Structural Dynamics and the Seismic Response Control Laboratory at Duke University

Structural Dynamics and the Seismic Response Control Laboratory
Room 122, Hudson Engineering Center
Department of Civil and Environmental Engineering
Edmund T. Pratt School of Engineering
Duke University - Box 90287, Durham, NC 27708-0287

Henri Gavin - Associate Professor - Henri.Gavin@Duke.edu - tel: 919-660-5201 - fax: 919-660-5219

Introduction

The loads acting upon a structure over its entire life are often not foreseen at the time of design or construction of the structure. An important example of this is in the design of damping systems for earthquake-resistant behavior. The characteristics of an eventual earthquake can vary substantially from those used for design. Structures which incorporate controllable elements can adapt their behavior based on measurements of their motion and the motion of their supports.

1. ER/MR Materials

The material properties of electrorheological (ER) and magnetorheological (MR) materials can be changed in milliseconds by an applied low-power electric, or magnetic, field. At zero electric field, these materials are viscous liquids. At high fields they behave like viscoelastic-plastic solids. Members making use of ER or MR fluids can regulate very large forces with almost no external energy.

Part of our research addresses oscillating ER and MR flows. Current research is providing information useful to the design of devices using ER and MR fluids and in the use of these devices for structural control applications for extreme and unforeseen loads, such as mitigating earthquake induced vibrations.

2. Vibration Control Devices

A multi-objective approach is being used for the design of damping devices using ER materials. With this methodology, a "feasible'' set of device designs is pre-defined. A current design paradigm is that of a multi-duct device with concentric electrodes. The electrodes are electrically parallel, but the ND flow ducts can be interconnected in 2ND-1 possible combinations; therefore, a wide range of device characteristics are possible in a given geometry. The basic design of the device is illustrated below.

Current studies show that an ER device capable of regulating 200 kN of force with a dynamic range of 10 and a response time of less than 15 ms is feasible. Furthermore, this device requires only 20 kJ to operate over the course of an earthquake. In order to experimentally evaluate the design equations, 3 smaller devices with different duct configurations are being tested.

A model for the damper including fluid compressibility device elasticity, fluid inertia, and device inertia will be developed.

3. Vibration Control Algorithms and Shake-Table Testing

A hydraulically-activated shaking table and a 2 kip, 100 Hz load frame provide a laboratory facility for testing structural control components and for performing vibration control experiments. The 1.2 m by 1.2 m table is driven by a 50 kN hydraulic actuator, and a 20 gpm, 90 Hz servovalve. The table and a (1/5) dynamically scaled model are subjected to actual (1-D) earthquake records, as well as random signals and sinusoidal signals. The results are extrapolated to full-scale structures.

The appeal of ER devices in structural control applications is due to their fast (milli-second) response times, direct transduction of an electrical signal to a control force, low operating power requirements, and simple implementation. Strategies for reducing vibrational kinetic and potential energies, using ER devices modeled by empirically verified constitutive relations, have been formulated. Experimentally, peaks of the ratio of spectral accelerations have been reduced as illustrated in the figure.

A drift-free hybrid analog/digital integrating circuit has been developed to provide real-time absolute velocity and absolute displacement measurements from a dc-stable accelerometer. This technology allows the states of a structure to be measured directly.

Selected Publications

Gavin, Henri P. ``Annular poiseuille flow of electrorheological and magnetorheological materials,'' Journal of Rheology, vol. 45, no. 4, (July-August 2001) 983--994.

Gavin, Henri P. ``Control of Seismically-Excited Vibration using Electrorheological Materials and Lyapunov Methods'' IEEE Transactions on Control Systems Technology, vol. 9, no. 1, (January 2001) 27--36.

Gavin, Henri P., ``Design method for high-force electrorheological dampers,'' Smart Materials and Structures, vol. 7, no. 5 (October 1998): 664--673.

Gavin, Henri P., Morales, Rodrigo, and Reilly, Kathryn, ``Drift-free integrators,'' Review of Scientific Instruments, vol. 69, no. 5 (May 1998): 2171--2175.

Gavin, Henri P., ``The Effect of Particle Concentration Inhomogeneities on the Steady Flow of Electro- and Magneto-Rheological Materials,'' Journal of Non-Newtonian Fluid Mechanics, vol. 71, (August 1997): 165--182.

