ABSTRACT The reliability of structural systems, lying in aggressive environments, changes over ti... more ABSTRACT The reliability of structural systems, lying in aggressive environments, changes over time. Proper maintenance is usually required to achieve a suitable performance level of life-cycle. The damage process affecting the systems often suffers from uncertainty due to the randomness involved in each environmental attack. Therefore, basing on suitable damage modeling as well as on probabilistic analysis, the main features of time-variant deterioration process are modeled and then the life-cycle is assessed.
Abstract A modern conceptual design of a bridge structure should be open to wider criteria, which... more Abstract A modern conceptual design of a bridge structure should be open to wider criteria, which assure that the structure is endowed with static, dynamic and ductile characteristics sufficient to tackle the seismic events. For the satisfaction of these requirements and for the exploration and the verification of innovative structural schemes, one must consider refined and subtle analysis formulations and tools. Such a kind of structural scheme is based on the two-blade slender bridge piers.
ABSTRACT: This paper presents a probabilistic model for the service life assessment of bridge det... more ABSTRACT: This paper presents a probabilistic model for the service life assessment of bridge deteriorating truss. Damage evolution of each structural member is dealt as a transition process through different states of performance. The transition process is modeled as a Markovian renewal process which formulation allows considering eventual improvements of the structural performance. In this way, the model is used to set up selective maintenance and/or rehabilitation interventions.
ABSTRACT: During the last decades the excessive deflections of many long span bridges received wi... more ABSTRACT: During the last decades the excessive deflections of many long span bridges received wide attention both in the research and maintenance fields. The faults of the original previsions can be attributed to (a) lacks in the models adopted for the structural assessment,(b) weak reliability of some shrinkage and creep formulations used for the analyses and (c) differences between the phases of the actual erection techniques and those planned during the design tasks.
ABSTRACT: Since its initial development, the Artificial Intelligence has found large applicabilit... more ABSTRACT: Since its initial development, the Artificial Intelligence has found large applicability in the filed of engineering. In particular, the so-called soft computing methods, have been shown to be very effective in the analysis and solution of ill-structured problems. This text examines the historical development of this discipline, with particular reference to the long span suspension bridges analysis.
Dopo alcuni richiami sulla stabilità degli archi, il problema viene specializzato a tre diversi s... more Dopo alcuni richiami sulla stabilità degli archi, il problema viene specializzato a tre diversi sistemi, caratterizzati da differenti rapporti di ribassamento f/L. ciascuno di tali sistemi possiede lo stesso vincolo orizzontale cedevole, che vuole simulare il comportamento di una palificata. Per tener conto delle incertezze associate a tali strutture, la rigidezza del vincolo a terra è considerata aleatoria ed è descritta da una distribuzione gaussiana. Mediante simulazioni Monte Carlo vengono ricavati i percorsi di equilibrio associati ad ogni singola rigidezza. Come ente della simulazione si assume il primo punto limite del percorso di equilibrio. Si costruisce in tal modo la statistica dei moltiplicatori di carico. I risultati ottenuti consentono di valutare gli effetti sia del ribassamento dell’arco sia delle incertezze di vincolo.
Two-blade bridge piers represent today an innovative solution to optimize the structural behavior... more Two-blade bridge piers represent today an innovative solution to optimize the structural behavior of long viaducts subjected to seismic actions. In fact, a proper design of the structure provides a correct transmission of vertical loads to the foundation structures and the possibility to allow horizontal displacements without the use of kinematics mechanisms. Due to the particular configuration of the pier (a rigid box section in the bottom part and two flexible blades at the top connected with the viaduct deck), the structural behavior can be achieved only using refined analysis formulations and effective numerical tools. In particular, during the nonlinear response, the shear effects are very important and can govern the structural behavior. Nonlinear models have to be able to consider the shear damaging with sufficient accuracy otherwise, the numerical response would be affected by heavy errors. In addition, uncertainties on material characteristics can affect the numerical response. To handle these important uncertainties involved in the problem, the use of probabilistic or fuzzy approaches can be suitable. In this paper, to show the influence of the degradation on the structural response a new and a damaged two-blade pier will be analyzed. Probabilistic evaluation of the material properties are considered to improve the reliability of the numerical analyses. The aim of the paper is to show the importance of a reliable modeling of the damaged zone.
