130 pubblicazioni classificate nel seguente modo:

Code Provisions About λ-Factors of HDRBs for the Upper and Lower Bound Analyses: Hystorical Review
Lecture Notes in Civil Engineering
Autore/i: Ragni, L.; Gabriella Castellano, M.; Dall'Asta, A.; Gioiella, L.; Infanti, S.; Micozzi, F.
Editore: Springer Science and Business Media Deutschland GmbH
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Most of the current seismic codes on seismic isolation prescribe upper and lower bound analyses to account for the variability of mechanical properties of seismic isolators. This procedure should be based on experimental data provided by manufacturers during qualification tests. When such data are not available, codes provide the so-called property modification factors or λ-factors for different kind of devices, giving maximum upper and lower bound coefficients to apply to nominal properties of bearings. Different sources of variability are considered, from the variability due to the bearing production to environmental or behavioural effects (such as temperature, contamination, ageing or repeated cycles). However, the origin of these values is not straightforward: some of them are based on wide experimental data, whereas others are based on few and old indications given by technical literature. The aim of this paper is to illustrate in detail such factors, especially for HDRBs (High Damping Rubber Bearings). In particular, it is shown that in the European context, both the EN 1998—part 2 (on bridges) and the EN 15129 (on anti-seismic devices), provide values deriving (with some transcription inconsistencies) from the second version of the AASHTO guide specification, which in turn proposes values derived from the MCEER-99-0012 report written in 1999 and never updated. The aim of this paper is to illustrate in detail such factors and to make the reader aware that most of factors derive from limited and/or old data, especially for HDRBs (High Damping Rubber Bearings).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/315589

The Brittle Failure of Fluid Viscous Dampers and the Related Consequences on the Reliability of a Medium-Rise Steel Building
Lecture Notes in Civil Engineering
Autore/i: Gioiella, L.; Scozzese, F.; Tubaldi, E.; Ragni, L.; Dall'Asta, A.
Editore: Springer Science and Business Media Deutschland GmbH
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Damper failures are generally brittle mechanisms, which can compromise the capacity of the structure to withstand the seismic action, leading to a lack of robustness of the overall system. The brittle failure is due to the attainment of the maximum force capacity, because of end-stroke impacts, which causes an arising of the forces, or to an excessive velocity of the piston (over-velocity). Moreover, anti-seismic devices need to be designed with proper safety margins against their failure in order to reach a target safety level. Seismic standards generally prescribe safety factors (reliability factors), that in the case of Fluid Viscous Dampers (FVDs) are applied to stroke and velocity, with values that are not homogenous among seismic codes. The effect of damper failure and different reliability factors on both the fragility and the seismic risk of the structural system is investigated by performing multiple-stripe analysis and monitoring different global and local demand parameters of a medium-rise steel moment-resisting frame building, widely studied in literature, thanks to an advanced model implemented in OpenSees, which considers the brittle mechanism. Moreover, the problem of damper failure is also analysed in terms of fragility functions, providing information about the dependency of the probability of failure with the seismic intensity.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/315588

Statistical Analysis of Rubber Compounds Material Tests for Seismic Isolation Bearings and Code Provisions Comparison
Lecture Notes in Civil Engineering
Autore/i: Micozzi, F.; Dall'Asta, A.; Gioiella, L.; Ragni, L.; Quaglini, V.
Editore: Springer Science and Business Media Deutschland GmbH
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Rubber compounds are extensively used for manufacturing rubber bearings for seismic isolation. Current seismic codes prescribe the use of design properties of seismic isolators derived from experimental evaluations to account for the effects of strain rate representative of the design seismic condition, cyclic degradation, frequency and environmental conditions (especially the temperature variation). Moreover, ageing phenomena, which such devices undergo during their service life, should be taken into account. Such tests should be carried out on devices, even though the European Standard on seismic devices (EN 15129) allows for both high and low damping rubber bearings the use of data from material tests performed on the elastomer used in their manufacture, (although extrapolation the results of materials tests to the scale of isolation devices is not always straightforward). In this study a set of experimental data obtained from type tests performed by different manufacturers on both low and high damping compounds with nominal stiffness ranging from 0.4 MPa to 1.3 MPa is statistically analysed. The effects of shear deformation, cyclic degradation, ageing, frequency and temperature on equivalent shear stiffness and equivalent damping are shown, providing also a view of the intra-supplier variability and inter-supplier variability. As general modification factors, also known as λ-factors, are provided by the codes in case of unavailability of experimental data, a comparison between the codes values and the obtained experimental results is shown.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/315590

Variability of Dynamic Properties of Rubber Compounds for Elastomeric Bearings
STRUCTURAL CONTROL & HEALTH MONITORING
Autore/i: Micozzi, F.; Ragni, L.; Gioiella, L.; Quaglini, V.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: The -factors for stiffness and damping of rubber bearings should be experimentally assessed during the qualification process or deduced from tests performed on material specimens. Moreover, the -factors suggested in the informative annexes of EN 15129 and of EC8-part 2 can be also used as reference values. However, they are derived from outdated experimental campaigns and do not refer to all the sources of variability. In this paper, a statistical analysis on a significant set of rubber compounds, certified according to EN 15129 from different suppliers, is carried out to assess the current variability of the dynamic properties of such compounds. Different sources of variability may be identified by distinguishing between behavioural and environmental effects. For elastomeric bearings, especially high-damping rubber (HDR) ones, the main behavioural effects are strain amplitude, strain rate dependence, and cyclic degradation, whereas the environmental effects are due to temperature variation and ageing. All these sources of variability have been analysed in this paper. The results of the statistical analysis have been used to propose a new set of -factors for all the source of variability studied. Such new values have been compared with the ones suggested by the codes when available. The main inconsistencies found have been highlighted and commented in this paper. Finally, some considerations about the influence of such variability on the structural response of base-isolated structures have been drawn by focusing on both the isolation system and the superstructure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/325253

BUILDING BACK BETTER: THE CASE STUDY OF THE FAZZINI COLLEGE
COMPDYN Proceedings
Autore/i: Gioiella, L.; Micozzi, F.; Ragni, L.; Dall'Asta, A.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Passive protection systems have proven to be efficient solutions for the seismic protection of both new and existing buildings. Recently an increasing attention is paid towards their use in external configurations, especially for existing structures since their lower interferences with both the structures to protect and the activities carried on within the buildings. Retrofit and seismic upgrading based on external dissipative elements, indeed, are very promising in post-earthquake phases, making it possible a notable reduction of building downtime and impacts on users. This paper concerns the seismic retrofit of the Fazzini college, an existing r.c. frame building of the University of Camerino severely damaged during the 2016 Central Italy seismic sequence. The retrofit has been designed with an external passive system equipped with fluid viscous dampers aiming to prevent damage to both structural and non-structural components up to severe earthquakes.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/325254

INFLUENCE OF DESIGN PARAMETERS ON THE SEISMIC RELIABILITY OF BASE ISOLATED SYSTEMS
COMPDYN Proceedings
Autore/i: Micozzi, F.; Scozzese, F.; Ragni, L.; Dall'Asta, A.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Seismic isolation is considered an effective solution to protect buildings and reduce seismic losses. However, the reliability level achieved by code-conforming base-isolated structures can be not uniform due to the different behavior of the most used isolation bearings (elastomeric or sliding bearings) as well as the different design choices that strongly influence the seismic reliability of base-isolate structures. In this paper High Damping Rubber Bearings (HDRBs) are considered and a parametric analysis is performed to assess the overall reliability of base-isolated buildings designed according to Eurocodes and Italian seismic codes. In particular, the case of ordinary residential buildings is considered, and the following parameters have been considered and varied, within the range of most common values: the bearings design shear deformation and the superstructure design over-strength ratio. Probabilistic analyses are performed using a robust direct simulation approach (Subset Simulation) and a bidirectional stochastic ground motion model. For each case analyzed, results are provided in terms of demand hazard curves of the most relevant response parameters characterizing the isolation system and the superstructure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/325255

λ-Factors for the Upper and Lower Bound Analyses of Base-Isolated Structures: Historical Review of Code Provisions for Elastomeric Bearings †
APPLIED SCIENCES
Autore/i: Ragni, L.; Micozzi, F.; Gioiella, L.; Castellano, M. G.; Infanti, S.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: The seismic response of base-isolated structures is notably influenced by mechanical properties of isolation devices due to their essential role in structural behavior. Consequently, the variability of such properties should be accounted for in the design process. The current seismic codes prescribe a simplified approach based on structural analyses in two extreme situations resulting from the upper and lower bound design properties of bearings (upper and lower bound analyses). In the case that experimental data are not provided by manufacturers, seismic codes provide the so-called “property modification factors” or “λ-factors”, i.e., modification coefficients to be applied to the nominal dynamic properties of bearings to obtain their upper or lower design properties. The aim of this paper is to provide a historical review of values provided for such factors by the main seismic codes by highlighting the limits, as well as some clerical errors, present in some codes. In particular, the European seismic codes are illustrated in detail, i.e., the Eurocode for bridges (EN 1998-2) and product standard on anti-seismic devices (EN 15129). Both these codes account for different sources of variability, such as the bearings production and the environmental and behavioral effects. For all these effects, the same λ-factor values are provided by the two codes, deriving from the second version of the AASHTO guide specifications for seismic isolation of bridges (AASHTO 1999), which are based on limited and/or old data, especially for high damping rubber bearings (HDRBs), and were never updated in the successive versions. More recent standards are also illustrated, providing different perspectives that deserve attention, even though they require further investigations to be applied in the design practice.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/325252

