Karen Khanlari - Academia.edu (original) (raw)

Papers by Karen Khanlari

Research paper thumbnail of Dynamic condensation of non-classically damped structures using the method of Maclaurin expansion of the frequency response function in Laplace domain

Journal of Sound and Vibration, Jul 1, 2018

Abstract As the number of degrees of freedom (DOFs) in structural dynamic problems becomes larger... more Abstract As the number of degrees of freedom (DOFs) in structural dynamic problems becomes larger, the analyzing complexity and CPU usage of computers increase drastically. Condensation (or reduction) method is an efficient technique to reduce the size of the full model or the dimension of the structural matrices by eliminating the unimportant DOFs. After the first presentation of condensation method by Guyan in 1965 for undamped structures, which ignores the dynamic effects of the mass term, various forms of dynamic condensation methods were presented to overcome this issue. Moreover, researchers have tried to expand the dynamic condensation method to non-classically damped structures. Dynamic reduction of such systems is far more complicated than undamped systems. The proposed non-iterative method in this paper is introduced as 'Maclaurin Expansion of the frequency response function in Laplace Domain' (MELD) applied for dynamic reduction of non-classically damped structures. The present approach is implemented in four numerical examples of 2D bending-shear-axial frames with various numbers of stories and spans and also a floating raft isolation system. The results of natural frequencies and dynamic responses of models are compared with each other before and after the dynamic reduction. It is shown that the result accuracy has acceptable convergence in both cases. In addition, it is indicated that the result of the proposed method is more accurate than the results of some other existing condensation methods.

Research paper thumbnail of Collapse load factor of planar frames using a modified genetic algorithm

Communications in Numerical Methods in Engineering, Sep 9, 2004

In this article an analytical method is developed for identifying basic collapse mechanisms of ri... more In this article an analytical method is developed for identifying basic collapse mechanisms of rigidjointed two-dimensional frames. In this approach, the deformation of each member is completely deÿned by four translations and one rotation. The behaviour of such an element lies in between that of a truss element and a exural one. Once the basic collapse mechanisms are identiÿed, the genetic algorithm is used to identify the mechanism corresponding to the least possible load factor. Examples are included to illustrate the e ciency of the present method compared to the use of a simple genetic algorithm. Copyright ? 2004 John Wiley & Sons, Ltd.

Research paper thumbnail of A Combined Analytical Method for Intelligent Control of Friction Damped Structures

pertanika journal of science and technology, Sep 21, 2021

Controlling structures and increasing the prognosis of their behaviour before natural disasters a... more Controlling structures and increasing the prognosis of their behaviour before natural disasters are the most critical issues in structural engineering. To that end, predicting the destructive effects of earthquakes on both acceleration and displacement of structures would be beneficial. This paper suggests an intelligent control system that realises simultaneous control of acceleration and displacement parameters. There are two modules in the system. First, the preserving module aims to estimate the crisis thresholds of acceleration and displacement based on the historical seismic data of each area. Second, the processing module finds the optimum value of the slip load of the friction damper so that both acceleration and displacement are controlled. We introduce an analytical method based on a matrix analysis approach and heuristic algorithm (MAHA) as a core of the processing module. MAHA would analyse the structure response, and the friction damper would determine the optimum slip load. The numerical and software simulation results for various one-bay and two-bay steel structures show that the proposed intelligent control system applies to multiple frictions damped structures under different earthquake records. In addition, a control level of 80% in acceleration and displacement of structures is achieved compared to an uncontrolled state. Moreover, the mentioned system enables the engineers to find appropriate friction dampers during the design of structures.

Research paper thumbnail of A New Algorithm for the System Identification of Shear Structures

Advanced Materials Research, 2012

In general terms, the aim of &amp... more In general terms, the aim of "System Identification" is to determine the dynamic characteristics of mechanical systems. These characteristics include both frequency characteristics (frequencies, mode shapes, and damping ratios) and the system's characteristic matrices (the matrices of mass, viscous damping, stiffness, Coulomb damping or coefficients of friction, and the Duffing stiffness). In such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more so, by identifying these matrices, the intended goals in Damage Detection can be achieved. In line with such identification, a new algorithm for the system identification of shear structures is presented in the paper. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of system identification, this method helps to achieve noise attenuation by trimming noisy records in the frequency domain, in parallel with the identification of the structural system. The efficiency and precision of the method have been examined through the application of a "closed loop solution" to a five storey model of shear structure.