In this work are presented applications for the design of reinforced concrete structures using th... more In this work are presented applications for the design of reinforced concrete structures using the Stringer Panel Method (S&PM); a discrete model which divided a structure into elementary subsystem working in tension or compression (stringers) and in membrane shear stress (panels). Stringers are dimensioned for normal forces, panels for shear forces. A simple beam and a squat cantilever is studied, and is shown as the S&PM is able to get the right global and local results in this two antithetical cases.
This paper deal with analysis and design of the long suspension bridge. In particular the design ... more This paper deal with analysis and design of the long suspension bridge. In particular the design of transversal and longitudinal devices is developed. The seismic analysis, developed under 400 earthquake simulations, shows the dynamical behavior of the bridge.
In many typical R.C. applications, the reinforcing bars along certain alignments must be maintain... more In many typical R.C. applications, the reinforcing bars along certain alignments must be maintained continuous. Such continuity is usually obtained through overlapping arrangements and suitable end bents of the bars. In the more critical contests, like in the case of buildings in seismic areas, more reliable continuity solutions are required. The same holds for blast scenarios. To this purpose a new type of coupling device assuring the bar continuity has been recently proposed. This device is made of a steel external shell, which encloses a certain volume around the bars to be connected. The interstitial volume is filled by VHS Concrete which embeds the bar and assures the continuity with the steel envelope. To assess the efficiency of this new device, many experimental tests were performed. In particular, it was analyzed the behavior under cyclic loading of columns having different height connected to the foundation structure by these continuity devices and the behavior of a beam-column junction. This paper presents the analysis for the investigations of the behavior of a precast column having section 0.5 x 0.5 meters and 5 meters high. Both experimental and numerical results are presented with particular attention to the definition of the numerical model.
The behavior of pre-stressed and of cable stayed concrete bridges may be strongly affected by the... more The behavior of pre-stressed and of cable stayed concrete bridges may be strongly affected by the time dependent response due to the creep and shrinkage of concrete. The assessment of safety and serviceability performance of these structures during their whole service life requires a reliable estimation of the influence of these phenomena. The conventional design of pre-stress losses and, in general, of the time dependent behavior of non homogeneous structures, like cable stayed bridges, uses tools of analysis which involve many uncertain quantities, such as environmental factors, the material characteristics and the intensities of the tension in cables. Also construction imperfections may strongly influence the final structural response. After some brief recalls regarding the time dependent analysis in presence of creep and shrinkage, this paper studies, through a probabilistic approach, the effects due to a large variations of the basic variables. Two cases are studied: the first one is less sensitive to uncertain data, while the second is strongly affected by them. In the case of a cable stayed bridge, made of a concrete deck, subjected to creep effects and suspended to a set of pretensioned cables, the role of uncertainties in the pretensioning forces, in the relative humidity and in the concrete strength do not influence the time dependent behavior sensibly. The standard deviation with respect to the mean tension in the cables is relatively small and, most of all, it progressively reduces. Hence the system seems to be self-stabilizing over time. On the contrary, in the case of a prestressed cantilever beam, the effects of uncertainties in the pretensioning forces and in the concrete strength cause a significant variance of the tip deflections. Both deflections and their variance increase over time and, speaking about bridges, they may strongly modify the vertical attitude of the structure. These effects are emphasized when the prestressing is applied a few days after curing. Such results outline the limits of the traditional deterministic analyses and suggest the need of further studies on this topic.
In questo lavoro si descrive un’applicazione del calcolo di edifici monopiano industriali in acci... more In questo lavoro si descrive un’applicazione del calcolo di edifici monopiano industriali in acciaio con il metodo plastico. Tale metodo, già da tempo previsto dall’EC3-1-1, è stato recentemente inserito tra i possibili metodi d’analisi dei telai in acciaio dalle nuove Norme Tecniche delle Costruzioni (NTC). Per alcune tipologie di telaio in acciaio, come ad esempio quella monopiano, il metodo porta a delle economie di progetto come da tempo dimostrato nel Regno Unito dove rappresenta, in questi casi, l’unico metodo di calcolo utilizzato. L’analisi evolutiva, utilizzata nel lavoro, permette di mettere in evidenza la sequenza di formazione delle cerniere plastiche sino a collasso, fornendo utili suggerimenti progettuali a riguardo di alcuni particolari costruttivi (vincoli torsionali e rinforzi nodali) che divengono necessari con questo metodo di progettazione. L’influenza degli effetti del secondo ordine è valutata attraverso un fattore amplificativo, come suggerito dall’EC3-1-1 nel caso di modeste azioni verticali. In ultimo, viene riportato uno studio comparato su tre differenti edifici monopiano, allo scopo di mettere in luce quali edifici possono effettivamente trarre vantaggio da questo metodologia. Una versione più estesa di questo lavoro, comprendente tutte le verifiche di dettaglio del caso, è riportata in (Colombi & Sgambi, 2008).