Push-and-release tests of a steel building with hybrid base isolation
ENGINEERING STRUCTURES
Autore/i: Dall'Asta, A.; Leoni, G.; Gioiella, L.; Micozzi, F.; Ragni, L.; Morici, M.; Scozzese, F.; Zona, A.
Classificazione: 1 Contributo su Rivista
Abstract: Experimental testing of a two-storey 5875 square meters steel braced-frame structure resting on a reinforced concrete slab isolated from the foundations through a hybrid system (28 high-damping rubber bearings and 36 low-friction sliding bearings) is presented. The building incorporates a push-and-release device to evaluate its actual global dynamic response up to displacement amplitudes induced by extreme seismic events, allowing test repetitions during its service life. The testing set up and the experimental campaign, consisting of quasi-static push tests (slow loading and unloading) and push-and-release dynamic tests (slow loading and subsequent sudden release), are described. The experimental results have peculiarities related to the building (structural typology and size, foundation geometry on a steep slope, presence of the push-and-release device for future additional tests), the magnitude of the maximum horizontal displacement never achieved before (285 mm and 227 mm in the quasi-static and dynamic tests, respectively), the global and local monitored parameters (horizontal and vertical displacements, strains, accelerations, in addition to environmental conditions) providing a comprehensive insight into the behaviour of the hybrid isolation system and superstructure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308521

Modelling and Seismic Response Analysis of Existing Italian Residential RC Buildings Retrofitted by Seismic Isolation
JOURNAL OF EARTHQUAKE ENGINEERING
Autore/i: Cardone, D.; Viggiani, L. R. S.; Perrone, G.; Telesca, A.; Di Cesare, A.; Ponzo, F. C.; Ragni, L.; Micozzi, F.; Dall’Asta, A.; Furinghetti, M.; Pavese, A.
Classificazione: 1 Contributo su Rivista
Abstract: The seismic performance of existing RC frame buildings seismically retrofitted by base isolation is examined. Two different types of isolation systems are considered, i.e.: rubber-based and friction-based isolation systems, respectively. Two different performance levels are examined, namely: Global collapse prevention and Usability preventing damage. Seismic performance is assessed by multi-stripe nonlinear time-history analysis, considering earthquake intensity levels with return period ranging from 10 to 100000 years. Results point out that seismic isolation works effectively in limiting damage well beyond the design limit state level while it shows a limited margin with respect to collapse beyond the design limit state level
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/299443

Seismic reliability of base isolated systems: sensitivity to design choices
ENGINEERING STRUCTURES
Autore/i: Micozzi, F.; Scozzese, F.; Ragni, L.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: Seismic isolation is considered an effective solution to protect buildings and related content from earthquakes, and consequently reduce seismic losses. However, the overall reliability levels achieved on these systems by following the design rules suggested by codes are not uniform and they may be strongly influenced by some choices made in the structural design. This study aims to investigate the seismic reliability of structural systems equipped with high-damping rubber bearings, which is a widely used class of isolators. An extensive parametric analysis is performed to assess the influence of design choices on the failure probability, considering design parameters concerning both the isolation system and the superstructure, such as: isolation period; bearings shear strain; percentage of flat sliders (i.e., bearing shape factors); superstructure overstrength ratio. A set of case studies have been configurated by varying and combining all the aforesaid parameters. A stochastic model is used for the bidirectional seismic input and the generation of horizontal ground motion components, whereas full probabilistic analyses are performed via Subset Simulation to achieve accurate estimates of the demand hazard curves up to very small failure probabilities. To reduce the computational effort, a 3D-model with a reduced number of DOFs (Degrees of Freedoms) is adopted for each case study. It consists of an uncoupled bidirectional elastoplastic model of the superstructure, and an advanced nonlinear 3D model of the rubber isolators, accounting for the coupling between vertical and horizontal response in large displacements. For each case analysed, demand hazard curves are evaluated to illustrate the probabilistic properties of the seismic response for both isolation system and superstructure. Results show a noticeable sensitivity of the system reliability with respect to the examined design choices and in some cases the achieved structural performance can be far from the safety levels required by the Codes.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/299444

Risk Assessment of Reinforced Concrete Buildings with Rubber Isolation Systems Designed by the Italian Seismic Code
JOURNAL OF EARTHQUAKE ENGINEERING
Autore/i: Micozzi, F.; Flora, A.; Viggiani, L. R. S.; Cardone, D.; Ragni, L.; Dall’Asta, A.
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/299442

Field tests and numerical analysis of the effects of scour on a full-scale soil–foundation–structural system
JOURNAL OF CIVIL STRUCTURAL HEALTH MONITORING
Autore/i: Tubaldi, E.; Antonopoulos, C.; Mitoulis, S. A.; Argyroudis, S.; Gara, F.; Ragni, L.; Carbonari, S.; Dezi, F.; Vratsikidis, A.; Pitilakis, D.; Anastasiadis, A.
Classificazione: 1 Contributo su Rivista
Abstract: Scour is the prevailing cause of bridge failure worldwide, leading not only to traffic disruption, but also to social and economic losses and even to casualties. Many vibration-based monitoring techniques have been proposed for identifying the scour location and extent, based on the evaluation of the changes of the bridge modal properties due to scour. This study describes the experimental and numerical research carried out to investigate the effects of scour on the dynamic properties of structures with shallow foundations. Although these are the most vulnerable ones, they have received less attention compared to structures founded on pile foundations. To fill some existing knowledge gaps, field experiments were carried out on EuroProteas, a structural prototype with shallow foundation that was subjected to increasing levels of scour. The changes of the dynamic properties of the system are evaluated by postprocessing the ambient vibration recordings and by developing various models of the soil–foundation–structural system with different descriptions of the soil–structure interaction problem. The study results shed light on the effects of scour on systems with shallow foundations and on the accuracy of alternative modelling approaches. They are presented here to inform the development and validation of vibration-based techniques and modelling strategies for bridge scour identification.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/306181

Influence of viscous dampers ultimate capacity on the seismic reliability of building structures
STRUCTURAL SAFETY
Autore/i: Scozzese, Fabrizio; Gioiella, Laura; Dall'Asta, Andrea; Ragni, Laura; Tubaldi, Enrico
Classificazione: 1 Contributo su Rivista
Abstract: Anti-seismic devices should be designed with proper safety margins against their failure, because the reliability of the structural system where they are installed is strongly influenced by their reliability. Seismic Standards generally prescribe safety factors (reliability factors) amplifying the device responses at the design condition, in order to reach a target safety level. In the case of Fluid Viscous Dampers (FVDs), these factors are applied to the stroke and velocity, and their values are not homogeneous among seismic codes. This paper investigates the influence of the values of the safety factors for FVDs on the reliability of the devices and of the structural systems equipped with them. An advanced FVD model is employed to account for the impact forces arising when the dampers reach the end-stroke and the brittle failure due to the attainment of the maximum force capacity. The effect of damper failure on both the fragility and the seismic risk of the structural system is investigated by performing multiple-stripe analysis and monitoring different global and local demand parameters. In particular, a parametric study has been carried out, considering two case studies consisting of a low-rise and a medium-rise steel building, coupled with a dissipative system with linear and nonlinear properties and studying the consequences of different values of safety factors for stroke and forces. The study results give evidence to the potential brittle behaviour of the coupled system and provide information about the relationships between damper safety factors and effective structural reliability. Some preliminary suggestions are given on possible improvements of current design approaches and on the values of the reliability factors to be considered for future code revision.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/299441

Scour-induced dynamic properties modification of masonry arch bridges with different geometry
COMPDYN Proceedings
Autore/i: Scozzese, F.; Ragni, L.; Tubaldi, E.; Gara, F.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: This paper, focused on the effect of local scour actions on masonry bridges, represents a followup of a previous study conducted by the authors aimed at analysing the effect of a localised scour-induced settlement of the pier on the modal properties of the bridge (i.e., frequencies and mode shapes). Results from the previous study showed as the scour phenomenon, even at its early stages could induced a non-negligible variability of the transverse modal shape of a masonry arch bridge selected as case study. In this paper, the work is continued by analysing how the bridge geometry can affect the aforesaid results. To this aim, bridges with three different geometry (130 m length, 100 m length, 50 m length) are analysed by simulating the scour evolution under the piers and by monitoring the modal response at different stages of the excavation. Accurate finite element models are developed in Abaqus, accounting for both mechanical and geometrical nonlinearities.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/300471

An advanced model for the fluid viscous damper brittle failure
COMPDYN Proceedings
Autore/i: Gioiella, L.; Scozzese, F.; Tubaldi, E.; Ragni, L.; Dall'Asta, A.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Fluid viscous dampers have proven to be a very efficient solution for reducing the seismic demand on structural and non-structural components, for both new and existing structures. Nowadays, the topics, which need to be further investigated, deal with the reliability and robustness of such kind of energy dissipating devices. Damper failures are generally brittle mechanisms, which can compromise the capacity of the structure to withstand the seismic action, leading to a lack of robustness of the overall system. In this study, an advanced model, which is able to describe the fluid viscous damper brittle failure, has been developed in OpenSees and is discussed. The failure of a damper is related to the exceedance of its strength capacity and can be attained because of the forces arising related to the end-stroke impact or can be due to excessive piston velocity (over-velocity). The effect of damper failure on the seismic performance of the structural system is investigated by performing multi-stripe analyses and monitoring different global and local demand parameters. The proposed model for the damper is applied to a benchmark structure, consisting on a 3-storey steel moment resisting frame.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/300467

