ACTIVE/PASSIVE SEISMIC CONTROL OF STRUCTURES

In civil engineering, structural integrity and safety are of utmost importance as the consequences of failure are devastating. Maintaining the structural integrity becomes particularly important when the structures are subjected to severe earthquakes and strong wind-loading. Various passive and active control means have been considered to avoid catastrophic failure due to seismic or wind excitations. In this paper, a new class of hybrid actuators is presented which consists of a piezoelectric stack actuator combined with a viscoelastic damper to form a passive/active brace system (PAB). The actuator is used for mitigating structural dynamic responses of a three-storey structure subjected to simulated earthquakes loading. The proposed hybrid actuator is selected because it combines the attractive attributes of active and passive systems as well as because it has high stiffness-weight ratio, high frequency bandwidth, and low power consumption. The theoretical and experimental performance characteristics of the three-storey structure with the hybrid PAB actuator are presented. Comparisons are also included when the structure is controlled with conventional viscoeiastic dampers or conventional active control braces that operate without any viscoelastic damping. These comparisons emphasize the effectiveness of the hybrid actuator in damping out simulated seismic vibrations.     

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.     

INSTANTANEOUS OPTIMAL CONTROL FOR SEISMIC ANALYSIS OF NON-LINEAR STRUCTURES

In this paper, an effective active control algorithm is developed for the vibration control of non-linear structural systems subjected to earthquake excitation. It is an attempt to include the non-linear characteristics of the structural behaviour throughout the entire analysis (design and validation), accounting for the eventual cumulative structural damage and energy dissipation. This is a very important factor since, in current design practice, structures are assumed to behave nonlinearly when subjected to strong ground motion. The proposed algorithm focusses on the instantaneous optimal control approach for the development of the control algorithm where the nonlinearities are brought into the analysis through a non-linear state vector and a non-linear open loop term. A performance index that is quadratic in the control force and in the non-linear states and is subjected to a non-linear constraint equation, is minimised at every time step. The effectiveness of the proposed non-linear instantaneous optimal control (NIOC) strategy is critically evaluated in comparison with currently available active control techniques. Numerical simulation results indicate that the proposed approach provides a significant reduction of the peak response quantities, such as maximum response deformation, maximum response acceleration, ductility of the system, associated with a reduced maximum control force.     

Optimal Control of Accelerations in a Base-Isolated Building using Magneto-Rheological Dampers and Genetic Algorithms

This article presents a numerical study aimed at improving effectiveness of the isolation system of an actual building by adding magneto-rheological (MR) dampers that act in parallel to the existing rubber bearings (RB). The building itself is modeled with uniaxial elastic elements. Additional elements that include the RBs and the MR dampers are added at the base of the building and two different genetic algorithms are used to optimize operation of the MR dampers. Maximum acceleration and relative displacement at the top of the building are taken as the variables to be minimized. Records of destructive earthquakes are used as input. A comparison is made between the building responses with RB and the one with the additional control system.     

SEISMIC RESPONSE CONTROL OF CABLE-STAYED BRIDGE USING DIFFERENT CONTROL STRATEGIES

The goal of this research is to study the effect of cable vibration through a number of control cases of a cable-stayed bridge. In order to consider the complicated dynamic behaviour of the full-scale bridge, a three-dimensional numerical model of the MATLAB-based analysis tool has been developed by the complete simulation of the Gi-Lu bridge. The dynamic characteristics of cables in the cable-stayed bridge are verified between the field experiment and the result from numerical simulation using geometrically nonlinear beam elements in MATLAB program. Three types of control devices are selected to reduce the response of the bridge deck which includes: actuators, viscous-elastic dampers with large capacity, and base isolations. Moreover, two types of control devices, MR dampers and viscous dampers, are installed either between the deck and cables and/or between two neighbouring cables for controlling the cable vibration. A modified bi-viscous model combined with convergent rules is used to describe the behaviour of MR dampers. Finally, through evaluation criteria the control effectiveness on the cable-stayed bridge using different control strategies is examined.     

Mixed Force and Displacement Control for Testing Base-Isolated Bearings in Real-Time Hybrid Simulation

This paper presents a robust mixed force and displacement control strategy for testing of base isolation bearings in real-time hybrid simulation. The mixed-mode control is a critical experimental technique to impose accurate loading conditions on the base isolation bearings. The proposed mixed-mode control strategy consists of loop-shaping and proportional-integral-differential controllers. Following experimental validation, the mixed-mode control was demonstrated through a series of real-time hybrid simulation. The experimental results showed that the developed mixed-mode control enables accurate control of dynamic vertical force on the base isolation bearings during real-time hybrid simulation.     

