romero

REUJAT Symposium July 12, 2002 : REUJAT Symposium July 12, 2002 Susane L. Romero Undergraduate Researcher Department of Civil Engineering The City College of New York


The City College of the City University of New York : The City College of the City University of New York Founded in 1847 36 acre campus, St. Nicholas Heights in northern Manhattan Student body 11,000


Slide3 : Current Research in Earthquake Engineering at CCNY [Prof. Agrawal] Development of an Electromagnetic Shape Memory Alloy Friction Damper for Protection from Near-Field Earthquakes The friction forces is regulated through electromagnetic force and shape memory alloy springs. Closed-Form Approximations of Near-Fault Ground Motion Pulses for Optimization of Damper Parameters The closed-form approximation captures kinematic characteristics of most of the ground motion pulses. Effectiveness of Supplemental Dampers for Near-Fault Earthquake Ground Motions Research to determine when viscous or friction dampers may be most effective Development of Smart Bridge Bearings A Bridge Bearing equipped with sensors to measure reactions. Experimental Research on Passive, Semi-Active and Active Control Systems Using 10,000 lb Shaking Table System


Research Plan in Japan at Tokyo University and Kajima Technical Research Institute : Research Plan in Japan at Tokyo University and Kajima Technical Research Institute Theoretical research on semi-active and active structural controls Semi-Active Hydraulic damper Active Variable Stiffness System


Research Plan in Japan at Tokyo University and Kajima Technical Research Institute : Research Plan in Japan at Tokyo University and Kajima Technical Research Institute Experimental research: Observation of shake table experiments


Current Research at City College of New York : Current Research at City College of New York


Semi Active Friction Damper To Reduce Dynamic Structural Response : Semi Active Friction Damper To Reduce Dynamic Structural Response Principle Investigator Anil K. Agrawal, Ph.D., P.E. Assistant Professor Department of Civil Engineering The City College of New York Research Assistant Susane Romero Research Sponsored by a Grant from National Science Foundation


Semi-Active Electromagnetic Friction Damper (SAEMFD) : Semi-Active Electromagnetic Friction Damper (SAEMFD)


Why Semi-Active Friction Damper ? : Why Semi-Active Friction Damper ? Friction is inherently dissipative and Passive Friction Dampers are widely used. Friction force in the semi-active damper can be varied using an electromagnetic field. Electromagnetic field depends on the current, damper material and spacing. Preliminary results show: The variable friction force capability is effective during near field earthquakes for long period structures. Has excellent performance for base-isolated buildings.


Semi-Active Electromagnetic Friction Damper (SAEMFD) : Friction pad sandwiched between two steel plates. 3 layers slot-bolted together for sliding between steel plates and friction pad. Outer surfaces of steel plates installed with insulated solenoids, current I regulated such that attraction force exists across plates. Normal force N(t) and friction force F(t) regulated by current in solenoids across damper without any significant time delay. Effect of electromagnetic induction modelled quite accurately. Semi-Active Electromagnetic Friction Damper (SAEMFD)


Semi-Active Electromagnetic Friction Damper : Semi-Active Electromagnetic Friction Damper


Slide12 : Semi-Active Electromagnetic Friction Damper


Semi-Active Energy Dissipation : Semi-Active Energy Dissipation Control Force = f (displacement and velocity across the damper, external excitation)


Slide14 : Objective: Regulation of friction force as a function of drift of isolator bearings. (2) From eqns. (1) & (2): Normal force in the damper is regulated using peak drift across the damper. Semi-Active Friction Controller Previous Peak of xi Where: b = controller gain


Slide15 : With continuous slippage will dissipate energy without sticking [Discontinuous Semi-Active Friction (DSAF) Controller] This controller high-speed chattering in the vicinity of acceleration spikes. Eliminate using boundary layer around the controller. Linear Boundary Layer Semi-Active Friction (LBLSAF) Controller, friction force varies linearly in vicinity of Semi-Active Friction Controller


Semi-Active Friction Controller : Numerical Results 5-Story Base Isolated Building Period = 2.5 Seconds Damping Ratio = 4% Frequency range 0.1 to 5 rad/sec b = 300000,600000,900000 Semi-Active Friction Controller


Response to Sinusoidal Excitation [Discontinuous Semi-Active Friction Controller] : Response to Sinusoidal Excitation [Discontinuous Semi-Active Friction Controller] A discontinuous controller may give rise to high acceleration spikes in low frequency regions.


Response to Sinusoidal Excitation [Discrete Boundary Layer Controller, d = 0.1] : Response to Sinusoidal Excitation [Discrete Boundary Layer Controller, d = 0.1] Introducing boundary layer is effective in removing acceleration spikes.


Slide19 : Numerical Results 5-Story Base Isolated Building Period = 2.5 Seconds Damping Ratio = 4% Drift of Isolators = 28.5 cm During El Centro NS earthquake with PGA = 0.314 g Objective: Design a Control System to protect the base isolated building from Near-Field Earthquakes: m=0.2, b=1.2e6 About 70% reduction in base displacement Semi-Active Friction Controller


ResultsSemi Active Friction Damper : Results Semi Active Friction Damper


Conclusions : Conclusions Performance of semi-active friction dampers depend on the type of control algorithm used. Semi-Active Friction Dampers have been found quite effective for flexible structures subject to near-field earthquakes. Experimental verification and fabrication of the damper is under planning and will be conducted soon.


Future Research : Future Research Optimal placement and corresponding optimal capabilities of Semi-Active Electromagnetic Friction damper for a range of earthquakes. Shake table experiments with Semi-Active Electromagnetic friction damper.


Acknowledgements : Acknowledgements City College of New York Professor Anil Agrawal REUJAT Professor Shirley Dyke National Science Foundation (NSF) Tokyo University Professor Abe & Professor Fujino Kajima Corporation Dr. Narito Kurata Japan Society for Promotion of Sciences (JSPS)


Thank You! : Thank You!