig. 1.4 The concept of supplementary damping devices
Additional engineered and accurate damping can be very easily added to buildings by installing certain mechanical devices called dampers. Dampers can provide damping up to 25-30% of the critical, thereby ensuring that the building will perform very well in seismic conditions as also strong winds in case of very tall buildings.
Dampers act as shock absorbers and energy dissipaters during any type of motion and thus prevent the building from damage. By using dampers the designer is able to overcome the uncertainties of low intrinsic damping and this helps in predicting the dynamic response accurately. By adding additional damping the stiffness and building mass can also be reduced thereby ensuring that the building is now subjected to lower seismic forces.
The advantages of additional damping is reduced building sway thus preventing damage to structural and nonstructural components, reduced design forces as much of the energy is dissipated by the dampers and the uncertainty in the level of intrinsic damping is overcome through engineered supplementary damping.
Supplementary damping is also the most efficient and cost effective way to achieve energy dissipation in buildings. This would inadvertently mean decreasing the energy dissipation demand on the structural components i.e. beams/columns/slabs thereby increasing the survivability of the building structure. Dampers are mechanical devices that look somewhat like huge shock absorbers and their function is to absorb and dissipate the energy supplied by the ground movement during an earthquake so that the building remains unharmed.
Whenever the building is in motion during an earthquake tremor or excessive winds, dampers help in restricting the building from swaying excessively and thereby preventing structural damage. The energy absorbed by dampers gets converted into heat which is then dissipated harmlessly into the atmosphere.
Dampers thus work to absorb earthquake shocks ensuring that the structural members i.e. beam and columns remain unharmed. There are four types of dampers i.e. Viscoelastic, Friction, Metallic Yield and Fluid Viscous
2. THE PRINCIPLES OF ENERGY DISSIPATION DEVICE
2.1 BASIC PRINCIPLES AND METHOD ANALYSIS
With recent development and implementation of modern structural protective systems, the entire structural engineering discipline is now undergoing a major change. The traditional idealization of a building or bridge as a static entity is no longer adequate. Instead, structures must be analyzed and designed by considering their dynamic behavior.
It is with this in mind that we present some basic concepts related to topics that are of primary importance in understanding, analyzing, and designing structures that incorporate structural protective systems.
FIG 2.1 TRANSFORMING OF GROUND MOTION
In what follows, a simple single-degree-of-freedom (SDOF) structural model is discussed. This represents the prototype for dynamic behavior. Particular emphasis is given to the effect of damping. As we shall see, increased damping can significantly reduce system response to time-varying disturbances.
While this model is useful for developing an understanding of dynamic behavior, it is not sufficient for representing real structures. We must include more detail. Consequently, a multi-degree-of-freedom (MDOF) model is then introduced, and several numerical procedures are outlined for general dynamic analysis. A discussion comparing typical damping characteristics in traditional and control-augmented structures is also included. Finally, a treatment of energy formulations is provided.
Essentially one can envision an environmental disturbance as an injection of energy into a structure. Design then focuses on the management of that energy. As we shall see, these energy concepts are particularly relevant in the discussion of passively or actively damped structures.
2.2 SINGLE DEGREE OF FREEDOM STRUCTURAL SYSTEMS
If a single coordinate is sufficient to define at instant of time of the position of the mass of the system, it is referred to as a single degree of freedom system (SDOF).
Consider the lateral motion of the basic SDOF model, shown in Figure 2.2, consisting of a mass, m, supported by springs with total linear elastic stiffness, k, and a damper with linear viscosity, c. This SDOF system is then subjected to an external disturbance, characterized by f(t). The excited model responds with a lateral displacement, x(t), relative to the ground, which satisfies the equation of motion:
(a)
(b)
FIG. 2.2 SDOF MODEL
mx ??+cx ??+kx=f(t)
in which a superposed dot represents differentiation with respect to time. For a specified input, f(t),and with known structural parameters, the solution of this equation can be readily obtained.
In the above, f(t) represents an arbitrary environmental disturbance such as wind or an earthquake.
In the case of an earthquake load,
f(t)=-m(x_g ) ??(t)
g(t) is ground acceleration.
Consider now the addition of a generic passive or active control element into the SDOF model, as indicated in Figure 2.3. The response of the system is now influenced by this additional element.
FIG 2.3 SDOF MODEL WITH CONTROL ELEMENT
The symbol ?? in Figure 2.3 represents a generic integro differential operator, such that the force corresponding to the control device is written simply as ??x. This permits quite general response characteristics, including displacement, velocity, or acceleration-dependent contributions, as well as hereditary effects. The equation of motion for the extended SDOF model then becomes, in the case of an earthquake load,
mx ??+cx ??+kx+??x=-(m+m ?? ) x ??_g
With m representing the mass of the control element.
