Federico Perotti - Academia.edu (original) (raw)

Papers by Federico Perotti

Research paper thumbnail of On the Estimation of Von Mises Equivalent Stress in Random Vibration Analysis

Research paper thumbnail of Computational aspects in direct frequency domain analysis

Research paper thumbnail of Detailed analysis of a typical overcrossing

Research paper thumbnail of Non linear response of a suspended cable under non stationary excitation

Research paper thumbnail of A Stochastic and Continuous Model of Aeolian Vibrations of Conductors Equipped with Stockbridge Dampers

Suspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to... more Suspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to aeolian vibrations, resulting from the alternate shedding of vortices in the wake of the cable. These vibrations can occur under light to moderate wind and, whenever not properly controlled, can induce wear damage and fatigue failures of the cables. Nonlinear passive control devices such as Stockbridge dampers, hence, are often installed along the line spans to reduce the vibration severity. The technical approach to the assessment of aeolian vibrations is based on the Energy Balance Method (EBM) and relies on the simplifying assumption of mono-modal oscillations. Typical aeolian vibration records, however, clearly show that several modes can be simultaneously excited due to wind variations in time and along the span. Aiming at overcoming the mono-modal vibration assumption of the EBM, in the present paper wind forces are modeled as a narrow band stochastic process, centered around the ...

Research paper thumbnail of Translational and rotational excitation for the seismic analysis of base-isolated structures

The development of a complete "6-dimensional" seismic input model is addressed for the ... more The development of a complete "6-dimensional" seismic input model is addressed for the analysis of large structures resting on rigid mat foundations. The topic is first illustrated within the framework of the linearized theory of dynamic soil-structure interaction and the nature of the kinematic transformation between the free-field seismic motion and the motion of the rigid mat is cleared and discussed. On this basis, the complete spectral description (direct and cross power density functions) of the 6D motion of the rigid mat is derived from the space-time stochastic model of the free field displacement. To this aim different forms of the coherency function relating the horizontal and vertical motion at a point are proposed and tested. The rigid-mat excitation model is then applied to the dynamic analysis of the reactor building designed within the IRIS international project, this being a classical example of rigid system, i.e. of a structural system which, once base-iso...

Research paper thumbnail of Seismic Assessment of an Unconventional Structure: The Cryostat of “Cuore” Experiment

Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017

This paper deals with the seismic assessment of a complex structure supporting the CUORE experime... more This paper deals with the seismic assessment of a complex structure supporting the CUORE experiment (Cryogenic Underground Observatory for Rare Events). The main issues, that require a special computational treatment, are: (i) non-linear geometric behavior of the suspended vessels; (ii) multiple contacts between the nested vessels and between the cryostat and the external shields; (iii) non-linear constitutive law of the HDR bearings. The problem has been tackled by building a 3D detailed finite element model, that has been used for simulating, via an explicit step-by-step algorithm, the dynamic response to artificial spectrumcompatible accelerograms. The results of the analyses have been used for introducing some specific structural improvements.

Research paper thumbnail of Wind induced vibrations of a high tapered obelisk: wind tunnel tests, numerical analysis and design of countermeasures

Procedia Engineering

The structure studied in this paper is a 85 meters high tapered obelisk, made of reinforced concr... more The structure studied in this paper is a 85 meters high tapered obelisk, made of reinforced concrete for the first 9 meters and of steel welded plates for the upper 76 meters. Its bluff cross section consists of two closely spaced triangular sections that are scaled linearly with the height from ground. Having a complex bluff section and being a light structure, aerodynamic instabilities and vortex induced vibrations were investigated using a mixed experimental-numerical approach, in order to define wind loads for the structural design, and possible interventions aimed at mitigating the dynamic effects due to wind action. Exploiting the regular tapering of the obelisk section, a rigid sectional model with constant section was initially tested in wind tunnel: static aerodynamic coefficients and vortex-induced response as a function of the Scruton number were measured for several angles of attack. The experimental sectional results were successively used to assess numerically the response of the structure considering tapering, the gradient of wind speed, the modal shapes, and the correlation of wind actions. Even though the numerical analysis showed that the tapering drastically reduces aerodynamic issues, the achieved results underlined the pressing need to increase the damping of the structure in order to avoid galloping and vortex induced vibrations for wind speeds within the design range; to this aim tuned mass dampers were designed.

