International Conference on Earthquake Engineering and Seismology (ICEES 2011), NUST, Islamabad, Pakistan April 25-26, 2011
by
Muhammad Usman, Sajjad Ahmad, Hyung-Jo Jung
Study on laminated rubber bearing base isolators for seismic protection of st...eSAT Journals
Abstract
Base isolation or seismic base isolation is an effective means for protection of structures, its contents and its occupants during the event of an earthquake. The principle of base isolation is vibration isolation. It decouples the building from damaging action of the earthquake. The isolator partially reflects and partially absorbs input seismic energy before it gets transmitted to the superstructure. Laminated Rubber Bearing Isolators are placed between the superstructure and foundation, which reduces the horizontal stiffness of the system. It thereby increases the time period of the structure and decreases the spectral acceleration of the structure. The superstructure acts like a rigid body, thus inter storey drift is reduced. Such type of isolators are used in practice in India, yet a proper design procedure based on IS code is unavailable. The paper presents design procedure for LRB adopting the procedure of IS 1893:2002 (Part-1) for earthquake resistant design of buildings. Design charts have been developed and presented in this paper which gives isolator diameter and rubber thickness as design outputs. The design procedure requires different input parameters like fundamental period and damping of the fixed base structure, axial load on the column, seismic zone, type of soil and shore hardness of rubber. These design charts enable the designer to easily arrive at the isolator parameters to achieve seismic isolation. Using the charts, case study has been done using SAP2000. Building displacement and acceleration are compared for model with and without base isolator. Comparative study of linear and non-linear base isolators has also been carried out. Linear and non-linear time history analysis has been done using El Centro earthquake.
Keywords: base isolation, laminated rubber bearing, IS Code, seismic protection, design charts, time history analysis, SAP2000
Static Aeroelasticity Analysis of Spinning Rocket for Divergence Speed -- Zeu...Abhishek Jain
Above Research Paper can be downloaded from www.zeusnumerix.com
The research paper aims to develop a method to model the spin effects of rocket for Aeroelastic analysis. As the speed of the rocket increases, the structural integrity of the fins becomes more dependent on aeroelastic loads. Methods exist to analyze aeroelasticity of fins for non-spinning missiles. Most software use panel methods for calculation of load distribution. The current research replaces the panel methods to RANS CFD and introduces source terms in equations to model spin. The results of new formulation are validated w.r.t. published data on non-spinning projectile and then the method is used to simulate current projectile. Mode shapes up to 6th mode are delivered as result. Authors - Sanjay Kumar and Prof GR Shevare (Zeus Numerix), Subhash Mukane and PT Rojatkar (ARDE, DRDO)
Seismic analysis of high damping rubber bearings for base isolationeSAT Journals
Abstract
Base isolation is a mechanism that provides earthquake resistance to the new structure. The base isolation system decouples the building from the horizontal ground motion induced by earthquake, and offers very stiff vertical components to the base level of the superstructure in connection to substructure (foundation). It shifts the fundamental lateral period, dissipates the energy in damping, and reduces the amount of the lateral forces that transferred to the building, inter-story drift, and the floor acceleration.
The work deals with modelling and finite element analysis of a high damping rubber bearing in ANSYS 12.0. A displacement controlled transient analysis was done to analyse the behaviour of the isolator during earthquakes.
Keywords: Base isolation, High damping rubber, Transient analysis
Study on laminated rubber bearing base isolators for seismic protection of st...eSAT Journals
Abstract
Base isolation or seismic base isolation is an effective means for protection of structures, its contents and its occupants during the event of an earthquake. The principle of base isolation is vibration isolation. It decouples the building from damaging action of the earthquake. The isolator partially reflects and partially absorbs input seismic energy before it gets transmitted to the superstructure. Laminated Rubber Bearing Isolators are placed between the superstructure and foundation, which reduces the horizontal stiffness of the system. It thereby increases the time period of the structure and decreases the spectral acceleration of the structure. The superstructure acts like a rigid body, thus inter storey drift is reduced. Such type of isolators are used in practice in India, yet a proper design procedure based on IS code is unavailable. The paper presents design procedure for LRB adopting the procedure of IS 1893:2002 (Part-1) for earthquake resistant design of buildings. Design charts have been developed and presented in this paper which gives isolator diameter and rubber thickness as design outputs. The design procedure requires different input parameters like fundamental period and damping of the fixed base structure, axial load on the column, seismic zone, type of soil and shore hardness of rubber. These design charts enable the designer to easily arrive at the isolator parameters to achieve seismic isolation. Using the charts, case study has been done using SAP2000. Building displacement and acceleration are compared for model with and without base isolator. Comparative study of linear and non-linear base isolators has also been carried out. Linear and non-linear time history analysis has been done using El Centro earthquake.
