Costas Providakis - Academia.edu (original) (raw)

Papers by Costas Providakis

International Journal of Solids and Structures, 2000

A direct boundary element algorithm is developed for the dynamic analysis of thin elastoplastic b... more A direct boundary element algorithm is developed for the dynamic analysis of thin elastoplastic building floor slabs directly supported by columns. The formulation employs the classical boundary element methodology dedicated to the analysis of elastoplastic plates. The method uses the static fundamental solution of the thin elastic plate problem. In this case, boundary as well as interior elements are used in the space descritization of the problem. This is due to the presence of plasticity and inertial effects in the integral formulation. An explicit time integration algorithm, employed on the incremental form of the matrix equation of motion, leads to the solution of the problem. Simple practical examples illustrate the accuracy and the efficiency of the proposed algorithm.

Key Engineering Materials, 2007

In the present paper, the repair of a cracked structure under dynamic load using the electromecha... more In the present paper, the repair of a cracked structure under dynamic load using the electromechanical admittance (EMA) approach is investigated. Conceptually, appropriate electrical field are applied on the outer surfaces of piezoelectric (PZT) patches to effect closure of the crack. This has the effect of altering the electromechnaical (E/M) admittance signature, extracted at the electrical terminals of a specific PZT patch, considered as an admittance calculating sensor (ACS) patch, towards that of the healthy structure, which is the criterion concept used for the repair in this paper. To demonstrate the present repair methodology, a cantilever 3D beam numerical example is considered in combination with a FEM-based minimization of the difference between the healthy and cracked structure’s (E/M) admittance signature, for specific frequency ranges.

Recent Advances in Boundary Element Methods, 2009

This paper presents a procedure for analyzing crack-tip regions of creeping, cracked structural c... more This paper presents a procedure for analyzing crack-tip regions of creeping, cracked structural components using the strain energy density rate concept and boundary element methodology. The investigated structural components are considered to undergo time-dependent, two-dimensional creep deformation and to be subjected to remote loading conditions while theirs deformation is assumed to be described by the elastic power law creep model. Some special boundary elements were used to simulate the time-dependent singular behavior of stress and strain fields at the crack tip of the investigated creeping materials. The strain energy density rate theory is applied to determine the direction of the crack initiation for a center cracked plate in tension which is subjected to Mode I loading conditions.

Key Engineering Materials, 2009

The present work considers the possibility of simultaneous health monitoring and active repair of... more The present work considers the possibility of simultaneous health monitoring and active repair of the edge debonding in dynamically loaded smart concrete structures strengthened with fiber reinforced plastic (FRP) composite materials. This is achieved by using local piezoelectric (PZT) actuators/sensors, the electro-mechanical admittance concept and extreme value statistics.

Computer Methods in Applied Mechanics and Engineering, 1991

Computational Mechanics ’88, 1988

Two direct BEM approaches for dynamic analysis of thin, elastic, flexural plates obeying Kirchhof... more Two direct BEM approaches for dynamic analysis of thin, elastic, flexural plates obeying Kirchhoff’s theory are presented and compared. The first approach utilizes the dynamic, while the second one the static fundamental solution of the problem. Thus, the first approach requires only a boundary discretization, while the second one requires a boundary as well as an interior discretization. Both free and forced vibrations are considered. Forced vibrations ate treated with the aid of Laplace transform with respect to time. Two numerical examples are presented for illustration purposes. The first example corresponds to free and the second one to forced vibrations of plates as treated by both BEM approaches.

Theoretical and Applied Fracture Mechanics, 2002

A direct formulation of the boundary element method using a complex variable numerical approach i... more A direct formulation of the boundary element method using a complex variable numerical approach is presented for the time-dependent inelastic stresses in edge notched and cracked creeping metallic structural components subject to high temperature gradients. Particular attention is focused on the numerical evaluation of energy rate contour integrals in single edge cracked specimens in tension. The constitutive models used in the numerical calculation are internal state variable creep-plasticity or elastic power law creep model. Numerical results are compared with solution obtained from other methods for different loading rates.

Soil Dynamics and Earthquake Engineering, 2009

Numerical simulations are performed to assess the effects of near-fault ground motions on base-is... more Numerical simulations are performed to assess the effects of near-fault ground motions on base-isolated buildings that consist of either lead-rubber (LRB) or friction-pendulum system (FPS) bearings in addition to supplemented viscous dampers. While LRB and FPS isolation systems have been applied for a number of years, the addition of supplemental damping devices is being currently considered for strong ground motions to reduce the isolator displacements. However, the main problem in this case is that the addition of damping may increase both internal deformation and absolute accelerations of the superstructure and thus may defeat many of the gains for which base isolation is intended. In the present paper, a detailed and systematic investigation on the performance of LRB and FPS isolation systems, provided with supplemental viscous damping under the effect of near-fault ground motions, has been carried out by using commercial finite element software.