Research paper thumbnail of A new approach to the definition of self-damping for stranded cables

Meccanica, 2016

Aim of the paper is to propose a new approach for the determination of the so termed self-damping... more Aim of the paper is to propose a new approach for the determination of the so termed self-damping, or internal damping, of metallic cables. The formulation is developed starting from a recent mechanical model of a strand, from which the hysteretic bending behavior of stranded cables is derived. Each wire of the cable is individually modeled as an elastic curved thin rod. A kinematic model is defined to relate the axial strain and bending curvature of the strand to the generalized strains of the wire. The interaction among the wires belonging to adjacent layers is then studied by neglecting deformations of the contact surfaces and assuming a classic Amontons–Coulomb friction law. In the adopted strand mechanical model a function is derived, which defines the domain of admissible values of the wire axial force to prevent sliding. A simplified model of the cable hysteretic bending behavior is then derived from the cyclic response predicted with the adopted mechanical formulation of the strand, leading to a closed-form upper-bound estimate of the energy dissipated when the cable cross section is subjected to alternate bending. This expression is used as the starting block for the definition of an analytical equation giving an upper-bound estimate of the cable self-damping. The predictions of the proposed model are compared to available data resulting from experiments and empirical literature equations: the comparison is extended to a wide range of strands and parameters that characterize practically most of the configuration commonly used in overhead electrical lines.

Research paper thumbnail of On the numerical solution of

Research paper thumbnail of Numerical integration of the equations of motion of structural systems undergoing large 3D rotations: dynamics of corotational slender beam elements

Meccanica, 2014

This paper deals with the numerical simulation of the dynamic response of frame structures underg... more This paper deals with the numerical simulation of the dynamic response of frame structures undergoing large displacements and 3D rotations.The corotational and the geometrically exact approaches are combined in the formulation of a 3D beam element. Inertia forces are evaluated starting from an exact expression of the element kinetic energy. This last is defined only in terms of nodal variables in the global inertial frame of the mechanical problem, so to avoid cumbersome calculations coming from the corotational decomposition of the motion. The proposed procedure is formally independent from the definition of the corotated frame. The performance of the proposed formulation is discussed with reference to some classic benchmarks involving slender frame structures undergoing large 3D rotations and displacements.

Research paper thumbnail of A Reduced Model for the Dynamic Analyses of Power Transmission Lines with Truss Supporting Towers

ABSTRACT This paper presents some advances in a research program focusing on the dynamic behavior... more ABSTRACT This paper presents some advances in a research program focusing on the dynamic behavior of transmission lines under dynamic environmental excitation. In the paper a reduced model of a vertical double circuit steel transmission tower for a power transmission line is described. The model, consisting in a sequel of beam elements placed along the axis of the tower and of the crossarms, permits to reduce the total number of the degrees of freedom in the dynamic analysis of the tower-conductors coupled system. The equivalent bending, shear and torsional sectional properties of the beam element are completely determined from the geometrical characteristics of the truss tower. The mass of the tower has been reproduced using lumped masses at the ends of each element. The adequacy of the simplified model in reproducing the tower behavior is assessed against a second, more refined, three-dimensional model in which the entire tower has been modeled using beam elements. The ability of the simplified model in simulating the vibrating characteristics of the tower in a power-line is checked comparing the natural frequencies and modal shapes of a portion of a power transmission line.

Research paper thumbnail of Fluid-Structure Interaction and Co-Simulation: Analysis of a Beam-Supported Sphere for VIV Application