The specific form of ??x needs to be specified before Equation can be analyzed, which is
necessarily highly dependent on the device type. For passive energy dissipation systems, it can be represented by a force-displacement relationship such as the one, representing a rate-independent elastic-perfectly plastic element. For an active control system, the form of ??x is governed by the control law chosen for a given application. Let us first note that, denoting the control force applied to the structure by u(t), the resulting dynamical behavior of the structure is governed by Equation with
??x= ‘ u(t)
Suppose that a feedback configuration is used in which the control force, u(t), is designed to be a linear function of measured displacement, x(t), and measured velocity, (x ) ??(t). The control force, u(t),takes the form
u(t)=g_1 x(t)+g_2 x ??(t)
In view of Equation , we have
??x=-[g_1+(g_2 d)/dt]x
The control law is, of course, not necessarily linear in x(t) and( x) ??(t) as given by Equation. In fact, nonlinear control laws may be more desirable for civil engineering applications. Thus, for both passive and active control cases, the resulting Equation can be highly nonlinear.
Assume for illustrative purposes that the base structure has a viscous damping ratio = 0:05 and that a simple mass less yielding device is added to serve as a passive element. The force-displacement relationship for this element, depicted in Figure 2.2, is defined in terms of an initial stiffness,k ?? and a yield force, f ??_y. Consider the case where the passively damped SDOF model is subjected to the 1940 El Centro S00E ground motion. The initial stiffness of the elastoplastic passive device is specified as k ??=k, while the yield force, f ??_y , is equal to 20% of the maximum applied ground force. That is,
f ??_y=0.20max'{m|(X_G ) ?? |}
The resulting relative displacement and total acceleration time histories are presented.There is significant reduction in response compared to that of the base structure without the control element. Force-displacement loops for the viscous and passive elements are displayed. In this case, the size of these loops indicates that a significant portion of the energy is dissipated in the control device. This tends to reduce the forces and displacements in the primary structural elements, which of course is the purpose of adding the control device.
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3. TYPES OF ENERGY DISSIPATION DEVICES
3.1 GENERAL
‘The resistance to motion which developed due to internal friction of the material or due to drag effect of surrounding air or other fluids, in which the structure is immersed is known damping”, damping reduce the amplitude of vibration. In damping the energy of the vibrating is dissipated by various mechanisms, and often more than one mechanism and that time we can define the energy dissipation devices.
To protect structures from significant damping and response reduction of structures under such severe earthquakes has become an important topic in structural engineering. Conventionally, structures are designed to resist dynamic forces through a combination of strength, deformability and energy absorption. These structures may deform well beyond the elastic limit, for example, in a severe earthquake. For all above purposes there are following types energy dissipation device are we can used.
3.2 CLASSIFICATION OF THE ENERGY DISSIPATION DEVICES
3.2.1 PASSIVE ENERGY DISSIPATION DEVICES
A passive control device is a device that develops forces at the location of the device by utilizing the motion of the structure. Through the forces developed, a passive control device reduces the energy dissipation demand on the structure by absorbing some of the input energy. Thus, a passive control device cannot add energy to the structural system. Furthermore, a passive control device does not require an external power supply.
FIG 3.1 PASSIVE ENERGY DISSIPATION DEVICES
Examples of passive devices include: 1. Base isolation,
2. Tuned mass dampers (TMD),
3. Tuned liquid dampers (TLD),
4. Metallic yield dampers,
5. Viscous fluid dampers,
6. Friction dampers.
3.2.2 ACTIVE ENERGY DISSIPATION DEVICES
The active control systems are the opposite side of passive systems, because they can provide additional energy to the controlled structure and opposite to that delivered by the dynamic load. Active control devices require considerable amount of external power to operate actuators that supply a control force to the structure. An active control strategy can measure and estimate the response over the entire structure to determine appropriate control forces. As a result, active control strategies are more complex than passive strategies, requiring sensors and evaluator / controller equipments. Cost and maintenance of such systems are also significantly higher than that of passive devices.
FIG 3.2 ACTIVE CONTROL DAMPING DEVICE
Examples among active control devices include:-1. Active tuned mass damper,
2. Active tuned liquid column damper,
3. Active variable stiffness damper.
3.2.3 SEMI ACTIVE CONTROL DAEVICES
Semi-active control devices combine the positive aspects of passive and active control devices. Like passive control devices, semi-active control devices generate forces as a result of the motion of the structure and cannot add energy to the structural system. However, like an active control device, feedback measurements of the excitation and/or structural system are used by a controller to generate an appropriate signal for the semi-active device. Extensive studies have indicated that appropriately implemented semi-active systems perform significantly better than passive devices and have the potential to achieve the majority of the performance of fully active systems, thus allowing for the possibility of effective response reduction during a wide array of dynamic loading conditions.
One means of achieving a semi-active damping device is to use a controllable, electromechanical, variable-orifice valve to alter the resistance to flow of a conventional hydraulic fluid damper. In addition, only a small external power source is required for operation of a semi-active control device.
