NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Since 1970’s, the idea to use energy dissipative means in protecting building structural
systems against un-wanted vibrations caused by extreme events such as strong winds;
waves; destructive earthquakes; excessive man-made excitations, etc., has captured the
imagination of many researchers. To benefit from the advantages of passive and active
systems, semi-active systems, possessing the characteristics of passive and active systems,
such as: low power input requirements; adjustable dynamic characteristics; no spill-over
phenomenon; structural motion triggered operations; need for a suitable control algorithm
requirements; no time delay problems if using electric or magnetic fluid devices; cost
effective manufacturing and minor maintenance requirements; having fail-safe
characteristics is selected in this research.
This thesis presents a theoretical study of basic principles of controllable fluid flows
for device modellings; the development of semi-active fluid control devices, whose
dynamic range and desired damping level are investigated; and ‘proof-of-concept-tests’ of
the prototype fluid control devices using sudden release and shake table tests. The
performance of developed fluid control devices: prototype shear damper and smart pin
damper, are verified using experimental results. Numerical simulations using MATLAB
SIMULINK or tailor made ‘m’ code programs are furthermore used to gain insight into the
damper control characteristics.
The research scope involves the following five areas:
1. Studying basic principles and mechanism of controllable fluid flows treated as
single fluid (Non-Newtonian fluids), magnetic fluid and two fluid models with
magnetic forces. The study led to developing fluid dynamics-based device models
that were then verified with experimental results.
2. Design, fabrication and testing prototype Magneto-rheological (MR) control
devices: prototype shear (blade-column) damper and smart pin damper.
3. Characterization of damper performance in quasi-static and dynamic fashions using
curve fitting, model mapping and system identification methods for modelling of
4. Tailoring control algorithms to suit specific characteristics of devices.
5. Validation of device performance using numerical simulation and ‘proof-of-concept’
experiments of single storey plane frame models subjected to free
vibration, sinusoidal and earthquake excitations, conducted using sudden release,
impulse and shake table tests.
The research, commenced with mathematically studying the duct flows through a
parallel plate model for electro-rheological (ER) or magneto-rheological (MR) fluids,
treated as non-Newtonian fluids, such as Bingham, Herschel-Bulkley and author proposed
multi-piecewise linear viscous, which were introduced to develop the dashpot damper
The use of single fluid models, so far, cannot analytically explain the physical
mechanism behind electric or magnetic field-effects to the fluid rheological properties. The
field of magneto-hydrodynamics, once attracting researchers in early 1960’s, can partly
explain the fluid rheological property changes due to the presence of Lorentz force, which
can accelerate or de-accelerate fluid flows in a duct.
The accuracy of numerical or mathematical models for one dashpot damper MRD-
105 and two in-house designed and fabricated prototype shear and smart pin dampers is
assessed by verification and validation of numerical simulation results with corresponding
experimental results, tested in quasi-static and dynamic modes in the UTS Structures
laboratory. Results were characterised using curve fitting, model mapping and system
identification method in MATLAB package to determine the relationship between damper
force and velocity or DC current level input. Good agreement for dashpot damper was
obtained between the experimental results and proposed mathematical models: multi-piece
wise linear and Bingham-Maxwell models.
The prototype fluid dampers basically constituting three main components, namely,
electromagnetic circuit system, controllable fluid and mechanical part were studied to
elaborate the two important aspects in designing this kind of device: dynamic range and
desired damping level. The ‘proof-of concept-tests’ of these prototype dampers: shear and
pin dampers, respectively, mounted to a single-storey plane steel frame using an inverted
‘V’ brace truss, and as a beam-column connector, were later conducted using shake table
for performance investigation. The dynamic performance of both models was studied using
the experimental results of various free and forced vibration cases tested using sudden
release and shake table, respectively. While, the free vibration results were used to
characterise dynamic properties of the integrated structural systems using curve-fitting
method for static stiffness coefficient of bare frame and brace, Fast Fourier Transform
(FFT) for frequency, decay function and logarithmic decrement methods for static friction
and damping ratios. Together with the control algorithms, state feedback and clipped-optimal
controls employing Linear Quadratic Regulator (LQR) optimal and experimentally-tuned
gains, discrete-time state space models were simulated using SIMULINK of
MATLAB to validate sudden release and shake table experimental results of the shear
In this case, two benchmark earthquake excitations: El-Centro N-S 1940 and
Northridge N-S 1994, representing far- and near-field earthquakes, respectively, were
selected as two standard random excitations for six dynamic system conditions: no damper
(ND), passive-off (Poff), passive-on (Pon), State feedback control (Cl) and Clippedoptimal
control (C2). Experimental results confirmed that the prototype shear damper is
capable of suppressing the vibration responses of tested physical model, whose peak
displacement responses were reduced as exceeding 50% when compared with no damper
condition. Furthermore, good agreements for both free and forced vibration cases were
achieved between numerical simulations and experimental results.
Unlike, the smart pin-frame model, having non-linear DC current-based dynamic
properties, can alter its system frequency in accordance with the supplied DC current level
to the smart pin, The available linear control algorithms, therefore, cannot be implemented;
as the feedback term by the damper is not a control force, but pin rotational stiffness, The
sweep tests using sinusoidal excitations, conducted by the shake table, proved that the
efficiency of displacement response reductions could be enhanced by properly switching
the system frequency. Even though, the system performed moderately well when subjected
to earthquake excitations, further research to this preliminary investigation is absolutely
required to tailor the appropriate control strategy to this system.
Finally, the results of the analytical and experimental studies demonstrated the
advantages and potential use of semi-active MR fluid control devices: shear and smart pin
dampers. This research is expected to facilitate and accelerate the implementation of these
kinds of dampers in earthquake resistant structures of the future.