Keywords: base isolation, laminated rubber bearing, IS Code, seismic protection, design charts, time history analysis, SAP2000
Static Aeroelasticity Analysis of Spinning Rocket for Divergence Speed -- Zeu...Abhishek Jain
Above Research Paper can be downloaded from www.zeusnumerix.com
The research paper aims to develop a method to model the spin effects of rocket for Aeroelastic analysis. As the speed of the rocket increases, the structural integrity of the fins becomes more dependent on aeroelastic loads. Methods exist to analyze aeroelasticity of fins for non-spinning missiles. Most software use panel methods for calculation of load distribution. The current research replaces the panel methods to RANS CFD and introduces source terms in equations to model spin. The results of new formulation are validated w.r.t. published data on non-spinning projectile and then the method is used to simulate current projectile. Mode shapes up to 6th mode are delivered as result. Authors - Sanjay Kumar and Prof GR Shevare (Zeus Numerix), Subhash Mukane and PT Rojatkar (ARDE, DRDO)
Seismic analysis of high damping rubber bearings for base isolationeSAT Journals
Abstract
Base isolation is a mechanism that provides earthquake resistance to the new structure. The base isolation system decouples the building from the horizontal ground motion induced by earthquake, and offers very stiff vertical components to the base level of the superstructure in connection to substructure (foundation). It shifts the fundamental lateral period, dissipates the energy in damping, and reduces the amount of the lateral forces that transferred to the building, inter-story drift, and the floor acceleration.
The work deals with modelling and finite element analysis of a high damping rubber bearing in ANSYS 12.0. A displacement controlled transient analysis was done to analyse the behaviour of the isolator during earthquakes.
Keywords: Base isolation, High damping rubber, Transient analysis
EXPERIMENTAL STUDY ON CONCRETE BOX GIRDER BRIDGE UNDER TRAFFIC INDUCED VIBRATIONIAEME Publication
Many research studies have been carried out based on the ambient vibration test on different types of bridge. In present study, an ambient excitation is used to find the fundamental frequency of vibration of a concrete box girder bridge. Dynamics characteristics of the bridge are identified through traffic induced vibration. The bridge vibration can be recorded for 24 hours using an accelerometer installed on the bridge. The acceleration time histories are recorded using data acquisition system (National Instruments) and recorded signal data were processed using modal analysis performed by using Stochastic Subspace Identification (Time Domain method). The vibration parameters such as modal frequencies, mode shapes and damping ratio were identified for tested bridge.
SEISMIC PROTECTION OF RC FRAMES USING FRICTION DAMPERSIAEME Publication
The increasing infrastructural growth incurs large investments and large section of society
being served by them, it is necessary to make them safer against earthquakes and let people
feel confident in their structures. The need for structural response control has gained pace in
application around the globe. This paper discusses the use and effectiveness of one such
device, friction dampers, for response control of structures. In this paper a non-linear time
history analysis has been carried out on a 3D model of a 12 story RCC MRF building using 3-
directional synthetic accelerogram. Two different cases of building models with and without
friction dampers have been analyzed using ETABS. The response of the structure to seismic
excitation in terms of absolute maximum displacement and story drift has been compared.
Time history response plots have also been compared for various responses viz. roof
displacement and acceleration, base shear and story shear forces, along with the various
energy components and damping behavior. The results of the time history analysis are in close
conformation with previous investigations and represent the effectiveness of dampers in
improving the structural response as well as damping demand on structural systems.