Research paper thumbnail of A Systematic Literature Review of Rammed Earth Walls

Soil Mechanics and Foundation Engineering, Oct 16, 2021

Rammed earth structures consist of soil piers, natural materials, and water, which are hammered i... more Rammed earth structures consist of soil piers, natural materials, and water, which are hammered in thin layers in a container. Rammed earth walls are the primary elements of rammed earth structures and offer high-quality insulation properties as well as recyclability. Unfortunately, only minimal information is available regarding rammed earth structures, especially in new material areas such as nanomaterials and finite element modeling. In this context, this paper reviews the factors that can be used to identify the environmental impacts of rammed earth walls and demonstrates the need for using new materials in rammed earth structures. Several previous experimental and numerical studies are discussed to establish a framework for better understanding the history and future of rammed earth structures.

Research paper thumbnail of A Simplified Matrix Analysis Approach to Multi-story Buildings Involving a Friction Damper

Periodica Polytechnica-civil Engineering, Sep 22, 2021

Damping through friction tends to be one of the most efficient methods to suppress damage to stru... more Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction-damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-story friction-damped buildings. The behavior of friction-damped systems has analyzed more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end-to-end solution is proposed to find the responses of structures. The displacement response of each story has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction-damped structures depicts the proposed approach consists with the commercial finite element method and is applicable for the analysis various types of structures. It is noted that the acceleration and displacement responses of the structures investigated under the proposed method and the traditional finite element method are so consistent that only a 1.5% difference is observed. Moreover, as a result of the proper allocation of degrees of freedom during the analysis, this method yields a reduction in computational costs especially in large buildings.

Research paper thumbnail of Control point grid improvement in isogeometric analysis of axisymmetric structures using error estimation methods based on stress recovery

Modares Civil Engineering journal, Sep 10, 2015

Research paper thumbnail of A Systematic Literature Review of Rammed Earth Walls

Soil Mechanics and Foundation Engineering

Rammed earth structures consist of soil piers, natural materials, and water, which are hammered i... more Rammed earth structures consist of soil piers, natural materials, and water, which are hammered in thin layers in a container. Rammed earth walls are the primary elements of rammed earth structures and offer high-quality insulation properties as well as recyclability. Unfortunately, only minimal information is available regarding rammed earth structures, especially in new material areas such as nanomaterials and finite element modeling. In this context, this paper reviews the factors that can be used to identify the environmental impacts of rammed earth walls and demonstrates the need for using new materials in rammed earth structures. Several previous experimental and numerical studies are discussed to establish a framework for better understanding the history and future of rammed earth structures.

Research paper thumbnail of Where Nurses' Aides Don't Do All the Nursing Care

Journal of Gerontological Nursing, 1976

Research paper thumbnail of A Practical Algorithm for Modeling of Friction Damped-Based Structures

With the emergence of friction damper, it becomes economically feasible to significantly increase... more With the emergence of friction damper, it becomes economically feasible to significantly increase the earthquake resistance and damage control potential of a structure. Friction dampers are of the most efficient methods of dissipating seismic energy. In general, friction tools well perform against earthquake and their response is independent of loading range, frequency and number of loading cycles. Damping through friction tends to be one of the most efficient methods of dissipating seismic energy. Therefore, dynamic modeling of friction dampers have found a significant aspect in the exploration of performance and reliability of them within structures. However, traditional methods are highly depending on the rectangular hysteretic loop in which the whole structure behavior is only modelled by spring-mass system. This paper deals with a practical algorithm to analyze the behavior of various bending, braced, and specifically friction–damped based structures. The novelty of the present...