The New Camerino University research center: Design of the base-isolated buinding and dynamic testing
COMPDYN Proceedings
Autore/i: Dall'Asta, A.; Leoni, G.; Micozzi, F.; Gioiella, L.; Ceccolini, N.; Ragni, L.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: This paper deals with the new Research Centre designed for the University of Camerino and entirely financed by the national Civil Protection Department (DPC), following the seismic events in Central Italy in 2016. The building consists of a base-isolated steel braced superstructure and r.c. sub-structures able to adapt to the complex morphology of the area. In particular, the first part of the paper illustrates the design choices made to achieve a high level of resilience and robustness of the building, i.e. to limit damage to structural and non-structural components and equipment under moderate and design seismic actions and to avoid disproportionate consequences in the event of extreme actions, larger than the design ones. The second part of the paper is focused on static and dynamic tests performed during the construction phase of the building. At the end of the structural system construction (including sub-structures, the isolation system composed by elastomeric bearings and flat sliders and the steel superstructure), the building has been tested by means of static and dynamic (snap-back) in-field tests up to a displacement of the isolation system of 280mm and 220mm, respectively. Displacements have been imposed by means of a properly designed testing mechanism and different measure instruments have been placed in the building to register the structural response.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/300473

Behaviour of Structures Isolated by HDNR Bearings at Design and Service Conditions
JOURNAL OF EARTHQUAKE ENGINEERING
Autore/i: Ragni, L.; Micozzi, F.; Tubaldi, E.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: High-Damping Natural Rubber (HDNR) bearings are widely employed for seismic isolation. These bearings are characterized by a remarkable nonlinear behaviour and often by a degrading cyclic response, induced by the addition of filler to enhance its dissipation capacity. This latter phenomenon, denoted as stress-softening or Mullins effect, can significantly influence the nonlinear dynamic response of isolated structures leading to a variability of the seismic response of isolated buildings. Moreover, the behaviour of HDNR bearings may produce an amplification of response, due to higher modes contribution, which can affect the performance of non-structural components and equipment. Models providing an accurate description of the nonlinear behaviour of HDNR bearings with significant stress-softening have been proposed only recently. Thus, the studies in the literature are generally based on simplified models. In this paper, an advanced HDNR model, accounting for variation of stiffness and damping with the strain amplitude and deformation history, is used to analyse the seismic performance of isolated structures at different intensity levels. First, a parametric analysis is carried out on a two-degree of freedom system to study different configurations of practical interest. Subsequently, a multi-degree of freedom system representing a realistic building is analysed to evaluate the response at different floors and the contribution of higher modes of vibration. The influence of practical aspects, such as the superstructure damping and the friction of the sliders, is also investigated.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/289918

Dynamic monitoring of bridges during static load tests: influence of the dynamics of trucks on the modal parameters of the bridge
JOURNAL OF CIVIL STRUCTURAL HEALTH MONITORING
Autore/i: Gara, F.; Nicoletti, V.; Carbonari, S.; Ragni, L.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: This paper presents results of an extensive experimental campaign carried out during the construction phases of a base-isolated bridge across the Potenza river in central Italy. The structure is constituted by a half-through steel arch bridge composed by two coupled weathering steel tubular arches sustained by thirty couples of hangers and by two approaching viaducts. The bridge has a continuous twin-girder steel–concrete composite deck. During construction, impact load tests were carried out on hangers as well as on other tie elements to estimate their tension force from the relevant resonance frequencies. During the proof test, relative displacements occurred between the upper and lower plates of the seismic isolators are measured for different loading conditions. In addition, ambient vibration tests are performed during the final static load tests to investigate the bridge dynamics subjected to different loading conditions. Comparisons of test results with the numerical predicted values contributed to evaluate the consistency between the design and the real structure at different construction stages. Dynamic identification tests contributed to identify the significance of the truck–bridge interaction in the interpretation of the bridge dynamics evaluated experimentally.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/273422

A Design Method for Viscous Dampers Connecting Adjacent Structures
FRONTIERS IN BUILT ENVIRONMENT
Autore/i: Tubaldi, E.; Gioiella, L.; Scozzese, F.; Ragni, L.; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: This paper investigates the seismic design of fluid viscous dampers connecting adjacent structural systems. A simplified dampers design strategy is proposed, which relies on a linearized reduced order model of the coupled system. A stochastic linearization technique is adopted with the aim of extending the design method to non-linear viscous dampers. The effectiveness of the design method and of the coupling strategy are assessed via numerical analysis of two adjacent buildings with shear-type behavior connected by linear or non-linear viscous dampers and subjected to Gaussian stochastic base acceleration. Different dampers locations are analyzed. The accuracy of the reduced order model is assessed, by comparing the relevant response statistics to those provided by a refined multi degree of freedoms model. Finally, a parametric study is performed to assess the effectiveness of dissipative connection for different values of seismic intensity and dampers parameters (i.e., viscous coefficients and velocity exponents).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/279155

A Resilience and Robustness Oriented Design of Base-Isolated Structures: The New Camerino University Research Center
FRONTIERS IN BUILT ENVIRONMENT
Autore/i: Dall'Asta, A.; Leoni, G.; Micozzi, F.; Gioiella, L.; Ragni, L.
Classificazione: 1 Contributo su Rivista
Abstract: This paper analyses the new Research Centre designed for the University of Camerino and entirely financed by the national Civil Protection Department (DPC), following the seismic events in Central Italy in 2016. The building has been designed to guarantee speed of execution as well as a high level of safety, especially regarding seismic actions. The structural solution was to create an isolated system with a steel braced super-structure with pinned joints and r.c. sub-structures able to adapt to the complex morphology of the area. As described in the first part of the paper, design choices have been made to achieve a high level of resilience and robustness, i.e., to limit damage to structural and non-structural components and equipment under moderate and design seismic actions and to avoid disproportionate consequences in the event of extreme actions, larger than the design ones. In the second part of the paper, specific risk analyses have been carried out to evaluate the real performance of the building under increasing intensity levels, with reference to both serviceability and ultimate conditions. To this purpose a site-specific hazard study was first conducted, then non-linear analyses were performed using a hazard-consistent set of records with return periods ranging from TR = 60 years to TR = 10000 years. The main demand parameters of both the isolation system and the super-structure were recorded and capacity values corresponding to different ultimate and damage limit conditions were defined. The results obtained in terms of demand hazard curves show that the building performances in terms of robustness and resilience are very high, confirming the efficacy of the strategies adopted in the design.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/289919

Advanced and semplified models of HDNR bearings for the seismic performance evaluation of base-isolated structures
Atti del XVIII convegno ANIDIS
Autore/i: Ragni, L.; Micozzib, F.; Tubaldi, E.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277795

SEISMIC RESPONSE OF A R.C. STRUCTURE ISOLATED BY HDNR BEARINGS BY USING ADVANCED AND SIMPLIFIED MODELS
SECED 2019 Proceedings
Autore/i: Ragni, Laura; Micozzi, Fabio; Tubaldi, Enrico; Dall’Asta, Andrea
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277804

Field tests on a soil-foundation-structure system subjected to scour
Atti del XVIII Convegno ANIDIS L'ingegneria sismica in Italia
Autore/i: Tubaldi, Enrico; Lupo, Rosa; Mitoulis, Stergios; Argyroudis, Sotiris; Gara, Fabrizio; Ragni, Laura; Carbonari, Sandro; Dezi, Francesca
Editore: Pisa University Press srl
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Earthquakes and foundation scour are the major causes of bridge failure worldwide. Many bridges in earthquake-prone countries have shallow foundations, whose stability and seismic vulnerability can be significantly undermined by flood-induced scour. This article provides the first results of the “DYMOBRIS” project (DYnamic identification and MOnitoring of scoured BRIdgeS under earthquake hazard), a H2020-SERA EU-funded project aiming at i) developing a methodology for non-invasive detection of scour in bridges with shallow foundations based on vibration monitoring, and ii) quantifying the effects of scour on the seismic vulnerability of these Soil-Foundation-Structure (SFS) systems. The experimental campaign involves various tests, from ambient vibration to force vibration, on the EuroProteas prototype under different scour conditions. The preliminary finite element models developed for defining the scour profile to be imposed in the in-field tests are presented here, together with some results concerning the effects of scour on the SFS dynamic properties.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/269908

Preliminary fragility analysis of a r.c. frame school building retrofitted by an external dissipative system
Atti del XVIII Convegno ANIDIS
Autore/i: Gioiella, Laura; Ragni, Laura; Gara, Fabrizio; Dall’Asta, Andrea
Editore: Pisa University Press srl
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Seismic events occurred in the last decade in Italy led the attention to the evaluation of the health and need of interventions on the existing school buildings heritage, whose collapse or loss in functionality after an earthquake may lead to significant economic and social losses. For this reason, this study focuses on the preliminary fragility assessment of a typical school r.c. frame building, retrofitted through an external configuration based on the use of fluid viscous dampers (FVDs). The case study is a two elevations moment resisting frame structure, built in Italy in the sixties without seismic code. The external retrofit configuration is a rocking base system consisting of a pinned-rocking braced frames equipped with fluid viscous dampers at their base. Fragility curves, built by accounting for different level of inter-storey drift and for seven intensity measures of the seismic action, provide useful insights about the efficiency and dynamic response of the r.c. frame before and after the retrofitting works.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/274077

Comportamento dei dispositivi HDRB sotto grandi spostamenti ed elevati carchi assiali
Atti XVIII CONVEGNO ANIDIS
Autore/i: Ragni, Laura; Micozzi, Fabio; Brandonisio, Giuseppe; Dall’Asta, Andrea; De Luca, Antonello; Di Cesare, Antonio; Mossucca, Antonello; Nigro, Domenico; Ponzo, Felice C.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277798