Soil Dynamics and Earthquake Engineering, 1997

A direct boundary element method for the dynamic analysis of thin elastoplastic flexural plates o... more A direct boundary element method for the dynamic analysis of thin elastoplastic flexural plates of arbitrary geometry on a Winkler-type elastic foundation is presented. The method employs the elastostatic fundamental solution of an infinite plate. This creates not only boundary integrals but surface integrals as well involving inertia, plasticity and foundation pressure effects. By discretizing the integral equations and integrating the resulting matrix equation of motion forward in time by an explicit integration scheme, the response of the plate on an elastic foundation is obtained. Applications involving impacted plates of arbitrary planform on several different foundations serve to illustrate the method and demonstrate its merits.

Engineering Fracture Mechanics, 1999

Various constitutive relations have recently been proposed to solve boundary value problems in cr... more Various constitutive relations have recently been proposed to solve boundary value problems in creeping deformation of metallic plates. In this paper the direct formulation of the boundary element method is presented for the inelastic analysis of stress concentration problems arising in V-notched creeping plates at high temperatures. The deformation of the plate is simulated using a viscoplastic model developed recently. The model was formulated on the basis of a state variable theory for characterising the time-dependent behaviour of metals and alloys under general loading conditions. The accuracy and efficiency of the method is demonstrated by obtaining stress distribution for a number of specimens with a single edge notch and subjected to pure bending. Simulation portrayed by the present formulation is further compared with other numerical solutions obtained for different bending stressing rates.

Engineering Analysis with Boundary Elements, 1994

ABSTRACT

Engineering Analysis with Boundary Elements, 1996

A direct boundary element approach is developed for the determination of the transient response o... more A direct boundary element approach is developed for the determination of the transient response of thin elastoplastic flexural plates of arbitrary shape, and simple or double connectivity. All kinds of boundary conditions (uniform or mixed) are treated, and the effects of comers and internal supports are considered. The method employs the static fundamental solution of the problem and this creates not only boundary integrals but surface integrals as well owing to the presence of the plasticity effect, the inertial and external lateral load. Thus, boundary as well as domain (interior) elements are used in the space descretization of the problem. Linear isoparametric elements with a Hermitian interpolation for the deflection and quadratic isoparametric elements are employed for the boundary and interior descretization, respectively. Subsequently, using an explicit time integration scheme employed on the incremental form of the matrix equation of motion, the solution is obtained. Several examples are presented to illustrate the efficiency and accuracy of the proposed method.

Engineering Analysis with Boundary Elements, 1993

A direct boundary element method (BEM) is developed for the determination of the time-dependent i... more A direct boundary element method (BEM) is developed for the determination of the time-dependent inelastic deflection of plates of arbitrary planform and under arbitrary boundary conditions to general lateral loading history. The governing differential equation is the nonhomogeneous biharmonic equation for the rate of small transverse deflection. The boundary integral formulation is derived by using a combination of the BEM and finite element methodology. The plate material is modelled as elastic-viscoplastic. Numerical examples for sample problems are presented to illustrate the method and to demonstrate its merits.

Computers & Structures, 1986

ABSTRACT

Computer Methods in Applied Mechanics and Engineering, 1991

ABSTRACT

Computational Mechanics, 2002

This paper presents a procedure for modelling singular crack tip regions of creeping, cracked str... more This paper presents a procedure for modelling singular crack tip regions of creeping, cracked structural components using singular boundary elements. These special boundary elements correctly simulate the timedependent singular behaviour of stress and strain fields at the crack tip of creeping materials. The investigated structural components are considered to undergo timedependent, two-dimensional creep deformation and to be subjected to remote loading conditions. The deformation of the components is assumed to be described by the elastic power law creep model. Examples of various crack problems are investigated to illustrate the efficiency of the proposed singular boundary elements for analysing creep stress and strain distribution problems and for determining some important creep fracture parameters. The effectiveness of the proposed approach is demonstrated and its accuracy is compared with the results obtained by finite element solutions for different creep conditions.

