Submitted by MAHESH CHAND SHARMA MTECH III SEM 201112 2010PST116 Guided by Dr MKShrimali Dr SD Bharti Department of Structural Engineering ID: 674709
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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 Engineering
Malaviya National Institute of Technology JaipurSlide2
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.Slide3
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)Slide4
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.Slide5
Structure Control systems
1.Passive control systems2.Active Control systems
3.Semi-active control systems4.Hybrid control systemsSlide6
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 controlledSlide7
The passive control devices includes
1. Base Isolation2. Passive Energy Dissipating (PED) DevicesSlide8
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 energySlide9
Behavior of Building Structure with Base Isolation System
Conventional Structure
Base-Isolated Structurehttp://www.earthquakeprotection.com.Slide10
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 BearingSlide11
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
http://www.earthquakeprotection.com.Slide12
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
http://www.earthquakeprotection.com.Slide13
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
http://www.earthquakeprotection.com.Slide14
Lead-Rubber Bearings
damping properties can be improve by plugging a lead core into the bearingdamping of the lead-plug bearing varies from 15% to 35%.The Performance depends on the imposed lateral forceThe 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,Slide15
Sliding Bearings
The imposed lateral force is resisted by the product of the friction coefficient and the vertical load applied on the bearingSlide16
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 DampersVisco-elastic Dampers
Viscous Fluid Dampers, And
Tuned Mass Dampers And Tuned Liquid Dampers.Slide17
Metallic Yield Dampers
Metallic yield damper: relies on the principle that the metallic device deforms plastically, thus dissipating vibratory energy
http://www.earthquakeprotection.com.Slide18
Friction Dampers
here friction between sliding faces is used to dissipate energy
Instructional Material Complementing FEMA 451,Slide19
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.
http://www.earthquakeprotection.com.Slide20
Viscous Fluid DampersA 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 http://www.earthquakeprotection.com.Slide21
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 structureTuned liquid dampers are similar to tuned mass dampers except that the mass-spring-damper system is replaced by the container filled with fluidSlide22
Tuned mass dampers
Tuned liquid dampers http://www.earthquakeprotection.com.Slide23
Active Control systems
In 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 structureSlide24
Types of Active Control systems
Active Mass Damper SystemsActive Tendon SystemsActive Brace SystemsSlide25
Active Mass Damper SystemsIt evolved from TMDs with the introduction of an active control mechanism.
http://www.earthquakeprotection.com.Slide26
Active Tendon Systems
Active tendon control systems consist of a set of pre-stressed tendons whose tension is controlled by electro-hydraulic servomechanisms
http://www.earthquakeprotection.com.Slide27
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 batterySlide28
Semi-active devices
1.Stiffness control devices 2.Electro-rheological dampers 3.Magnetorhelogical dampers 4.Friction control devices 5.Fluid viscous dampers 6.Tuned mass dampers
7.Tuned liquid dampers Slide29
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.
http://www.earthquakeprotection.com.Slide30
Stiffness control devices
Modify: - the stiffness -the natural vibration characteristicsSo create a non-resonant condition during earthquakeSlide31
Magneto-rheological Dampers
MR fluid contains micron-size, magnetically polarizable particles dispersed in a viscous fluidWhen 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.
http://www.earthquakeprotection.com.Slide32
Hybrid control systems
Combine controls system togetherPassive + ActivePassive + Semi-ActiveSmart base-isolationReduce external power requirementImprove reliabilityWhen loss of electric during earthquake, hybrid control can act as a passive controlReduce construction and maintenance costs due to active or semi-activeSlide33
References:1. Agrawal, A.K. and ang, J.N., Hybrid control of seismic response using nonlinear
output 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 Earthquake
Spectra, 9, 335, 1993.4. Aizawa, S. et al., An experimental study on the active mass damper, in Proceedingsof 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 Proceedings
of the Sixth Canadian Conference on Earthquake Engineering, Toronto, Canada,
1991, p. 367.Slide34
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