For advanced systems, like long span suspension bridges, it is necessary to set the global design... more For advanced systems, like long span suspension bridges, it is necessary to set the global design process in the philosophy of the Performance-based design (P.B.D.), rather than in the conventional prescriptive-based design. In this work a performance approach to the design problem is represented dividing the general treatment of this subject in two points: one related to the performance approach applied to the Messina Strait Bridge, the other related to the modeling phase.
This paper deals with the seismic analisys of long suspension bridge. The passive control devices... more This paper deals with the seismic analisys of long suspension bridge. The passive control devices of the bridge was optimized using a multiobjective criterion considering static and kinematics parameters. Many asynchronous analyses was developed in order to consider the uncertainties involved in the seismic input.
This paper studies analytical modeling of reinforced concrete (RC) structures subjected to cyclic... more This paper studies analytical modeling of reinforced concrete (RC) structures subjected to cyclic loading. Special attention must be given to nonlinear material behavior when RC structures are subjected to cyclic loading. The material nonlinearity is due to characteristics such as: concrete orthotropic behavior, non symmetric material resistance (compression–tension), opening and closing cracks, and tension stiffening. In order to reliably predict the response of RC structures, the elements and the constitutive laws used in the analytical models must be able to properly account for these characteristics. In this paper, a three-dimensional generalization of a membrane constitutive law [1] is used to model concrete cyclic behavior. The constitutive law is a rotating crack model, which considers concrete orthotropic behavior in each phase of loading (loading, unloading and reloading). The model is able to estimate, with good accuracy, the response of concrete under generic cyclic loads, accounting for opening and closing cracks. The material law has been implemented in a finite element program with an explicit formulation. Using the program, cyclic response of a structural wall is calculated and compared with the corresponding experimental results and a good agreement is achieved.
Loosening of cemented femoral hip component is one of the major failure mode in cemented total hi... more Loosening of cemented femoral hip component is one of the major failure mode in cemented total hip arthroplasty. The stem-cement and bone-cement interface conditions strongly influence the load transfer mechanism in the implant system and then the stress distribution in the bone, the stem and cement mantle. Non linear Coulomb friction model was often used in the literature to study the stem-cement interface. On the other hand the bone-cement interface was usually considered to be bonded and a tissue layer between the bone and the cement was introduced to model the long term behaviour of a total hip arthroplasty. More recently, experimental investigations were carried out to study the general mechanical behaviour of the bone-cement interface under tensile or shear loading. Under tensile loading the results showed that the post-yield tensile behaviour contributes substantially to the energy required to produce the failure of the bone-cement interface. Moreover the post-yield behaviour showed a positive correlation with the amount of interdigitation or bone density. The goal of this paper is to introduce a microstructural model based on a continuum damage mechanics for studying the bone-cement interface condition. The present study is limited to the tensile behaviour since more detailed experimental data are available in this particular case. The numerical results show a good agreement with the experimental one and represent a first step toward the study of the bone-cement interface under combined normal and shear loading.
The time dependent behaviour of two elementary structures, one made of a concrete can... more The time dependent behaviour of two elementary structures, one made of a concrete cantilever beam, suspended at the tip by a pretensioned stay, and the other made of a concrete cantilever beam, post-tensioned through a horizontal cable, has been studied. After a short recall, which would outline how a suitable stay pretensioning or a suitable cable post tensioning, may balance the deflections due to selfweight only under elastic hypotheses, the effects of creep on the tip vertical displacement and on the tension in stay are studied. The influence on such effects, due to different stay slopes, is discussed. As well known, the data needed for these analyses involve many uncertain quantities. Thus, in a second part of the paper, through a probabilistic approach, the effects due to large variations of the tension in the cable are studied. On the basis of the achieved results, we can distinguish between two different kinds of structures: those which have a low sensitivity and those which are greatly affected both by creep effects and by uncertainties.