Gavin, Henri P., Hanson, Robert D., and Filisko, Frank E., ``Electrorheological Dampers I: Analysis and Design,'' ASME J. Applied Mechanics, vol. 63, (September 1996): 669--675.

Gavin, Henri P., Hanson, Robert D., and McClamroch, N. Harris, ``Electrorheological Dampers II: Testing and Modeling,'' ASME J. Applied Mechanics, vol. 63, (September 1996): 676--682.

Gavin, H.P., Hoagg, J. and Dobossy, M., ``Optimal Design of MR Dampers,'' Proc. U.S.-Japan Workshop on Smart Structures for Improved Seismic Performance in Urban Regions, 14 August 2001, Seattle WA, ed. K. Kawashima, B.F. Spencer, and Y. Suzuki, pp. 225--236.

Gavin, H.P. and U. Aldemir, ``Behavior and Response of Auto-Adaptive Seismic Isolation,'' Proc. 3rd U.S.-Japan Cooperative Research Program in Urban Earthquake Disaster Mitigation, 15--16 August 2001, Seattle WA, ed. S. Otani and M.A. Sozen, pp. 120--128.

Aldemir, U. and H.P. Gavin, ``Auto-Adaptive Seismic Isolation,'' Proc. 2001 Structures Congress, 21--23 May 2001, Washington, DC, ed. S.S. Sunder, ASCE Press, (cd-rom).

Gavin, Henri P. and Dobossy, Mark, ``Optimal Design of an MR Device,'' Proc. SPIE, 8th Annual International Symposium on Smart Structures and Materials, 3 -- 8 March 2001, Newport Beach, CA.

Gavin, Henri P., ``Multi-duct electrorheological dampers'' Proc. SPIE, 8th Annual International Symposium on Smart Structures and Materials, 3 -- 8 March 2001, Newport Beach, CA.

Gavin, Henri, Dobossy, Mark, and Lamberton, Jason, ``Designing and Testing Devices for Semi-Active Structural Control,'' Proc. 3rd Intl. Workshop on Structural Control, Paris, France, July 7-9, 2000.

Gavin, Henri, Lee, Heungil, and Aldemir, Unal, ``Optimal Semi-Active Control,'' Proc. 2nd European Conference on Structural Control, Paris, France, July 3-7, 2000.

Gavin, Henri and Cheng, Shuxing, ``Semi-Active Mass Damper for Wind Excited Structures,'' Proc. 2nd European Conference on Structural Control, Paris, France, July 3-7, 2000.

Gavin, Henri P., and Doke, Nitin S., ``Variable Property Devices for Structural Control,'' Proc. ASCE Structures Congress, New Orleans LA, April 18-21, 1999.

Gavin, Henri P., and Doke, Nitin S., ``Resonance suppression through variable stiffness and damping mechanisms ,'' Proc. SPIE, 6th Annual International Symposium on Smart Structures and Materials, 1 -- 5 March 1999, Newport Beach, CA.

Doke, Nitin S., and Gavin, Henri P., ``Non-proportional damping and semi-active control,'' Proc. 13th I.M.A.C., February 1999, Orlando, FL.

Gavin, Henri P., ``Structural Control Using Variable Stiffness Materials,'' Proc. Structural Engineering World Conference, 19 -- 23 July 1998, San Francisco, CA.

Gavin, Henri P., and Hanson, Robert D., ``Seismic Protection using ER Damping Walls,'' Proc. 2nd World Conference on Structural Control, 28 June -- 1 July, 1998, Kyoto, Japan.

Baltimore, Craig V., and Gavin, Henri P., ``Field-Flow Orientation Effects in Magnetorheological (MR) Devices,'' Proc. 2nd World Conference on Structural Control, 28 June -- 1 July, 1998, Kyoto, Japan.

Gavin H., Yuan, S., Grossman, J., Pekelis, E., and Jacob, K., Low-level Dynamic Characteristics of Four Tall Flat-Plate Buildings in New York City, NCEER Technical Report 92--0034 (Buffalo: National Center for Earthquake Engineering Research, 28 Dec. 1992).

Ghanem, Roger G. and Gavin Henri P., Experimental Verification of a Number of Parameter Estimation Routines, NCEER Technical Report 91--0024 (Buffalo: National Center for Earthquake Engineering Research, 18 Sep. 1991).