Solar Panel Control System using an Intelligent Control: T2FSMC and Firefly A...TELKOMNIKA JOURNAL
Solar panel is a solar energy converter to electrical energy. On solar tracker, there is a controller which sets the movement of solar panel such that it is perpendicular with solar rays. Previous research had designed Type 2 Fuzzy Sliding Mode Control (T2FSMC) controller to control the position of solar panel. However, there was trial and error process to determine gain scale factor so the development of optimization method is needed. This paper aims to modify gain scale factor using Firefly algorithm to increase performance of system. The simulation shows that T2FSMC Firefly has better performance than T2FSMC. T2FSMC Firefly shows the increase of performance on rise time, settling time, and integral time absolute error.
Bearingless Permanent Magnet Synchronous Motor using Independent ControlIJPEDS-IAES
Bearingless permanent magnet synchronous motor (BPMSM) combines the
characteristic of the conventional permanent magent synchronous motor and
magnetic bearing in one electric motor. BPMSM is a kind of high
performance motor due to having both advantages of PMSM and magnetic
bearing with simple structure, high efficiency, and reasonable cost. The
research on BPMSM is to design and analyse BPMSM by using Maxwell 2-
Dimensional of ANSYS Finite Element Method (FEM). Independent
suspension force model and bearingless PMSM model are developed by
using the method of suspension force. Then, the mathematical model of
electromagnetic torque and radial suspension force has been developed by
using Matlab/Simulink. The relation between force, current, distance and
other parameter are determined. This research covered the principle of
suspension force, the mathematical model, FEM analysis and digital control
system of bearingless PMSM. This kind of motor is widely used in high
speed application such as compressors, pumps and turbines.
Parametric study of response of an asymmetric building for various earthquake...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
BEB801 - Project 1: Energy absorbing beam column connectionsKeagan Leamy
The beam column connection is often one of the most vulnerable locations in a structure due to the way the energy is transferred through the connection, this is even more so when the structure is subjected to seismic loading. The following presentation proposes a friction device that can be retrofit to the beam column connection in the hopes it will dissipate some of the energy induced through the seismic loading.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Copper Bulk General (Cu) was chosen for the pivot material on its merits of possessing good
electrical conductivity and optimised flexibility and stiffness for elastic recovery.
The simulation, using Intellisuite, attained a working switch design, with an ‘Air-Gap’ of
1µm between the contacts, thus providing isolation when the switch is open-circuited.
EXPERIMENTAL STUDY ON CONCRETE BOX GIRDER BRIDGE UNDER TRAFFIC INDUCED VIBRATIONIAEME Publication
Many research studies have been carried out based on the ambient vibration test on different types of bridge. In present study, an ambient excitation is used to find the fundamental frequency of vibration of a concrete box girder bridge. Dynamics characteristics of the bridge are identified through traffic induced vibration. The bridge vibration can be recorded for 24 hours using an accelerometer installed on the bridge. The acceleration time histories are recorded using data acquisition system (National Instruments) and recorded signal data were processed using modal analysis performed by using Stochastic Subspace Identification (Time Domain method). The vibration parameters such as modal frequencies, mode shapes and damping ratio were identified for tested bridge.
SEISMIC PROTECTION OF RC FRAMES USING FRICTION DAMPERSIAEME Publication
The increasing infrastructural growth incurs large investments and large section of society
being served by them, it is necessary to make them safer against earthquakes and let people
feel confident in their structures. The need for structural response control has gained pace in
application around the globe. This paper discusses the use and effectiveness of one such
device, friction dampers, for response control of structures. In this paper a non-linear time
history analysis has been carried out on a 3D model of a 12 story RCC MRF building using 3-
directional synthetic accelerogram. Two different cases of building models with and without
friction dampers have been analyzed using ETABS. The response of the structure to seismic
excitation in terms of absolute maximum displacement and story drift has been compared.
Time history response plots have also been compared for various responses viz. roof
displacement and acceleration, base shear and story shear forces, along with the various
energy components and damping behavior. The results of the time history analysis are in close
conformation with previous investigations and represent the effectiveness of dampers in
improving the structural response as well as damping demand on structural systems.
