Paolo Franchin | Università degli Studi "La Sapienza" di Roma (original) (raw)
Papers by Paolo Franchin
Earthquake Spectra, 2014
This study focuses on the evaluation of the seismic vulnerability of the Italian roadway bridge s... more This study focuses on the evaluation of the seismic vulnerability of the Italian roadway bridge stock, within the framework of a Civil Protection sponsored project. A comprehensive database of existing bridges (17,000 bridges with different level of knowledge) was implemented. At the core of the study stands a procedure for automatically carrying out state-of-the-art analytical evaluation of fragility curves for two performance levels—damage and collapse—on an individual bridge basis. A WebGIS was developed to handle data and results. The main outputs are maps of bridge seismic risk (from the fragilities and the hazard maps) at the national level and real-time scenario damage-probability maps (from the fragilities and the scenario shake maps). In the latter case, the WebGIS also performs network analysis to identify routes to be followed by rescue teams. Consistency of the fragility derivation over the entire bridge stock is regarded as a major advantage of the adopted approach.
Journal of Engineering Mechanics-asce, 2004
The assessment of safety for structures subjected to earthquake excitation is a time-variant reli... more The assessment of safety for structures subjected to earthquake excitation is a time-variant reliability problem whose practical solution, when the structure behaves inelastically and uncertainty in the mechanical parameters is taken into account, is traditionally sought by ...
Earthquake Engineering & Structural Dynamics, 2007
Journal of Earthquake Engineering, 2010
Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In ord... more Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In order to take into account the uncertainty in the knowledge of structural properties, EC8-3 defines, analogously to the ordinary material partial factors, an adjustment factor, called “confidence factor (CF),” whose value depends on the level of knowledge (KL) of properties such as geometry, reinforcement layout and detailing, and materials. This solution is plausible from a logical point of view but it cannot yet profit from the experience of its use in practice, hence it needs to be substantiated by a higher level probabilistic analysis accounting for and propagating epistemic uncertainty (i.e., incomplete knowledge of a structure) throughout the seismic assessment procedure. This article investigates the soundness of the format proposed in EC8-3. The approach taken rests on the simulation of the entire assessment procedure and the evaluation of the distribution of the assessment results (distance from the limit state of interest) conditional on the acquired knowledge. Based on this distribution, a criterion is employed to calibrate the CF values. The obtained values are then critically examined and compared with code-specified ones. The results pinpoint a number of deficiencies that appear to somewhat invalidate the approach. The methodological significance of the work extends beyond the assessment procedure in EC8-3, since similar factors appear in other international guidelines (e.g., the knowledge factor of FEMA356).
Probabilistic Engineering Mechanics, 2002
Thin-walled Structures, 2000
Journal of Earthquake Engineering, 2008
The vector-valued ground motion intensity measure (IM) consisting of spectral acceleration at two... more The vector-valued ground motion intensity measure (IM) consisting of spectral acceleration at two different periods is considered for seismic risk assessment of structures. The first component of the IM is the spectral acceleration at the first-mode structural period T 1. The second period is selected to increase efficiency in the estimation of seismic risk (i.e., minimizing dispersion). A method to assess vector structural fragility using a scalar global measure of structural performance is proposed. With reference to an example RC frame structure, the accuracy of prediction of the seismic risk using the considered vector IM vs. a conventional scalar IM is presented. In both cases, probabilistic seismic hazard analysis (scalar and vector) is carried out by means of a subset simulation approach that employs a stochastic model of ground motion. Results show that an effective choice of the second period T2 leads to an estimate of the seismic risk close to that obtained employing the scalar IM consisting of Sa(T1) only, while reducing the associated dispersion in the estimate. For the examined example structure, however, the reduction is negligible in light of the effort required for switching from a scalar to a vector IM.
Journal of Earthquake Engineering, 2006
This paper presents a probabilistic method for seismic loss estimation. The method accounts for t... more This paper presents a probabilistic method for seismic loss estimation. The method accounts for the dependence of the structural response on the ground-motion and on the mechanical properties through an approximate response model based on a limited number of nonlinear structural analyses using recorded ground-motions. This response model is the key element in keeping affordable the procedure that uses simulation to compute the distribution of monetary loss. The main advantage of the formulation is that all sources of uncertainty and correlation among loss terms are accounted for. The procedure is illustrated by way of an application to an RC arch bridge. The application highlights the need for further research on models that describe states of increasing damage in terms of repair actions.