Research paper thumbnail of Reserach on force loading servo control method with feedforward compensation for electro-hydraulic servo actuator

CSAA/IET International Conference on Aircraft Utility Systems (AUS 2020), 2021

Research paper thumbnail of New System Identification Approaches For The Identification of The Dynamic Characteristic Matrices of Structures

System Identification is an important concept in numerous engineering fields, such as those of st... more System Identification is an important concept in numerous engineering fields, such as those of structural, mechanical and aerospace engineering. It could be said that the purpose of System Identification is the determination of the dynamic characteristics of systems, which are, in addition to the frequencies, mode shapes, damping ratios and other modal characteristics, the matrices corresponding to mass, viscous damping, stiffness, Coulomb damping and Duffing stiffness. Without access to dynamic characteristics of structures, a well-defined diagnosis of the situation and of the rate of damage is not possible. If some of the nonlinear characteristics of structures, such as Coulomb damping and Duffing stiffness, are taken into account then identification errors can be reduced. In some cases, e.g. in the Damage Detection of structures, identification of the characteristic matrices of the system (mass, damping, stiffness, etc.) is as important as the modal characteristics (frequency, mo...

Research paper thumbnail of An Iterative Algorithm for Noise Reduction in the System Identification of Shear Structures

The objective of this work was to reduce the noise adverse effect on the "System Identificat... more The objective of this work was to reduce the noise adverse effect on the "System Identification" (SI) of linear shear structures. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of SI, the proposed method facilitates direct noise attenuation in the domain of time in parallel with the identification of structural system. Since in such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more, the proposed method tries to identify the matrices of mass, damping and stiffness of shear structures. Efficiency and precision of the method have been examined through application of "closed loop solution" to two structures with analytical model.

Research paper thumbnail of A New Algorithm for the System Identification of Shear Structures

Advanced Materials Research, 2012

In general terms, the aim of &amp... more In general terms, the aim of "System Identification" is to determine the dynamic characteristics of mechanical systems. These characteristics include both frequency characteristics (frequencies, mode shapes, and damping ratios) and the system's characteristic matrices (the matrices of mass, viscous damping, stiffness, Coulomb damping or coefficients of friction, and the Duffing stiffness). In such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more so, by identifying these matrices, the intended goals in Damage Detection can be achieved. In line with such identification, a new algorithm for the system identification of shear structures is presented in the paper. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of system identification, this method helps to achieve noise attenuation by trimming noisy records in the frequency domain, in parallel with the identification of the structural system. The efficiency and precision of the method have been examined through the application of a "closed loop solution" to a five storey model of shear structure.

Research paper thumbnail of Detection of damage to bending structures using a crack index

Proceedings of the ICE - Structures and Buildings, 2014

The damage that can occur to structures by way of deformation in bending under the excitation of ... more The damage that can occur to structures by way of deformation in bending under the excitation of random forces (referred to hereafter as ‘bending structures') is considered a local state due to the harm caused by cracks. Its effects on the behaviour of the structure are discussed as discontinuity phenomena. For the simulation of such discontinuities, the bilinear stiffness reduction function, which results in asymmetrical behaviour of a damaged member when loaded in opposite directions, has been defined together with a corresponding crack index. For different damage scenarios, the effect of the non-linear behaviour of affected members has been investigated according to which damaged members can be identified by means of a crack index. The proposed damage identification method is not hampered by the existence of any kind of noise. The effectiveness and accuracy of the proposed method have been examined by applying a ‘closed-loop solution' to a six- and an eight-storey bending...

Research paper thumbnail of Identification of structural systems with full characteristic matrices under single point excitation

Journal of Sound and Vibration, 2014

The aim of "System Identification" is to determine the modal and system properties of structural ... more The aim of "System Identification" is to determine the modal and system properties of structural systems. Because of various constraints in practice only single excitation and partial measurement at selected degrees of freedom is possible. In this paper, to identify a structural system, dynamic load was applied only along one of the degrees of freedom of the structure and the responses corresponding to a few degrees of freedom have been measured. To identify characteristic matrices of a system with this sort of restricted information, a new approach was intrtoduced. Taking into account the significant effect of noise reduction in improving the system identification accuracy levels, a noise reduction technique was also proposed. It was shown that as noise level increases, identification errors will also increase though to an acceptable range. The method's efficiency and precision were examined through the application of a "closed loop solution" to a six-storey flexural structure.