Seismic Response of Base-Isolated Benchmark Building with Variable Sliding Isolators

The seismic response of base-isolated benchmark building with variable sliding isolators like variable friction pendulum system (VFPS), variable frequency pendulum isolator (VFPI), and variable curvature friction pendulum system (VCFPS), along with conventional friction pendulum system (FPS), was studied under the seven earthquakes. The earthquakes are applied bi-directionally in the horizontal plane ignoring vertical ground motion component. The shear type base-isolated benchmark building is modeled as three-dimensional linear elastic structure having three degrees of freedom at each floor level. Time domain dynamic analysis of the benchmark building was carried out with the help of constant average acceleration Newmark-Beta method and nonlinear isolation forces was taken care by fourth-order Runge-Kutta method. The base-isolated benchmark building is investigated for uniform isolation and hybrid isolation in combination with laminated rubber bearings through the performance criteria and time history response of important structural response parameters like floor accelerations, base displacement, etc. It is observed that variable sliding isolators performed better than conventional FPS due to their varying characteristic properties which enable them to alter the isolator forces depending upon their isolator displacements thus improves the performance of the structure. The VFPS efficiently controls large isolator displacements and VFPI and VCFPS improve super structural response on the cost of isolator displacement. It is also observed that the hybrid isolation is relatively better in comparison to the uniform isolation for the benchmark building.     

Seismic Protection of the Piers of Integral Bridges using Sliding Bearings

Seismic resilience and continued operation of bridges after earthquakes are important seismic design criteria. A new seismic protection concept for integral bridge piers is explored that uses sliding bearings to separate the superstructure from the piers. The influence of sliding bearings on the seismic response of a representative 3-span integral highway bridge is investigated. With sliding bearings, the pier column shear force was limited to the bearing design friction force. Furthermore, the abutment ductility demands were found to be insensitive to the friction forces in the sliding bearings because the bridge displacement demands were controlled by the equal displacement rule.     

INDEPENDENT HARMONIC CONTROL FOR STRUCTURAL ENGINEERING

In a previous paper [Baratta and Corbi, 1999] one has defined a procedure allowing to identify a closed-ioop control algorithm with feedback based on the whole record of the response time-history rather than on instantaneous response parameters. The control force results from control of each harmonic component of the forcing function, simply integrated over the frequency domain. Every harmonic is controlled, independently of each other, by a classical linear control whose coefficients are calibrated in way to make the relevant response component a minimum compatibly with the control effort one wants to apply at the corresponding frequency. The distribution of this control intensity over the frequency range remains a arbitrary choice; such a choice however lends itself to be effectively assisted by intuition, much more than similar choices in other procedures (e.g.: the coefficients of the quadratic norms in the J-index optimization). The result is that every harmonic remains controlled by a different couple of optimal coefficients (corresponding to the proportional and to the derivative terms in the linear control law), and the overall control force for an arbitrary disturbance, after Fourier inverse transformation, is produced by feedback integration over the whole response time-history.

The procedure, tested with reference to simple and composed harmonic excitations incoming a s.d.o.f. structural system, has proved a good agreement of the numerical results with the theoretical treatment; furthermore it has shown that the main limit of such an approach consists of referring the dynamic equilibrium solution to a particular solution, that, neglecting the initial conditions, may introduce some unstable components in the oscillation. In the paper the effects induced in the controlled structural system response by the adoption of the proposed procedure are deepened and an improved strategy is presented, able to overcome the detrimental transient effects determined by the original algorithm. The final adopted control law is shown to achieve an improved time response, both in the transient and in the steady-state field, in comparison to a control strategy based on classical linear control minimizing the response norm conditioned by a bounded control.     

Smart Lead Rubber Bearings Equipped with Ferrous Shape Memory Alloy Wires for Seismically Isolating Highway Bridges

Shape memory alloys (SMA) can substantially improve the damping capacity and re-centering capability of elastomeric isolators. The objective of this study is to assess the seismic performance of smart lead rubber bearings (LRBs) equipped with double cross ferrous SMA wires. Hysteretic shear response of SMA wire-based LRB is determined using finite element method. The seismic response of a multispan continuous steel girder bridge isolated by SMA-LRB is evaluated. Hybrid SMA-LRB bearing exhibits a significantly lower shear strain demand (up to 46% reduction) and a higher energy dissipation capacity (up to 31% increase) compared to the LRB.     