FIG 3.3 SEMI-ACTIVE DEVICE
Examples of semi-active devices include:-1. Variable orifice dampers,
2. Variable friction dampers,
3. Variable stiffness damper,
4. Controllable fluid dampers.
3.2.4 HYBRID CONTROL DEVICES
A hybrid control system typically consists of a combination of passive and active or semi-active device. Because multiple control devices are operating, hybrid control systems can alleviate some of the restrictions and limitations that exist when each system is acting alone. Thus, higher levels of performance may be achieved. Since a portion of the control objective is accomplished by the passive system, less active control effort, implying less power resource, is required. A side benefit of hybrid systems is that, in the case of a power failure, the passive components of the control still offer some degree of protection, unlike a fully active control system.
FIG 3.4 HYBRID CONTLOL DEVICE
Examples of hybrid control devices include:-1. Hybrid mass damper,
2. Hybrid base isolation.
3.3 FUNCTION OF ENERGY DISSIPATION DEVICES
1. Energy dissipation device’s main function is to absorb and dissipate the energy supplied by the ground movement during an earthquake so that the building remains unharmed, their functioning is also akin to shock absorbers.
2. Whenever the building is in motion during a earthquake tremor they help in restricting the building from swaying excessively and thereby preventing structural damage.
3. The earthquake energy absorbed by them and gets converted into heat which is then dissipated into the atmosphere. thus they are work to absorb earthquake shocks ensuring that the structural members i.e. beam and columns remain unharmed.
4. This devices can be installed in existing and new buildings with ease. This makes them extremely versatile for retrofit projects
5. When they used in bridges the orifice of the giant shock absorbers is substantially reduced so as to get what is known as Shock Transmission Unit (STU).
6. If a structure had 100% of critical damping you could pull it to the side, let go, and it would only slowly spring back to the original position and go no farther’vibration would be damped out and stop right there.
4. DETAIL DESCRIPTION OF SEISMIC DAMPER
4.1 Friction damper
Using the dampers or energy dissipation devices are one of the controlling methods of structures vibration under seismic loads. The applications of these devices in design the new buildings and retrofitting the existence buildings are possible. Friction dampers are one of the passive control systems which have an increasing application in moment frames. These are lots of project of such dampers all over the world. Friction damper is functioned according to friction mechanism among rigid materials. In fact, friction is a great mechanism of energy dissipation, employed in car brake systems successfully and extensively. A base metal selection of friction damper is of high importance. Since, there are different materials employed for slippery surfaces. A new friction damper device was employed for the first time by Mualla in his PhD thesis. Full scale experiments for three stories structure equipped with such damper on shaking table was done in Taiwan. In order to increase the seismic capacity of existing structures, it is possible to use the friction damping system connected to high strength tendons. Three steel moment frames with 3, 7 and 12 stories equipped by friction damper devices are investigated under nonlinear time history analysis in present study. The influence of dampers on seismic performance of frames is studied by comparing the parameters like base shear, displacement and energy dissipation of frames with and without dampers
The components of friction damper device are central vertical plate, two lateral horizontal plates and two circle friction pads placed between the steel plates; (Fig. 1).
A single story frame equipped with friction damper device is presented in Fig. 2. When a lateral external force excites a frame, the beam starts to displace horizontally. The damper will follow the horizontal movement of the frame because of the hinge connection, which transfer the forces to the damper parts. The bracing system and the frictional forces developed between the frictional surfaces of steel plates and friction pad materials will resist the horizontal movement. The central plate will start to move horizontally and rotate around the hinge. The clamping force in the bolt, which makes the damper parts stick to each other, and due to this introduces frictional forces. These frictional forces will rotate the horizontal plates within the same value of rotation and direction as the central plate dose, because they are higher than the applied forces. The damper will continue being in sticking phase until the applied forces in the damper exceed the frictional forces, at this slip moment, starts and the central plate rotates relatively to the friction pads, around the bolt.
The horizontal plates also start to slip and rotate but in another direction because of the tensile forces in the bracing. In this sliding phase, the damper will dissipates energy by means of friction between the sliding surfaces. This phase will keep on and later will be changed to the sticking phase when the load reverses its direction. To prevent the buckling of compression bar, the bars are pretensioned by Fp force according to equation 1.
F_(P=M_(F ) )??2h_a cosv
…… (eq-1)
In which v is the bar slope angle with horizontal line. Therefore the cross-sectional area of bars is determined according to equation 2.
A_(b=) M_f’?_y h_a cosv ….. (eq-2)
In which is the yielding stress of bracing bar. Friction damper has two phases: sticking and sliding phases. The stiffness of damping system in sticking phase is calculated according to equation 3.