Journal of Earthquake Engineering, 2010
The last 15 years have seen fundamental advances in both the definition of the hazard and on the ... more The last 15 years have seen fundamental advances in both the definition of the hazard and on the criteria in codified seismic design, creating a situation whereby even relatively modern constructions may represent an unchecked risk. This article deals with a case of particular relevance, i.e., the seismic risk of bridges and viaducts on the Italian highway network. After a brief outline of the present state of the network, the article concentrates on the solutions adopted in the upgrading, for increasing both the traffic and the seismic capacities, through the illustration of two case studies. The second, main part of the article deals in more detail with one of the case studies, examining alternative design options and the corresponding analytical aspects. Finally, the opportunity is taken to investigate the relevance of two aspects not commonly taken into account in design practice, i.e., differential support motion and soil-structure interaction.
Journal of Earthquake Engineering, 2002
The core of the paper consists of the illustration of a method for seismic reliability analysis o... more The core of the paper consists of the illustration of a method for seismic reliability analysis of non-linear structures. The method, which is a development over a recent previous proposal, is quite comprehensive in scope since it includes consideration of randomness in the input, in the mechanical properties of the structure and in the limit-state, or capacity, conditions. Essentially, the problem is formulated as the out-crossing of the response process out of a (scalar) safe threshold, and this problem is solved by time-invariant FORM methods. An application to an idealised five-storey building demonstrates the salient theoretical and computational features of the method. The new approach is presented in a broader framework, which involves a discussion on present trends and capabilities in the area of probabilistic seismic design. For the sake of this discussion, two approaches just appeared in the literature are outlined, which are less demanding from a theoretical standpoint, and hence closer to engineering practice, but also less general in scope. It is argued that their introduction on code-assisted design would be feasible immediately with obvious advantages, while approaches of more rigorous nature would be given some more time to mature and to become more accessible to professional use.
Journal of Earthquake Engineering, 2003
A statistical approach for time-variant system-reliability problems has been developed and invest... more A statistical approach for time-variant system-reliability problems has been developed and investigated in this study. The basic proposal is to use a response surface, characterised by a statistical model of the mixed type, to represent the capacity part in an analytical limit state function. The fragility of the system is then calculated by SORM analysis, with the constructed empirical limit state function as input. The developed method has been applied to a reinforced concrete frame: investigations have been carried out to check the stability and accuracy of the suggested procedure.
Journal of Earthquake Engineering, 2009
A criterion is proposed for deciding whether, after a damaging mainshock, a bridge can still be o... more A criterion is proposed for deciding whether, after a damaging mainshock, a bridge can still be open for either emergency or ordinary traffic. The criterion is based on the comparison between the collapse risk of the mainshock-damaged structure and the pre-mainshock risk of the intact structure. The approach requires fragilities for multiple damage states for the intact structure, and transition probabilities from these states to collapse for the damaged structure. The aftershock risk decreases with time, hence a decision for reopening might have to wait until the risk level goes down to an acceptable value. A realistic application demonstrates the approach.
Earthquake Engineering & Structural Dynamics, 2003
In this work a probabilistic methodology, recently developed by Cornell and co-workers for seismi... more In this work a probabilistic methodology, recently developed by Cornell and co-workers for seismic risk assessment of moment-resisting steel frames, is investigated for possible applications to RC bridge structures. The basic theory is first illustrated; it is characterized by a remarkably simple but accurate mathematical formulation and by a light computational effort to estimate the risk. A simple extension to account for uncertainties in the mechanical parameters is then proposed. The methodology is applied to an existing RC bridge. The study has confirmed the robustness of the methodology with respect to the simplifying assumptions on which it is based, in particular to the reduced number of accelerograms required for a stable and accurate estimate of risk, and demonstrates the applicability to the case of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd.
The chapter presents an overview of recent research on the seismic assessment/retrofit and design... more The chapter presents an overview of recent research on the seismic assessment/retrofit and design of bridges, focussing on some of the aspects which are still not adequately covered in the codes. These are: The level of protection to be provided when upgrading an existing bridge, and in particular whether this should be differentiated between new designs and retrofit of existing bridges; The appropriate methods of analysis and modelling, with emphasis on the scope of nonlinear static methods and to the problems related to the selection of the input for dynamic analysis; Soil-foundation-structure interaction and non uniform support input, representing two controversial issues that may be mature for an inclusion in routine bridge analysis.
Structural Safety, 2004
A statistical approach for time-variant system reliability problems is developed and investigated... more A statistical approach for time-variant system reliability problems is developed and investigated. The basic proposal is to use a response surface, characterised by a statistical model of the mixed type, to represent the capacity in an analytical limit-state function. The ...