Modal properties variation and collapse assessment of masonry arch bridges under scour action
ENGINEERING STRUCTURES
Autore/i: Scozzese, F.; Ragni, L.; Tubaldi, E.; Gara, F.
Classificazione: 1 Contributo su Rivista
Abstract: This paper investigates the problem of flood-induced scour on masonry arch bridges through the analysis of a real case study, Rubbianello Bridge. This is a multi-span masonry arch bridge located in Central Italy, which suffered the collapse of two of the seven spans due to foundation scour during a severe flood in December 2013. The study has a twofold aim: to evaluate with a numerical model the level of scour which led to the bridge failure in 2013 and the corresponding collapse mechanism, and to assess the sensitivity of the bridge’s modal properties (vibration frequencies and mode shapes) to different levels of scour. An accurate nonlinear three-dimensional model of the bridge is developed, whose elastic properties are calibrated to match the results of dynamic identification tests performed via Operational Modal Analysis (OMA) on the remaining portion of the bridge. A numerical simulation of the effects of the scour hole progression is also performed on the full bridge, according to recently proposed techniques. The study results provide useful insights on both the cause of collapse of the bridge and the suitability of OMA for bridge scour monitoring.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/270806

Sustainable Engineering for Resilient Built and Natural Environments
The First Outstanding 50 Years of “Università Politecnica delle Marche”
Autore/i: Alici, Antonello; Bocci, Maurizio; Bonvini, Paolo; Brocchini, Maurizio; Calamai, Alessandro; Canestrari, Francesco; Capozucca, Roberto; Carbonari, Alessandro; Carbonari, Sandro; Cardone, Fabrizio; Clementi, Francesco; Clini, Paolo; Cocchi, Giammichele; Corvaro, Sara; Darvini, Giovanna; Davì, Fabrizio; Dezi, Luigino; Di Giuseppe, Elisa; D’Orazio, Marco; Ferretti, Maddalena; Ferrotti, Gilda; Gara, Fabrizio; Giretti, Alberto; Graziani, Andrea; Lancioni, Giovanni; Lemma, Massimo; Lenci, Stefano; Lorenzoni, Carlo; Malinverni, Eva Savina; Mancinelli, Alessandro; Mariano, Fabio; Mentrasti, Lando; Mondaini, Gianluigi; Montecchiari, Piero; Munafò, Placido; Naticchia, Berardo; Postacchini, Matteo; Quagliarini, Enrico; Quattrini, Ramona; Ragni, Laura; Serpilli, Michele; Soldini, Luciano; Virgili, Amedeo; Zampini, Giovanni
Editore: Springer
Classificazione: 2 Contributo in Volume
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/272866

An Overview of the Structural Safety-Oriented Research in the Region Marche Seismic Area
The First Outstanding 50 Years of “Università Politecnica delle Marche”
Autore/i: Capozucca, R.; Carbonari, S.; Clementi, F.; Cocchi, G.; Davi, F.; Dezi, L.; Gara, F.; Lancioni, G.; Lenci, S.; Mentrasti, L.; Ragni, L.; Serpilli, M.
Editore: Springer, Cham
Classificazione: 2 Contributo in Volume
Abstract: In recent years, Italy has been hit by earthquakes, causing significant damage to masonry and reinforced concrete (RC) structures. Especially, common buildings and ordinary structures in many small historical towns of Italian central regions, such as Marche, have suffered dramatic consequences and destruction. Dynamic analysis and seismic structural safety are important topics in civil engineering, which have been studied and deepened for many years by the researchers of the Structural Division of the Department of Civil and Building Engineering, and Architecture of UnivPM. The researches have been oriented towards the investigation of structures under seismic loads in order to improve the knowledge of the structural response under high actions, due to the soil dynamic movements and, thus, define adequate techniques to strengthen the damaged structures. In this paper we present a wide spectrum of main results of our research group, comprising experimental studies, vulnerability analysis and assessment of existing structures, new methods of modelling and theoretical approaches to define the dynamic behavior of structures, also in presence of damage. Finally, we show and discuss new prospects of research for safety, employing advanced techniques and materials to prevent collapse and/or relevant damages in structures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/281739

The seismic retrofit by external dissipative systems: A case study
COMPDYN Proceedings
Autore/i: Gioiella, L.; Tubaldi, E.; Ragni, L.; Gara, F.; Dall'Asta, A.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: External dissipative systems are seismic retrofit solutions for existing building frames that present some feasibility advantages with respect to more classic solutions involving dissipative devices installed within existing frames. This study analyses and compares the effectiveness of three alternative external retrofit configurations based on the use of fluid viscous dampers (FVDs) with reference to a case study involving the seismic upgrading of a typical school r.c. frame. In particular, the three considered systems are: a rocking base system consisting of a pinned-rocking braced frames equipped with fluid viscous dampers at their base, a fixed base system consisting of external fixed-base braced frames connected to the frame through dampers located at floor levels and a diagonal bracings system similar to the traditional arrangement, but installed adjacent to the frame. All the proposed retrofit solutions are analysed taking into account the non-linear behaviour of the r.c. frame building (designed with inadequate seismic detailing) and both the linear and non-linear behaviour of the FVDs. The obtained results show that all the systems are effective solutions, even if performances in terms of interstorey-drifts, absolute floor accelerations, forces and strokes of the dampers are different.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277590

Seismic behaviour of a RC frame isolated by HDNR bearings under increasing intensity levels
COMPDYN Proceedings
Autore/i: Ragni, L.; Micozzi, F.; Tubaldi, E.; Dall'Asta, A.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: High Damping Natural Rubber (HDNR) bearings are characterized by stiffness and damping capacity that significantly depend on the shear deformation amplitude. More in details, at low deformations stiffness and damping increase, whereas at large deformations the stiffness remarkably increase but the damping capacity decreases. Additionally, this kind of bearings show a loading hysteresis dependence, due to the internal damage of the rubber occurring as the deformation history progresses. This effect, also known as stress-softening, becomes significant for large deformation amplitudes and represents a source of uncertainty, which has recently caused a limitation of the use of this kind of isolators. However, consequences of this nonlinear behaviour of HDNR bearings on the response of isolated structures are not comprehensively investigated, primarily because advanced models have been only recently developed. In this paper some investigations are carried out by using a nonlinear constitutive law recently developed by some of the authors describing the behaviour of a HDNR with significant stress-softening complying with the limits of European code on anti-seismic devices. Analyses are carried out on a multi-degree of freedom system by considering different seismic intensity levels and different response parameters, including floor response spectra. A linear visco-elastic model calibrated at each seismic intensity level is also adopted in the analyses. The obtained results show that some response amplifications happen due to the higher modes of the superstructure, which are underestimated by linear models and may cause damages to non-structural components and equipment.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277559

Dynamic properties of a masonry arch bridge subjected to local scour up to failure
Proceedings of ICONHIC 2019
Autore/i: Ragni, Laura; Scozzese, Fabrizio; Gara, Fabrizio; Tubaldi, Enrico
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277800

RINTC-E project: The seismic risk of existing Italian RC buildings retrofitted with seismic isolation
COMPDYN Proceedings
Autore/i: Cardone, D.; Conte, N.; Dall'Asta, A.; Di Cesare, A.; Flora, A.; Lamarucciola, N.; Micozzi, F.; Ponzo, F. C.; Ragni, L.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: This paper reports on the results of an ongoing Research Project, funded by the Italian Civil Protection Department, aimed at the evaluation of the risk of collapse and usability-preventing performance levels for existing buildings. This paper, in particular, describes the results of nonlinear time-history analyses (NTHA) carried out on two different RC buildings retrofitted with isolation systems. The two buildings are located in two different sites, Naples and L’Aquila characterized by medium and high seismicity for Italy, and are designed for gravity loads only and according to outdated seismic codes respectively. The buildings have been retrofitted using three different isolation systems: (i) high damping rubber bearings; (ii) rubber bearings and flat sliding bearings; (iii) curved surface sliders. The results point out that all isolation systems work effectively in limiting the onset of damage of non-structural members for seismic intensities much higher than the action required by the current design code. On the other hand, they show a little margin towards collapse, beyond the design intensity level. In particular, the collapse of the superstructure turns out to be the dominant collapse mode, especially for the building designed for gravity loads only.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/277592

Dynamic identification and collapse assessment of Rubbianello Bridge
Report of IABSE SYMPOSIUM "Towards a Resilient Built Environment"
Autore/i: Ragni, L.; Scozzese, F.; Gara, F.; Tubaldi, E.
Editore: IABSE c/o ETH Zurich
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: This paper investigates the causes of failure of Rubbianello Bridge, a multi-span masonry arch bridge located in Central Italy, which suffered the collapse of two of the seven spans due to foundation scour during a very severe flood in December 2013 and the collapse of two more spans during another major flood event in 2016. An accurate nonlinear 3D model of the bridge is developed. The elastic properties of the model are calibrated based on both material tests and an experimental campaign carried out for the dynamic identification (in terms of vibration frequencies and modal shapes) via operational modal analysis of the remaining part of the bridge. A numerical simulation of the scour hole progression is performed in order to identify the collapse mechanism of the bridge under the first major flood and estimate the level of scour that caused the bridge failure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/265467

Statistical modelling of HDNR bearing properties variability for the seismic response of isolated structures
6th European Conference on Computational Mechanics
Autore/i: Micozzi, Fabio; Ragni, L.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: This paper reports some results of an ongoing Research Project called RINTC aimed at computing the risk of collapse of buildings conforming to the Italian Seismic Design Code. The project involves different areas of application (reinforced concrete, masonry, steel buildings, etc.) including reinforced concrete (RC) buildings equipped with isolation systems. In particular, this paper focuses on seismic isolation systems based on High Damping Natural Rubber (HDNR) bearings, which are widely employed for buildings and other structures. The aim of the paper is to evaluate the response dispersion due to the uncertainties in the seismic input as well as the variability of the isolation system properties. The study proposes a model to define the production variability of the bearing properties, taking into account the tolerance allowed in factory production control tests (FPCT) by the European code on anti-seismic devices (EN15129). To this purpose, in the first part of the paper, experimental results of groups of HDNR bearings belonging to different batches (classes) has been analysed, focusing on the values of shear stiffness and damping coefficient at design deformation and their correlation inside and between device groups. Both the intra-class and inter-class variability affecting the HDNR isolator properties are evaluated, by using a proper statistical model. Successively, the effect on the properties variability of the FPCT acceptance criteria provided by the European code is evaluated. In the second part of the paper, results of multi-stripe analyses carried out on a base isolated prototype consisting of a 6-storey RC building are presented for increasing ground motion intensities. In particular, several varied parameters of bearings are sampled starting from mean properties and by using the statistical model calibrated from test data. The influence of the bearings parameters variability on the most interesting engineering demand parameters (EDPs) and on collapse modalities is evaluated and discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/265465

