Presentation on theme: " 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."— Presentation transcript:
Submitted by: MAHESH CHAND SHARMA M.TECH. –III SEM ( ) (2010PST116) Guided by: Dr. M.K.Shrimali Dr. S.D. Bharti Department of Structural Engineering Malaviya National Institute of Technology Jaipur
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.
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 )
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 respon se.
1.Passive control systems 2.Active Control systems 3.Semi-active control systems 4.Hybrid control syste ms
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
1. Base Isolation 2. Passive Energy Dissipating (PED) Devices
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
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
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
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
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,
The imposed lateral force is resisted by the product of the friction coefficient and the vertical load applied on the bearing
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 damper: relies on the principle that the metallic device deforms plastically, thus dissipating vibratory energy
here friction between sliding faces is used to dissipate energy Instructional Material Complementing FEMA 451,
Visco-elastic (VE) dampers utilize high damping from VE materials to dissipate energy through shear deformation. Such materials include rubber, polymers, and glassy substances.
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
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 dampersTuned liquid dampers
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 structure
Active Mass Damper Systems Active Tendon Systems Active Brace Systems
It evolved from TMDs with the introduction of an active control mechanism.
Active tendon control systems consist of a set of pre-stressed tendons whose tension is controlled by electro- hydraulic servomechanisms
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
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
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.
Modify: - the stiffness -the natural vibration characteristics So create a non- resonant condition during earthquake
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.
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
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 and Computation, Cheng, F.Y. (ed.), 1996, p Aiken, I.D. and Kelly, J.M., Comparative study of four passive energy dissipation systems, Bulletin of New Zealand National Society of Earthquake Engineering, 25, 175, Aiken, I.D. et al., Testing of passive energy dissipation systems, EERI Earthquake Spectra, 9, 335, Aizawa, S. et al., An experimental study on the active mass damper, in Proceedings of the Ninth World Conference on Earthquake Engineering, International Association 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.