Benché sia forse il materiale da costruzione più diffuso, il comportamento delle strutture in cal... more Benché sia forse il materiale da costruzione più diffuso, il comportamento delle strutture in calcestruzzo armato in campo non lineare presenta ancora diversi aspetti di non facile comprensione e modellazione. In questo lavoro si vuole eseguire una panoramica sullo sviluppo dei modelli matematici atti a definire il comportamento di questo materiale, analizzando i legami costitutivi presenti nei più diffusi codici di calcolo commerciali. Una serie di test sono eseguiti allo scopo di confrontare differenti codici di calcolo sulla loro capacità di riprodurre i classici domini di rottura (in regime uniassiale, biassiale e triassiale). Un esempio finale, su di una trave a shed dalla geometria complicata, mette in evidenza le capacità di modellazione numerica dei moderni software.
Nella normale progettazione, strutture “complicate” vengono modellate con teorie “semplificative”... more Nella normale progettazione, strutture “complicate” vengono modellate con teorie “semplificative” in grado di fornire risultati di interesse ingegneristico con un minimo dispendio di energia. Elementi di trave, di membrana, di guscio sono il prodotto di teorie che semplificano il problema reale tridimensionale. I risultati ottenuti con tali teorie possono ritenersi accettabili se la struttura fisica ricade nelle ipotesi alla base delle teorie assunte nella costruzione del modello matematico, ma possono portare ad errori non trascurabili se le ipotesi semplificative non sono soddisfatte nella loro interezza. Analizzare il problema nella sua tridimensionalità significa introdurre meno ipotesi nel modello matematico utilizzato per descrivere il reale comportamento della struttura, a fronte di un maggiore impegno macchina.
ABSTRACT The reliability of structural systems, lying in aggressive environments, changes over ti... more ABSTRACT The reliability of structural systems, lying in aggressive environments, changes over time. Proper maintenance is usually required to achieve a suitable performance level of life-cycle. The damage process affecting the systems often suffers from uncertainty due to the randomness involved in each environmental attack. Therefore, basing on suitable damage modeling as well as on probabilistic analysis, the main features of time-variant deterioration process are modeled and then the life-cycle is assessed.
Abstract A modern conceptual design of a bridge structure should be open to wider criteria, which... more Abstract A modern conceptual design of a bridge structure should be open to wider criteria, which assure that the structure is endowed with static, dynamic and ductile characteristics sufficient to tackle the seismic events. For the satisfaction of these requirements and for the exploration and the verification of innovative structural schemes, one must consider refined and subtle analysis formulations and tools. Such a kind of structural scheme is based on the two-blade slender bridge piers.
ABSTRACT: This paper presents a probabilistic model for the service life assessment of bridge det... more ABSTRACT: This paper presents a probabilistic model for the service life assessment of bridge deteriorating truss. Damage evolution of each structural member is dealt as a transition process through different states of performance. The transition process is modeled as a Markovian renewal process which formulation allows considering eventual improvements of the structural performance. In this way, the model is used to set up selective maintenance and/or rehabilitation interventions.
ABSTRACT: During the last decades the excessive deflections of many long span bridges received wi... more ABSTRACT: During the last decades the excessive deflections of many long span bridges received wide attention both in the research and maintenance fields. The faults of the original previsions can be attributed to (a) lacks in the models adopted for the structural assessment,(b) weak reliability of some shrinkage and creep formulations used for the analyses and (c) differences between the phases of the actual erection techniques and those planned during the design tasks.
ABSTRACT: Since its initial development, the Artificial Intelligence has found large applicabilit... more ABSTRACT: Since its initial development, the Artificial Intelligence has found large applicability in the filed of engineering. In particular, the so-called soft computing methods, have been shown to be very effective in the analysis and solution of ill-structured problems. This text examines the historical development of this discipline, with particular reference to the long span suspension bridges analysis.