Research paper thumbnail of New approaches for non-classically damped system eigenanalysis

Earthquake Engineering & Structural Dynamics, 2005

This paper presents three new approaches for solving eigenvalue problems of non-classically dampe... more This paper presents three new approaches for solving eigenvalue problems of non-classically damped linear dynamics systems with fewer calculations than the conventional state vector approach. In the latter, the second-order di erential equation of motion is converted into a ÿrst-order system by doubling the size of the matrices. The new approaches simplify the approach and reduce the number of calculations. The mathematical formulations for the proposed approaches are presented and the numerical results compared with the existing method by solving a sample problem with di erent damping properties. Of the three proposed approaches, the expansion approach was found to be the simplest and fastest to compute. Copyright ? 2005 John Wiley & Sons, Ltd.

Research paper thumbnail of Collapse load factor of planar frames using a modified genetic algorithm

Research paper thumbnail of A Combined Analytical Method for Intelligent Control of Friction Damped Structures

Pertanika Journal of Science and Technology

Controlling structures and increasing the prognosis of their behaviour before natural disasters a... more Controlling structures and increasing the prognosis of their behaviour before natural disasters are the most critical issues in structural engineering. To that end, predicting the destructive effects of earthquakes on both acceleration and displacement of structures would be beneficial. This paper suggests an intelligent control system that realises simultaneous control of acceleration and displacement parameters. There are two modules in the system. First, the preserving module aims to estimate the crisis thresholds of acceleration and displacement based on the historical seismic data of each area. Second, the processing module finds the optimum value of the slip load of the friction damper so that both acceleration and displacement are controlled. We introduce an analytical method based on a matrix analysis approach and heuristic algorithm (MAHA) as a core of the processing module. MAHA would analyse the structure response, and the friction damper would determine the optimum slip ...

Research paper thumbnail of A Simplified Matrix Analysis Approach to Multi Storey Buildings Involving a Friction Damper

Slovak Journal of Civil Engineering

Damping through friction tends to be one of the most efficient methods to suppress damage to stru... more Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction- damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-storey friction- damped buildings. We have analyzed the behavior of friction- damped systems more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end- to- end solution is proposed to find the responses of structures. The displacement response of each storey has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction- damped struct...

Research paper thumbnail of Dynamic condensation of non-classically damped structures using the method of Maclaurin expansion of the frequency response function in Laplace domain

Journal of Sound and Vibration, Jul 1, 2018

Abstract As the number of degrees of freedom (DOFs) in structural dynamic problems becomes larger... more Abstract As the number of degrees of freedom (DOFs) in structural dynamic problems becomes larger, the analyzing complexity and CPU usage of computers increase drastically. Condensation (or reduction) method is an efficient technique to reduce the size of the full model or the dimension of the structural matrices by eliminating the unimportant DOFs. After the first presentation of condensation method by Guyan in 1965 for undamped structures, which ignores the dynamic effects of the mass term, various forms of dynamic condensation methods were presented to overcome this issue. Moreover, researchers have tried to expand the dynamic condensation method to non-classically damped structures. Dynamic reduction of such systems is far more complicated than undamped systems. The proposed non-iterative method in this paper is introduced as 'Maclaurin Expansion of the frequency response function in Laplace Domain' (MELD) applied for dynamic reduction of non-classically damped structures. The present approach is implemented in four numerical examples of 2D bending-shear-axial frames with various numbers of stories and spans and also a floating raft isolation system. The results of natural frequencies and dynamic responses of models are compared with each other before and after the dynamic reduction. It is shown that the result accuracy has acceptable convergence in both cases. In addition, it is indicated that the result of the proposed method is more accurate than the results of some other existing condensation methods.

Research paper thumbnail of Collapse load factor of planar frames using a modified genetic algorithm

Communications in Numerical Methods in Engineering, Sep 9, 2004

In this article an analytical method is developed for identifying basic collapse mechanisms of ri... more In this article an analytical method is developed for identifying basic collapse mechanisms of rigidjointed two-dimensional frames. In this approach, the deformation of each member is completely deÿned by four translations and one rotation. The behaviour of such an element lies in between that of a truss element and a exural one. Once the basic collapse mechanisms are identiÿed, the genetic algorithm is used to identify the mechanism corresponding to the least possible load factor. Examples are included to illustrate the e ciency of the present method compared to the use of a simple genetic algorithm. Copyright ? 2004 John Wiley & Sons, Ltd.