Biaxial shear behaviour of HDNR with Mullins effect and deformation-induced anisotropy
ENGINEERING STRUCTURES
Autore/i: Ragni, Laura; Tubaldi, Enrico; Dall'Asta, Andrea; Ahmadi, Hamid; Muhr, Alan
Classificazione: 1 Contributo su Rivista
Abstract: High damping natural rubber (HDNR) bearings, commonly employed to isolate structures, are subjected to biaxial horizontal deformations by the seismic motion. If they have virgin material properties, biaxial models including the stress softening due to the Mullins effect should be used for describing their force–deformation behaviour. Specific studies oriented at characterizing and modelling the biaxial behaviour of HDNR bearings accounting for the stress-softening are very few in number because they would require a large number of virgin isolators or long times of rest between two consecutive tests. Moreover, available studies consider the Mullins effect as an isotropic phenomenon, whereas experimental investigations have shown that it is direction-dependent and thus induces anisotropy of the rubber behaviour. This paper describes an extensive experimental campaign carried out on a large number of small material test pieces aimed at achieving a satisfactory characterization of the biaxial anisotropic response of a highly dissipative rubber compound. These results are then used to develop a two-dimensional constitutive model for the virgin HDNR material accounting for the directiondependence of the Mullins effect, based on the concept of representative directions applied to the biaxial shear deformation state. Because for commonly employed laminated HDNR bearings under design actions the approximation of uniform simple shear is realistic, the proposed material model can also be used to simulate the global bidirectional horizontal response of the bearings.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/254464

Modelling and Seismic Response Analysis of Italian Code-Conforming Base-Isolated Buildings
JOURNAL OF EARTHQUAKE ENGINEERING
Autore/i: Ragni, L.; Cardone, D.; Conte, N.; Dall’Asta, A.; Di Cesare, A.; Flora, A.; Leccese, G.; Micozzi, F.; Ponzo, C.
Classificazione: 1 Contributo su Rivista
Abstract: This paper reports on results of nonlinear analyses performed within the RINTC project on an RC building isolated with different systems (High Damping Rubber Bearings, High Damping Rubber Bearings and Flat Sliding Bearings, Friction Pendulum System) and designed according to the Italian design code. The seismic response has been evaluated under different seismic input levels of two sites with different hazard and by considering two Limit States: Global Collapse and Usability-Preventing Damage. The influence of seismic stoppers and modelling uncertainties is also evaluated. Results permit to compute the implicit collapse risk and to identify critical aspects of current design procedures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/265813

Modelling Uncertainties of Italian Code-Conforming Structures for the Purpose of Seismic Response Analysis
JOURNAL OF EARTHQUAKE ENGINEERING
Autore/i: Franchin, Paolo; Ragni, Laura; Rota, Maria; Zona, Alessandro
Classificazione: 1 Contributo su Rivista
Abstract: This paper describes the multivariate statistical model of the structure-related modelling uncertainty, developed with reference to reinforced concrete, masonry, steel, and seismically isolated buildings, within the framework of the RINTC project. The model describes the variability of material properties as well as the uncertainty associated with the adopted response models. Specific aspects of each structural typology are also discussed, with a focus on the statistical dependence of the random variables in the model. Finally, the paper describes also the efficient sampling procedure adopted. Effect of model uncertainty on response for each typology are discussed in the corresponding papers within this special issue dedicated to the RINTC project.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/265814

An evaluation of stress-softening behaviour of HDNR bearings on the seismic response of base-isolated structures
Proceedings of the 16WCEE 2017
Autore/i: Tubaldi, Enrico; Ahmadi, Hamid; Muhr, Alan; Ragni, Laura; Dall'Asta, Andrea
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: In the last few decades, high damping natural rubber (HDNR) bearings have been extensively employed for seismic isolation of bridges and buildings because of their low horizontal stiffness and high damping capacity, which allows shifting the vibration period of the isolated structure away from where the earthquake input has the highest energy content and at the same time controlling the motion of the system. In HDNR material, filler is added to the natural rubber in order to improve its properties such as stiffness and dissipative capacity. The addition of the filler induces also a stress-softening behavior, known as “Mullins effect”. This effect makes the response of HDNR bearings path-history dependent and thus may influence the seismic performance of isolated systems. Published literature has suggested that the initial “virgin” properties of the material are eventually recovered. Accordingly, current seismic codes make the assumption that “Mullins effect” is a reversible phenomenon. The present work aims at studying the consequences of such strain-history dependent behavior on the seismic response of structural systems isolated with HDNR bearings. In particular, the first part of the paper reports a wide experimental campaign carried out on a large number of virgin rubber samples in order to better investigate some aspects of the stress-softening behavior of filled rubber, such as the direction-dependence and the recovery prosperities, and to characterize the stable and transient response under different strain histories. Test results are used to define a model for simulating the behavior of HDNR bearings in shear, which is an advancement in the description of both the stable and the transient behaviors. The proposed model has been used to analyze the seismic response of a simplified isolated structure modeled as a S-DOF (single degree of freedom) system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The obtained results show that, except for the special case of near-fault (NF) ground motions, the differences between the responses are limited although not negligible, whereas for NF records, the assumption of the virgin (or fully recovered) condition significantly reduces the effect of this type of motion on isolated structures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/247246

Deformation-induced anisotropy due to the Mullins effect in the biaxial response of HDNR bearings
Atti XVII ANIDIS
Autore/i: Ragni, L.; Tubaldi, E.; A., Dall'Ast; Ahmadi, H.; Muhr, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/259537

Seismic reliability of multi-storey buildings equipped with viscous dampers
Proceedings 16WCEE 2017
Autore/i: Dall'Asta, Andrea; Ragni, Laura; Tubaldi, Enrico; Scozzese, Fabrizio
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Viscous dampers are energy dissipation devices widely employed for the seismic control of new and existing building frames. To date, the performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches, i.e. by using a one-to-one relationship between the seismic intensity and a response parameters (usually coinciding with the mean response of a set of ground motions with a specific intensity level). However, these approaches neglects the response dispersion due to input uncertainties (the site seismic hazard condition and the record-torecord variability effects) as well as uncertainties of dampers properties. A more comprehensive performance assessment can be carried out by using probabilistic methodologies cable of fully accounting for different sources of uncertainty and the relevant effects on the structural reliability. This paper analyzes the probabilistic seismic performance of building frames equipped with viscous dampers by adopting a probabilistic methodology based on response hazard curves, providing the mean annual frequency (MAF) of exceedance of the response parameters of interest for the performance assessment of building structural and non-structural components and dampers. Finally, in order to quantify the difference between the demands evaluated by the probabilistic and deterministic approaches, ratios (REDP) between the probabilistic demand (characterized by different values of the MAF of exceedance) and the deterministic demand are evaluated. An application example is developed by considering a multi-storey steel frame selected from the SAC Phase II project and widely used in studies on seismic response control problems. A set of cases involving dampers with different exponents α designed for the same deterministic performance objective at a reference seismic intensity is considered. The probability distribution and the demand hazard of the response parameters of interest are evaluated and discussed in a range of variation of annual frequency of exceedance spanning from service to ultimate limit states, considering a range of the nonlinear exponent spanning from 0.15 to 1.00. Particular attention is focused on response parameters relevant to dampers (stroke and force). The ratios R are calculated from these parameters and the obtained values may be interpreted as amplification factors to be applied to the deterministic demand in order to obtain a desired safety level for the damper design. It is shown that the damper nonlinearity strongly affects the building and dampers performance and different trends are observed for different demand parameters. A comparison with code provisions shows that amplification factors currently used for the structural design provide non-homogeneous safety levels and should be improved by considering response variations due to the linear/nonlinear behaviour of the viscous dampers.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/247249

Reliability of systems equipped with viscous dampers accounting for the damper property variability
Atti convegno XVII ANIDIS
Autore/i: Dall'Asta, A.; Scozzese, F.; Ragni, L.; Tubaldi, E.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/259536

Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures
EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS
Autore/i: Tubaldi, E.; Ragni, Laura; Dall'Asta, A.; Ahmadi, H.; Muhr, A.
Classificazione: 1 Contributo su Rivista
Abstract: High-damping natural rubber (HDNR) bearings are extensively employed for seismic isolation of structures because of their low horizontal stiffness and high damping capacity. Filler is used in HDNR formulations to increase the dissipative capacity, and it induces also a stress softening behaviour, known as the Mullins effect. In this paper, a wide experimental campaign is carried out on a large number of virgin HDNR samples to better investigate some aspects of the stress softening behaviour, such as the direction dependence and recovery properties, and to characterize the stable and softening response under different strain histories. Test results are also used to define a model for simulating the response of HDNR bearings in shear that advances the state of the art in the description of the stress softening, which can be significant during the earthquake time history. The proposed model is used to analyse the seismic response of a simplified isolated structure modelled as an SDOF system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The results show that, in the case of far-field records, the differences between the responses are limited although not negligible, whereas for near-fault records, modelling the bearings as being in their virgin state significantly reduces the effect of this kind of motion on isolated structures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/247176

