This paper summarizes the application of a rational methodology for the assessment of older reinf... more This paper summarizes the application of a rational methodology for the assessment of older reinforced concrete Tunisian bridges. This methodology is based on ambient vibration measurement of the bridge, identification of the structure's modal signature and finite element model updating. The selected case study is the SidiBouAli river bridge which is an eight-span simply supported bridge with a continuous slab. Each span has a length of 25 m and is supported by rubber bearings at the supports. Ambient vibration tests with output-only measurements were conducted on the bridge using a data acquisition system with nine force-balance accelerometers placed at selected locations of the bridge. The Enhanced Frequency Domain Decomposition technique, known to be robust with respect to the complex non-stationary nature of the unmeasured excitation, was applied to extract the dynamic characteristics of the bridge. For model updating, it was assumed that the parameters that can be changed i...
STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2005; 12:179195 Published... more STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2005; 12:179195 Published online 8 November 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/stc.55 ... Seismic evaluation and innovative ...
ABSTRACT For civil engineering structures, ambient vibration tests are preferred over forced vibr... more ABSTRACT For civil engineering structures, ambient vibration tests are preferred over forced vibration ones because the artificially excitation of large structures having low natural frequencies is quite difficult and expensive. In the ambient vibration tests, operation disturbances can be avoided and the measured response is representative of the actual operating conditions of the structures which vibrate due to natural excitation. The proposed damage identification method is intended for moderate degrees of damage and requires vibration data relative to the current and reference states of the structure as well as a parametric finite element model. It is based on a residual generated from a modal filtering approach by the calculation of the error between the measurements at the current state and their projections onto the incomplete modal basis of the structure as identified at reference state. To detect and locate damage, the residual is evaluated by means of global, sensitivity and rejection tests, modified to allow only physically feasible simple and multiple damage scenarios. The mean of the residual, which turns out to be normally distributed, is used in the final phase of damage quantification. The proposed damage diagnosis method is validated experimentally via ambient vibration tests conducted on full-scale reinforced concrete beams and slabs which contain various simple and multiple damage configurations. With damage expressed in terms of loss of flexural stiffness, the damage detection, localization and quantification are found to be successful for degrees of damage less than about 28% of the initial flexural stiffness of the tested specimens. The exception is that, for multiple damage scenarios, the relative quantification errors may be unacceptable in locations where poor accuracy is expected.
Abstract: This article proposes a rational methodology for the structural assessment of a reinfor... more Abstract: This article proposes a rational methodology for the structural assessment of a reinforced concrete bridge in Tunisia. This methodology is based on ambient vibration measurement of the bridge, identification of its modal signature, finite element model updating and ...
ABSTRACT The goal of the present paper is to improve our understanding of the response of the in-... more ABSTRACT The goal of the present paper is to improve our understanding of the response of the in-plane loaded rectangular plates containing initial geometric imperfection. Besides the frequency responses and FFT curves, which were used as diagnostic tools in previous investigations, the temporal response and the phase diagram have been added to better study the transition zones between two kinds of vibration modes. The phase portrait shows that the plate response has a number of “unusual and perhaps chaotic” characteristics in the transition from one mechanism of vibration of another, which distinguished it from the more classical periodic response. Moreover, the effect of one particular spatial mode of imperfection on a different mode of vibration has been investigated for the first time. It was found that the maximum amplitude of forced vibrations is large when vibration and imperfection are in the same mode while the first mode of vibration is always excited whatever the mode of imperfection is.
ABSTRACT The potential use of Cu-based shape memory alloys (SMA) in retrofitting historical monum... more ABSTRACT The potential use of Cu-based shape memory alloys (SMA) in retrofitting historical monuments is investigated in this paper. This study is part of the ongoing work conducted in Tunisia within the framework of the FP6 European Union project (WIND-CHIME) on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The present investigation consists of a finite element simulation, as a preliminary to an experimental study where a cantilever masonry wall, representing a part of a historical monument, is subjected to monotonic and quasi-static cyclic loadings around a horizontal axis at the base level. The wall was retrofitted with an array of copper SMA wires with different cross-sectional areas. A new model is proposed for heat-treated copper SMAs and is validated based on published experimental results. A series of nonlinear finite element analyses are then performed on the wall for the purpose of assessing the SMA device retrofitting capabilities. Simulation results show an improvement of the wall response for the case of monotonic and quasi-static cyclic loadings.