Research paper thumbnail of A Combined Analytical Method for Intelligent Control of Friction Damped Structures

pertanika journal of science and technology, Sep 21, 2021

Controlling structures and increasing the prognosis of their behaviour before natural disasters a... more Controlling structures and increasing the prognosis of their behaviour before natural disasters are the most critical issues in structural engineering. To that end, predicting the destructive effects of earthquakes on both acceleration and displacement of structures would be beneficial. This paper suggests an intelligent control system that realises simultaneous control of acceleration and displacement parameters. There are two modules in the system. First, the preserving module aims to estimate the crisis thresholds of acceleration and displacement based on the historical seismic data of each area. Second, the processing module finds the optimum value of the slip load of the friction damper so that both acceleration and displacement are controlled. We introduce an analytical method based on a matrix analysis approach and heuristic algorithm (MAHA) as a core of the processing module. MAHA would analyse the structure response, and the friction damper would determine the optimum slip load. The numerical and software simulation results for various one-bay and two-bay steel structures show that the proposed intelligent control system applies to multiple frictions damped structures under different earthquake records. In addition, a control level of 80% in acceleration and displacement of structures is achieved compared to an uncontrolled state. Moreover, the mentioned system enables the engineers to find appropriate friction dampers during the design of structures.

Research paper thumbnail of A New Algorithm for the System Identification of Shear Structures

Advanced Materials Research, 2012

In general terms, the aim of &amp... more In general terms, the aim of "System Identification" is to determine the dynamic characteristics of mechanical systems. These characteristics include both frequency characteristics (frequencies, mode shapes, and damping ratios) and the system's characteristic matrices (the matrices of mass, viscous damping, stiffness, Coulomb damping or coefficients of friction, and the Duffing stiffness). In such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more so, by identifying these matrices, the intended goals in Damage Detection can be achieved. In line with such identification, a new algorithm for the system identification of shear structures is presented in the paper. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of system identification, this method helps to achieve noise attenuation by trimming noisy records in the frequency domain, in parallel with the identification of the structural system. The efficiency and precision of the method have been examined through the application of a "closed loop solution" to a five storey model of shear structure.

Research paper thumbnail of A Systematic Literature Review of Rammed Earth Walls

Soil Mechanics and Foundation Engineering, Oct 16, 2021

Rammed earth structures consist of soil piers, natural materials, and water, which are hammered i... more Rammed earth structures consist of soil piers, natural materials, and water, which are hammered in thin layers in a container. Rammed earth walls are the primary elements of rammed earth structures and offer high-quality insulation properties as well as recyclability. Unfortunately, only minimal information is available regarding rammed earth structures, especially in new material areas such as nanomaterials and finite element modeling. In this context, this paper reviews the factors that can be used to identify the environmental impacts of rammed earth walls and demonstrates the need for using new materials in rammed earth structures. Several previous experimental and numerical studies are discussed to establish a framework for better understanding the history and future of rammed earth structures.

Research paper thumbnail of A Simplified Matrix Analysis Approach to Multi-story Buildings Involving a Friction Damper

Periodica Polytechnica-civil Engineering, Sep 22, 2021

Damping through friction tends to be one of the most efficient methods to suppress damage to stru... more Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction-damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-story friction-damped buildings. The behavior of friction-damped systems has analyzed more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end-to-end solution is proposed to find the responses of structures. The displacement response of each story has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction-damped structures depicts the proposed approach consists with the commercial finite element method and is applicable for the analysis various types of structures. It is noted that the acceleration and displacement responses of the structures investigated under the proposed method and the traditional finite element method are so consistent that only a 1.5% difference is observed. Moreover, as a result of the proper allocation of degrees of freedom during the analysis, this method yields a reduction in computational costs especially in large buildings.