Solar Panel Control System using an Intelligent Control: T2FSMC and Firefly A...TELKOMNIKA JOURNAL
Solar panel is a solar energy converter to electrical energy. On solar tracker, there is a controller which sets the movement of solar panel such that it is perpendicular with solar rays. Previous research had designed Type 2 Fuzzy Sliding Mode Control (T2FSMC) controller to control the position of solar panel. However, there was trial and error process to determine gain scale factor so the development of optimization method is needed. This paper aims to modify gain scale factor using Firefly algorithm to increase performance of system. The simulation shows that T2FSMC Firefly has better performance than T2FSMC. T2FSMC Firefly shows the increase of performance on rise time, settling time, and integral time absolute error.
Bearingless Permanent Magnet Synchronous Motor using Independent ControlIJPEDS-IAES
Bearingless permanent magnet synchronous motor (BPMSM) combines the
characteristic of the conventional permanent magent synchronous motor and
magnetic bearing in one electric motor. BPMSM is a kind of high
performance motor due to having both advantages of PMSM and magnetic
bearing with simple structure, high efficiency, and reasonable cost. The
research on BPMSM is to design and analyse BPMSM by using Maxwell 2-
Dimensional of ANSYS Finite Element Method (FEM). Independent
suspension force model and bearingless PMSM model are developed by
using the method of suspension force. Then, the mathematical model of
electromagnetic torque and radial suspension force has been developed by
using Matlab/Simulink. The relation between force, current, distance and
other parameter are determined. This research covered the principle of
suspension force, the mathematical model, FEM analysis and digital control
system of bearingless PMSM. This kind of motor is widely used in high
speed application such as compressors, pumps and turbines.
Parametric study of response of an asymmetric building for various earthquake...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
BEB801 - Project 1: Energy absorbing beam column connectionsKeagan Leamy
The beam column connection is often one of the most vulnerable locations in a structure due to the way the energy is transferred through the connection, this is even more so when the structure is subjected to seismic loading. The following presentation proposes a friction device that can be retrofit to the beam column connection in the hopes it will dissipate some of the energy induced through the seismic loading.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Copper Bulk General (Cu) was chosen for the pivot material on its merits of possessing good
electrical conductivity and optimised flexibility and stiffness for elastic recovery.
The simulation, using Intellisuite, attained a working switch design, with an ‘Air-Gap’ of
1µm between the contacts, thus providing isolation when the switch is open-circuited.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Applications of dampers for vibration control of structures an overvieweSAT Journals
Abstract
Dampers have become more popular recently for vibration control of structures, because of their safe, effective and economical
design. This paper presents an overview of literature related to the behavior of dampers on seismically affected structures. The review
includes different types of dampers like metallic dampers, viscoelastic dampers, frictional dampers etc.
Keywords: Seismic response, dampers, structural control systems
Applications of dampers for vibration control of structures an overvieweSAT Journals
Abstract
Dampers have become more popular recently for vibration control of structures, because of their safe, effective and economical
design. This paper presents an overview of literature related to the behavior of dampers on seismically affected structures. The review
includes different types of dampers like metallic dampers, viscoelastic dampers, frictional dampers etc.
Keywords: Seismic response, dampers, structural control systems.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Seismic Behaviour of Multi-Storied Building by Using Tuned Mass Damper and Ba...IJERA Editor
Earthquakes create vibrations on the ground that are translated into dynamic loads which cause the ground and anything attached to it to vibrate in a complex manner and cause damage to buildings and other structures. Civil engineering is continuously improving ways to cope with this inherent phenomenon. Conventional strategies of strengthening the system consume more materials and energy. Moreover, higher masses lead to higher seismic forces. Alternative strategies such as passive control systems are found to be effective in reducing the seismic and other dynamic effects on civil engineering structures. A Tuned mass damper (TMD) is a device consisting of a mass, and spring that is attached to a structure in order to reduce the dynamic response of the structure. Tuned Mass Damper (TMD) has been found to be most effective for controlling the structural responses for harmonic and wind excitations. Base isolation is nowadays widely considered as an effective strategy to protect structures subject to seismic excitations. The performance of linear base isolation system along with tuned mass damper to mitigate seismic response of structures is investigated.
Vibration control of Multi Degree of Freedom structure under earthquake excit...IOSR Journals
In this paper, Control system performance, as a passive and active control on the example building
under the Bam earthquake excitation, was studied. In order to passive and active control the structure TMD
system mounted on the top floor of the building and FLC method was used, respectively. Active control system
first applied to the lowest floor then to the highest point of the structure (applied to the TMD system).