In order to describe the macroscopic behavior of granular media, a statistical micro to macro lev... more In order to describe the macroscopic behavior of granular media, a statistical micro to macro level transition model is first developed, based on Jaynes' principle of maximum entropy. The model formulation translates into a strictly convex, nonlinear optimization problem. It is tested by solving model examples of two dimensional granular structures. Next, a Lagrangian dual formulation of the maximum entropy
Directional drilling with water jet is an increasingly utilized technique in oil industry. Howeve... more Directional drilling with water jet is an increasingly utilized technique in oil industry. However, prediction of the dynamics of water jet drilling tubes is difficult because of the multiplicity of interacting and often complex phenomena that govern their behaviour. Indeed, This highly nonlinear dynamic problem involves fluid structure interaction, dynamic instability and unilateral contact. Simulation tools help improve understanding of
ABSTRACT The behavior of soils reinforced by micropile networks is still not fully understood due... more ABSTRACT The behavior of soils reinforced by micropile networks is still not fully understood due to the lack of accurate modelling capabilities. Particularly, the complex geometry of large soil-micropile systems makes accurate calculation of the bearing capacity of the reinforced soil a computational challenge. This complexity requires highly detailed and finely discretized models to achieve reasonable accuracy using direct numerical methods. Such models lead to large scale numerical optimization problems that are hardly tractable using a personal computer. Recently a decomposition strategy with domain overlap has proved successful in solving very large kinematic and static limit analysis problems with limited computing resources. It consists of splitting the original problem into limit analysis subproblems that are smaller in size. The present paper reports enhancements made to the original decomposition method. In particular, the method is made capable of solving the classical punch problem with Tresca or Coulomb soils. This benchmark problem is considered as a limit case of a soil reinforced by micropiles. The paper then describes the application of the decomposition method to determine rigorous kinematic and static bounds to the bearing capacity of a soil reinforced by a micropile group according to a 2D plane strain model.
ABSTRACT A new algorithm for solving the duals of separable convex optimization problems is prese... more ABSTRACT A new algorithm for solving the duals of separable convex optimization problems is presented. The algorithm is based on an active set strategy in conjunction with a variable metric method. This first order algorithm is more reliable than Newton's method used in DUAL-2 because it does not break down when the Hessian matrix becomes singular or nearly singular. A perturbation technique is introduced in order to remove the nondifferentiability of the dual function which arises when linear constraints are present in the approximate problem.
ABSTRACT A decomposition approach of the kinematical method of limit analysis is first presented.... more ABSTRACT A decomposition approach of the kinematical method of limit analysis is first presented. It is based on a mixed variational approach and on a convex interior point solver, using linear or quadratic discontinuous velocity fields. Exposed in plane strain, this method appears rapidly convergent, as verified in the Tresca compressed bar problem. Then the method is applied to the classical problem of the stability factor of a Tresca vertical slope: the upper bound is lowered from 3.882 to 3.7778. This value is to be compared to the lower bound just increased from 3.772 to 3.7752 by using the same solver in the extension of the method to the statical decomposition problem with infinite elements.
In the present work a modified phenomenological model of the shape memory alloy (SMA) constitutiv... more In the present work a modified phenomenological model of the shape memory alloy (SMA) constitutive law is proposed that is capable of reproducing some aspects of SMA thermomechanical behavior like superelasticity and the one-way shape memory effect. The modified law uses strain and temperature as control variables, which eliminates the need for transformation correctors in finite element analysis. It is
The purpose of the present study is to propose a strategy for identifying the mechanical characte... more The purpose of the present study is to propose a strategy for identifying the mechanical characteristics of fibers and the damage in composite materials, based on an inverse method coupled with homogenization. It consists, in a general and systematic way, in coupling a homogenization procedure chosen by the user, with an appropriate numerical optimization algorithm. The method can be interpreted as a procedure for passage from macroscopic to mesoscopic scale. In this respect, it is shown that our method is capable of providing estimates of mesoscopic properties that are difficult to obtain experimentally. The proposed identification method is applied to examples of damaged and undamaged composites including those made of woven and unwoven natural fibers of Alfa and a polyester resin matrix. Identification results obtained by the proposed inverse method are compared to data taken from the literature to show its effectiveness.