Research paper thumbnail of Control point grid improvement in isogeometric analysis of axisymmetric structures using error estimation methods based on stress recovery

Modares Civil Engineering journal, Sep 10, 2015

Research paper thumbnail of A Systematic Literature Review of Rammed Earth Walls

Soil Mechanics and Foundation Engineering

Rammed earth structures consist of soil piers, natural materials, and water, which are hammered i... more Rammed earth structures consist of soil piers, natural materials, and water, which are hammered in thin layers in a container. Rammed earth walls are the primary elements of rammed earth structures and offer high-quality insulation properties as well as recyclability. Unfortunately, only minimal information is available regarding rammed earth structures, especially in new material areas such as nanomaterials and finite element modeling. In this context, this paper reviews the factors that can be used to identify the environmental impacts of rammed earth walls and demonstrates the need for using new materials in rammed earth structures. Several previous experimental and numerical studies are discussed to establish a framework for better understanding the history and future of rammed earth structures.

Research paper thumbnail of Where Nurses' Aides Don't Do All the Nursing Care

Journal of Gerontological Nursing, 1976

Research paper thumbnail of A Practical Algorithm for Modeling of Friction Damped-Based Structures

With the emergence of friction damper, it becomes economically feasible to significantly increase... more With the emergence of friction damper, it becomes economically feasible to significantly increase the earthquake resistance and damage control potential of a structure. Friction dampers are of the most efficient methods of dissipating seismic energy. In general, friction tools well perform against earthquake and their response is independent of loading range, frequency and number of loading cycles. Damping through friction tends to be one of the most efficient methods of dissipating seismic energy. Therefore, dynamic modeling of friction dampers have found a significant aspect in the exploration of performance and reliability of them within structures. However, traditional methods are highly depending on the rectangular hysteretic loop in which the whole structure behavior is only modelled by spring-mass system. This paper deals with a practical algorithm to analyze the behavior of various bending, braced, and specifically friction–damped based structures. The novelty of the present...

Research paper thumbnail of Reserach on force loading servo control method with feedforward compensation for electro-hydraulic servo actuator

CSAA/IET International Conference on Aircraft Utility Systems (AUS 2020), 2021

Research paper thumbnail of New System Identification Approaches For The Identification of The Dynamic Characteristic Matrices of Structures

System Identification is an important concept in numerous engineering fields, such as those of st... more System Identification is an important concept in numerous engineering fields, such as those of structural, mechanical and aerospace engineering. It could be said that the purpose of System Identification is the determination of the dynamic characteristics of systems, which are, in addition to the frequencies, mode shapes, damping ratios and other modal characteristics, the matrices corresponding to mass, viscous damping, stiffness, Coulomb damping and Duffing stiffness. Without access to dynamic characteristics of structures, a well-defined diagnosis of the situation and of the rate of damage is not possible. If some of the nonlinear characteristics of structures, such as Coulomb damping and Duffing stiffness, are taken into account then identification errors can be reduced. In some cases, e.g. in the Damage Detection of structures, identification of the characteristic matrices of the system (mass, damping, stiffness, etc.) is as important as the modal characteristics (frequency, mo...

Research paper thumbnail of An Iterative Algorithm for Noise Reduction in the System Identification of Shear Structures

The objective of this work was to reduce the noise adverse effect on the "System Identificat... more The objective of this work was to reduce the noise adverse effect on the "System Identification" (SI) of linear shear structures. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of SI, the proposed method facilitates direct noise attenuation in the domain of time in parallel with the identification of structural system. Since in such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more, the proposed method tries to identify the matrices of mass, damping and stiffness of shear structures. Efficiency and precision of the method have been examined through application of "closed loop solution" to two structures with analytical model.

Research paper thumbnail of A New Algorithm for the System Identification of Shear Structures

Advanced Materials Research, 2012

In general terms, the aim of &amp... more In general terms, the aim of "System Identification" is to determine the dynamic characteristics of mechanical systems. These characteristics include both frequency characteristics (frequencies, mode shapes, and damping ratios) and the system's characteristic matrices (the matrices of mass, viscous damping, stiffness, Coulomb damping or coefficients of friction, and the Duffing stiffness). In such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more so, by identifying these matrices, the intended goals in Damage Detection can be achieved. In line with such identification, a new algorithm for the system identification of shear structures is presented in the paper. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of system identification, this method helps to achieve noise attenuation by trimming noisy records in the frequency domain, in parallel with the identification of the structural system. The efficiency and precision of the method have been examined through the application of a "closed loop solution" to a five storey model of shear structure.