Rintc project: Nonlinear analyses of Italian code-conforming base-isolated buildings for risk of collapse assessment
COMPDYN 2017 - Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering
Autore/i: Cardone, D.; Conte, N.; Dall'Asta, A.; Di Cesare, A.; Flora, A.; Leccese, G.; Mossucca, A.; Micozzi, F.; Ponzo, C.; Ragni, L.
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/258595

Effect of the damper property variability on the seismic reliability of linear systems equipped with viscous dampers
BULLETIN OF EARTHQUAKE ENGINEERING
Autore/i: Dall’Asta, Andrea; Scozzese, Fabrizio; Ragni, Laura; Tubaldi, Enrico
Classificazione: 1 Contributo su Rivista
Abstract: Viscous dampers are dissipation devices widely employed for seismic structural control. To date, the performance of systems equipped with viscous dampers has been extensively analysed only by employing deterministic approaches. However, these approaches neglect the response dispersion due to the uncertainties in the input as well as the variability of the system properties. Some recent works have highlighted the important role of these seismic input uncertainties in the seismic performance of linear and nonlinear viscous dampers. This study analyses the effect of the variability of damper properties on the probabilistic system response and risk. In particular, the paper aims at evaluating the impact of the tolerance allowed in devices’ quality control and production tests in terms of variation of the exceedance probabilities of the Engineering Demand Parameters (EDPs) which are most relevant for the seismic performance. A preliminary study is carried out to relate the variability of the constitutive damper characteristics to the tolerance limit allowed in tests and to evaluate the consequences on the device’s dissipation properties. In the subsequent part of the study, the sensitivity of the dynamic response is analysed by harmonic analysis. Finally, the seismic response sensitivity is studied by evaluating the influence of the allowed variability of the constitutive damper characteristics on the response hazard curves, providing the exceedance probability per year of EDPs. A set of linear elastic systems with different dynamic properties, equipped with linear and nonlinear dampers, are considered in the analyses, and subset simulation is employed together with the Markov Chain Monte Carlo method to achieve a confident estimate of small exceedance probabilities.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/254639

Influence of the nonlinear behavior of viscous dampers on the seismic demand hazard of building frames
EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS
Autore/i: Dall'Asta, Andrea; Tubaldi, Enrico; Ragni, Laura
Classificazione: 1 Contributo su Rivista
Abstract: This paper analyzes the influence of damper properties on the probabilistic seismic performance of building frames equipped with viscous dampers. In particular, a probabilistic methodology is employed to evaluate the influence of the damper nonlinearity, measured by the damper exponent, on the performance of structural and nonstructural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. The performance variations due to changes in the damper nonlinearity level are evaluated and highlighted by considering two realistic design scenarios and by comparing the results of a set of cases involving dampers with different exponents designed to provide the same deterministic performance. By this way, it is possible to evaluate the influence of the nonlinear response and of its dispersion on the demand hazard. It is shown that the damper nonlinearity level strongly affects the seismic performance and different trends are observed for the demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas accounting for the damping nonlinearity level.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233674

Design and Experimental Analysis of an Externally Prestressed Steel and Concrete Footbridge Equipped with Vibration Mitigation Devices
JOURNAL OF BRIDGE ENGINEERING
Autore/i: Dall'Asta, Andrea; Ragni, Laura; Alessandro, Zona; Nardini, Luca; Salvatore, Walter
Classificazione: 1 Contributo su Rivista
Abstract: A 142-m, three-span continuous footbridge over the Esino River (Italy) is considered as a case study to illustrate a number of challenging aspects in its static and dynamic design. The adoption of an optimized steel deck with a variable cross section together with the use of external prestressing tendons in the central span allows a substantial reduction of structural weights. The resulting footbridge requires a proper model for the assessment of its behavior up to the ultimate limit state as well as attention to vibration control under pedestrian loading at the service limit state. The former issue is addressed through the use of a specifically developed material and geometric nonlinear finite-element formulation. Regarding vibration control, an original combination of two different systems is used, i.e., high damping rubber (HDR) stripes and tuned mass dampers (TMDs). The HDR stripes, applied between the steel deck and the concrete floor, increase the overall damping of the footbridge, whereas the TMDs significantly reduce the accelerations at the most critical frequencies. The design of this nonconventional solution for vibration control is discussed, and the results of experimental tests in the early stage of the footbridge construction are illustrated. The experimental results allow the validation of the structural model used in the design as well as the evaluation of the influence of the HDR stripes and of the nonstructural components on the modal properties of the completed footbridge, permitting fine-tuning of the TMDs before they are installed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/236198

Reliability of systems equipped with viscous dampers with variable properties
ECCOMAS Congress 2016 - Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering
Autore/i: Dall'Asta, Andrea; Ragni, Laura; Scozzese, Fabrizio; Tubaldi, Enrico
Editore: National Technical University of Athens
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Viscous dampers are energy dissipation devices widely employed for the seismic control of structures. The performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches. However, these approaches ne-glect the response dispersion due to the uncertainties in the input as well as in the structural system properties. Some recent works highlighted the important role of these uncertainties in the seismic performance of systems with linear or nonlinear viscous dampers. The present study focuses on the uncertainty in the damper properties and it aims at evaluating its influ-ence on the probabilistic response of the damped system. In particular, the variability of the damper properties is assumed to be constrained by the tolerances allowed in qualification and production control tests. A preliminary study on the damper response is carried out to relate the constitutive damper characteristics to the parameters controlled in the experi-mental tests and to evaluate the consequences of damper parameter variations on the dissipa-tion properties of the device. In the subsequent part of the study, the response hazard curves, providing the relation between the values of the response parameters of interest and the rele-vant yearly exceedance probability, are evaluated. In the analyses, a simplified structural sys-tem is considered, and the Subset Simulation (SS) algorithm is employed together with the Markov Chain Monte Carlo method to achieve a good estimate of small probabilities of exceedance. A sensitivity analysis, considering the expected variations in the damper proper-ties, is finally carried out by employing the Augmented SS method to study the influence of the device acceptance ranges on the hazard curves.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/247243

Influence of the stress-softening behaviour of HDNR bearings on the seismic response isolated bridges
Atti XVI ANIDIS
Autore/i: Tubaldi, Enrico; Ahmadi, Hamadi; Muhr, Alan; Ragni, Laura; Dall'Asta, Andrea
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233688

Influence of high damping natural rubber bearing model on the seismic response evaluation of isolated bridges
proceedings of SECED 2015
Autore/i: Ragni, Laura; Ahmadi, Hamid; Muhr, Alan; Tubaldi, Enrico; Dall'Asta, Andrea
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233691

Uncertainties propagation in the seismic response of structures with nonlinear viscous dampers
Atti XVI ANIDIS
Autore/i: Dall'Asta, Andrea; Ragni, Laura; Tubaldi, Enrico
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233683

Influence of connections modeling on the seismic behaviour of industrial buildings
Proceedings of COMPDYN 2015
Autore/i: Tassotti, Luca; Radi, Mohammed; Gara, Fabrizio; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Many industrial buildings with a precast concrete structure have been designed in accordance with non-seismic provisions by considering only gravity loads or, in some other cases, in accordance with not adequate seismic detailing requirements .In particular, seismic events that occurred in the recent past have shown that the connections between the main structural elements play an important role on the dynamic and seismic behaviour of the pre-cast concrete structure. Nowadays, the more advanced technical standards require mechani-cal connections between the precast elements; however codes do not furnish exhaustive information about the design and modelling of these connections neither in the seismic vul-nerability assessment of existing buildings nor in the design of new constructions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233472

Probabilistic seismic demand analysis of buildings equipped with nonlinear viscous dampers
CIVIL-COMP 2015
Autore/i: Dall'Asta, Andrea; Tubaldi, Enrico; Ragni, Laura
Editore: CIVIL_COMP PRESS
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Viscous dampers are energy dissipation devices widely employed for the seismic control of new and existing building frames. To date, the performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches neglecting the response dispersion due to the site seismic hazard condition and the record-to-record variability effects. This paper analyzes the probabilistic seismic performance of building frames equipped with viscous dampers by highlighting the influence of damper properties. In particular, a probabilistic methodology based on response hazard curves is employed to evaluate the effect of the damper nonlinearity, measured by the damper exponent, on the performance of structural and non-structural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. A case study consisting of a steel frame equipped with nonlinear viscous dampers is considered and the performance variations due to changes in the damper nonlinearity level are evaluated by considering design scenarios corresponding to dampers having different exponents designed to provide the same deterministic performance. Both response statistics at different seismic intensity levels and demand hazard curves for the monitored engineering parameters are employed as performance measures. It is shown that the damper nonlinearity strongly affects the seismic performance and different trends are observed for the various demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas for the dampers accounting for their nonlinearity level.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233679

Seismic response assessment of base-isolated bridges by accounting for the stress-softening behavior of HDNR bearings
proceedings of CIVIL-COMP 2015
Autore/i: Tubaldi, Enrico; Ahmadi, Hamid; Muhr, Alan; Ragni, Laura; Dall'Asta, Andrea
Editore: CIVIL-COMP PRESS
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: In the last few decades, high damping natural rubber (HDNR) bearings have been extensively employed for seismic isolation of bridges and buildings because of their low horizontal stiffness and high damping capacity, which allows shifting the vibration period of the isolated structure away from where the earthquake input has the highest energy content and at the same time controlling the motion of the system. In HDNR material, filler is added to the natural rubber in order to improve its properties such as stiffness and dissipative capacity. The addition of the filler induces also a stress-softening behaviour, known as “Mullins effect”. This effect makes the response of HDNR bearings path-history dependent and thus may influence the seismic performance of isolated systems. Published literature has shown that the initial “virgin” properties of the material are recovered. Accordingly, current seismic codes make the assumption that “Mullins effect” is a reversible phenomenon. Thus, they suggest simplified methods based on the use of property modification factors for the bearing model properties to account for this effect in the seismic response evaluation of structures isolated with HDNR bearings. The present paper is a study of the consequences of such strain-history dependent behaviour on the seismic response of structural systems isolated with HDNR bearings. In particular, the bearing behaviour is described by a non-linear processdependent constitutive model based on one previously developed. This model allows separation of the contribution to the response due to the path-history dependent component from the contribution resulting from the stable (scragged) component. The model properties are calibrated against double-shear tests carried out on HDNR compounds commonly employed for seismic isolators. In particular, the response of a realistic isolated bridge is analyzed under ground motions with different characteristics by considering two different conditions for the bearings, one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The results obtained for the two different conditions are compared to evaluate the influence of the Mullins effect on the bridge performance. This also permits an evaluation of the accuracy of simplified bearing models and relevant property modification factors suggested by the codes for the preliminary design and analysis of bridges isolated with HDNR bearings.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/233859