Seismic Tests and Numerical Modeling of a Rolling-ball Isolation System

For the seismic isolation of light structures, the use of laminated rubber bearings is neither economical nor, for most cases, technically suited. For the isolation of this type of structure a new system, consisting of steel balls rolling on rubber tracks, has been developed at TARRC (Tun Abdul Razak Research Centre).

This article presents the results of experimental tests carried out for the characterization of the behavior of this new device. A numerical model is also proposed that can be used to assess the seismic response of structures with this isolation system.

Comparison of the predictions of the numerical model with the experimental data shows that the model is adequate to perform the correct assessment of the seismic response of isolated structures. The results of the experimental campaign of shaking-table tests, as well as the numerical simulations, show that there is an effective reduction of the acceleration levels induced in the isolated structures.     

Seismic Displacement Demands on Skewed Bridge Decks Supported on Elastomeric Bearings

The unseating of decks is one of the most prevalent failure modes of bridges after earthquake events, as observed in the 2010 Chile Earthquake. Damaged bridges in Chile often had skew angles and were supported on elastomeric bearings. Similar bridge construction practices with decks supported on elastomeric bearings are also common in the central and eastern U.S. (CEUS). The seismic displacement demands on skewed bridges are more complicated than those on bridges without skew angles due to the coupling of translational modes with the rotational mode of vibration. The study presented in this article seeks to understand the seismic response of skewed bridge decks supported on elastomeric bearings. The scope of the study is limited to one- and two-span bridges, which constitute a large portion of bridge inventory in the CEUS. The vibration modes of skewed bridge decks are derived in closed form and the modes are compared when the gaps between the bridge deck and the abutment are open and when one of the gaps is closed due to seismic excitation. Nonlinear response history analyses are carried out to understand the effects of vertical ground motion, skew angles, aspect ratios, and different ground motion types on the seismic displacement demand in these cases. Amplification factors that approximate the increase in the displacement demand due to the skew angle are proposed.     

Molecular Electronics Electronic Applications of Organic Molecules and Polymers

Abstract

This article reviews some of the ways in which organic molecules and polymers are currently being used in the generation of electronic devices. Polymers can be used both actively and passively in electronic circuits. The traditional use of polymers in a passive sense has been as insulators and more recently we have seen polymers used in an active way both from the point of view of their optical and electrical responses. Organic molecules containing donors and acceptors connected by conjugated structures are capable of exhibiting non-linear optical responses and are likely to play an important role in the production of optoelectronic devices in the future. Similarly, polymers doped so that fast conduction can occur between conjugated electronic structures are likely to play an important role in the fabrication of biosensor devices. Polymeric structures in which ions are dispersed may also be used in the future to produce conducting polymer electrolytes for construction of totally solid state battery systems. Ways in which organic structures are likely to make an impact in terms of development of electronics in the next decade are reviewed and the breadth of the area of molecular electronics summarised.     

SEISMIC RESPONSE CONTROL OF A CABLE-STAYED BRIDGE BY VARIABLE DAMPERS

Cable-stayed bridges exhibit unique responses under a strong motion. It is partly due to the complexity in their damping mechanism. Recently, the benchmark problem of a cable-stayed bridge was developed to clarify the effectiveness of various seismic control strategies. Due to the new development of magnetorheological dampers, the application of variable dampers in bridges becomes possible. In this study, the effectiveness of the nonlinear viscous damping force scheme and the two-step friction damping force scheme are investigated. It is found that the nonlinear viscous damping force scheme is effective to control the response of the cable-stayed bridge with less demand for the damping force capacity of a damper. In addition, the two-step friction damping force scheme shows the improvement over conventional friction damping because the energy dissipation of a damper can be increased.     

Shake Table Test and Numerical Analysis of a Bridge Model Supported on Elastomeric Pad Bearings

Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.     

A Base Isolation System for Developing Countries Using Discarded Tyres Filled with Elastomeric Recycled Materials

This article studies the performance of economic base isolators using tyres filled with elastomeric recycled materials. The research was conducted to analyze base isolators to be used in developing nations, where the application of conventional elastomeric rubber bearings due to economic reasons is limited.

