3.1 Advanced Control Systems for Seismic Protection
A Full-Scale Experimental Study on Seismic Behaviour of Vibration Isolated Mechanical/Electrical Equipment
Fan-Ru Lin, Ching-Wen Cheng, Min-Fu Chen, Shiang-Jung Wang, J.S. Hwang & K.C. Chang
ABSTRACT: In resent major earthquake events in Taiwan, several damaged spring isolated equipment cases were observed and showed high vulnerability of spring isolators. Recognizing the particular significance of the spring isolators in affecting the earthquake resistant capacity of critical mechanical/electrical systems, such as emergency power supply, water supply and air conditioning system, the purpose of this research is to study the seismic behaviour of the spring isolators in comparison with the Isolation/Restraint system which is composed of spring isolators and snubbers. A diesel generator was used as test specimen to observe realistic seismic responses of spring isolated equipment. Quasi-static cyclic loading tests and shake table tests were conducted to study elastic and inelastic behaviour of spring isolators. Testing results were preliminary analyzed to investigate damage states and dynamic characteristics of spring isolators, and the appropriateness of the dynamic amplification factor for spring isolated equipment was discussed as well.
Upgrading the Seismic Performance of Soft First Storey Frame Structures by Isolators with Multiple Sliding Surfaces
M.Y. Fakhouri & A. Igarashi
ABSTRACT: Soft storey failure was one of the most observed failures through many earthquakes in the past. In this study, the seismic performance of soft first storey frame structures is upgraded by installing a recently developed multiple-slider bearing on the top of the middle columns and rubber bearing at the top of edge columns. The multiple-slider bearing is a simple sliding device consisting of one horizontal and two inclined plane sliding surfaces at both ends set in series. These three surfaces based on PTFE and highly polished stainless steel interface. The main purpose to develop such a device was the need for a seismic bearing that is simple, and effective in reducing the horizontal displacement with a low cost in order to be implemented in multi-span continuous bridges. The idea and concept are extended to be applied in frame structures, specifically in upgrading the seismic performance of soft-first-storey frame structures. The proposed system also offers a feasible solution for seismic retrofit of existing buildings with soft stories. A five-storey reinforced concrete shear frame with a soft first storey is considered to demonstrate the efficiency of the proposed isolation system in reducing the ductility demand and damage in the structure while maintaining at the same time the superstructure above the bearings to behave nearly in the elastic range. Comparative study with the conventional system is also performed. The results show the effectiveness of the multiple-slider bearing in minimizing the damage from earthquake and preserving the soft first storey from excessive large ductility demand due to its unique geometry.
Adaptive Control of Tall Buildings under Seismic Excitation
Maryam Bitaraf & Stefan Hurlebaus
ABSTRACT: The effectiveness of an adaptive control strategy to control the performance of tall buildings under seismic loads is investigated in this study. The adaptive controller used in this research is based on the simple adaptive control method (SACM), which is a type of direct adaptive control approach. This method is applicable to multi-input multi-output systems. Also, it does not depend on plant parameter estimates. The SACM requires less prior knowledge of controlled structural systems. In addition, it is practical for online control of large-scale structures. These characteristics show that the SACM can be an appropriate method to control tall buildings with many degrees of freedom. The objective of the SACM is to make the plant, the controlled system, track the behavior of the structure with the optimum performance. In this study, the response of a 20-storey building is controlled by a direct adaptive control strategy using ideal active devices. The SACM is employed to obtain the required force which results in the optimum performance of the structure. Time-history analyses of the 20-storey building are performed to evaluate the performance of the adaptive controller. The SACM performance is compared to the performance of LQR. Results show that SACM can successfully improve the seismic response of controlled buildings against external loadings.
Development and Spectral Analysis of an Advanced Control Law for Semi-Active Resetable Devices
J.Geoffrey Chase, Geoffrey W. Rodgers, Sylvain Corman & Gregory A. MacRae
ABSTRACT: Passive energy dissipation has advantages such as low cost, easily predictable response, and ease of implementation, which are offset by difficulty tuning or designing devices for optimum behaviour over a range of inputs and responses. Semi-active systems offer customised response and provide a control input that adapts to structural response without excessive energy input. Specific control laws can simultaneously reduce displacement and total base-shear transmitted to the foundation – a unique semi-active capability. These significant advantages can be offset by the Ltd energy dissipation that can arise as a result.