Probabilistic seismic response assessment of linear systems equipped with nonlinear viscous dampers
EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS
Autore/i: Tubaldi, Enrico; Ragni, Laura; Dall'Asta, Andrea
Classificazione: 1 Contributo su Rivista
Abstract: The paper aims at evaluating the influence of damper properties on the probabilistic seismic response of structural systems equipped with nonlinear viscous dampers. For this purpose, a linear single-degree-of-freedom system with an added linear or nonlinear viscous damper is considered, and the response statistics are evaluated for a set of natural records describing the ground motion uncertainty. A dimensional analysis of the seismic problem is carried out first to identify the minimum set of characteristic parameters describing the system and controlling the seismic response. An extensive parametric study is then performed to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e. maximum displacements, accelerations and damper forces), for a wide range of values of the characteristic parameters. Finally, a set of case studies is investigated to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system reliability and to highlight some limitations of current deterministic approaches neglecting the probabilistic properties of the response.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/225408

Seismic performance reduction in steel braced frames due to uneven brace over-strength distributions
Proceedings of EUROSTEEL 2014
Autore/i: Dall’Asta, Andrea; Zona, Alessandro; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/225414

Analisi sismica di edifici prefabbricati con connessioni deformabili
Atti del Workshop tecniche innovative per il miglioramento sismico di edifici prefabbricati
Autore/i: Tassotti, Luca; Radi, Mohamed; Gara, Fabrizio; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Nel contesto nazionale le strutture prefabbricate monopiano risultano in larga parte concepite mediante concezioni strutturali superate dagli attuali criteri antisismici. Gli eventi sismici recenti e del passato hanno evidenziato come la loro vulnerabilità sia spesso associata alle connessioni tra elementi strutturali. Le norme attuali risultano tuttavia carenti nel fornire indicazioni in merito alla progettazione e alla modellazione delle stesse. Nella presente memoria viene presentata una procedura di modellazione delle connessioni a spinotto per la valutazione della vulnerabilità sismica degli edifici esistenti. La metodologia proposta viene applicata a due capannoni industriali esistenti. Dai risultati delle analisi dinamiche lineari e statiche non lineari condotte è emerso che una modellazione delle connessioni rigide può portare a sovrastime della domanda sismica in esse e alla variazione della risposta sismica globale dell’edificio, modificando l’esito delle verifiche di sicurezza sia globali che locali.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/234008

Influence of nonlinear viscous dampers on the probabilistic seismic response of linear structure
Proceedings of the 2ECCE 2014
Autore/i: Tubaldi, Enrico; Ragni, Laura; Dall’Asta, Andrea
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The paper aims at evaluating the influence of damper properties on the probabilistic seismic response of structural systems equipped with nonlinear viscous dampers. For this purpose, a linear single-degree-of-freedom system with an added linear or nonlinear viscous damper is considered, and the response statistics due to a set of natural records describing the ground motion uncertainty is analyzed in detail. A dimensional analysis of the seismic problem is applied first to identify the minimum set of characteristic parameters describing the system and controlling the seismic response. An extensive parametric study is then carried out to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e., maximum displacements, accelerations and forces), for a wide range of values of the characteristic parameters. Finally, a set of case studies is investigated in order to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system reliability and to highlight some limitations of current approaches neglecting the probabilistic properties of the response
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/234007

Local and Global Response Parameters in Seismic Risk Assessment of RC Frames Retrofitted by BRBs
Atti dell’A.N.I.D.I.S. 2013
Autore/i: Freddi, F.; Tubaldi, E.; Dall’Asta, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/151706

Reduction of the seismic performance of steel braced frames due to irregular brace over-strength distributions
Atti dell’A.N.I.D.I.S. 2013
Autore/i: Dall’Asta, A.; Zona, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/151703

Influence of HDR model in the seismic response evaluation of isolated bridges
Atti dell’A.N.I.D.I.S. 2013
Autore/i: Ragni, Laura; Tubaldi, E.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/151704

Analysis of the seismic performance reduction in steel braced frames due to irregular brace over-strength distributions
Atti XXIV congresso CTA
Autore/i: Dall’Asta, A.; Zona, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/163737

Gradient-based study on seismic performance reduction of steel braced frames due to irregular brace over-strength distributions
Proceedings of the COMPDYN 2013
Autore/i: Dall’Asta, A.; Zona, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/151702

Probabilistic performance assessment of low-ductility reinforced concrete frames retrofitted with dissipative braces
EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS
Autore/i: Freddi, F.; Tubaldi, E.; Ragni, Laura; Dall'Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: The paper illustrates a probabilistic methodology for assessing the vulnerability of existing reinforced concrete (RC) buildings with limited ductility capacity retrofitted by means of dissipative braces. The aim is to highlight the most important parameters controlling the capacity of these coupled systems and specific aspects concerning the response uncertainties. The proposed methodology is based on the use of local engineering demand parameters for monitoring the seismic response and on the development of component and system fragility curves before and after the retrofit. In the first part of the paper, the methodology is illustrated by highlighting its advantages with respect to the existing approaches. Then, its capability and effectiveness are tested by considering a benchmark two-dimensional RC frame designed for gravity-loads only. The frame is retrofitted by introducing elasto-plastic dissipative braces designed for different levels of base shear capacity. The obtained results show the effectiveness of the methodology in describing the changes in the response and in the failure modalities before and after the retrofit, for different retrofit levels. Moreover, the retrofit effectiveness is evaluated by introducing proper synthetic parameters describing the fragility curves and by stressing the importance of employing local engineering demand parameters (EDPs) rather than global EDPs in the seismic risk evaluation of coupled systems consisting in low-ductility RC frames and dissipative braces.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/81996

Influence of brace over-strength distributions on the seismic response of steel braced frames
- Proceedings of the 15WCEE
Autore/i: Ragni, Laura; Zona, A.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/86400

Component-based Probabilistic Methodology for the Vulnerability Assessment of RC Frames Retrofitted with Dissipative Braces
Proceedings of the 15WCEE
Autore/i: Freddi, F.; Tubaldi, E.; Ragni, Laura; Dall'Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/86399

Sensitivity-based study of the influence of brace over-strength distributions on the seismic response of steel frames with BRBs
ENGINEERING STRUCTURES
Autore/i: Zona, A.; Ragni, Laura; Dall’Asta, A.
Classificazione: 1 Contributo su Rivista
Abstract: Steel frames with buckling-restrained braces (BRBs) have low lateral post-elastic stiffness, especially in the case of non-moment resisting beam-to-column connections, due to the brace limited post-yield stiffness. Thus, a tendency to soft storey formation, fostered by nonhomogeneous distributions of brace overstrength, might be observed during seismic events. The objective of this paper is to study the effects of brace over-strength distributions on the expected maximum reduction of seismic performance, as measured by local and global engineering demand parameters (EDPs). This goal is pursued using response sensitivity analysis and solving a constrained extreme problem. The general framework of the proposed sensitivity-based approach is presented and its application to steel frames with BRBs is described in detail. Realistic case studies are considered, taking as reference solution the design based on the modal response spectrum method. Interstorey drifts are used as global EDPs related to the damage of nonstructural elements, while maximum plastic strains and cumulative plastic strains of the braces are considered as local EDPs to monitor the damage of braces. The brace over-strength patterns that are the most unfavourable for each EDP are identified and the relevant maximum increment of each EDP with respect to the reference design solution is determined, obtaining a relation between the maximum seismic performance reduction and the brace over-strength used in the design. In this way, the proposed approach can be used as a tool for safer and more effective seismic designs of steel frames with BRBs.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63653

Experimental tests and numerical modelling of wall sandwich panels
ENGINEERING STRUCTURES
Autore/i: Gara, Fabrizio; Ragni, Laura; Roia, Davide; Dezi, Luigino
Classificazione: 1 Contributo su Rivista
Abstract: This paper presents the first part of an experimental investigation carried out on a construction system based on completed in situ sandwich panels with non-shear connectors, concerning the study of vertical panels used as structural walls. Compression tests with axial and eccentric loads were carried out on several full scale panel specimens with different slenderness ratios in order to study the behaviour of panels under vertical in-plane forces. Additionally, diagonal compression tests were performed on square specimens in different configurations in order to study the behaviour of panels under horizontal in-plane forces. The most significant load-displacement diagrams for increasing load are illustrated and the failure modalities are discussed. The semi-composite behaviour of the panels, guaranteed by the internal layer of polystyrene and the reinforced concrete beams at the panel ends, is highlighted. Finally, some numerical simulations are performed with non-linear finite element models and some useful design indications are given. (C) 2011 Elsevier Ltd. All rights reserved.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/75125