K_bd=2EAb/l ‘cos’^2 v+(_L^2F)p ‘sin’^2 v ……(eq-3)
Where E is elasticity module, is bracing bar area, l is length of the bracing bar and L is length between the hinge which is existed on the top of the friction damper device and the end of bracing bar. The stiffness of damping system is ignored in sliding phase, as it is negligible .
FIG 4.1 VISCO ELASTIC OR FRICTION DAMPER
4.2 VISCOUS DAMPER DESCRIPTION
The viscous damper for structures outwardly resembles the shock absorber on an automobile, but operates at a much higher output. Base isolation dampers are significantly larger than automotive dampers, and are constructed of stainless steel and other extremely durable materials as required to furnish a life of at least 40 years. The damping fluid is silicone oil, which is inert, non-flammable, non-toxic, and stable for extremely long periods of time. The seals in the viscous damper are a patented high technology design based on aerospace fluid elements, and provide totally leak free service. This design has been proven through rigorous testing and has been in use for over 40 years.
The damping action is provided by the flow of fluid across the piston head. The piston head is made with a deliberate clearance between the inside of the cylinder and the outside of the head, which forms an annular orifice. The fluid flows through this orifice at high speed as the damper strokes. The shape of the piston head determines the damping characteristics. The force/velocity relationship for this kind of damper can be characterized as F=CVn, where F is the output force in pounds, V is the relative velocity across the damper in inches per second, C is a constant determined mainly by the damper diameter and the orifice area, and n is a constant exponent which can be any value from .40 to 1.95. The exact value for n depends upon the shape of the piston head.
The analytical results reported here use a value of ‘n’ of 1.0. It has been found that ‘n’ values closer to .5 often produce significantly better results. This is the value that has been incorporated in the San Bernardino Medical Center dampers. Constantinou reports reductions in displacement of 20% and reductions in total force of 10% by changing ‘n’ from 1.0 to 0.5.
As the orifice is provided by the annular clearance between the piston head and the cylinder body, it is possible to provide inherent thermal compensation by making these two parts from different materials. By choosing materials with the correct thermal coefficients of expansion, it is possible to make the variation in the gap compensate for the variation in fluid properties as temperature changes.
A series of tests was conducted at NCEER on Taylor Devices dampers with intrinsic thermal
compensation (Constantinou et al., 1992, 1993). It was found that the temperature range of 32oF to 122oF produced a change in damping from +44% to -25%, which is relatively small. Subsequent design improvements have resulted in even less variation in damping characteristic over a similar temperature range. For instance, total force tolerance band on the dampers produced for the new San Bernardino Medical Center is +/-15% over a similar temperature range, including the effects of tolerance variation.
FIG 4.2 VISCOUS DAMPER
4.3 Tuned Mass Dampers
Tuned mass dampers (TMDs) work by fastening a massblock to a structural component (such as a floor) via a spring. This system is set up so that, when the floor vibrates at a resonant frequency (which could be caused by dancing, for example), it induces analogous movement of the mass
FIG.4.3 FLOOR DEFLECTION IN FIRST MODE SHAPE.
where:
Ff(t) = idealized, periodic forcing function on dance floor
Yt= deflection of tip of floor in first mode
Yf = deflection of floor under forcing function
block and spring. By the conservation of energy, the TMD motion in turn reduces the amplitude of the floor’s vibration.A damping device (dashpot) is usually connected in parallel
with the spring between the mass-block and floor, increasing the TMD’s effectiveness over a range of frequencies and taking a small amount of mechanical energy out of the system as heat.
Because each TMD is “tuned” to a particular resonant frequency, individual TMDs need to be installed for each excited floor frequency. Because they rely only on floor vibrations to operate, they do not need to be fastened to a nearby stationary object. By the same token, TMDs are most effective when located where the floor’s amplitudes are the greatest.
TMDs were considered the only viable passive damping system to employ at the Terrace because they did not require fastening to a nearby stationary object. They were also particularly well suited to the Terrace because there was only one floor frequency per ballroom to damp, reducing the required number of TMDs, and the TMDs could be installed at locations where the floor amplitudes were largest (Fig. 5), maximizing their efficiency.
FIG 4.4 TUNNED MASS DAMPER
4.3.1 Active Mass Dampers
Active mass dampers, which are computer controlled and can also be configured to work without relying on the relative motion between the floor and a stationary object, were also considered. These systems, currently the subject of much research for controlling wind and earthquake induced vibrations,8 are a generally attractive solution to vibration problems because they are so effective. These systems were rejected for the Terrace on the basis of their high installation cost, and their need for regular continuing maintenance, which could not be ensured over the life of the structure.
FIG.4.5 Active Mass Dampers
5. COSTING OF ENERGY DISSIPATION DEVICES
Regardless of the answers to the why and how equations, the cost of energy dissipation device will always be an important consideration and this is one of the first questions asked by most engineers considering is seismic damper. There are both direct and indirect costs and cost savings to consider.