This paper summarizes the application of a rational methodology for the assessment of older reinf... more This paper summarizes the application of a rational methodology for the assessment of older reinforced concrete Tunisian bridges. This methodology is based on ambient vibration measurement of the bridge, identification of the structure's modal signature and finite element model updating. The selected case study is the SidiBouAli river bridge which is an eight-span simply supported bridge with a continuous slab. Each span has a length of 25 m and is supported by rubber bearings at the supports. Ambient vibration tests with output-only measurements were conducted on the bridge using a data acquisition system with nine force-balance accelerometers placed at selected locations of the bridge. The Enhanced Frequency Domain Decomposition technique, known to be robust with respect to the complex non-stationary nature of the unmeasured excitation, was applied to extract the dynamic characteristics of the bridge. For model updating, it was assumed that the parameters that can be changed i...
STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2005; 12:179195 Published... more STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2005; 12:179195 Published online 8 November 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/stc.55 ... Seismic evaluation and innovative ...
ABSTRACT For civil engineering structures, ambient vibration tests are preferred over forced vibr... more ABSTRACT For civil engineering structures, ambient vibration tests are preferred over forced vibration ones because the artificially excitation of large structures having low natural frequencies is quite difficult and expensive. In the ambient vibration tests, operation disturbances can be avoided and the measured response is representative of the actual operating conditions of the structures which vibrate due to natural excitation. The proposed damage identification method is intended for moderate degrees of damage and requires vibration data relative to the current and reference states of the structure as well as a parametric finite element model. It is based on a residual generated from a modal filtering approach by the calculation of the error between the measurements at the current state and their projections onto the incomplete modal basis of the structure as identified at reference state. To detect and locate damage, the residual is evaluated by means of global, sensitivity and rejection tests, modified to allow only physically feasible simple and multiple damage scenarios. The mean of the residual, which turns out to be normally distributed, is used in the final phase of damage quantification. The proposed damage diagnosis method is validated experimentally via ambient vibration tests conducted on full-scale reinforced concrete beams and slabs which contain various simple and multiple damage configurations. With damage expressed in terms of loss of flexural stiffness, the damage detection, localization and quantification are found to be successful for degrees of damage less than about 28% of the initial flexural stiffness of the tested specimens. The exception is that, for multiple damage scenarios, the relative quantification errors may be unacceptable in locations where poor accuracy is expected.
Abstract: This article proposes a rational methodology for the structural assessment of a reinfor... more Abstract: This article proposes a rational methodology for the structural assessment of a reinforced concrete bridge in Tunisia. This methodology is based on ambient vibration measurement of the bridge, identification of its modal signature, finite element model updating and ...
ABSTRACT The goal of the present paper is to improve our understanding of the response of the in-... more ABSTRACT The goal of the present paper is to improve our understanding of the response of the in-plane loaded rectangular plates containing initial geometric imperfection. Besides the frequency responses and FFT curves, which were used as diagnostic tools in previous investigations, the temporal response and the phase diagram have been added to better study the transition zones between two kinds of vibration modes. The phase portrait shows that the plate response has a number of “unusual and perhaps chaotic” characteristics in the transition from one mechanism of vibration of another, which distinguished it from the more classical periodic response. Moreover, the effect of one particular spatial mode of imperfection on a different mode of vibration has been investigated for the first time. It was found that the maximum amplitude of forced vibrations is large when vibration and imperfection are in the same mode while the first mode of vibration is always excited whatever the mode of imperfection is.
ABSTRACT The potential use of Cu-based shape memory alloys (SMA) in retrofitting historical monum... more ABSTRACT The potential use of Cu-based shape memory alloys (SMA) in retrofitting historical monuments is investigated in this paper. This study is part of the ongoing work conducted in Tunisia within the framework of the FP6 European Union project (WIND-CHIME) on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The present investigation consists of a finite element simulation, as a preliminary to an experimental study where a cantilever masonry wall, representing a part of a historical monument, is subjected to monotonic and quasi-static cyclic loadings around a horizontal axis at the base level. The wall was retrofitted with an array of copper SMA wires with different cross-sectional areas. A new model is proposed for heat-treated copper SMAs and is validated based on published experimental results. A series of nonlinear finite element analyses are then performed on the wall for the purpose of assessing the SMA device retrofitting capabilities. Simulation results show an improvement of the wall response for the case of monotonic and quasi-static cyclic loadings.