This research focuses on a more effective resetable device control law called the “diamond control law,” for its unique semi-actively enabled device hysteresis loop, which maximises energy dissipation while simultaneously minimising the impact on base shear forces. It achieves this affect by controlling the release of stored energy in the resetable device - smart dissipation in place of maximum or instantaneous uncontrolled release typically used in such devices. A spectral analysis shows that this new an approach enables a decrease of 30-40% for both displacement and structural force, which is equivalent to 15-20% critical viscous damping for an uncontrolled base structure. The total base shear is also decreased by 40%, which has significant potential benefits for retrofit applications. This level of displacement and base shear reductions was not available (in combination) from prior resetable device control approaches, nor from any passive device or system, and thus represents a significant expansion of the design space and capability for seismic energy dissipation.
Active Valve Control for Controlled Energy Release in Non-Linear Semi-Active Devices
Sylvain Corman, J.Geoffrey Chase, Gregory A. MacRae & Geoffrey W. Rodgers
ABSTRACT: Semi-active devices are strictly dissipative, low power control devices designed to reduce seismic structural response damage in buildings using the building’s own motion to produce resistive forces. New semi-active resetable devices with independently controlled valves and chambers can sculpt the device and structural hysteresis loops for specific applications. However, some of the most advantageous hysteresis loops and applications are not possible without active valve control to control the release of stored energy, in contrast to current resettable device control laws that rely on a maximum, fixed rate of stored energy release.
This study uses proportional/derivative feedback control to closely track a desired, ideal reference force-displacement response curve. It is validated with a unique diamond-shaped control law under sinusoidal and seismically induced, random input motions. A spectral analysis is also done to compare the non-linear, actively controlled results to those obtained with an ideal, linear model. The results show tracking to within 3-5% of the desired force-displacement curve, with mean errors below 1%. Valve delay is the main limitation, where the ratio of valve delay to structural period must be 1/10 or smaller to ensure adequate tracking, thus prescribing valve performance as a function of the structural period of the application. The overall results show that active feedback control of energy release, via active control of the valves, can dramatically increase the design space of possible resettable device hysteresis loops that can be obtained, and thus significantly increase their performance envelope and application potential. The results and approach are fully generalisable to a wide range of energy dissipation devices.
Seismic Control of Nonlinear Benchmark Building with a Novel Re-Centering Variable Friction Device
Osman E. Ozbulut & Stefan Hurlebaus
ABSTRACT: This paper investigates the seismic response control of a nonlinear benchmark building with a new re-centering variable friction device (RVFD). The RVFD consists of three parts: (i) a friction generation unit, (ii) a piezoelectric actuator, and (iii) shape memory alloy wires. The friction unit and piezoelectric actuator compose the first subcomponent of the hybrid device that is a variable friction damper (VFD). The clamping force of the VFD can be adjusted according to the current level of ground motion by adjusting the voltage level of piezoelectric actuators. The second subcomponent of this hybrid device consists of shape memory alloy (SMA) wires that exhibit a unique hysteretic behaviour and full recovery following post-yielding deformations. In general, installed SMA devices have the ability to re-center structures upon end of the motion and VFDs can increase the energy dissipation capacity of structures. The full realization of these devices into a singular, hybrid form which complements the performance of each device is investigated. A neuro-fuzzy model is used to capture rate- and temperature-dependent nonlinear behaviour of the SMA components of the hybrid device. A fuzzy logic controller is developed to adjust voltage level of VFDs for favourable performance in a RVFD hybrid application. Numerical simulations of seismically excited nonlinear benchmark building are conducted to evaluate the performance of the hybrid device. Results show that the RVFD modulated with a fuzzy logic control strategy can effectively reduce interstory drifts without increasing acceleration response of the benchmark building for most cases.