In most cases, a new seismic damper building will cost more than a non- seismic damper building usually in the range of 5% to 15% of total cost more. The installation of the is seismic damper system adds to first cost as a non- building seismic damper would not have bearings. The structure is designed for a higher level of performance than non- seismic damper buildings and full advantage is not taken of the reduction in forces to reduce costs in the structure above the seismic damper (the ductility is less than one-half that for a non-isolated building). This restricts saving in the structural system that might otherwise offset the seismic damper system costs.
For the retrofit of buildings, a solution using seismic damper will often cost less than other non-energy dissipation devices strengthening schemes. This is because ductile design is less common in retrofit and so the seismic damper and non- seismic damper designs are more comparable.
5.1 DESIGN ENGINEERING AND DOCUMENT COSTS
An ENERGY DISSIPATION DEVICES structure requires lots of extra engineering effort to analyze, design, detail and document ‘ the scope can be appreciated from the tasks in the design process described above. The extra costs associated with this very much depend on the project. A few things to consider:
‘ Analysis effort is usually the largest added engineering cost. The analysis type, and cost, depends on the building and location. Few energy dissipater structures can be analyzed using the equivalent static load method so at least a response spectrum analysis is required. Some structure requires a time history analysis. Even if a non- energy dissipater building would be analyzed the same way, an energy dissipater structural analysis requires more effort. For example, a response spectrum analysis of an energy dissipater building is usually iterative as the stiffness properties and damping are a function of the displacement, which is itself a function of stiffness and damping.
‘ The vendor will often perform design of the dissipation system and so this may not add a lot to the engineering costs. However, there will still be time involved in evaluating designs.
‘ Details of the energy dissipater connections is an added cost. The large displacements causes secondary moments effect which involve significant design effort.
‘ At the tender stage, you will generally have to evaluate a number of proposals, often complex and difficult to verify.
‘ You will need to allow for supervision and evaluation of prototype and production tests.
‘ Extra site supervision may be needed for installation.
No cost savings in design and documentation from using energy dissipater come to mind. There may be simplifications from using elastic design versus ductile design but that is unusual.
5.2 COSTS OF ENERGY DISSIPATION DEVICES
There is a wide range of cost of energy dissipater. For most types, the cost influenced most by the maximum displacement and to a lesser extent by the loads that they support. For a given level of seismic load, displacement is proportional to dissipation period and so the greater the extent of seismic damper, the greater the cost.
The cost per device can range from $1000 to $15000 or more (US dollars, year 2001). 56
The total cost for the seismic damper system depends on the efficiency of the dissipater’s layout. Generally, the higher the load supported per energy dissipater the higher the efficiency. For example, the total system cost for a structure supported on 25 energy dissipater in a high seismic zone will be probably about 20% to 40% less than if a structure of the same weight were supported on 50 energy dissipater. This is because energy dissipater sizes, and so cost, will be determined primarily by the displacement and is only a weak function of axial load for most device types.
5.3 STUCTURAL CHANGES AND ITS COSTS
The cost of changes to the structural configuration is potentially the largest component of the first cost and is very much a function of the building layout. A building with a basement can often be seismic damper either above or below the ground floor level with little added cost. A building that would have a slab on grade will require a suspended floor. The difference in cost between a suspended floor and a slab on grade will add significantly to the construction cost.
Other costs may arise for the portion of the structure below the energy dissipater plane. For example, if the energy dissipater are on top of basement walls, below ground floor, they will apply out-of-plane loads to the basement walls. Pilasters or buttresses may be needed to resist these loads.
Obviously, the costs of structural changes to accommodate dissipation are very project specific. They generally range from 0% to a high of perhaps 20% of structural costs, although the extremes are unlikely. The most common added cost will be in the range of 1% to 3%. In some cases, other savings above the energy dissipater will offset these.
5.4 SERVICES, ARCHETECTURAL CHANGES AND NON-STRUCTUREAL MATERIAL
Most added architectural costs arise from the detailing of the separation around the building. There can be no obstructions within a distance equal to at least the maximum displacement of the seismic energy dissipater system. This will require special detailing, especially as regards entrances to the building. Stairs will need to cantilever down from the isolated superstructure or be supported on sliding bearings.
As for structural changes, the cost of these items varies widely and the range of costs is usually similar to the structural changes, about 2 % to 5% of structural cost.
5.5 SAVINGS IN STRUCTURAL MATERIAL SYSTEM COSTS
The philosophy of seismic dissipation is to reduce earthquake forces on the structural system and so it follows that a system designed for lower forces will cost less. The extent of force reduction depends on the structure, the level of seismicity and the extent of dissipation. Generally the earthquake forces will be reduced by a factor of at least 3 and may be reduced by a factor 8 or more for ideal situations.