Journal of Engineering Mechanics-asce, 2006
Earthquake Spectra, 2014
This study focuses on the evaluation of the seismic vulnerability of the Italian roadway bridge s... more This study focuses on the evaluation of the seismic vulnerability of the Italian roadway bridge stock, within the framework of a Civil Protection sponsored project. A comprehensive database of existing bridges (17,000 bridges with different level of knowledge) was implemented. At the core of the study stands a procedure for automatically carrying out state-of-the-art analytical evaluation of fragility curves for two performance levels—damage and collapse—on an individual bridge basis. A WebGIS was developed to handle data and results. The main outputs are maps of bridge seismic risk (from the fragilities and the hazard maps) at the national level and real-time scenario damage-probability maps (from the fragilities and the scenario shake maps). In the latter case, the WebGIS also performs network analysis to identify routes to be followed by rescue teams. Consistency of the fragility derivation over the entire bridge stock is regarded as a major advantage of the adopted approach.
Journal of Engineering Mechanics-asce, 2004
The assessment of safety for structures subjected to earthquake excitation is a time-variant reli... more The assessment of safety for structures subjected to earthquake excitation is a time-variant reliability problem whose practical solution, when the structure behaves inelastically and uncertainty in the mechanical parameters is taken into account, is traditionally sought by ...
Earthquake Engineering & Structural Dynamics, 2007
Journal of Earthquake Engineering, 2010
Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In ord... more Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In order to take into account the uncertainty in the knowledge of structural properties, EC8-3 defines, analogously to the ordinary material partial factors, an adjustment factor, called “confidence factor (CF),” whose value depends on the level of knowledge (KL) of properties such as geometry, reinforcement layout and detailing, and materials. This solution is plausible from a logical point of view but it cannot yet profit from the experience of its use in practice, hence it needs to be substantiated by a higher level probabilistic analysis accounting for and propagating epistemic uncertainty (i.e., incomplete knowledge of a structure) throughout the seismic assessment procedure. This article investigates the soundness of the format proposed in EC8-3. The approach taken rests on the simulation of the entire assessment procedure and the evaluation of the distribution of the assessment results (distance from the limit state of interest) conditional on the acquired knowledge. Based on this distribution, a criterion is employed to calibrate the CF values. The obtained values are then critically examined and compared with code-specified ones. The results pinpoint a number of deficiencies that appear to somewhat invalidate the approach. The methodological significance of the work extends beyond the assessment procedure in EC8-3, since similar factors appear in other international guidelines (e.g., the knowledge factor of FEMA356).
Probabilistic Engineering Mechanics, 2002
Thin-walled Structures, 2000
Journal of Earthquake Engineering, 2008
The vector-valued ground motion intensity measure (IM) consisting of spectral acceleration at two... more The vector-valued ground motion intensity measure (IM) consisting of spectral acceleration at two different periods is considered for seismic risk assessment of structures. The first component of the IM is the spectral acceleration at the first-mode structural period T 1. The second period is selected to increase efficiency in the estimation of seismic risk (i.e., minimizing dispersion). A method to assess vector structural fragility using a scalar global measure of structural performance is proposed. With reference to an example RC frame structure, the accuracy of prediction of the seismic risk using the considered vector IM vs. a conventional scalar IM is presented. In both cases, probabilistic seismic hazard analysis (scalar and vector) is carried out by means of a subset simulation approach that employs a stochastic model of ground motion. Results show that an effective choice of the second period T2 leads to an estimate of the seismic risk close to that obtained employing the scalar IM consisting of Sa(T1) only, while reducing the associated dispersion in the estimate. For the examined example structure, however, the reduction is negligible in light of the effort required for switching from a scalar to a vector IM.
Journal of Earthquake Engineering, 2006
This paper presents a probabilistic method for seismic loss estimation. The method accounts for t... more This paper presents a probabilistic method for seismic loss estimation. The method accounts for the dependence of the structural response on the ground-motion and on the mechanical properties through an approximate response model based on a limited number of nonlinear structural analyses using recorded ground-motions. This response model is the key element in keeping affordable the procedure that uses simulation to compute the distribution of monetary loss. The main advantage of the formulation is that all sources of uncertainty and correlation among loss terms are accounted for. The procedure is illustrated by way of an application to an RC arch bridge. The application highlights the need for further research on models that describe states of increasing damage in terms of repair actions.