Mathematical model of the building is established in MATLAB. Equation of motion was written for high rise
building and it was solved by state-space method, the Results are illustrated and compared.
A robust dlqg controller for damping of sub synchronous oscillations in a ser...eSAT Journals
Abstract This paper investigates the use of Discrete Linear Quadratic Gaussian (DLQG) Compensator to damp sub synchronous oscillations in a Thyrisor Controlled Series Capacitor (TCSC) compensated power system. The study is conducted on IEEE First Benchmark Model (FBM) in which, TCSC is modelled as a discrete linear time-invariant modular unit in the synchronously rotating DQ reference frame. This modular TCSC is then integrated with the Linear Time Invariant (LTI) model of the rest of the system. The design of DLQG includes the design of a Kalman filter for full state estimation and a full state feedback for control. Since the order of the controller is as large as the order of the system considered here(27 states), the practical implementation of the controller is difficult. Hence by using Hankels norm approximation technique, the order of the controller is reduced from 27 to 15 without losing the significant system dynamics. The eigen analysis of the system shows that the use of DLQG can damp torsional oscillations as well as the swing mode oscillations simultaneously, which is practically difficult for a conventional sub-synchronous damping controller. The performance of the system with DLQG is appreciable for all operating conditions and it shows the robustness of the controller. Index Terms: Sub-Synchronous Resonance (SSR), Torsional Oscillations, Thyristor Controlled Series Capacitor (TCSC), Discrete Linear Quadratic Gaussian(DLQG)Compensator, Model Order Reduction (MOR).
A robust dlqg controller for damping of sub synchronous oscillations in a se...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
SEISMIC MITIGATION OF TWIN TOWER STRUCTURES USING AN ISOLATED CORRIDORharshilshah546931
The analytical expression of connected structures subjected to earthquake ground motions are derived and solve using step-by-step procedures. The seismic response of connected twin towers is compared with those of un-connected structures. It is
observed that the base isolated sky corridor reduces displacement demand, base shear and absolute acceleration significantly.
Similar to State-Switched Control Algorithm for Multi Degree of Freedom Smart Base Isolation System Employing MR Elastomer (20)
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
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2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
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June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
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State-Switched Control Algorithm for Multi Degree of Freedom Smart Base Isolation System Employing MR Elastomer
1. International Conference on Earthquake Engineering and Seismology
(ICEES 2011), NUST, Islamabad, Pakistan
April 25-26, 2011
State-Switched Control Algorithm for Multi Degree of Freedom Smart
Base Isolation System Employing MR Elastomer
Muhammad Usman1*
, Sajjad Ahmad 2
, Hyung-Jo Jung 3
1*
School of Civil and Environmental Engineering, National University of Sciences & Technology, NUST, H-12,
Islamabad, Pakistan
( concrete_157@yahoo.com)
2
School of Civil and Environmental Engineering, National University of Sciences & Technology, NUST, H-12,
Islamabad, Pakistan
3
Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea
Abstract
The vibration control of building structures under seismic loading is a very critical issue in the safety of the
structure. Base isolation is quite an effective and practical solution to this issue. The proposed magneto-
rheological elastomer(MRE)-based base isolation system eliminates the limitation of passive system by being
adaptable to various loading conditions. The proposed MR elastomer based system traditionally uses the Linear
Quadratic Regulator (LQR) algorithm which has its own limitations. State-Switched control algorithm was
proposed by the author in 2008[10] for the single degree of freedom system. In this work the proposed algorithm
has been upgraded for multi degree of freedom systems.
This paper describes the application of State-Switched control algorithm to multi DOF system and the
comparison of the response of a five degree of freedom system using proposed control algorithm, with that of a
system using Linear Quadratic Regulator (LQR) and the uncontrolled case. To assess the behavior of State-
Switched control algorithm simulations were performed by using historical data of El Centro, Hachinohi and
Northridge earthquakes. Simulations result indicate state-switched control algorithm to be much better in terms
of control performance and practicability as compared to the commonly used LQR algorithm.