Unfortunately, a reduction in forces by a factor of say 5 does not reduce costs by the same amount. The structural system must still resist other loads such as gravity and wind and these may set minimum sizes and strengths of structural elements.
More importantly, the forces reductions provided by dissipation are generally of the same order as the forces reductions used to account for structural ductility in a non-demper structure.
An energy dissipater building absorbs energy through the energy dissipater rather than through ductile response of the structural system. If the structure above the energy dissipater were designed for the same levels of ductility as for a non- energy dissipater structure then it is likely that the structural yielding would reduce the efficiency of the all services entering the building will cross the energy dissipater plane and so will have imposed displacements during earthquakes. The provision of flexible joints will have a cost. Elevator shafts will cross the energy dissipater plane and will require special detailing, often cantilevering down from the energy dissipater superstructure. Further, a ductile system softens and extensive ductility could lead to the period of the structure degrading to a value similar to that of the seismic energy dissipater system, leading to the possibility of coupling between the two systems is designed for very low levels of ductility, if any. Again using the UBC as an example, the response modification factor for energy dissipater structure, R1, ranges from a minimum of 1.4 for cantilevered column buildings to a maximum of 2.0 for special moment-resisting frames.
A consequence of this restriction on the extent of ductile response in energy dissipater structure is that the potential for cost savings in the structural system is highest for structural types with low inherent ductility. For very ductile systems, such as special moment resisting frames, there are unlikely to be any savings in the structural system cost.
.5.6 REDUCTION OF DAMAGE COSTS
The reality is, no matter how much first cost saving is targeted; the energy dissipater building will be less damaged than a non- energy dissipater building. This is because of the lower levels of ductility designed into the energy dissipater building. The reduced costs may be even more dramatic in the non-structural items and constants of the structure than it is the structural system. This arises from the reductions in floor accelerations and in structural drifts.
It is difficult to quantify reduced damage costs because life cycle analysis is not usually performed for most structures. As performance based design become more widespread it is possible that this may occur. In the meantime there are some tools available to assess the reduced costs of damages.
With life cycle cost analysis the costs of earthquake damage are estimated from data such as that. There are two components of damage in earthquakes:
1. Drift related damage
‘ Impose deformations from drift will damage the primary structure and also non-structural components such as cladding, windows, partitions etc.
2. Accelerations
‘ Inertia forces from floor accelerations will damage components such as ceilings and contents.
For non- energy dissipater buildings, it is difficult to control both of these causes of damage. A building can be designed stiffer to reduce drifts and reduce damage costs from this cause but the floor accelerations tends to be higher in stiffer buildings and so acceleration-related damage will increase.
Unless the building is of special importance, it is rare for life cycle costs to be calculated and so earthquake damage cost reduction can only be accounted for in a qualitative way. For example, assume a seismic energy dissipater system reduces drifts from 2% to 0.5% and accelerations from 0.5g to 0.18g, reductions which are usually easily achieved with energy dissipater. The average drifts related damage cost ratios will reduce from 0.39 to 0.07 and the acceleration costs from 0.47 to 0.11. On average, damage costs will reduce from about 30% of the total building cost to about 10% of the building cost. On this basis, a first cost increase of less than 7% is well justified.
The reduction in PML will generally show a positive net return from the use of energy dissipater. In some earthquake prone regions, such as California, building purchasers and financiers take into account the Probable Maximum Loss (PML) for a structure in determining its value.
5.7 ADDITIONAL COSTS
The additional engineering and documentation costs compared to a non-isolated design will probably be at least 30% and may be much more for your first projects. The total range of costs will be about that as per standard code. Excluding reduced damage costs, the added costs may range from a minimum of -3.7% to +13% of the total building cost.
6. APPLICATION AND USE OF EMERGY DISSIPATION DEVICES IN THE WORLD
6.1 GENERAL
In recent years energy dissipation device has become an increasingly applied structural design technique for buildings and bridges in highly seismic areas. Many types of structures have been built using this approach, and many others are in the design phase or under construction. Most of the completed buildings and those under construction use damper in some way in the energy dissipation system.
It main concept to energy dissipate due to produce by either earthquake or wind. Dampers are not allowing to the shock and vibration from ground to structure. Ductility of the structures is increase by providing damper technique. It is absorbing shock; vibration and maximum deform of the structure.
The concept and overview of the present state of seismic damping device system with special emphasis and a brief on applications and uses of seismic damping device system.
6.2 U.S APPLICATIONS
6.2.1 WORLDTRADE CENTRE
The application of viscoelastic materials to vibration control of civil engineering structures appears to begun in 1969 when approximately 10,000 viscoelastic dampers were installed in each of the twin towers of the World Trade Center in New York to reduce wind-induced vibrations.
In addition to World Trade Center in New York viscoelastic dampers have been utilized in
other buildings.
