vibration control of civil structures

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Page 1: vibration control of civil structures

WELCOME

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VIBRATION CONTROL OF CIVIL STRUCTUTRES USING PIEZOCERAMIC SMART MATERIALS

PRESENTED BY

RAKHI T R1st year mupgovt.engg.college

thrissur

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INTRODUCTION Structural vibrations are one of the main causes of failure in

civil structures which effects the structural and serviceability characteristics of the structure .

This paper tries to discuss and club the various experimental investigations for the vibration control of structures using piezoceramic smart materials.

The common feature that is observed from these studies, carried out all over the world is that piezoceramic smart materials are very much effective and economical in controlling structural vibrations.

Numbers of researches are still running on the same topic, reinforcing the point that we are not far from the large scale piezoceramic actuators can see in action in large building structures.

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SMART STRUCTURES

Structure that can sense external disturbances &

respondsaccordingly

Capability to change its characteristics under external

field

Fundamental parts are solid state actuators & sensors based on smart materials

Involvs 5 key elements

SMART STRUCTURE

S

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5 KEY ELEMENTSStructural material

Sensors Control Strategies

Actuators

Power conditioning electronics

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SMART MATERIALS These materials are capable of reversibly changing their mechanical

properties –viscocity,stiffness,shape –due to the influence of temperature change or an electrical or magnetic field

By some of these materials the reverse effect can be used for sensor tasks meaning that a mechanical load generates an electrical or magnetic field.

They can be used as both actuators & sensors Includes –

Shape memory alloysElectro strictive materials Magneto strictive materialsElectro – rheological & magneto – rheological fluidsPiezoceramic materials

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SMART MATERIALS ( CONT…) Mechanical & active properties of smart

materials can be varied by changing the possible compositions & manufacturing process.

Vibration control properties can be varied by changing the position of smart materials in the structure.

Piezoceramic materials are the most popular among the smart materials

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PIEZOCERAMIC MATERIALS

Light weight Low cost

Easy to implementSensing & actuation

capabilities

ADVANTAGES

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PIEZOCERAMIC MATERIALS• Can be surface bounded in

high strain areas• Can be embedded in

composite structures

Mode of applicatio

n• Aerospace• Mechanical Engineering• Civil Engineering

Field of applicatio

n

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BASICS OF PIEZOCERAMICS

PIEZO ELECRIC EFFECT

Direct effectElectric charge is produced when it

is stressed-used in sensorsConverse effect

An electic field can create Stress or strain – used in actuators

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Piezo electric properties are induced in a material by POLING process

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The relationship between the applied forces and resultant responses of piezoelectric material depend upon a number of parameters such as the piezoelectric properties of the material, its size shape and the direction in which forces or electrical fields are applied relative to the material’s axis.

POLING PROCESS

Fig. shows an element of piezoelectric element material. Three axes are used to identify directions in the piezoelectric element termed 1, 2 and 3 in respective correspondence with the x, y and z-axes of rectangular coordinates. These axes are set during the poling process, which induces the piezoelectric properties of the material by applying a large D.C. voltage to the element for an extended period of time. The z-axis is taken parallel to the poling direction.01/05/2023 11

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FORMS OF PIEZOCERAMICSPatch

Actuator

Stack Actuator

s

Flexible Patch

Actuator

Macro fiber

composite

Amplified Piezo

electric Actuators

Active fiber

composites

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Commonly used piezoceramics in civil applications are stack type actuators, also known as multi-layered actuators. Multi-Layer piezoelectric Actuators (MLAs) offer many advantages, such as high energy density, compared to other active materials, and therefore they are increasingly used in various smart actuator applications. Typically, a 100 mm long with a cross-section area of 1 cm2 provides a free stroke of 100 μm and a blocked force of about 3 kN. These MLAs do have some disadvantages because of the low tensile strength. This is a source of failure in bending conditions, in vibration environments and in dynamic applications where high transient stresses are present.

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COMMON TYPES

Patch Actuators Macro Fiber Composite Stack Actuators

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Recently, mechanically Amplified Piezoelectric Actuators (APAs),are introduced to overcome the tensile stress limitation of MLAs, by applying a compressive prestress on the ceramic, which, additionally, enhances the piezoelectric deformation. The APA actuator form shows significant improvement in terms of output energy per actuator mass or per actuator volume.

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WORKING OF PIEZOCERAMIC MATERIALS IN VIBRATION

CONTROL

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OPERATION SEQUENCES

Step 1

• Structure experiences a kind of vibration .• Structural responses are recorded with the help of

sensors.