Journal of Earthquake Engineering, 2010
The last 15 years have seen fundamental advances in both the definition of the hazard and on the ... more The last 15 years have seen fundamental advances in both the definition of the hazard and on the criteria in codified seismic design, creating a situation whereby even relatively modern constructions may represent an unchecked risk. This article deals with a case of particular relevance, i.e., the seismic risk of bridges and viaducts on the Italian highway network. After a brief outline of the present state of the network, the article concentrates on the solutions adopted in the upgrading, for increasing both the traffic and the seismic capacities, through the illustration of two case studies. The second, main part of the article deals in more detail with one of the case studies, examining alternative design options and the corresponding analytical aspects. Finally, the opportunity is taken to investigate the relevance of two aspects not commonly taken into account in design practice, i.e., differential support motion and soil-structure interaction.
Journal of Earthquake Engineering, 2002
The core of the paper consists of the illustration of a method for seismic reliability analysis o... more The core of the paper consists of the illustration of a method for seismic reliability analysis of non-linear structures. The method, which is a development over a recent previous proposal, is quite comprehensive in scope since it includes consideration of randomness in the input, in the mechanical properties of the structure and in the limit-state, or capacity, conditions. Essentially, the problem is formulated as the out-crossing of the response process out of a (scalar) safe threshold, and this problem is solved by time-invariant FORM methods. An application to an idealised five-storey building demonstrates the salient theoretical and computational features of the method. The new approach is presented in a broader framework, which involves a discussion on present trends and capabilities in the area of probabilistic seismic design. For the sake of this discussion, two approaches just appeared in the literature are outlined, which are less demanding from a theoretical standpoint, and hence closer to engineering practice, but also less general in scope. It is argued that their introduction on code-assisted design would be feasible immediately with obvious advantages, while approaches of more rigorous nature would be given some more time to mature and to become more accessible to professional use.
Journal of Earthquake Engineering, 2003
A statistical approach for time-variant system-reliability problems has been developed and invest... more A statistical approach for time-variant system-reliability problems has been developed and investigated in this study. The basic proposal is to use a response surface, characterised by a statistical model of the mixed type, to represent the capacity part in an analytical limit state function. The fragility of the system is then calculated by SORM analysis, with the constructed empirical limit state function as input. The developed method has been applied to a reinforced concrete frame: investigations have been carried out to check the stability and accuracy of the suggested procedure.
Journal of Earthquake Engineering, 2009
A criterion is proposed for deciding whether, after a damaging mainshock, a bridge can still be o... more A criterion is proposed for deciding whether, after a damaging mainshock, a bridge can still be open for either emergency or ordinary traffic. The criterion is based on the comparison between the collapse risk of the mainshock-damaged structure and the pre-mainshock risk of the intact structure. The approach requires fragilities for multiple damage states for the intact structure, and transition probabilities from these states to collapse for the damaged structure. The aftershock risk decreases with time, hence a decision for reopening might have to wait until the risk level goes down to an acceptable value. A realistic application demonstrates the approach.
Earthquake Engineering & Structural Dynamics, 2003
In this work a probabilistic methodology, recently developed by Cornell and co-workers for seismi... more In this work a probabilistic methodology, recently developed by Cornell and co-workers for seismic risk assessment of moment-resisting steel frames, is investigated for possible applications to RC bridge structures. The basic theory is first illustrated; it is characterized by a remarkably simple but accurate mathematical formulation and by a light computational effort to estimate the risk. A simple extension to account for uncertainties in the mechanical parameters is then proposed. The methodology is applied to an existing RC bridge. The study has confirmed the robustness of the methodology with respect to the simplifying assumptions on which it is based, in particular to the reduced number of accelerograms required for a stable and accurate estimate of risk, and demonstrates the applicability to the case of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd.
The chapter presents an overview of recent research on the seismic assessment/retrofit and design... more The chapter presents an overview of recent research on the seismic assessment/retrofit and design of bridges, focussing on some of the aspects which are still not adequately covered in the codes. These are: The level of protection to be provided when upgrading an existing bridge, and in particular whether this should be differentiated between new designs and retrofit of existing bridges; The appropriate methods of analysis and modelling, with emphasis on the scope of nonlinear static methods and to the problems related to the selection of the input for dynamic analysis; Soil-foundation-structure interaction and non uniform support input, representing two controversial issues that may be mature for an inclusion in routine bridge analysis.
Structural Safety, 2004
A statistical approach for time-variant system reliability problems is developed and investigated... more A statistical approach for time-variant system reliability problems is developed and investigated. The basic proposal is to use a response surface, characterised by a statistical model of the mixed type, to represent the capacity in an analytical limit-state function. The ...
Journal of Engineering Mechanics-asce, 2006