FIG. 6.1 WORLD TRADE CENTRE, NEW YORK
6.2.2 The Columbia Sea First and Two Union Square buildings
The Columbia Sea First and Two Union Square buildings in Seattle utilized the dampers to reduce wind-induced vibrations.
FIG. 6.2 Two Union Square buildings
6.3 JAPAN APPLICATION
6.3.1 Trigon on Shinjuku Tower
Trigon on Shinjuku Tower is located in Shinjuku’Ku, Tokyo, with a floor area of 264,100 m2. The structure is made of steel and partially reinforced concrete frames. It is a 52-storeyed plus 5- basement structure, with a above-ground weight of 130,000 t-f. Three control devices are installed in the form of roller pendulum mass on the 36th floor. The control masses are 110 t each. Maximum stroke of the pendulum is 110 cm. Period adjusted is 3.7258 s, and the motor capacity to drive the pendulum is 75 kW.
FIG. 6.3 Trigon on Shinjuku Tower
6.3.2 MORI TOWER
The Mori Tower, a 54-storey building uses 356 variable-orifice dampers. Altogether, in Japan, the Kajima Corporation has recently finished nine buildings that employed a total of nearly 800 variable-orifice dampers for their buildings as structural control systems.
FIG. 6.4 MORI TOWER
6.4 CHINA APPLICATION
6.4.1 Dongting Lake Bridge
The Dongting Lake Bridge in Hunan, China retrofitted with stay-cable dampers, was the first full-scale implementation of MR dampers for bridge structures. Two Lord SD-1005 MR dampers are mounted on each cable to mitigate cable vibration. A total of 312 MR dampers are installed on 156 stayed cables. In 2003, MR dampers have been opted for implementation on the Binzhou Yellow River Bridge in China to reduce cable vibration.
FIG. 6.5 Dongting Lake Bridge
6.5 NEWZELAND APPLICATION
6.5.1 NZ Parliament Building AND New Museum of NZ
In New Zealand there are two large seismic isolation projects that have been completed. These were the retrofitting of isolation to the NZ Parliament Building and the associated Assembly Library and the new Museum of NZ. Both of these use LRB systems.
FIG. 6.6 NZ Parliament Building AND New Museum of NZ
7. ADVANTAGES AND DISADVANTAGES OF ENERGY DISSIPATION DEVICES
SR. NO Types of damper ADVANTAGES DISADVANTAGES
1 Viscous fluid damper
:-Activated at low displacement.
:-Minimal restoring force.
:-for linear damper modeling of it’s is simplified.
:-property largely frequency and temperature independent.
:-provern record of performance in military application. :-possible fluid seal leakage(reliability concern)
2 Viscoelastic solid damper :-activated at low displacement.
:-provides restoring force.
:-linear behavior,therfore simplified modelling of this type damper.
:-limited deformation capacity.
:-properties are frequency and temperature dependent.
:-possible debonding and tearing of VE material(reliability concern).
3 Metalic damper :-stable hysteretic behavior.
:-long term reliability-intensitivity to ambient temperature.
:-materials and behavior familiar to practicing engineers. :-device damaged after earthquake; may require replacement.
:-nonlinear behavior; may require nonlinear analysis.
4 Friction damper :-large energy dissipation per cycle.
:-it sensitivity to ambient temperature. :-sliding interface conditiond may change with time (reliability concern).
:-strongly nonlinear behavior ; may excite higher modes and require nonlinear analysis.
:-permanent displacements if no restoring force mechanism provided.
8. DESIGN OF BUILDING CASE STUDY IN SAP 2000
Analyse and design four storied building as shown in fig 1&2 using SAP2000V12
Fig no . 1 plan of building
1. Grade of concrete used is M20 and grade of steel used is FE 415.
2. Floor to floor height is 3.1m
3. Plinth height above GL is 0.55m.
4. Depth of foundation is 0.65m below GL.
5. Parapet height is 1.5m.
6. Slab thickness is 150 mm.
7. External wall thickness is 230 mm and internal wall thickness is 150 mm.
8. Size column is 300mm X 450 mm and size of beam 300mm X 450 mm.
9. Live load on floor is 3km/sq. m and live load on roof is 1.5kn/sq. m.
10. Floor finishes is 1 km/sq. m and roof treatment is 1.5 kn/sq. m.
11. Site located in seismic zone 4.
12. Building is resting on medium soil.
13. Take important factor as 1.
14. Building frame types is special moment resisting frame (SMRF).
15. Density of concrete is 25 kN/cu. M and density of masonry wall is 20 kN/ cu.m
Step 1 Begin new model
A. Click the file name > new model command or the new model button. The form shown in fig will display. Verify that the default units are set to KN,M,C.
