A SEMINAR ON STRUCTURE CONTROL SYSTEMS

A SEMINAR ON STRUCTURE CONTROL SYSTEMS

Submitted by: MAHESH CHAND SHARMA M.TECH. –III SEM (2011-12) (2010PST116)

Guided by: Dr. M.K.Shrimali Dr. S.D. Bharti

Department of Structural EngineeringMalaviya National Institute of Technology Jaipur

INTRODUCTION

Civil engineering structures located in environments where earthquakes or large wind forces are common will be subjected to serious vibrations during their lifetime. These vibrations can range from harmless to severe with the later resulting in serious structural damage and potential structural failure.

Seismic Protection of Structures The Traditional Technique of a

seismic Design ( increase the stiffness of structures by enlarging the section

of columns, beams, shear walls, or other elements) Modern Approach through

Structural Controls (by installing some devices, mechanisms, substructures in

the structure to change or adjust the dynamic performance of the structure)

Basic Principles of Seismic Response Control

Control systems add damping to the structure and/or alter the structure’s dynamic properties. Adding damping increases the structural energy-dissipating capacity, and altering structural stiffness can avoid resonance to external excitation, thus reducing structural seismic response.

Structure Control systems

1.Passive control systems

2.Active Control systems

3.Semi-active control systems

4.Hybrid control systems

Passive control systems

The passive control system does not require an external power source and being utilizes the structural motion to dissipate seismic energy or isolates the vibrations so that response of structure can be controlled

The passive control devices includes

1. Base Isolation

2. Passive Energy Dissipating (PED) Devices

Base Isolation A building mounted on a material with low

lateral stiffness, such as rubber, achieves a flexible base.

During the earthquake, the flexible base is able to filter out high frequencies from the ground motion and to prevent the building from being damaged or collapsing

- deflecting the seismic energy and - absorbing the seismic energy

Behavior of Building Structure with Base Isolation System

Conventional Structure Base-Isolated Structure

http://www.earthquakeprotection.com.

Various Type of Base Isolation Elastomeric Bearings: -Low-Damping Natural or Synthetic Rubber Bearing - High-Damping Natural Rubber Bearing - Lead-Rubber Bearing (Low damping natural rubber with lead core)

Sliding Bearings - Flat Sliding Bearing - Spherical Sliding Bearing

Elastomeric Bearings Major Components:- Rubber Layers: Provide

lateral flexibility- Steel Shims: Provide

vertical stiffness to support building weight while limiting lateral bulging of rubber

- Lead plug: Provides source of energy dissipation


Low Damping Natural or Synthetic Rubber Bearings

Linear behavior in shear for shear strains up to and exceeding 100%.

Damping ratio = 2 to 3%

Advantages: - Simple to manufacture - Easy to model - Response not strongly sensitive to rate of loading, history of loading, temperature, and aging. Disadvantage: -Need supplemental damping system


High-Damping Natural Rubber Bearings

• Damping increased by adding extra-fine carbon black, oils or resins, and other proprietary fillers

• Maximum shear strain = 200 to 350%

• Damping ratio = 10 to 20% at shear strains of 100% • Effective Stiffness and Damping depend on: - Elastomer and fillers - Contact pressure - Velocity of loading - Load history (scragging) - Temperature


Lead-Rubber Bearings damping properties can be improve

by plugging a lead core into the bearing

damping of the lead-plug bearing varies from 15% to 35%.

The Performance depends on the imposed lateral force

The hysteretic damping is developed with energy absorbed by the lead core.

Maximum shear strain = 125 to 200%

Design of structures with seismic isolation, in The Seismic Design Handbook , 2nd edition,

Sliding Bearings The imposed lateral force is

resisted by the product of the friction coefficient and the vertical load applied on the bearing

Passive Energy Dissipating Devices (PED)

Mechanical devices to dissipate or absorb a portion of structural input energy, thus reducing structural response and possible structural damage.

• Metallic Yield Dampers

• Friction Dampers

• Visco-elastic Dampers

• Viscous Fluid Dampers, And

• Tuned Mass Dampers And Tuned Liquid Dampers.