Advances in Engineering Software, 2002

A new boundary element approach for the solution of time-dependent inelastic problems arising in ... more A new boundary element approach for the solution of time-dependent inelastic problems arising in creeping metallic structures subjected to the combined action of high temperature gradient and quasi-static mechanical loading conditions is investigated. The new approach allows the use of complex variable techniques in the boundary element procedure for the evaluation of stress components as derivatives of the displacement integral equations. This methodology makes faster and more accurate the conventional boundary element method. To validate the efficiency of the proposed method in the implementation of Robinson's viscoplastic model, the results obtained using the present methodology are compared with those obtained by using known analytical and finite element solution for the analysis of a thick-walled internally pressurized cylinder and an experimental cylindrical thrust chamber in plane strain under general thermomechanical loading histories.

An effort for the detection of damages in the <br> reinforcement bars of reinforced concret... more An effort for the detection of damages in the <br> reinforcement bars of reinforced concrete members using PZTs is <br> presented. The damage can be the result of excessive elongation of <br> the steel bar due to steel yielding or due to local steel corrosion. In <br> both cases the damage is simulated by considering reduced diameter <br> of the rebar along the damaged part of its length. An integration <br> approach based on both electromechanical admittance methodology <br> and guided wave propagation technique is used to evaluate the <br> artificial damage on the examined longitudinal steel bar. Two <br> actuator PZTs and a sensor PZT are considered to be bonded on the <br> examined steel bar. The admittance of the Sensor PZT is calculated <br> using COMSOL 3.4a. Fast Furrier Transformation for a better <br> evaluation of the results is employed. An effort for the quantification <br> of the damage detec...

Cmes-computer Modeling in Engineering & Sciences, 2007

The method of Domain/Boundary Element is used to achieve a dynamic analysis of elastoplastic thic... more The method of Domain/Boundary Element is used to achieve a dynamic analysis of elastoplastic thick plates resting on internal supports. All possible boundary conditions on the edge of the plate with any interior support conditions such as isolated points (column), lines (walls) or regions (patches) can be treated without practical difficulties. The formulation presented includes the effects of shear deformation and rotatory inertia following Reissner-Mindlin’s deformation theory assumptions. The method employs the elastostatic fundamental solution of the problem resulting in both boundary and domain integrals due to inertia, plasticity and interior support effect terms. By discretizing the integral equations and integrating the resulting matrix equation of motion by an explicit step-by-step time integration algorithm, the dynamic inelastic response of the plate can be obtained. Several complicated examples for impacted thick plates with different internal support conditions are pres...

International Journal of Solids and Structures, 2000

A direct boundary element algorithm is developed for the dynamic analysis of thin elastoplastic b... more A direct boundary element algorithm is developed for the dynamic analysis of thin elastoplastic building floor slabs directly supported by columns. The formulation employs the classical boundary element methodology dedicated to the analysis of elastoplastic plates. The method uses the static fundamental solution of the thin elastic plate problem. In this case, boundary as well as interior elements are used in the space descritization of the problem. This is due to the presence of plasticity and inertial effects in the integral formulation. An explicit time integration algorithm, employed on the incremental form of the matrix equation of motion, leads to the solution of the problem. Simple practical examples illustrate the accuracy and the efficiency of the proposed algorithm.

Key Engineering Materials, 2007

In the present paper, the repair of a cracked structure under dynamic load using the electromecha... more In the present paper, the repair of a cracked structure under dynamic load using the electromechanical admittance (EMA) approach is investigated. Conceptually, appropriate electrical field are applied on the outer surfaces of piezoelectric (PZT) patches to effect closure of the crack. This has the effect of altering the electromechnaical (E/M) admittance signature, extracted at the electrical terminals of a specific PZT patch, considered as an admittance calculating sensor (ACS) patch, towards that of the healthy structure, which is the criterion concept used for the repair in this paper. To demonstrate the present repair methodology, a cantilever 3D beam numerical example is considered in combination with a FEM-based minimization of the difference between the healthy and cracked structure’s (E/M) admittance signature, for specific frequency ranges.

Recent Advances in Boundary Element Methods, 2009

This paper presents a procedure for analyzing crack-tip regions of creeping, cracked structural c... more This paper presents a procedure for analyzing crack-tip regions of creeping, cracked structural components using the strain energy density rate concept and boundary element methodology. The investigated structural components are considered to undergo time-dependent, two-dimensional creep deformation and to be subjected to remote loading conditions while theirs deformation is assumed to be described by the elastic power law creep model. Some special boundary elements were used to simulate the time-dependent singular behavior of stress and strain fields at the crack tip of the investigated creeping materials. The strain energy density rate theory is applied to determine the direction of the crack initiation for a center cracked plate in tension which is subjected to Mode I loading conditions.