The tested isolators are made of kart tyres filled with different recycled elastomeric materials and aggregates. Dynamic and static tests proved acceptable vertical to horizontal stiffness ratio of the bearings and shake table tests showed an excellent enhancement of the base isolated structural response compared to the corresponding fixed base structure.     

MODELLING OF STRUCTURAL ACCELERATIONS AND APPLICATION TO CONTROLLER DESIGN

In this paper a method for the identification of simplified linear models for building structures is applied to the case when acceleration, rather than displacement, is measured. A frame from benchmark structural controller studies is simulated, and from the input-output data of these simulations, simplified models for the acceleration response of the frame are obtained that have far fewer degrees of freedom. One of these simplified models is used to design a controller, which is tested using an evaluation model from the benchmark controller studies and found to be effective.     

CONCEPT AND DEVELOPMENT OF HYBRID SOLUTIONS FOR SEISMIC RESISTANT BRIDGE SYSTEMS

The development of alternative solutions for precast concrete buildings based on jointed ductile connections has introduced innovative concepts in the design of lateral-load resisting frame and wall systems. Particularly efficient is the hybrid system, where precast elements are connected via post-tensioning techniques and self-centring and energy dissipating properties are adequately combined to achieve the target maximum displacement with negligible residual displacements. In this contribution, the concept of hybrid system is extended to bridges as a viable and efficient solution for an improved seismic performance when compared with monolithic counterparts. Critical discussion on the cyclic behaviour of hybrid systems, highlighting the most significant parameters governing the response, is carried out.

The concept of a flexible seismic design (displacement-based) of hybrid bridge piers and systems is proposed and its reliability confirmed by quasi-static cyclic (push-pull) and nonlinear time-history analyses based on lumped plasticity numerical models.     

SLIDING MODE CONTROL OF BUILDING FRAMES UNDER RANDOM GROUND MOTION

A sliding mode control theory is presented to control the response of building frames to predominant frequency components of the random ground motions. The control algorithm is derived based on a sliding surface which is a function of a state vector containing the structural displacements and velocities and variables that dictate the predominant frequency components of the excitation. Three control mechanisms are employed to control the response of the building frame namely, (1) active mass damper (AMD) placed at the top storey of the building, (2) an actuator placed at a storey level and, (3) an actuator placed at a storey level along with a tuned mass damper (TMD) situated at the top storey level. Responses obtained by the proposed control strategy are compared with those obtained by the linear feedback and feedforward-feedback control strategies (conventional control strategies). Also, they are compared with those obtained by the sliding mode control strategy that considers in its state vector only structural displacements and velocities. It is shown that the proposed control strategy generally performs better than other control strategies in the higher range of control forces. For the lower range of control forces, conventional control strategies are more effective.     

COMPLEX MODE SUPERPOSITION ALGORITHM FOR SEISMIC RESPONSES OF NON-CLASSICALLY DAMPED LINEAR MDOF SYSTEM

This paper deals with a complex mode superposition method for the seismic responses of general multiple degrees of freedom (MDOF) discrete system with complex eigenvectors and eigenvalues. A delicate general solution, completely in real value form, for calculat-ing seismic time history response of the MDOF system which cannot be uncoupled by normal modes, is deduced based on the algorithms of the complex superposition method. This solution comprises of two parts which are in relation to the Duhamel integration to sine and cosine function respectively. The related term of the Duhamel integration to sine function is actually the displacement response of the oscillator with corresponding modal frequency and the damping ratio. The other can be transferred into a combina-tion of the displacement and velocity responses of the same oscillator. In order to meet the practical needs of seismic design based on code design spectra for various kinds of structures equipped by viscous dampers, the complex complete quadratic combination (CCQC) method is deduced following similar procedures such as the well-known CQC method, in which a new modal velocity correlation coefficient, together with a new modal displacement-velocity correlation coefficient are involved besides the modal displacement correlation coefficient in normal CQC formula. The new algorithm of CCQC is not only as concise as that of the normal CQC but also has explicit physical meaning. The results obtained from complex mode superposition approaches are discussed and verified in some examples through step by step integration computation under a prescribed earth-quake motion input. From these examplary analyses, it may be pointed that the CCQC algorithm normally yields conservative outcome and that the forced mode uncoupling approach has good approximation even the discussed examplary structures are strongly non-proportional.