Metallic Yield Dampers Metallic yield damper:

relies on the principle that the metallic device deforms plastically, thus dissipating vibratory energy


Friction Dampers

here friction between sliding faces is used to dissipate energy

Instructional Material Complementing FEMA 451,

Visco-elastic Dampers

Visco-elastic (VE) dampers utilize high damping from VE materials to dissipate

energy through shear deformation. Such materials include rubber, polymers, and glassy substances.


Viscous Fluid Dampers A viscous fluid damper

consists of a hollow cylinder filled with a fluid. As the damper piston rod and piston head are stroked, The fluid flows at high velocities , resulting in the development of friction


Tuned Mass Dampers And Tuned Liquid Dampers

A mass that is connected to a structure by a spring and a damping element without any other support,in order to reduce vibration of the structure

Tuned liquid dampers are similar to tuned mass dampers except that the mass-spring-damper system is replaced by the container filled with fluid

Tuned mass dampers Tuned liquid dampers


Active Control systemsIn the active control, an external source of energy is used to

activate the control system by providing an analog signal to it. This signal is generated by the computer following a control algorithm that uses measured responses of the structure

Types of Active Control systems

Active Mass Damper Systems

Active Tendon Systems

Active Brace Systems

Active Mass Damper Systems

It evolved from TMDs with the introduction of an active control mechanism.


Active Tendon Systems

Active tendon control systems consist of a set of pre-stressed tendons whose tension is controlled by electro-hydraulic servomechanisms


Semi-active Control Systems

It compromise between the passive and active control devices.

the structural motion is utilized to develop the control actions or forces through the adjustment of its mechanical properties

The action of control forces can maintained by using small external power supply or even with battery

Semi-active devices

1.Stiffness control devices2.Electro-rheological dampers

3.Magnetorhelogical dampers 4.Friction control devices 5.Fluid viscous dampers 6.Tuned mass dampers 7.Tuned liquid dampers

Electro-rheological Dampers ER fluids that contain

dielectric particles suspended within non-conducting viscous fluids

When the ER fluid is

subjected to an electric field, the dielectric particles polarize and become aligned, thus offering resistance to the flow.


Stiffness control devices

Modify: - the stiffness -the natural

vibration characteristics

So create a non-resonant condition during earthquake

Magneto-rheological Dampers MR fluid contains micron-size,

magnetically polarizable particles dispersed in a viscous fluid

When the MR fluid is exposed to a magnetic field, the particles in the fluid polarize, and the fluid exhibits visco-plastic behavior, thus offering resistance to the fluid flow.


Hybrid control systems

Combine controls system together› Passive + Active› Passive + Semi-Active

Smart base-isolation Reduce external power requirement Improve reliability

› When loss of electric during earthquake, hybrid control can act as a passive control

Reduce construction and maintenance costs due to active or semi-active

References:1. Agrawal, A.K. and ang, J.N., Hybrid control of seismic response using nonlinearoutput feedback, in Proceedings of the Twelfth ASCE Conference on Analysis andComputation, Cheng, F.Y. (ed.), 1996, p. 339.

2. Aiken, I.D. and Kelly, J.M., Comparative study of four passive energy dissipationsystems, Bulletin of New Zealand National Society of Earthquake Engineering,25, 175, 1992.

3. Aiken, I.D. et al., Testing of passive energy dissipation systems, EERI EarthquakeSpectra, 9, 335, 1993.

4. Aizawa, S. et al., An experimental study on the active mass damper, in Proceedings

of the Ninth World Conference on Earthquake Engineering, InternationalAssociation for Earthquake Engineering, Tokyo, 1988, V, p. 87l.

5. Akbay, A. and Aktan, H.M., Actively regulated friction slip braces, in Proceedingsof the Sixth Canadian Conference on Earthquake Engineering, Toronto, Canada,1991, p. 367.

THANK YOU

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A SEMINAR ON STRUCTURE CONTROL SYSTEMS