Volume 4: Fluid-Structure Interaction, 2014

The recent developments in numerical tools and computing resources seem to provide a suitable env... more The recent developments in numerical tools and computing resources seem to provide a suitable environment to perform numerical analyses of Fluid-Structure Interaction problems. The Co-Simulation technique, in particular, develops the idea of coupling a CFD software with a structural one in order to simulate complex FSI phenomena with a partitioned approach, stressing the concept of software modularity. In this way, it is possible to adopt software tools at the cutting edge of technology. Nonetheless, several difficulties may arise in the choice of the partitioning scheme and of the algorithmic details for the step-by-step time integration.This paper deals with the application of the Co-Simulation technique to a benchmark case experimentally investigated in previous works: the vortex-induced vibrations (VIV) of a beam supported sphere (that is, a sphere fixed to the end of a slender cantilever beam) in a free surface flow. This problem is challenging although apparently simple and it seems quite absent from literature so far. In this paper, the computational issues are thoroughly investigated and the model is validated by comparison with the experimental data. In this way, a robust framework is created in order to deal with VIV problems.Copyright © 2014 by ASME

Research paper thumbnail of A numerical procedure for computing the fragility of NPP components under random seismic excitation

Nuclear Engineering and Design, 2009

A numerical procedure is proposed in the paper for computing seismic fragility functions for equi... more A numerical procedure is proposed in the paper for computing seismic fragility functions for equipment components in Nuclear Power Plants. The procedure is based on the hypothesis, which is typical when seismic excitation of components is addressed, of linear behaviour of the building. Given the large size of the FE element models adopted for the building, which makes direct Monte Carlo simulation impossible, the response surface methodology is used to model the influence of the random variables on the dynamic response. To account for stochastic loading the latter is estimated by means of a simulation procedure. Once the response surfaces defining the statistical properties of the response are available, the Monte Carlo method is used to compute the failure probability. A procedure for refining the RS estimation is also proposed, based on the evaluation of risk for a prototype site. A validation example is given, regarding the simplified modelling of a reactor building resting on a base-isolation system; results obtained by plain Monte Carlo analysis are compared to those computed via the proposed procedure The latter is finally applied to a real life case, taken from the preliminary design of the auxiliary building within the IRIS international project.

Research paper thumbnail of Cyclic behaviour of axially loaded members: Numerical simulation and experimental verification

Journal of Constructional Steel Research, 1987

ABSTRACT This paper deals with the simulation of the cyclic behaviour of axially loaded members r... more ABSTRACT This paper deals with the simulation of the cyclic behaviour of axially loaded members required in order to assess the performance of bracing systems under strong seismic actions.A numerical model is first presented; the experimental cyclic tests performed by the authors following the procedure developed by the ECCS are then described.Finally the results obtained by the two approaches are compared and discussed.

Research paper thumbnail of Structural response to non-stationary multiple-support random excitation

Earthquake Engineering & Structural Dynamics, 1990

... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges t... more ... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges to stationary excitation was later extensively studied by Abdel-Ghaffar and Rubin; 5-7 the auto-and cross-spectrum characteristics of the input motion were directly obtained, in these ...

Research paper thumbnail of The Formation of Viscous Damping Matrices for the Dynamic Analysis of Mdof Systems

Earthquake Engineering & Structural Dynamics, 1996

ABSTRACT The paper deals with the representation of dissipative effects by means of equivalent vi... more ABSTRACT The paper deals with the representation of dissipative effects by means of equivalent viscous forces. A brief review of the classical analytical treatment of the subject is first presented devoting particular attention to the topics of hysteretic and modal damping. The problem of forming viscous matrices in the case of systems which are non-homogeneous from the point of view of dissipation is then addressed; soil–structure systems are first considered and some accepted techniques for forming the structure contribution to the viscous matrix are reviewed. A different technique is then proposed which avoids some of the drawbacks of the previously quoted methods. In the final section of the paper it is shown how this technique is easily applicable also in the case of systems having internal concentrated dampers of viscous type, this being a situation which is difficult to tackle with usual criteria.

Research paper thumbnail of Numerical models for the dynamic response of submerged floating tunnels under seismic loading