Step 2

• Transmitting to controller.• Compares the signals with predetermined control

algorithm.• And generate proper control signals.

step3

• Control signal is then send to actuator which is in contact with structures.

• Reduces the vibration of structure.

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APPLICATIONS IN CIVIL ENGINEERING

Cantilever structures

Truss Structures

Frame Structures

Cable stayed structures

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CANTILEVER STRUCTURES

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The control problem of cantilever flexible beams has been investigated by various researchers. Investigations on the vibration suppression using piezo ceramic patch actuators of a 3.3 m long pultruded fiber reinforced polymer I-beam set up in cantilevered configuration.

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TRUSS STRUCTURES

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Another typical example of the application of piezoceramic stack actuators is truss experiments. Although these truss structures experiments were meant for space applications, however their applicability extends to civil structures

It was experimentally demonstrated piezoelectric active members in a space truss for its precision control,developed in-house an active member consisting of nested thin walled three piezoelectric cylinders.This allowed them to implement collocated direct velocity feedback control of the large space truss. It was found that local force feedback, accompanied by small phase shift, achieved nearly optimal damping performance.

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FRAME STRUCTURES

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Seismic control of buildings is a challenging and large scale application of smart structures.The investigators subjected a structural model of a five-storey building about 2.5 m high to non- stationary random excitations such as earthquakes. Control was done through active braces using electromagnetic actuators for generation of the required control forces. Sensing was done through five accelerometers mounted on the structure and two were used for feedback control. The question whether the scaled model smart structure applications can be extended to large civil building structures depends on the development and performance of large scale piezoelectric actuators.

Using large scale piezoelectric actuator for active vibration control on an actual nine- storey building of steel frame structure 31 m in height and 273 t total mass. They concluded that a smart structure with large scale piezoelectric actuators could perform the same active control in stronger excitation than the hybrid mass damper could. Thus their research reinforces the point that we are not far from when these large scale piezoelectric actuators could be seen in action in large building structures.

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CABLE STAYED STRUCTURES

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The cable-stayed bridge/structure is another area where smart materials are now being used for vibration suppression. The cable-stayed bridges are more sensitive to wind and traffic induced vibrations, deck and pylon vibrations and to flutter instability, because of their high flexibility, relatively small mass, low structural damping and steadily increasing moving loads. They used active cables and showed the root mean square responses of the bridge can be reduced as much as 80% with active control systems. Thus concluded the feasibility of active control to cable-stayed bridges

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LIMITATIONS OF PIEZOCERAMIC SMART MATERIALS

Chances for small displacement for actuators during working

Introduction of stack actuators in structures causes some structural modifications

Requires a power source when it is used for active control

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CONCLUSION An overview was presented for vibration suppression

of civil structures with special emphasis laid upon smart structures with piezoelectric control actuation.

Piezoceramics material that have the advantages of being lightweight, low-cost, and easy-to-implement offer the sensing and actuation capabilities that can be utilized for active vibration control. A number of examples including the applications of piezoceramics to various kinds of civil engineering structures like truss, beams, buildings and cable structures were presented.

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CONT…….. Although there exists some limitations the benefits of this

technology far outweigh the problems of not using them. This is evident by the tremendous amount of contributions from the scientific community for introducing this technology into the mainstream of civil engineering.

However it is envisaged the community will see developments that shall reduce the power consumption and this may be in areas of the development of actuators or power efficient control algorithms.

Thus, we will continue to see the manifestation of this technology in civil structures.

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REFERENCES

Brain Breukelman, ‘Challenging Vibrations In Engineering Structures’,Journal Of Moedern Steel Construction, March 2004,pp 352-358

G. Song,V. ,Sethi,H.-N. L, Engineering Structures (Volume 28, Issue 11), September 2006, Pages 1513–1524

G. Song , P.Z.Qiao ,W.K Binienda ,and G.P.Zou , ‘Active Vibration Damping Of Composite Beam Using smart Sensors and Actutors’ Journal Of Aerospace Engineering , July 2002

K.P. Chong, S.C. Liu , and O.W. Dillon , ‘Engineering Research On Smart Materials And Structural Systems’ Journal Of Infrastructure System, June 1996

S. Hurlebaus, L. Gaul, Mechanical Systems and Signal Processing, (Volume 20, Issue 2), February 2006, Pages 255-281

S.E. Prasad, S. Varma, A. Ahmad, T.A. Wheat, J.B. Wallace and D.F. Jones, ‘Ceramic Sensors and Actuators for Smart Structures’ Robotics and Knowledge Based Systems Workshop, Canadian Space Agency, St. Hubert, October 1995

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