Keywords: Magneto-rheological Elastomers (MRE), Base isolation, Linear Quadratic Regulator (LQR), State-Switched
Control
1. Introduction
Base isolation of building structures has been the popular structural control technique to mitigate
the undesirable response of the structure under seismic loading. Initially the passive base isolation
using some laminated rubber bearings, lead rubber bearings and friction bearing have been in practice
to seismically isolate the building structure from the vibrating ground surface. The conventional base
isolation systems reduce the response of the structure by lengthening the natural period of the
structure. Also it reduces the inter-storey drift by increasing the base drift. But this excessive base
drift sometimes causes some problems in the building such as damaging the utility ducts and
sometimes it may be problematic to restore the structure to its original position. Active base isolation
system reduces some of these problems by limiting the base drift, but it may add to destabilizing
forces if the control force accidentally becomes in phase with the ground excitation. Also it requires
large power input which may also be a disadvantage in real applications. Semi active base isolation
system employing magneto rheological elastomers (MRE) overcome the disadvantages of both the
passive and active systems. On one hand it reduces the peak base drift being actively controlled and
2. International Conference on Earthquake Engineering and Seismology
(ICEES 2011), NUST, Islamabad, Pakistan
April 25-26, 2011
on the other hand it adds to the stability of the structure owing to its passive type mechanism.
Additionally it needs very less external power and hence it may continue working even on low power.
Several numerical investigations and studies have been carried out to check out the feasibility of
the semi active base isolation system employing MRE’s. Initially the typical structural models are
studied numerically with and without the proposed control system. First of all ([6]) single degree of
freedom structure was studied with conventional control algorithms. Then this study was further
extended ([9]) to multi degree of freedom system again using conventional (LQR) control algorithm.
Then in our previous work([10]) we proposed the state-switched control algorithm and studied that for
the single degree of freedom structure but at that time the applicability seemed to be a bit limited as in
case of single degree of freedom the structural stiffness is much larger than the isolator stiffness and
any switching criteria can be used as the base and the structural responses are almost the same. In this
work the state-switched control is proposed for the multi degree of freedom structure with semi active
base isolation system employing MRE’s.
2. MRE based semi active base isolation
Magneto rheological elastomers are the basically solid state analogues of MR fluids. MRE is
basically conventional elastomer, such as rubber etc., with micron sized iron particles embedded.
When magnetic field is applied across the MR elastomer the embedded iron particles align themselves
along the direction of the magnetic field as shown in Fig.1. This alignment of the particles causes the
stiffness of the elastomer to increase and hence the response of the whole structure to be modified.
Fig.1 Schematic representation of Magnetorheological elastomers
When base isolation bearing is used for the building structure it naturally lengthens the natural
period of the building and consequently reduces the response of the structure. In case of passive type
bearings the base drift is normally more than desirable range but the when semi active base isolation
bearings are used significantly reduced base drift is observed. This reduction obviously adds much to
the efficiency of the structure. Here there is another important issue worth mentioning that the semi
active system quite obviously implies the need of some sensors to measure the response of the
structure in real time. Hence there is the need to minimize the number of necessary responses to be
measured and sensors to make the system more compact and economical.
3. System model of the structure used for Numerical simulations
For the purpose of numerically investigating the proposed system a typical five storey building
structure was considered with the schematics as depicted in the Fig.2.
3. International Conference on Earthquake Engineering and Seismology
(ICEES 2011), NUST, Islamabad, Pakistan
April 25-26, 2011
Fig.2 Schematic representation of the building structures used
Here M, K and C represent the respective mass, stiffness and damping co-efficient for various
levels. The building was considered with the passive base isolation as well as with MRE based semi
active base isolation system. The structural parameters of the structure are given in the table 1.