Fig. no 3 new model form
B. The new model form allow for the quick generation of numerous model type using parametric generation techniques. However in this the model will be started using only the grid generation. When laying out the grid, it is important that the grid, it is important geometry defined accurately defined represents the major geometrical aspects of the model, so it is advisable to spend time carefully planning the number and spacing of the grid lines. Select the grid only button, and the form shown in fig 4 will display
Fig no 4 quick grid line form
Fig no 5 defined grid data form
C. The quick grid lines form is used to specify the grid and spacing in the X,Y and Z directions. Set the number of the grid lines to4 in the X and Y direction, and to 6 in the Z directions. Types 5,3,3.1 into X,Y,Z direction spacing spacing edit boxes respectively. The values specified in the first grid lines location area locate the origin of the grid lines; make sure that these values are all set to zero for the tutorial. Click OK button to cont.
1. Click the define menu> coordinate systems/grid command. The coordinate/grid systems form will displays. Make sure that the systems item on the coordinate/grid systems form has global highlighted and click the modify/show system button. The define grid data from fig.5 will display.
2. The define grid data from is used to specify the irregular spacing in the x,y, and z directions. Set the display grid as to spacing.
3. in Y grid data set spacing as 2 for grid ID 2 and In Z grid data set it to 1.2 for Z1 grid ID.
4. click the OK button the defined grid data from.
D. click the OK button to close coordinate system from fig. 6 will appear. Left side 2-D view of XY plan and 3D view of right side.
Fig.no.6 SAP 2000 windows
Step 2 defined material
A. click the defined menu > material command, the defined material from fig 7 than click the modify/show material button, show in fig 8.
Fig.no.7 define material form
Fig.no.8 material property data form – concrete
B. In the material name and display color edit box, type M20 and in the material type select concrete from drop down list.
C. density as 25. Set E as 22360679.774 ass per 5000*(Fck)^(1/2). Position ratio 0.15. specified concrete compressive strength to 2000 and than click ok button.
D. Same process for material Fe415 and material type select Rebar from drop down list. Set min. yield stress, fy, min tensile stress, fu, expected yield stress fye, and expected tensile stress fue, to 415000,498000, 518750, and 622500. Click ok button on material property data form and material to exit all form.
Fig.no. 9 material property data form ‘rebar
Fig.A. solution of step-2&3
Step 3 defined frame section
A. Click the define menu > section property > frame section as show in fig 10.
Fig.no. 10 frame properties form
B. Click to the add new property button as show in fig 11.
Fig.no.11 add frame sec. property form
C. in frame section property type select concrete and click rectangular button as show in fig 12. Type C – 300*450 and depth and width edit box, type 0.45 and 0.3 respectively.
Fig.no.12 rectangular sec. frame form
D. click the concrete reinforcement button and type value as show in fig 13 and 14.
E. same process for B ‘ 300*450.
Fig.no.13 reinforcement data form for column
Fig.no.14 reinforcement data form for beam
Step 4 Add frame objects
1. Draw frame objects (XZ plane)
A. used the draw menu > snap to > points and grid intersection. By default this command is active.
B. click the view menu > set 2D view command. In set 2D view form click on the on the X-z plane option.
Type 0 in to the Y = edit box to display the side view at the Y = 0 and click ok.
C. click the draw frame / cable/tendon button. The property of object as show in fig 15.
Fig.15 properties of objects
D. click in section drop dawn column and beam choose either column or beam and select the object in to 2D dia.
2. Add restraints
A. select the support nodes i.e. nodes at z=0.
B. click the assign menu > joint> restraints command to bring up the joint restrain form as shown in fig 16.
Fig.no.B.solution of step-4
C. click fix support button to assign restraints in the translation and rotation in 1,2,3 directions. Click the ok button to accept the change.
3. Modify column orientation.
A. select all column the column along the grid line X=0 and X=15.
B. click the assign menu > frame > local axes command show in fig 17.
Fig.no.17.Disply option for active window
4. Replicate object
A. click the edit menu > replicate command to bring up the show in fig 18.
Fig 18. Replicate form
B. on linear tab type 3, 5,8 in to dy edit box 1 by 1 and type 1 in the number edit box respectively. Click the ok button.
5. Draw frame object (YZ plan)
Same as per above process 1,2,3,4 for YZ plane @ X= 0 views is active.
Fig no C sol of .1,2,3,4,5.
Step 5 define load patent
A. click the define menu>load patterns command to bring up the define load patterns form fig 19.
Fig.no.19.Define load patterns for
Note: that self weight multiplier is set to 1 for the default case. This indicate that this load pattern will automatically include 1 time the self weight of all member.
B. Click the edit box for the load pattern name column. Type the name of the new load pattern dead wall. Select the type load from the drop down list, in this case, select super dead. Make sure that the self weight multiplier is set to zero. Click the ok add new load pattern button.
C. repeat item B, to add dead slab, dead FF , dead RT load case.
D. the define load form should now appear as shoe in dig 20. Click the ok button in that form to accept newly define static load case.
Fig.no.20.Define load patterns form
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