Key Engineering Materials, 2009

The present work considers the possibility of simultaneous health monitoring and active repair of... more The present work considers the possibility of simultaneous health monitoring and active repair of the edge debonding in dynamically loaded smart concrete structures strengthened with fiber reinforced plastic (FRP) composite materials. This is achieved by using local piezoelectric (PZT) actuators/sensors, the electro-mechanical admittance concept and extreme value statistics.

Computer Methods in Applied Mechanics and Engineering, 1991

Computational Mechanics ’88, 1988

Two direct BEM approaches for dynamic analysis of thin, elastic, flexural plates obeying Kirchhof... more Two direct BEM approaches for dynamic analysis of thin, elastic, flexural plates obeying Kirchhoff’s theory are presented and compared. The first approach utilizes the dynamic, while the second one the static fundamental solution of the problem. Thus, the first approach requires only a boundary discretization, while the second one requires a boundary as well as an interior discretization. Both free and forced vibrations are considered. Forced vibrations ate treated with the aid of Laplace transform with respect to time. Two numerical examples are presented for illustration purposes. The first example corresponds to free and the second one to forced vibrations of plates as treated by both BEM approaches.

Theoretical and Applied Fracture Mechanics, 2002

A direct formulation of the boundary element method using a complex variable numerical approach i... more A direct formulation of the boundary element method using a complex variable numerical approach is presented for the time-dependent inelastic stresses in edge notched and cracked creeping metallic structural components subject to high temperature gradients. Particular attention is focused on the numerical evaluation of energy rate contour integrals in single edge cracked specimens in tension. The constitutive models used in the numerical calculation are internal state variable creep-plasticity or elastic power law creep model. Numerical results are compared with solution obtained from other methods for different loading rates.

Soil Dynamics and Earthquake Engineering, 2009

Numerical simulations are performed to assess the effects of near-fault ground motions on base-is... more Numerical simulations are performed to assess the effects of near-fault ground motions on base-isolated buildings that consist of either lead-rubber (LRB) or friction-pendulum system (FPS) bearings in addition to supplemented viscous dampers. While LRB and FPS isolation systems have been applied for a number of years, the addition of supplemental damping devices is being currently considered for strong ground motions to reduce the isolator displacements. However, the main problem in this case is that the addition of damping may increase both internal deformation and absolute accelerations of the superstructure and thus may defeat many of the gains for which base isolation is intended. In the present paper, a detailed and systematic investigation on the performance of LRB and FPS isolation systems, provided with supplemental viscous damping under the effect of near-fault ground motions, has been carried out by using commercial finite element software.

Soil Dynamics and Earthquake Engineering, 1997

A direct boundary element method for the dynamic analysis of thin elastoplastic flexural plates o... more A direct boundary element method for the dynamic analysis of thin elastoplastic flexural plates of arbitrary geometry on a Winkler-type elastic foundation is presented. The method employs the elastostatic fundamental solution of an infinite plate. This creates not only boundary integrals but surface integrals as well involving inertia, plasticity and foundation pressure effects. By discretizing the integral equations and integrating the resulting matrix equation of motion forward in time by an explicit integration scheme, the response of the plate on an elastic foundation is obtained. Applications involving impacted plates of arbitrary planform on several different foundations serve to illustrate the method and demonstrate its merits.

Engineering Fracture Mechanics, 1999

Various constitutive relations have recently been proposed to solve boundary value problems in cr... more Various constitutive relations have recently been proposed to solve boundary value problems in creeping deformation of metallic plates. In this paper the direct formulation of the boundary element method is presented for the inelastic analysis of stress concentration problems arising in V-notched creeping plates at high temperatures. The deformation of the plate is simulated using a viscoplastic model developed recently. The model was formulated on the basis of a state variable theory for characterising the time-dependent behaviour of metals and alloys under general loading conditions. The accuracy and efficiency of the method is demonstrated by obtaining stress distribution for a number of specimens with a single edge notch and subjected to pure bending. Simulation portrayed by the present formulation is further compared with other numerical solutions obtained for different bending stressing rates.

Engineering Analysis with Boundary Elements, 1994

ABSTRACT

Engineering Analysis with Boundary Elements, 1996

A direct boundary element approach is developed for the determination of the transient response o... more A direct boundary element approach is developed for the determination of the transient response of thin elastoplastic flexural plates of arbitrary shape, and simple or double connectivity. All kinds of boundary conditions (uniform or mixed) are treated, and the effects of comers and internal supports are considered. The method employs the static fundamental solution of the problem and this creates not only boundary integrals but surface integrals as well owing to the presence of the plasticity effect, the inertial and external lateral load. Thus, boundary as well as domain (interior) elements are used in the space descretization of the problem. Linear isoparametric elements with a Hermitian interpolation for the deflection and quadratic isoparametric elements are employed for the boundary and interior descretization, respectively. Subsequently, using an explicit time integration scheme employed on the incremental form of the matrix equation of motion, the solution is obtained. Several examples are presented to illustrate the efficiency and accuracy of the proposed method.