Earthquake Engineering & Structural Dynamics, 2008

The modeling of tethering elements of seabed anchored floating structures is addressed, with part... more The modeling of tethering elements of seabed anchored floating structures is addressed, with particular reference to the so-called Archimedes Bridge (submerged floating tunnel, SFT) solution for deep water crossing; attention is devoted to the design solution encompassing slender bars as anchor elements. Two numerical tools are proposed: firstly, a geometrically nonlinear finite element (NWB model), developed in previous work, has been refined in order to capture the effect of higher flexural modes of anchor bars. Secondly, a 3D beam element, based on the classical corotational formulation (CR model), has been developed and coded. Both elements are implemented in a numerical procedure for the dynamic time domain step-by-step analysis of nonlinear discretized systems; seismic loading is introduced by generating artificial time histories of spatially variable seismic motion. An example of application of the NWB element is shown regarding the behavior of the dynamic model of a complete SFT. The model was subjected to extreme multiple-support seismic loading. The seismic behavior is here illustrated and commented, especially in light of the effect of higher local vibration modes of the anchor bars. Finally, a comparison between the performances of the two modeling approaches is presented. Both harmonic and seismic excitations are considered in the test; the results justify the use of the simpler NWB approach, especially in the SFT design phase.

Research paper thumbnail of Some observations on the probabilistic interpretation of short-term earthquake precursors

Earthquake Engineering & Structural Dynamics, 1984

This paper analyses the uncertainties in probabilistic interpretation of short-term earthquake pr... more This paper analyses the uncertainties in probabilistic interpretation of short-term earthquake precursors, even when the statistical information commonly indicated in the literature as sufficient to define the characteristics of these precursors is assumed to be known. The wide margins for uncertainty in the interpretation of such data are pointed out. One of the principal causes of uncertainty, as an example, lies in the physical origin of false alarms. Depending on this physical origin, the conditional probability of an earthquake, other conditions being equal, may vary in certain cases from values around 0.1 to as much as 0.7 or even higher. The utility of an alarm system, defined as the ratio between the mean number of favourable cases (successful alarms) and the mean number of unfavourable cases (false and missed alarms) is analysed. It is shown that an alarm system based on monitoring n 2 precursors, if the alarm is set off only after a combination of all precursors, may be considerably less useful than a system based on monitoring only one of the considered precursors.

Research paper thumbnail of Structural response to non‐stationary multiple‐support random excitation

Earthquake Engineering & Structural Dynamics, 1990

... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges t... more ... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges to stationary excitation was later extensively studied by Abdel-Ghaffar and Rubin; 5-7 the auto-and cross-spectrum characteristics of the input motion were directly obtained, in these ...

Research paper thumbnail of On the Estimation of Von Mises Equivalent Stress in Random Vibration Analysis

Research paper thumbnail of Computational aspects in direct frequency domain analysis

Research paper thumbnail of Detailed analysis of a typical overcrossing

Research paper thumbnail of Non linear response of a suspended cable under non stationary excitation

Research paper thumbnail of A Stochastic and Continuous Model of Aeolian Vibrations of Conductors Equipped with Stockbridge Dampers

Suspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to... more Suspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to aeolian vibrations, resulting from the alternate shedding of vortices in the wake of the cable. These vibrations can occur under light to moderate wind and, whenever not properly controlled, can induce wear damage and fatigue failures of the cables. Nonlinear passive control devices such as Stockbridge dampers, hence, are often installed along the line spans to reduce the vibration severity. The technical approach to the assessment of aeolian vibrations is based on the Energy Balance Method (EBM) and relies on the simplifying assumption of mono-modal oscillations. Typical aeolian vibration records, however, clearly show that several modes can be simultaneously excited due to wind variations in time and along the span. Aiming at overcoming the mono-modal vibration assumption of the EBM, in the present paper wind forces are modeled as a narrow band stochastic process, centered around the ...

Research paper thumbnail of Translational and rotational excitation for the seismic analysis of base-isolated structures

The development of a complete "6-dimensional" seismic input model is addressed for the ... more The development of a complete "6-dimensional" seismic input model is addressed for the analysis of large structures resting on rigid mat foundations. The topic is first illustrated within the framework of the linearized theory of dynamic soil-structure interaction and the nature of the kinematic transformation between the free-field seismic motion and the motion of the rigid mat is cleared and discussed. On this basis, the complete spectral description (direct and cross power density functions) of the 6D motion of the rigid mat is derived from the space-time stochastic model of the free field displacement. To this aim different forms of the coherency function relating the horizontal and vertical motion at a point are proposed and tested. The rigid-mat excitation model is then applied to the dynamic analysis of the reactor building designed within the IRIS international project, this being a classical example of rigid system, i.e. of a structural system which, once base-iso...