Research paper thumbnail of Detection of damage to bending structures using a crack index

Proceedings of the ICE - Structures and Buildings, 2014

The damage that can occur to structures by way of deformation in bending under the excitation of ... more The damage that can occur to structures by way of deformation in bending under the excitation of random forces (referred to hereafter as ‘bending structures') is considered a local state due to the harm caused by cracks. Its effects on the behaviour of the structure are discussed as discontinuity phenomena. For the simulation of such discontinuities, the bilinear stiffness reduction function, which results in asymmetrical behaviour of a damaged member when loaded in opposite directions, has been defined together with a corresponding crack index. For different damage scenarios, the effect of the non-linear behaviour of affected members has been investigated according to which damaged members can be identified by means of a crack index. The proposed damage identification method is not hampered by the existence of any kind of noise. The effectiveness and accuracy of the proposed method have been examined by applying a ‘closed-loop solution' to a six- and an eight-storey bending...

Research paper thumbnail of Identification of structural systems with full characteristic matrices under single point excitation

Journal of Sound and Vibration, 2014

The aim of "System Identification" is to determine the modal and system properties of structural ... more The aim of "System Identification" is to determine the modal and system properties of structural systems. Because of various constraints in practice only single excitation and partial measurement at selected degrees of freedom is possible. In this paper, to identify a structural system, dynamic load was applied only along one of the degrees of freedom of the structure and the responses corresponding to a few degrees of freedom have been measured. To identify characteristic matrices of a system with this sort of restricted information, a new approach was intrtoduced. Taking into account the significant effect of noise reduction in improving the system identification accuracy levels, a noise reduction technique was also proposed. It was shown that as noise level increases, identification errors will also increase though to an acceptable range. The method's efficiency and precision were examined through the application of a "closed loop solution" to a six-storey flexural structure.

Research paper thumbnail of New approaches for non-classically damped system eigenanalysis

Earthquake Engineering & Structural Dynamics, 2005

This paper presents three new approaches for solving eigenvalue problems of non-classically dampe... more This paper presents three new approaches for solving eigenvalue problems of non-classically damped linear dynamics systems with fewer calculations than the conventional state vector approach. In the latter, the second-order di erential equation of motion is converted into a ÿrst-order system by doubling the size of the matrices. The new approaches simplify the approach and reduce the number of calculations. The mathematical formulations for the proposed approaches are presented and the numerical results compared with the existing method by solving a sample problem with di erent damping properties. Of the three proposed approaches, the expansion approach was found to be the simplest and fastest to compute. Copyright ? 2005 John Wiley & Sons, Ltd.

Research paper thumbnail of Collapse load factor of planar frames using a modified genetic algorithm

Research paper thumbnail of A Combined Analytical Method for Intelligent Control of Friction Damped Structures

Pertanika Journal of Science and Technology

Controlling structures and increasing the prognosis of their behaviour before natural disasters a... more Controlling structures and increasing the prognosis of their behaviour before natural disasters are the most critical issues in structural engineering. To that end, predicting the destructive effects of earthquakes on both acceleration and displacement of structures would be beneficial. This paper suggests an intelligent control system that realises simultaneous control of acceleration and displacement parameters. There are two modules in the system. First, the preserving module aims to estimate the crisis thresholds of acceleration and displacement based on the historical seismic data of each area. Second, the processing module finds the optimum value of the slip load of the friction damper so that both acceleration and displacement are controlled. We introduce an analytical method based on a matrix analysis approach and heuristic algorithm (MAHA) as a core of the processing module. MAHA would analyse the structure response, and the friction damper would determine the optimum slip ...

Research paper thumbnail of A Simplified Matrix Analysis Approach to Multi Storey Buildings Involving a Friction Damper

Slovak Journal of Civil Engineering

Damping through friction tends to be one of the most efficient methods to suppress damage to stru... more Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction- damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-storey friction- damped buildings. We have analyzed the behavior of friction- damped systems more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end- to- end solution is proposed to find the responses of structures. The displacement response of each storey has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction- damped struct...