Engineering Analysis with Boundary Elements, 1993

A direct boundary element method (BEM) is developed for the determination of the time-dependent i... more A direct boundary element method (BEM) is developed for the determination of the time-dependent inelastic deflection of plates of arbitrary planform and under arbitrary boundary conditions to general lateral loading history. The governing differential equation is the nonhomogeneous biharmonic equation for the rate of small transverse deflection. The boundary integral formulation is derived by using a combination of the BEM and finite element methodology. The plate material is modelled as elastic-viscoplastic. Numerical examples for sample problems are presented to illustrate the method and to demonstrate its merits.

Computers & Structures, 1986

ABSTRACT

Computer Methods in Applied Mechanics and Engineering, 1991

ABSTRACT

Computational Mechanics, 2002

This paper presents a procedure for modelling singular crack tip regions of creeping, cracked str... more This paper presents a procedure for modelling singular crack tip regions of creeping, cracked structural components using singular boundary elements. These special boundary elements correctly simulate the timedependent singular behaviour of stress and strain fields at the crack tip of creeping materials. The investigated structural components are considered to undergo timedependent, two-dimensional creep deformation and to be subjected to remote loading conditions. The deformation of the components is assumed to be described by the elastic power law creep model. Examples of various crack problems are investigated to illustrate the efficiency of the proposed singular boundary elements for analysing creep stress and strain distribution problems and for determining some important creep fracture parameters. The effectiveness of the proposed approach is demonstrated and its accuracy is compared with the results obtained by finite element solutions for different creep conditions.

Advances in Engineering Software, 2002

A new boundary element approach for the solution of time-dependent inelastic problems arising in ... more A new boundary element approach for the solution of time-dependent inelastic problems arising in creeping metallic structures subjected to the combined action of high temperature gradient and quasi-static mechanical loading conditions is investigated. The new approach allows the use of complex variable techniques in the boundary element procedure for the evaluation of stress components as derivatives of the displacement integral equations. This methodology makes faster and more accurate the conventional boundary element method. To validate the efficiency of the proposed method in the implementation of Robinson's viscoplastic model, the results obtained using the present methodology are compared with those obtained by using known analytical and finite element solution for the analysis of a thick-walled internally pressurized cylinder and an experimental cylindrical thrust chamber in plane strain under general thermomechanical loading histories.

An effort for the detection of damages in the <br> reinforcement bars of reinforced concret... more An effort for the detection of damages in the <br> reinforcement bars of reinforced concrete members using PZTs is <br> presented. The damage can be the result of excessive elongation of <br> the steel bar due to steel yielding or due to local steel corrosion. In <br> both cases the damage is simulated by considering reduced diameter <br> of the rebar along the damaged part of its length. An integration <br> approach based on both electromechanical admittance methodology <br> and guided wave propagation technique is used to evaluate the <br> artificial damage on the examined longitudinal steel bar. Two <br> actuator PZTs and a sensor PZT are considered to be bonded on the <br> examined steel bar. The admittance of the Sensor PZT is calculated <br> using COMSOL 3.4a. Fast Furrier Transformation for a better <br> evaluation of the results is employed. An effort for the quantification <br> of the damage detec...

Cmes-computer Modeling in Engineering & Sciences, 2007

The method of Domain/Boundary Element is used to achieve a dynamic analysis of elastoplastic thic... more The method of Domain/Boundary Element is used to achieve a dynamic analysis of elastoplastic thick plates resting on internal supports. All possible boundary conditions on the edge of the plate with any interior support conditions such as isolated points (column), lines (walls) or regions (patches) can be treated without practical difficulties. The formulation presented includes the effects of shear deformation and rotatory inertia following Reissner-Mindlin’s deformation theory assumptions. The method employs the elastostatic fundamental solution of the problem resulting in both boundary and domain integrals due to inertia, plasticity and interior support effect terms. By discretizing the integral equations and integrating the resulting matrix equation of motion by an explicit step-by-step time integration algorithm, the dynamic inelastic response of the plate can be obtained. Several complicated examples for impacted thick plates with different internal support conditions are pres...