Research paper thumbnail of Seismic Assessment of an Unconventional Structure: The Cryostat of “Cuore” Experiment

Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2017

This paper deals with the seismic assessment of a complex structure supporting the CUORE experime... more This paper deals with the seismic assessment of a complex structure supporting the CUORE experiment (Cryogenic Underground Observatory for Rare Events). The main issues, that require a special computational treatment, are: (i) non-linear geometric behavior of the suspended vessels; (ii) multiple contacts between the nested vessels and between the cryostat and the external shields; (iii) non-linear constitutive law of the HDR bearings. The problem has been tackled by building a 3D detailed finite element model, that has been used for simulating, via an explicit step-by-step algorithm, the dynamic response to artificial spectrumcompatible accelerograms. The results of the analyses have been used for introducing some specific structural improvements.

Research paper thumbnail of Wind induced vibrations of a high tapered obelisk: wind tunnel tests, numerical analysis and design of countermeasures

Procedia Engineering

The structure studied in this paper is a 85 meters high tapered obelisk, made of reinforced concr... more The structure studied in this paper is a 85 meters high tapered obelisk, made of reinforced concrete for the first 9 meters and of steel welded plates for the upper 76 meters. Its bluff cross section consists of two closely spaced triangular sections that are scaled linearly with the height from ground. Having a complex bluff section and being a light structure, aerodynamic instabilities and vortex induced vibrations were investigated using a mixed experimental-numerical approach, in order to define wind loads for the structural design, and possible interventions aimed at mitigating the dynamic effects due to wind action. Exploiting the regular tapering of the obelisk section, a rigid sectional model with constant section was initially tested in wind tunnel: static aerodynamic coefficients and vortex-induced response as a function of the Scruton number were measured for several angles of attack. The experimental sectional results were successively used to assess numerically the response of the structure considering tapering, the gradient of wind speed, the modal shapes, and the correlation of wind actions. Even though the numerical analysis showed that the tapering drastically reduces aerodynamic issues, the achieved results underlined the pressing need to increase the damping of the structure in order to avoid galloping and vortex induced vibrations for wind speeds within the design range; to this aim tuned mass dampers were designed.

Research paper thumbnail of A new approach to the definition of self-damping for stranded cables

Meccanica, 2016

Aim of the paper is to propose a new approach for the determination of the so termed self-damping... more Aim of the paper is to propose a new approach for the determination of the so termed self-damping, or internal damping, of metallic cables. The formulation is developed starting from a recent mechanical model of a strand, from which the hysteretic bending behavior of stranded cables is derived. Each wire of the cable is individually modeled as an elastic curved thin rod. A kinematic model is defined to relate the axial strain and bending curvature of the strand to the generalized strains of the wire. The interaction among the wires belonging to adjacent layers is then studied by neglecting deformations of the contact surfaces and assuming a classic Amontons–Coulomb friction law. In the adopted strand mechanical model a function is derived, which defines the domain of admissible values of the wire axial force to prevent sliding. A simplified model of the cable hysteretic bending behavior is then derived from the cyclic response predicted with the adopted mechanical formulation of the strand, leading to a closed-form upper-bound estimate of the energy dissipated when the cable cross section is subjected to alternate bending. This expression is used as the starting block for the definition of an analytical equation giving an upper-bound estimate of the cable self-damping. The predictions of the proposed model are compared to available data resulting from experiments and empirical literature equations: the comparison is extended to a wide range of strands and parameters that characterize practically most of the configuration commonly used in overhead electrical lines.

Research paper thumbnail of On the numerical solution of

Research paper thumbnail of Numerical integration of the equations of motion of structural systems undergoing large 3D rotations: dynamics of corotational slender beam elements

Meccanica, 2014

This paper deals with the numerical simulation of the dynamic response of frame structures underg... more This paper deals with the numerical simulation of the dynamic response of frame structures undergoing large displacements and 3D rotations.The corotational and the geometrically exact approaches are combined in the formulation of a 3D beam element. Inertia forces are evaluated starting from an exact expression of the element kinetic energy. This last is defined only in terms of nodal variables in the global inertial frame of the mechanical problem, so to avoid cumbersome calculations coming from the corotational decomposition of the motion. The proposed procedure is formally independent from the definition of the corotated frame. The performance of the proposed formulation is discussed with reference to some classic benchmarks involving slender frame structures undergoing large 3D rotations and displacements.