Dopo alcuni richiami sulla stabilità degli archi, il problema viene specializzato a tre diversi s... more Dopo alcuni richiami sulla stabilità degli archi, il problema viene specializzato a tre diversi sistemi, caratterizzati da differenti rapporti di ribassamento f/L. ciascuno di tali sistemi possiede lo stesso vincolo orizzontale cedevole, che vuole simulare il comportamento di una palificata. Per tener conto delle incertezze associate a tali strutture, la rigidezza del vincolo a terra è considerata aleatoria ed è descritta da una distribuzione gaussiana. Mediante simulazioni Monte Carlo vengono ricavati i percorsi di equilibrio associati ad ogni singola rigidezza. Come ente della simulazione si assume il primo punto limite del percorso di equilibrio. Si costruisce in tal modo la statistica dei moltiplicatori di carico. I risultati ottenuti consentono di valutare gli effetti sia del ribassamento dell’arco sia delle incertezze di vincolo.
Two-blade bridge piers represent today an innovative solution to optimize the structural behavior... more Two-blade bridge piers represent today an innovative solution to optimize the structural behavior of long viaducts subjected to seismic actions. In fact, a proper design of the structure provides a correct transmission of vertical loads to the foundation structures and the possibility to allow horizontal displacements without the use of kinematics mechanisms. Due to the particular configuration of the pier (a rigid box section in the bottom part and two flexible blades at the top connected with the viaduct deck), the structural behavior can be achieved only using refined analysis formulations and effective numerical tools. In particular, during the nonlinear response, the shear effects are very important and can govern the structural behavior. Nonlinear models have to be able to consider the shear damaging with sufficient accuracy otherwise, the numerical response would be affected by heavy errors. In addition, uncertainties on material characteristics can affect the numerical response. To handle these important uncertainties involved in the problem, the use of probabilistic or fuzzy approaches can be suitable. In this paper, to show the influence of the degradation on the structural response a new and a damaged two-blade pier will be analyzed. Probabilistic evaluation of the material properties are considered to improve the reliability of the numerical analyses. The aim of the paper is to show the importance of a reliable modeling of the damaged zone.
In this work are presented applications for the design of reinforced concrete structures using th... more In this work are presented applications for the design of reinforced concrete structures using the Stringer Panel Method (S&PM); a discrete model which divided a structure into elementary subsystem working in tension or compression (stringers) and in membrane shear stress (panels). Stringers are dimensioned for normal forces, panels for shear forces. A simple beam and a squat cantilever is studied, and is shown as the S&PM is able to get the right global and local results in this two antithetical cases.
This paper deal with analysis and design of the long suspension bridge. In particular the design ... more This paper deal with analysis and design of the long suspension bridge. In particular the design of transversal and longitudinal devices is developed. The seismic analysis, developed under 400 earthquake simulations, shows the dynamical behavior of the bridge.
In many typical R.C. applications, the reinforcing bars along certain alignments must be maintain... more In many typical R.C. applications, the reinforcing bars along certain alignments must be maintained continuous. Such continuity is usually obtained through overlapping arrangements and suitable end bents of the bars. In the more critical contests, like in the case of buildings in seismic areas, more reliable continuity solutions are required. The same holds for blast scenarios. To this purpose a new type of coupling device assuring the bar continuity has been recently proposed. This device is made of a steel external shell, which encloses a certain volume around the bars to be connected. The interstitial volume is filled by VHS Concrete which embeds the bar and assures the continuity with the steel envelope. To assess the efficiency of this new device, many experimental tests were performed. In particular, it was analyzed the behavior under cyclic loading of columns having different height connected to the foundation structure by these continuity devices and the behavior of a beam-column junction. This paper presents the analysis for the investigations of the behavior of a precast column having section 0.5 x 0.5 meters and 5 meters high. Both experimental and numerical results are presented with particular attention to the definition of the numerical model.