Table 1: Structural parameters of the structural modal considered
Location Mass (kg) Stiffness (kN/m) Damping (kNs/m)
Base 6800 232 3.74
1st
Floor 5897 33732 67
2nd
Floor 5897 29093 58
3rd
Floor 5897 28621 57
4th
Floor 5897 24954 50
5th
Floor 5897 19059 38
4. Equations of Motion
Assuming the structural motion is sufficiently small such that nonlinear effects may be
neglected, and denoting the base and structure displacements relative to the ground by [ ]T
sb xxx = , the
equations of motion of the base-isolated system may be expressed as
gxMtKxCxM &&&&& Γ−=++ )(
(1)
or
gxMfxKxCxM &&&&& Γ−Λ=++ 0
(2)
where x ( [ ]T
sb xxx = ) is displacement vector of the structure and base isolator; M, C and K are
the mass, damping, and stiffness matrices, respectively; f is the supplemental force exerted by the
MRE’s, Λ ( [ ]T
01=Λ ) vector represents the position of the supplemental damper force; Γ vector are
unity vector; gx&& is the ground acceleration. The system matrices can be expressed as
⎥
⎦
⎤
⎢
⎣
⎡
=
s
b
m
m
M
0
0
,
⎥
⎦
⎤
⎢
⎣
⎡
−
−+
=
ss
ssb
cc
ccc
C
,
⎥
⎦
⎤
⎢
⎣
⎡
−
−+
=
ss
ssb
kk
kkk
K0
(3)
M
5M
4M
3M
2M
M 1
M R E base-isolation system B ase-isolation system
1M
M 2
M 3
M 4
M 5
M b
K 5 5C
C 44K
C 33K
C 22K
C 11K
C bbK (t) K b bC
K 1 1C
K 2 2C
K 3 3C
K 4 4C
C 55K
b
4. International Conference on Earthquake Engineering and Seismology
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April 25-26, 2011
Defining the state vectors as [ ]T
xxz &= and the output vector to be regulated as [ ]T
xxxy &&&= ,
the state-space form of the equations of motion can be given by
gxEBfAzz &&& ++=
(4)
gyyy xFfDzCy &&++=
(5)
where
⎥
⎦
⎤
⎢
⎣
⎡
−−
= −−
CMKM
I
A 11
0
,
⎥
⎦
⎤
⎢
⎣
⎡
Λ
= −1
0
M
B
,
⎥
⎦
⎤
⎢
⎣
⎡
Γ−
=
0
E
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−−
=
−−
CMKM
I
I
Cy
11
0
0
,
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
Λ
=
−1
0
0
M
Dy and
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
Γ−
= 0
0
yF
The state-state equations can be modeled using the MATLB/SIMULINK environment for
numerical analysis of the system. The simulation model along with detailed system and simulation
parameters are presented in the following section.
5. Semi-active control of MRE stiffness
The stiffness of the MRE should be varied in real time to reduce the response of the structure.
For this purpose the various control algorithms can be selected. The most commonly used one is
linear quadratic regulator (LQR) algorithm. In this work another type of algorithm is proposed for
changing the stiffness in real time, which is state-switched control.
5.1. LQR control Algorithm
Linear quadratic regulator (LQR) control algorithm is basically optimal control algorithm. Basic
concept behind this control algorithm is to minimize the following cost function,
dttRututQztzJ
t
TT
∫ +=
0
)]()()()([
with respect to the control input u(t) and subject to the constraining equation
0)0()()()()( zztHftButAztz =++=&
In regulator type algorithm problems the system is assumed to be in equilibrium and the purpose
of the control algorithm is to maintain the equilibrium despite being subjected to the disturbances and
also minimize the response of the structure due to the disturbances of any nature. The main
disadvantage of the LQR algorithm is that to control the structure using this algorithm the full state
response of the structure has to be measured. For a multi storey building structure full state means
displacement, velocity and acceleration at each floor which is almost impossible in the real structure.
5.2. State-switched control Algorithm
Basically state-switched control considers two discrete values of the stiffness for the isolation
device i.e. MRE and switches among them based on the structural response. Basically with two
stiffness values we have two natural frequencies for the structure to switch between. Here we have
selected two discrete stiffness values as 0.5K0 and 1.5K0, which are within the range mentioned above
and therefore now the range of control force will be
5. International Conference on Earthquake Engineering and Seismology
(ICEES 2011), NUST, Islamabad, Pakistan
April 25-26, 2011
)(5.0)()(5.0 00 txKtftxK ≤≤−
(6)
Now the criterion based on which the stiffness values can be switched has to be selected.
