Active toggle and scissor-jack damper-brace systems for structural vibration control

Mirfakhraei, S 2015, Active toggle and scissor-jack damper-brace systems for structural vibration control, Doctor of Philosophy (PhD), Civil, Environmental and Chemical Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Active toggle and scissor-jack damper-brace systems for structural vibration control
Author(s) Mirfakhraei, S
Year 2015
Abstract Active vibration control has recently attracted significant attention, particularly in relation to the mitigation of seismic risks in building structures. It involves measurement of structural response, determination of control force magnitudes via control algorithms, and production of control forces to suppress building vibrations. Active vibration control offers several advantages over conventional passive vibration control, for example, the adding of dampers to a structure. One major advantage is that it is adaptive in nature and an optimized, weighted function of control force and structural response can be achieved. However, a crucial problem exists which hinders the dissemination of the technology; that is, the control forces that are required in civil structures are usually very large; thus, very large force delivery devices or actuators are needed.

This thesis explores the effects of the installation of actuators in toggle and scissor-jack configurations in a building structure. Analytical and experimental investigations are conducted. For both configurations, single- and multi-degree-of-freedom systems have been theorized. The toggle configuration involves connecting the actuator to two hinged members, while the scissor-jack configuration involves four hinged members. Both configurations enable the actuator to generate a larger effective control force due to their amplification mechanisms; in other words, much smaller control forces are required to attain the same level of vibration reduction. The amplification is a nonlinear characteristic which is dependent on frame geometries, and its relationship with beam, column and brace dimensions are presented. The building is simplified into a lumped-mass shear building model and equations of motion are formulated. Numerical simulations are carried out on Matlab® in which the control forces are determined using the well-known LQR (Linear Quadratic Regulator) control algorithm. The active tendon control system with no amplification mechanism is used as a comparison. Under conditions occurring in two historical earthquakes, it is demonstrated numerically that close to 90% actuator force reduction is attained by both configurations.

In this thesis, an experimental investigation is also presented. A single-degree-of-freedom frame with an actuator mounted on a modified toggle configuration is fabricated. The frame is tested on a shake table manufactured by Quanser Corporation. Three historical earthquakes are selected as input excitations. Acceleration of the building model is measured using a piezoelectric accelerometer connected to a microcontroller board. The microcontroller board is interfaced with a PC, in which the signal is conditioned and control force is calculated in Matlab® using LQR control algorithm. The computed control force commands are transmitted back to the microcontroller board and the control force is delivered via an electric servomotor. Acceleration of the building model is measured and it is demonstrated experimentally that an active control system installed in a toggle mechanism significantly suppresses building response.

This thesis presents the finding of a comprehensive research work which theorizes and evaluates the effect of a toggle and scissor-jack brace system on actively controlled structures. Numerical and experimental evidence suggests that the required actuator forces can be reduced significantly. Subsequently, a much smaller and less expensive actuator hardware becomes feasible, and thus, feasibility of active control systems in building structures is improved significantly.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Civil, Environmental and Chemical Engineering
Subjects Earthquake Engineering
Structural Engineering
Control Systems, Robotics and Automation
Keyword(s) Earthquake Engineering
Structural Engineering
Smart Structures
Structural Vibration Control
Earthquake Vibration Control
Active Control System
Toggle Configuration
Scissor-Jack Configuration
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Created: Tue, 24 Apr 2018, 09:38:06 EST by Keely Chapman
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