The behavior of pre-stressed and of cable stayed concrete bridges may be strongly affected by the... more The behavior of pre-stressed and of cable stayed concrete bridges may be strongly affected by the time dependent response due to the creep and shrinkage of concrete. The assessment of safety and serviceability performance of these structures during their whole service life requires a reliable estimation of the influence of these phenomena. The conventional design of pre-stress losses and, in general, of the time dependent behavior of non homogeneous structures, like cable stayed bridges, uses tools of analysis which involve many uncertain quantities, such as environmental factors, the material characteristics and the intensities of the tension in cables. Also construction imperfections may strongly influence the final structural response. After some brief recalls regarding the time dependent analysis in presence of creep and shrinkage, this paper studies, through a probabilistic approach, the effects due to a large variations of the basic variables. Two cases are studied: the first one is less sensitive to uncertain data, while the second is strongly affected by them. In the case of a cable stayed bridge, made of a concrete deck, subjected to creep effects and suspended to a set of pretensioned cables, the role of uncertainties in the pretensioning forces, in the relative humidity and in the concrete strength do not influence the time dependent behavior sensibly. The standard deviation with respect to the mean tension in the cables is relatively small and, most of all, it progressively reduces. Hence the system seems to be self-stabilizing over time. On the contrary, in the case of a prestressed cantilever beam, the effects of uncertainties in the pretensioning forces and in the concrete strength cause a significant variance of the tip deflections. Both deflections and their variance increase over time and, speaking about bridges, they may strongly modify the vertical attitude of the structure. These effects are emphasized when the prestressing is applied a few days after curing. Such results outline the limits of the traditional deterministic analyses and suggest the need of further studies on this topic.
In questo lavoro si descrive un’applicazione del calcolo di edifici monopiano industriali in acci... more In questo lavoro si descrive un’applicazione del calcolo di edifici monopiano industriali in acciaio con il metodo plastico. Tale metodo, già da tempo previsto dall’EC3-1-1, è stato recentemente inserito tra i possibili metodi d’analisi dei telai in acciaio dalle nuove Norme Tecniche delle Costruzioni (NTC). Per alcune tipologie di telaio in acciaio, come ad esempio quella monopiano, il metodo porta a delle economie di progetto come da tempo dimostrato nel Regno Unito dove rappresenta, in questi casi, l’unico metodo di calcolo utilizzato. L’analisi evolutiva, utilizzata nel lavoro, permette di mettere in evidenza la sequenza di formazione delle cerniere plastiche sino a collasso, fornendo utili suggerimenti progettuali a riguardo di alcuni particolari costruttivi (vincoli torsionali e rinforzi nodali) che divengono necessari con questo metodo di progettazione. L’influenza degli effetti del secondo ordine è valutata attraverso un fattore amplificativo, come suggerito dall’EC3-1-1 nel caso di modeste azioni verticali. In ultimo, viene riportato uno studio comparato su tre differenti edifici monopiano, allo scopo di mettere in luce quali edifici possono effettivamente trarre vantaggio da questo metodologia. Una versione più estesa di questo lavoro, comprendente tutte le verifiche di dettaglio del caso, è riportata in (Colombi & Sgambi, 2008).
For advanced systems, like long span suspension bridges, it is necessary to set the global design... more For advanced systems, like long span suspension bridges, it is necessary to set the global design process in the philosophy of the Performance-based design (P.B.D.), rather than in the conventional prescriptive-based design. In this work a performance approach to the design problem is represented dividing the general treatment of this subject in two points: one related to the performance approach applied to the Messina Strait Bridge, the other related to the modeling phase.
This paper deals with the seismic analisys of long suspension bridge. The passive control devices... more This paper deals with the seismic analisys of long suspension bridge. The passive control devices of the bridge was optimized using a multiobjective criterion considering static and kinematics parameters. Many asynchronous analyses was developed in order to consider the uncertainties involved in the seismic input.
This paper studies analytical modeling of reinforced concrete (RC) structures subjected to cyclic... more This paper studies analytical modeling of reinforced concrete (RC) structures subjected to cyclic loading. Special attention must be given to nonlinear material behavior when RC structures are subjected to cyclic loading. The material nonlinearity is due to characteristics such as: concrete orthotropic behavior, non symmetric material resistance (compression–tension), opening and closing cracks, and tension stiffening. In order to reliably predict the response of RC structures, the elements and the constitutive laws used in the analytical models must be able to properly account for these characteristics. In this paper, a three-dimensional generalization of a membrane constitutive law [1] is used to model concrete cyclic behavior. The constitutive law is a rotating crack model, which considers concrete orthotropic behavior in each phase of loading (loading, unloading and reloading). The model is able to estimate, with good accuracy, the response of concrete under generic cyclic loads, accounting for opening and closing cracks. The material law has been implemented in a finite element program with an explicit formulation. Using the program, cyclic response of a structural wall is calculated and compared with the corresponding experimental results and a good agreement is achieved.
