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Research is being conducted in the Advanced Hazards Mitigation Laboratory at the University of Connecticut in various aspects of Semiactive Stiffness and Damping Technologies, Performance-Based Engineering, and Structural Health Monitoring. Additionally, research is making use of the shared-used Network for Earthquake Engineering Simulation (NEES) testing facility at the University of Colorado at Boulder. 

These activities are funded by the National Science Foundation (NSF) under grant CMS 06-12661, the Connecticut Cooperative Research Program, and the Japan Society for the Promotion of Science (JSPS Short Term Fellowship) and through generous equipment donations from the Lord Corporation. 

This page contains brief descriptions and selected papers that document these efforts.

Full-Scale Experimental Verification of Semiactive Structural Control

Link to Project Website

Description: Semiactive structural control shows great potential for hazard mitigation in civil structures. Semiactive control provides supplemental damping to more efficiently dissipate the energy due to dynamic loads and thereby increases the safety and performance of the structure. Semiactive control has typically been designed for and applied to linear structures. Civil structures, however, are designed to yield, thus behaving nonlinearly during extreme dynamic loading. Because they cannot inject mechanical energy into the controlled system, semiactive devices are inherently stable and well suited for application to structures with uncertainties and systems with potential to behave nonlinearly. 

Semiactive control in the presence of nonlinear structural behavior has yet to be demonstrated experimentally. The full-scale experimental dynamic testing of a nonlinear controlled building is a challenging task that can be addressed by the NEES Fast Hybrid Test System at the University of Colorado at Boulder. 

This research examines the experimental verification of semiactive control through the use of real-time hybrid testing. These experiments will employ hybrid testing of three semiactive large-scale Magneto-Rheological (MR) fluid dampers while simulating in real-time the nonlinear response of a building structure subjected to suites of simulated and recorded earthquakes.

Selected Publications:

    • A. Emmons, R. Christenson and B. Bass Proposed Full-Scale Experimental Verification of Semiactive Control Applied to a Nonlinear Structure”, submitted to ASCE Journal of Structural Engineering Special Issue dedicated to the 17th Analysis and Computation Conference. 
    • R.E. Christenson and A.T. Emmons, “Semiactive Structural Control of a Nonlinear Building Model: Considering Reliability,” 2005 Structures Congress, New York, NY.

Extending the Lifespan of Existing Highway Bridges through Controllable Stiffness and Damping Devices

Description: This project, just underway, will conduct analytical studies and provide a detailed design methodology to retrofit a highway bridge with controllable stiffness and damping devices that will serve to both reduce peak stresses and improve the health monitoring of structural components on highway bridges.

Coupled Building Control

Description: Connecting adjacent buildings for response reduction has been shown to be an effective method of structural control. As buildings are built taller and more flexible the resulting long periods become increasing more difficult to control using traditional methods of structural control (e.g. tuned and active mass dampers). Coupling adjacent buildings can provide the necessary level of safety and performance.

Active coupled building control was implemented in 2001 in the recently constructed Triton Square office complex in Tokyo, Japan. These 45-, 40- and 35-story office buildings are connected near the top floors with 35-ton actuators.

This research examines active coupled building control through analytical studies and conducting experimental tests to verify acceleration feedback control strategies, considered the affect of building configuration and damper location on passive and active control strategies, proposed semiactive coupled building control, and examining the ability to control dynamically similar structures.

Selected Publications:

    • R.E. Christenson, B.F. Spencer, Jr., E.A. Johnson, K. SetoCoupled Building Control Considering the Effects of Building Configurations,” ASCE Journal of Structural Engineering., 132(6), pp. 853-863, 2006.
    • R.E. Christenson, N. Hori, B.F. Spencer, Jr., and K. Seto, “Coupled Building Control Using Acceleration Feedback,” Computer-Aided Civil and Infrastructure Eng., 18(1), pp. 3-17, 2003.  
    • R.E. Christenson, B.F. Spencer, Jr., E.A. Johnson “Semiactive Coupled Building Control for Adjacent Multi-Degree of Freedom Buildings,” accepted for publication to ASCE Journal of Engineering Mechanics.  
    • K. Makita , R.E. Christenson, K. Seto , and T. Watanabe “Optimal Design Strategy of Connected Control Method for Two Dynamically Similar Structures”, submitted to ASCE Journal of Engineering Mechanics. 

Semiactive Control of Cable Vibration

Description: Stay cables, such as are used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Transversely-attached passive viscous dampers have been implemented in many bridges to dampen such vibration. However, only minimal damping can be added if the attachment point is close to the bridge deck. For longer bridge cables, the relative attachment point becomes increasingly smaller, and passive damping may become insufficient. 

In 2002, MR dampers were applied to 156 of the stay cables on the Dongting Lake Bridge in the Hunan Province of China for protection against rain-wind induced vibration. Currently the MR dampers on the Dongting Lake Bridge are operated in a passive mode with constant optimal voltage applied to the dampers during rain-wind conditions.

This research examines and demonstrates that "smart" semiactive cable damping employing feedback control can provide increased supplemental damping. The smart damping control strategy employs H2/LQG clipped optimal control using only force and displacement measurements at the damper for an inclined flat-sag cable. Both analytical and experimental studies have been conducted. Cable response is seen to be substantially reduced by the smart damper.

Selected Publications:

Probabilistic Measure to Assess the Efficacy of Semiactive Control

Description: Semiactive (smart) damping technology has been proposed to protect civil structures from dynamic loads. Each application of smart damping control provides varying levels of performance relative to active and passive control strategies. Currently, researchers compare the relative efficacy of smart damping control to active and passive strategies by running numerous simulations. These simulations can require significant computation time and resources. Because of this, it is desirable to develop an approach to asses the applicability of smart damping technology which requires less computation time.

This research identifies a control design method that utilizes a probabilistic approach to determine the efficacy of smart damping technology.

Selected Publications:

Nonlinear Test Structure for Structural Control Applications

Description: Experimental verification of analytical and numerical studies is very important in the area of structural dynamics and control due to the presence of higher mode participation, control structure interaction, sensor noise and potential nonlinear behavior. 

This research developed and examined a bench-scale test structure that extends the typical capabilities of test structures able to incorporate higher mode participation, control structure interaction and sensor noise to include nonlinear material behavior. A portal frame test structure is designed and built to simulate the formation of plastic hinges without actually receiving any damage. 

To demonstrate the nonlinear test structure’s use, a semiactive control strategy employing a shear mode magnetorheological (MR) fluid damper and acceleration feedback is applied to the test structure for seismic protection. The performance of the semiactive controlled structure is compared to the uncontrolled structure for a broad range of ground motion intensities and varying levels of nonlinear structural behavior to observe the improved reliability of the semiactive controlled structure.

Selected Publications:

 
University of Connecticut School of Engineering Department of Civil & Environmental Engineering
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