Kenneth et al. (2000) proposed the switching criterion based on the product of base velocity and
relative velocity. In our case the relative velocity between structure and the base may not be an
efficient factor to contribute in switching criterion. Therefore following criterion was adopted for our
system to switch the stiffness values. First of all the control command u(t) is calculated by the simple
product
{ }nn xxtu &&=)(
(7)
Then it is saturated between 0 and 1 to get the modified output v(t) with well defined maximum
and minimum values so that the switching value can be decided more conveniently around 0.5.
⎪
⎭
⎪
⎬
⎫
⎪
⎩
⎪
⎨
⎧
=
<
>
=
5.0)(0
5.0)(
5.0)(
))(( 2
1
tvif
tvifK
tvifK
tvK s
s
(8)
Here Ks1 and Ks2 correspond to the extreme values of the control force range shown in the
Equation (6) and K0 is the middle value of the range i.e. base line stiffness of the MRE without any
magnetic field applied. The main advantage with the state-switched control is that instead of full state
only the displacement and acceleration is required and that too at the top most level only. In this way
it becomes most viable and practical control algorithm.
6. Numerical Simulation
The numerical simulations were performed to verify the effectiveness of the proposed state-
switched control system using the numerical models mentioned above. The responses for the passive,
semi-active with LQR and semi-active with SS control are compared. The figures show the base drift,
top floor acceleration and the storey drift at first floor for all the three cases. And then the peak
responses are compared in the following table. Here follow three sets of results for various earthquake
input excitations.
EL CENTRO
0 5 10 15 20 25 30
-200
-100
0
100
200
time(sec)
Basedrift(mm)
Passive
MRE-SS
MRE-LQR
0 5 10 15 20 25 30
-1.5
-1
-0.5
0
0.5
1
time(sec)
Structureacceleration(m/sec2)
Passive
MRE-SS
MRE-LQR
7. International Conference on Earthquake Engineering and Seismology
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NORTHRIDGE
Fixed Base MRE (SS) MRE (LQR)
Base Drift 486.13 330.81 299.39
Top Floor Acc. 2.96 0.970 2.663
1st Floor storey drift 2.730 0.931 1.986
Top Displ. 495.79 334.12 305.8967
Above simulation results for various input excitation levels quite obviously imply that some of the
responses have improved significantly such as the peak acceleration and the inter-storey drift. Whereas
the base drift in general is a bit more than the LQR case but still less than the passive base isolation
system. In consequence of base drift the top floor displacement also exceeds the LQR case and again
still less than the passive case. Here we can observe clearly that the state-switched control has proven
to be much better than the LQR in terms of response as well as the fact that we only need to measure
displacement and acceleration at the top floor. Also state-switched control is also much simpler than
the conventional control algorithms and we only need to switch between two stiffness values, which
enhances the practicability of the control system in whole.
7. Conclusions
This study concludes that the state-switched control system is far more practical than the
conventional LQR algorithm and also numerical investigations show significant reduction in the
response of the structure compared to the convention control system. As we know that the main
disadvantage of the active control system lies in the chance of being accidentally unstable and
requirement of large external power. The proposed control system eliminates both of these limitations
0 5 10 15 20 25 30
-500
0
500
time(sec)
Basedrift(mm)
Passive
MRE-SS
MRE-LQR
0 5 10 15 20 25 30
-4
-2
0
2
4
time(sec)
Structureacceleration(m/sec2
)
Passive
MRE-SS
MRE-LQR
0 5 10 15 20 25 30
-4
-2
0
2
4
time(sec)
Structuredriftat1stfloor(mm)
Passive
MRE-SS
MRE-LQR
8. International Conference on Earthquake Engineering and Seismology
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without being impractical as in the case of LQR where the measurement of full state response of the
structure is almost impossible. Now the proposed system must be analyzed experimentally before it
can be implemented in some real scale building structure. Besides the application to the multi storey
structure it can find many other potential applications like isolation of building structure from some
highly vibrating machine equipment installed within the structure.
8. Acknowledgements
This research was supported by the Smart Infra-Structure Technology Center (funded by the
Korea Science and Engineering Foundation), the Construction Core Technology Program (funded by
the Ministry of Land, Transport and Maritime Affairs of Korea), and Higher Education Commission,
Government of Pakistan. Their financial supports are gratefully acknowledged.
9. References
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[4] Kelly, J.M., Leitmann, G., and Soldatos, A.G. (1987), ‘‘Robust control of base-isolated
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