Loosening of cemented femoral hip component is one of the major failure mode in cemented total hi... more Loosening of cemented femoral hip component is one of the major failure mode in cemented total hip arthroplasty. The stem-cement and bone-cement interface conditions strongly influence the load transfer mechanism in the implant system and then the stress distribution in the bone, the stem and cement mantle. Non linear Coulomb friction model was often used in the literature to study the stem-cement interface. On the other hand the bone-cement interface was usually considered to be bonded and a tissue layer between the bone and the cement was introduced to model the long term behaviour of a total hip arthroplasty. More recently, experimental investigations were carried out to study the general mechanical behaviour of the bone-cement interface under tensile or shear loading. Under tensile loading the results showed that the post-yield tensile behaviour contributes substantially to the energy required to produce the failure of the bone-cement interface. Moreover the post-yield behaviour showed a positive correlation with the amount of interdigitation or bone density. The goal of this paper is to introduce a microstructural model based on a continuum damage mechanics for studying the bone-cement interface condition. The present study is limited to the tensile behaviour since more detailed experimental data are available in this particular case. The numerical results show a good agreement with the experimental one and represent a first step toward the study of the bone-cement interface under combined normal and shear loading.
The time dependent behaviour of two elementary structures, one made of a concrete can... more The time dependent behaviour of two elementary structures, one made of a concrete cantilever beam, suspended at the tip by a pretensioned stay, and the other made of a concrete cantilever beam, post-tensioned through a horizontal cable, has been studied. After a short recall, which would outline how a suitable stay pretensioning or a suitable cable post tensioning, may balance the deflections due to selfweight only under elastic hypotheses, the effects of creep on the tip vertical displacement and on the tension in stay are studied. The influence on such effects, due to different stay slopes, is discussed. As well known, the data needed for these analyses involve many uncertain quantities. Thus, in a second part of the paper, through a probabilistic approach, the effects due to large variations of the tension in the cable are studied. On the basis of the achieved results, we can distinguish between two different kinds of structures: those which have a low sensitivity and those which are greatly affected both by creep effects and by uncertainties.
Benché sia forse il materiale da costruzione più diffuso, il comportamento delle strutture in cal... more Benché sia forse il materiale da costruzione più diffuso, il comportamento delle strutture in calcestruzzo armato in campo non lineare presenta ancora diversi aspetti di non facile comprensione e modellazione. In questo lavoro si vuole eseguire una panoramica sullo sviluppo dei modelli matematici atti a definire il comportamento di questo materiale, analizzando i legami costitutivi presenti nei più diffusi codici di calcolo commerciali. Una serie di test sono eseguiti allo scopo di confrontare differenti codici di calcolo sulla loro capacità di riprodurre i classici domini di rottura (in regime uniassiale, biassiale e triassiale). Un esempio finale, su di una trave a shed dalla geometria complicata, mette in evidenza le capacità di modellazione numerica dei moderni software.
Nella normale progettazione, strutture “complicate” vengono modellate con teorie “semplificative”... more Nella normale progettazione, strutture “complicate” vengono modellate con teorie “semplificative” in grado di fornire risultati di interesse ingegneristico con un minimo dispendio di energia. Elementi di trave, di membrana, di guscio sono il prodotto di teorie che semplificano il problema reale tridimensionale. I risultati ottenuti con tali teorie possono ritenersi accettabili se la struttura fisica ricade nelle ipotesi alla base delle teorie assunte nella costruzione del modello matematico, ma possono portare ad errori non trascurabili se le ipotesi semplificative non sono soddisfatte nella loro interezza. Analizzare il problema nella sua tridimensionalità significa introdurre meno ipotesi nel modello matematico utilizzato per descrivere il reale comportamento della struttura, a fronte di un maggiore impegno macchina.
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Papers by Luca Sgambi
To assess the efficiency of this new device, many experimental tests were performed. In particular, it was analyzed the behavior under cyclic loading of columns having different height connected to the foundation structure by these continuity devices and the behavior of a beam-column junction.
This paper presents the analysis for the investigations of the behavior of a precast column having section 0.5 x 0.5 meters and 5 meters high. Both experimental and numerical results are presented with particular attention to the definition of the numerical model.