Research paper thumbnail of A Reduced Model for the Dynamic Analyses of Power Transmission Lines with Truss Supporting Towers

ABSTRACT This paper presents some advances in a research program focusing on the dynamic behavior... more ABSTRACT This paper presents some advances in a research program focusing on the dynamic behavior of transmission lines under dynamic environmental excitation. In the paper a reduced model of a vertical double circuit steel transmission tower for a power transmission line is described. The model, consisting in a sequel of beam elements placed along the axis of the tower and of the crossarms, permits to reduce the total number of the degrees of freedom in the dynamic analysis of the tower-conductors coupled system. The equivalent bending, shear and torsional sectional properties of the beam element are completely determined from the geometrical characteristics of the truss tower. The mass of the tower has been reproduced using lumped masses at the ends of each element. The adequacy of the simplified model in reproducing the tower behavior is assessed against a second, more refined, three-dimensional model in which the entire tower has been modeled using beam elements. The ability of the simplified model in simulating the vibrating characteristics of the tower in a power-line is checked comparing the natural frequencies and modal shapes of a portion of a power transmission line.

Research paper thumbnail of Fluid-Structure Interaction and Co-Simulation: Analysis of a Beam-Supported Sphere for VIV Application

Volume 4: Fluid-Structure Interaction, 2014

The recent developments in numerical tools and computing resources seem to provide a suitable env... more The recent developments in numerical tools and computing resources seem to provide a suitable environment to perform numerical analyses of Fluid-Structure Interaction problems. The Co-Simulation technique, in particular, develops the idea of coupling a CFD software with a structural one in order to simulate complex FSI phenomena with a partitioned approach, stressing the concept of software modularity. In this way, it is possible to adopt software tools at the cutting edge of technology. Nonetheless, several difficulties may arise in the choice of the partitioning scheme and of the algorithmic details for the step-by-step time integration.This paper deals with the application of the Co-Simulation technique to a benchmark case experimentally investigated in previous works: the vortex-induced vibrations (VIV) of a beam supported sphere (that is, a sphere fixed to the end of a slender cantilever beam) in a free surface flow. This problem is challenging although apparently simple and it seems quite absent from literature so far. In this paper, the computational issues are thoroughly investigated and the model is validated by comparison with the experimental data. In this way, a robust framework is created in order to deal with VIV problems.Copyright © 2014 by ASME

Research paper thumbnail of A numerical procedure for computing the fragility of NPP components under random seismic excitation

Nuclear Engineering and Design, 2009

A numerical procedure is proposed in the paper for computing seismic fragility functions for equi... more A numerical procedure is proposed in the paper for computing seismic fragility functions for equipment components in Nuclear Power Plants. The procedure is based on the hypothesis, which is typical when seismic excitation of components is addressed, of linear behaviour of the building. Given the large size of the FE element models adopted for the building, which makes direct Monte Carlo simulation impossible, the response surface methodology is used to model the influence of the random variables on the dynamic response. To account for stochastic loading the latter is estimated by means of a simulation procedure. Once the response surfaces defining the statistical properties of the response are available, the Monte Carlo method is used to compute the failure probability. A procedure for refining the RS estimation is also proposed, based on the evaluation of risk for a prototype site. A validation example is given, regarding the simplified modelling of a reactor building resting on a base-isolation system; results obtained by plain Monte Carlo analysis are compared to those computed via the proposed procedure The latter is finally applied to a real life case, taken from the preliminary design of the auxiliary building within the IRIS international project.

Research paper thumbnail of Cyclic behaviour of axially loaded members: Numerical simulation and experimental verification

Journal of Constructional Steel Research, 1987

ABSTRACT This paper deals with the simulation of the cyclic behaviour of axially loaded members r... more ABSTRACT This paper deals with the simulation of the cyclic behaviour of axially loaded members required in order to assess the performance of bracing systems under strong seismic actions.A numerical model is first presented; the experimental cyclic tests performed by the authors following the procedure developed by the ECCS are then described.Finally the results obtained by the two approaches are compared and discussed.