In order to describe the macroscopic behavior of granular media, a statistical micro to macro lev... more In order to describe the macroscopic behavior of granular media, a statistical micro to macro level transition model is first developed, based on Jaynes' principle of maximum entropy. The model formulation translates into a strictly convex, nonlinear optimization problem. It is tested by solving model examples of two dimensional granular structures. Next, a Lagrangian dual formulation of the maximum entropy
Directional drilling with water jet is an increasingly utilized technique in oil industry. Howeve... more Directional drilling with water jet is an increasingly utilized technique in oil industry. However, prediction of the dynamics of water jet drilling tubes is difficult because of the multiplicity of interacting and often complex phenomena that govern their behaviour. Indeed, This highly nonlinear dynamic problem involves fluid structure interaction, dynamic instability and unilateral contact. Simulation tools help improve understanding of
ABSTRACT The behavior of soils reinforced by micropile networks is still not fully understood due... more ABSTRACT The behavior of soils reinforced by micropile networks is still not fully understood due to the lack of accurate modelling capabilities. Particularly, the complex geometry of large soil-micropile systems makes accurate calculation of the bearing capacity of the reinforced soil a computational challenge. This complexity requires highly detailed and finely discretized models to achieve reasonable accuracy using direct numerical methods. Such models lead to large scale numerical optimization problems that are hardly tractable using a personal computer. Recently a decomposition strategy with domain overlap has proved successful in solving very large kinematic and static limit analysis problems with limited computing resources. It consists of splitting the original problem into limit analysis subproblems that are smaller in size. The present paper reports enhancements made to the original decomposition method. In particular, the method is made capable of solving the classical punch problem with Tresca or Coulomb soils. This benchmark problem is considered as a limit case of a soil reinforced by micropiles. The paper then describes the application of the decomposition method to determine rigorous kinematic and static bounds to the bearing capacity of a soil reinforced by a micropile group according to a 2D plane strain model.
ABSTRACT A new algorithm for solving the duals of separable convex optimization problems is prese... more ABSTRACT A new algorithm for solving the duals of separable convex optimization problems is presented. The algorithm is based on an active set strategy in conjunction with a variable metric method. This first order algorithm is more reliable than Newton's method used in DUAL-2 because it does not break down when the Hessian matrix becomes singular or nearly singular. A perturbation technique is introduced in order to remove the nondifferentiability of the dual function which arises when linear constraints are present in the approximate problem.
ABSTRACT A decomposition approach of the kinematical method of limit analysis is first presented.... more ABSTRACT A decomposition approach of the kinematical method of limit analysis is first presented. It is based on a mixed variational approach and on a convex interior point solver, using linear or quadratic discontinuous velocity fields. Exposed in plane strain, this method appears rapidly convergent, as verified in the Tresca compressed bar problem. Then the method is applied to the classical problem of the stability factor of a Tresca vertical slope: the upper bound is lowered from 3.882 to 3.7778. This value is to be compared to the lower bound just increased from 3.772 to 3.7752 by using the same solver in the extension of the method to the statical decomposition problem with infinite elements.
In the present work a modified phenomenological model of the shape memory alloy (SMA) constitutiv... more In the present work a modified phenomenological model of the shape memory alloy (SMA) constitutive law is proposed that is capable of reproducing some aspects of SMA thermomechanical behavior like superelasticity and the one-way shape memory effect. The modified law uses strain and temperature as control variables, which eliminates the need for transformation correctors in finite element analysis. It is
The purpose of the present study is to propose a strategy for identifying the mechanical characte... more The purpose of the present study is to propose a strategy for identifying the mechanical characteristics of fibers and the damage in composite materials, based on an inverse method coupled with homogenization. It consists, in a general and systematic way, in coupling a homogenization procedure chosen by the user, with an appropriate numerical optimization algorithm. The method can be interpreted as a procedure for passage from macroscopic to mesoscopic scale. In this respect, it is shown that our method is capable of providing estimates of mesoscopic properties that are difficult to obtain experimentally. The proposed identification method is applied to examples of damaged and undamaged composites including those made of woven and unwoven natural fibers of Alfa and a polyester resin matrix. Identification results obtained by the proposed inverse method are compared to data taken from the literature to show its effectiveness.
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Papers by H. Smaoui