In the case of a cable stayed bridge, made of a concrete deck, subjected to creep effects and suspended to a set of pretensioned cables, the role of uncertainties in the pretensioning forces, in the relative humidity and in the concrete strength do not influence the time dependent behavior sensibly. The standard deviation with respect to the mean tension in the cables is relatively small and, most of all, it progressively reduces. Hence the system seems to be self-stabilizing over time. On the contrary, in the case of a prestressed cantilever beam, the effects of uncertainties in the pretensioning forces and in the concrete strength cause a significant variance of the tip deflections. Both deflections and their variance increase over time and, speaking about bridges, they may strongly modify the vertical attitude of the structure. These effects are emphasized when the prestressing is applied a few days after curing. Such results outline the limits of the traditional deterministic analyses and suggest the need of further studies on this topic.
In this paper, a three-dimensional generalization of a membrane constitutive law [1] is used to model concrete cyclic behavior. The constitutive law is a rotating crack model, which considers concrete orthotropic behavior in each phase of loading (loading, unloading and reloading). The model is able to estimate, with good accuracy, the response of concrete under generic cyclic loads, accounting for opening and closing cracks. The material law has been implemented in a finite element program with an explicit formulation. Using the program, cyclic response of a structural wall is calculated and compared with the corresponding experimental results and a good agreement is achieved.
After a short recall, which would outline how a suitable stay pretensioning or a suitable cable post tensioning, may balance the deflections due to selfweight only under elastic hypotheses, the effects of creep on the tip vertical displacement and on the tension in stay are studied. The influence on such effects, due to different stay slopes, is discussed.
As well known, the data needed for these analyses involve many uncertain quantities. Thus, in a second part of the paper, through a probabilistic approach, the effects due to large variations of the tension in the cable are studied. On the basis of the achieved results, we can distinguish between two different kinds of structures: those which have a low sensitivity and those which are greatly affected both by creep effects and by uncertainties.
To assess the efficiency of this new device, many experimental tests were performed. In particular, it was analyzed the behavior under cyclic loading of columns having different height connected to the foundation structure by these continuity devices and the behavior of a beam-column junction.
This paper presents the analysis for the investigations of the behavior of a precast column having section 0.5 x 0.5 meters and 5 meters high. Both experimental and numerical results are presented with particular attention to the definition of the numerical model.
In the case of a cable stayed bridge, made of a concrete deck, subjected to creep effects and suspended to a set of pretensioned cables, the role of uncertainties in the pretensioning forces, in the relative humidity and in the concrete strength do not influence the time dependent behavior sensibly. The standard deviation with respect to the mean tension in the cables is relatively small and, most of all, it progressively reduces. Hence the system seems to be self-stabilizing over time. On the contrary, in the case of a prestressed cantilever beam, the effects of uncertainties in the pretensioning forces and in the concrete strength cause a significant variance of the tip deflections. Both deflections and their variance increase over time and, speaking about bridges, they may strongly modify the vertical attitude of the structure. These effects are emphasized when the prestressing is applied a few days after curing. Such results outline the limits of the traditional deterministic analyses and suggest the need of further studies on this topic.
In this paper, a three-dimensional generalization of a membrane constitutive law [1] is used to model concrete cyclic behavior. The constitutive law is a rotating crack model, which considers concrete orthotropic behavior in each phase of loading (loading, unloading and reloading). The model is able to estimate, with good accuracy, the response of concrete under generic cyclic loads, accounting for opening and closing cracks. The material law has been implemented in a finite element program with an explicit formulation. Using the program, cyclic response of a structural wall is calculated and compared with the corresponding experimental results and a good agreement is achieved.
After a short recall, which would outline how a suitable stay pretensioning or a suitable cable post tensioning, may balance the deflections due to selfweight only under elastic hypotheses, the effects of creep on the tip vertical displacement and on the tension in stay are studied. The influence on such effects, due to different stay slopes, is discussed.
As well known, the data needed for these analyses involve many uncertain quantities. Thus, in a second part of the paper, through a probabilistic approach, the effects due to large variations of the tension in the cable are studied. On the basis of the achieved results, we can distinguish between two different kinds of structures: those which have a low sensitivity and those which are greatly affected both by creep effects and by uncertainties.