Research paper thumbnail of Structural response to non-stationary multiple-support random excitation

Earthquake Engineering & Structural Dynamics, 1990

... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges t... more ... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges to stationary excitation was later extensively studied by Abdel-Ghaffar and Rubin; 5-7 the auto-and cross-spectrum characteristics of the input motion were directly obtained, in these ...

Research paper thumbnail of The Formation of Viscous Damping Matrices for the Dynamic Analysis of Mdof Systems

Earthquake Engineering & Structural Dynamics, 1996

ABSTRACT The paper deals with the representation of dissipative effects by means of equivalent vi... more ABSTRACT The paper deals with the representation of dissipative effects by means of equivalent viscous forces. A brief review of the classical analytical treatment of the subject is first presented devoting particular attention to the topics of hysteretic and modal damping. The problem of forming viscous matrices in the case of systems which are non-homogeneous from the point of view of dissipation is then addressed; soil–structure systems are first considered and some accepted techniques for forming the structure contribution to the viscous matrix are reviewed. A different technique is then proposed which avoids some of the drawbacks of the previously quoted methods. In the final section of the paper it is shown how this technique is easily applicable also in the case of systems having internal concentrated dampers of viscous type, this being a situation which is difficult to tackle with usual criteria.

Research paper thumbnail of Numerical models for the dynamic response of submerged floating tunnels under seismic loading

Earthquake Engineering & Structural Dynamics, 2008

The modeling of tethering elements of seabed anchored floating structures is addressed, with part... more The modeling of tethering elements of seabed anchored floating structures is addressed, with particular reference to the so-called Archimedes Bridge (submerged floating tunnel, SFT) solution for deep water crossing; attention is devoted to the design solution encompassing slender bars as anchor elements. Two numerical tools are proposed: firstly, a geometrically nonlinear finite element (NWB model), developed in previous work, has been refined in order to capture the effect of higher flexural modes of anchor bars. Secondly, a 3D beam element, based on the classical corotational formulation (CR model), has been developed and coded. Both elements are implemented in a numerical procedure for the dynamic time domain step-by-step analysis of nonlinear discretized systems; seismic loading is introduced by generating artificial time histories of spatially variable seismic motion. An example of application of the NWB element is shown regarding the behavior of the dynamic model of a complete SFT. The model was subjected to extreme multiple-support seismic loading. The seismic behavior is here illustrated and commented, especially in light of the effect of higher local vibration modes of the anchor bars. Finally, a comparison between the performances of the two modeling approaches is presented. Both harmonic and seismic excitations are considered in the test; the results justify the use of the simpler NWB approach, especially in the SFT design phase.

Research paper thumbnail of Some observations on the probabilistic interpretation of short-term earthquake precursors

Earthquake Engineering & Structural Dynamics, 1984

This paper analyses the uncertainties in probabilistic interpretation of short-term earthquake pr... more This paper analyses the uncertainties in probabilistic interpretation of short-term earthquake precursors, even when the statistical information commonly indicated in the literature as sufficient to define the characteristics of these precursors is assumed to be known. The wide margins for uncertainty in the interpretation of such data are pointed out. One of the principal causes of uncertainty, as an example, lies in the physical origin of false alarms. Depending on this physical origin, the conditional probability of an earthquake, other conditions being equal, may vary in certain cases from values around 0.1 to as much as 0.7 or even higher. The utility of an alarm system, defined as the ratio between the mean number of favourable cases (successful alarms) and the mean number of unfavourable cases (false and missed alarms) is analysed. It is shown that an alarm system based on monitoring n 2 precursors, if the alarm is set off only after a combination of all precursors, may be considerably less useful than a system based on monitoring only one of the considered precursors.

Research paper thumbnail of Structural response to non‐stationary multiple‐support random excitation

Earthquake Engineering & Structural Dynamics, 1990

... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges t... more ... FEDERICO PEROTTI Department of Slructural Engineering ... The response of suspended bridges to stationary excitation was later extensively studied by Abdel-Ghaffar and Rubin; 5-7 the auto-and cross-spectrum characteristics of the input motion were directly obtained, in these ...