Experimental behaviour and numerical analysis of floor sandwich panels
ENGINEERING STRUCTURES
Autore/i: Gara, Fabrizio; Ragni, Laura; Roia, Davide; Dezi, Luigino
Classificazione: 1 Contributo su Rivista
Abstract: This paper presents the second part of an experimental investigation carried out on a construction system based on completed in-situ sandwich panels with non-shear connectors, concerning the study of floor sandwich panels. Four-point flexural tests were carried out on several full-scale panel specimens with different slenderness ratios in order to study the behaviour of panels under vertical loads. Additionally, wall-floor nodes with different connection details were tested to analyze the effective degree of the rotational restraint of different realistic nodes. Furthermore, a loading test on the floor of a full scale 3D mock-up entirely built with sandwich panels was carried out to investigate the service and ultimate behaviour of a real floor. The most significant load-displacement diagrams for increasing load are illustrated and the failure modalities are discussed. The semi-composite behaviour of the panels, guaranteed by the internal layer of polystyrene and the reinforced concrete beams at the panel ends, is highlighted. The effects of the wall-floor connection and the bi-dimensional behaviour of the floor are also evaluated. Finally, some numerical simulations are performed with non-linear finite element models and some useful design indications are given. (C) 2011 Elsevier Ltd. All rights reserved.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/75126

Local and global damage control in steel frames with elastoplastic bracing systems
Atti XXIII congresso CTA
Autore/i: Ragni, Laura; Zona, A.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72347

Steel braced frames with viscoelastic or elastoplastic structural dampers.
Line 5 of the ReLUIS-DPC 2005-2008 Project
Autore/i: Dall'Asta, A.; Dezi, Luigino; Leoni, G.; Ragni, Laura; Zona, A.
Editore: Doppiavoce
Luogo di pubblicazione: Napoli
Classificazione: 2 Contributo in Volume
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/82251

Local and global damage control in steel frames with elastoplastic bracing systems
Atti dell’A.N.I.D.I.S.
Autore/i: Ragni, Laura; Zona, A.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72349

Sensitivity analysis of steel frames equipped with BRBs
Proceedings of EUROSTEEL 2011
Autore/i: Zona, A.; Ragni, Laura; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63661

Sensitivity analysis of steel frames with buckling-restrained braces
Atti dell’A.N.I.D.I.S.
Autore/i: Zona, A.; Ragni, Laura; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72352

Local and global damage control in steel frames with elastoplastic dissipative bracing systems
Proceedings of EUROSTEEL 2011
Autore/i: Ragni, Laura; Zona, A.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63659

Probabilistic performance assessment of low ductility r.c. frames retrofitted by elasto-plastic dissipative braces
Atti dell’A.N.I.D.I.S.
Autore/i: Ragni, Laura; Freddi, F.; Tubaldi, E.; Dall’Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72350

Analytical expressions for preliminary design of dissipative braces in steel frames
JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH
Autore/i: Ragni, Laura; A., Zona; A., Dallasta
Classificazione: 1 Contributo su Rivista
Abstract: In this paper a direct displacement-based design (DDBD) method for seismic design of steel frames equipped with dissipative braces is proposed. Attention is focused on concentric braced steel frames with pinned beam-to-column joints in which the bracing system (with viscoelastic or elastoplastic dissipative devices) is the main seismic resistant component. The proposed design method uses an equivalent continuous model where flexural deformability and shear deformability are related respectively to columns and diagonals of the bracing system. In this way, analytical expressions of the required flexural and shear stiffness distributions are obtained. These expressions are quite simple and can be conveniently used in preliminary design of dissipative diagonal braces and columns. Examples are shown for steel frames with dissipative braces based on elastomeric dampers (viscoelastic devices) and steel frames with buckling-restrained braces (elastoplastic devices). Results of time history analyses are illustrated and discussed in order to evaluate the effectiveness of the proposed DDBD procedure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/37873

Caratterizzazione sperimentale di un sistema costruttivo a pannelli sandwich: pannelli parete
Atti del 18° Congresso C.T.E.
Autore/i: Gara, Fabrizio; Ragni, Laura; Roia, Davide; Dezi, Luigino
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: SUMMARY This paper presents the first part of the experimental campaign carried out on the constructive system ”Concrewall”, consisting of sandwich panels by Schnell House. The tests are conducted at the Material and Structural Testing Laboratory of the “Università Politecnica delle Marche”. In particular, Single Composite Panels (PCSP) used as vertical structural wall are tested. Compression tests, with axial and eccentric loads, and diagonal compressive tests are carried out in order to study the behaviour of panels under vertical and horizontal forces. The main results of the experimental campaign and some numerical analyses are illustrated.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63579

Probabilistic performance assessment of low ductility r.c. frames retrofitted by elasto-plastic dissipative braces
Proceedings of the 14th European Conference on Earthquake Engineering
Autore/i: F., Freddi; E., TUBALDI E; Ragni, Laura; A., Dallasta
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46355

Finite element response sensitivity analysis of steel frames equipped with buckling-restrained braces
Proceedings of the 4th International Conference on Steel & Composite Structures
Autore/i: A., Zona; Ragni, Laura; A., Dallasta
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46485

Caratterizzazione sperimentale di un sistema costruttivo a pannelli sandwich: pannelli solaio
Atti del 18° Congresso C.T.E.
Autore/i: Gara, Fabrizio; Ragni, Laura; Roia, Davide; Dezi, Luigino
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: SUMMARY This paper presents the second part of the experimental campaign carried out on the constructive system ”Concrewall”, consisting of sandwich panels by Schnell House. The tests are conducted at the Material and Structural Testing Laboratory of the “Università Politecnica delle Marche”. In particular, Single Composite Panels (PCSP) used as roof panels are tested. Flexural tests are carried out on the panels in order to study the behaviour under vertical loads. Additionally, to investigate the behaviour of the connection between roof and wall panels cyclic tests are performed on two typical connection systems. Finally, a load test of a square roof of a real-scale 3-D mock-up is carried out to evaluate the behaviour of a real roof taking into account both the effects of the roof-wall connection and the roof bi-dimensional behaviour. The main results of the experimental campaign and some numerical analyses are illustrated in the paper.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63578

Response Sensitivity Analysis of Steel Frames with Buckling-Restrained Braces
Proceedings of the 14 European Conference on Earthquake Engineering
Autore/i: Ragni, Laura; A., ZONA A; A., Dallasta
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46486

A geometric nonlinear model for composite beams with partial interaction
ENGINEERING STRUCTURES
Autore/i: G., Ranzi; A., Dall'Asta; Ragni, Laura; A., Zona
Classificazione: 1 Contributo su Rivista
Abstract: In this paper a kinematical model for planar composite beams including longitudinal partial interaction as well as vertical uplift is developed within the nonlinear finite deformation theory. Afterwards a reduced formulation, useful for solving structural problems, is derived on the basis of the theory of small strain and moderate rotations. This simplification involves some limitations in the magnitude of displacements and strains, and in the geometry, which are compatible with the results commonly observed in civil structures. The resulting nonlinear problem is solved using a displacement-based finite element formulation, and some numerical results are illustrated in order to highlight the capabilities of the presented beam model.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/37872

Campagna sperimentale sul sistema costruttivo a pannelli sandwich “concrewall”
Nota Tecnica di Dipartimento n. 19, Department of Architecture, Construction and Structures, Università Politecnica delle Marche, Italy
Autore/i: Dezi, Luigino; Gara, Fabrizio; R., Giacchetti; Ragni, Laura; Roia, Davide
Luogo di pubblicazione: Ancona
Classificazione: 5 Altro
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/74888

Design methods for existing r.c. frames equipped with elasto-plastic or viscoelastic dissipative braces
Atti dell’A.N.I.D.I.S.
Autore/i: Dall’Asta, A.; Ragni, Laura; Tubaldi, E.; Freddi, F.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72355

The behaviour of composite steel-concrete members accounting for partial interaction and geometric nonlinearities
Proceedings of Progress in Structural Stability and Dynamics, Hong Kong.
Autore/i: Ranzi, G.; Dall'Asta, A.; Ragni, Laura; Zona, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/71966

Steel structures equipped with BRBs or HDR-based dissipative braces: a simplified displacement-based design procedure
Atti dell’A.N.I.D.I.S.
Autore/i: Dall’Asta, A.; Ragni, Laura; Zona, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72353

HDR devices for the seismic protection of frame structures: Experimental results and numerical simulation
EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS
Autore/i: Ragni, Laura; Dezi, Luigino; Dall’Asta, A.; Leoni, G.
Classificazione: 1 Contributo su Rivista
Abstract: As part of a national research programme an experimental campaign was carried out on a real scale mock-up consisting of a steel–concrete composite frame equipped with dissipative bracings, based on high damping rubber (HDR) devices. Free vibration tests, followed by force-controlled and displacementcontrolled cyclic tests were performed. The experimental tests were aimed at studying the dynamic response of the coupled system in order to demonstrate the effectiveness of HDR devices in increasing the stiffness and dissipation capacity of the frame and investigating the ability of the constitutive HDR model proposed by the authors to predict the dynamic response of the coupled system.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/58524

Simplified method for the analysis of externally prestressed steel-concrete composite beams
JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH
Autore/i: A., DALL'ASTA A; Ragni, Laura; A., Zona
Classificazione: 1 Contributo su Rivista
Abstract: The ultimate capacity of beams prestressed with external slipping tendons cannot be evaluated by a local analysis of the critical sections and a nonlinear analysis of the whole beam-tendon structural system is required. Since this type of analysis is complex, simplified approaches are of great assistance to engineers in the design process. In this work a new simplified method is introduced for evaluating the tendon traction increment at collapse and consequently the beam flexural strength without requiring a nonlinear analysis of the whole beam-tendon structural system. A detailed description of the proposed approach is given and some applications of practical interest to externally prestressed steelconcrete composite beams are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36746

Valutazione sperimentale del comportamento dinamico del ponte pedonale sul fiume Esino
Atti del III Workshop: Problemi di vibrazione nelle strutture civili e nelle costruzioni meccaniche
Autore/i: Chellini, G.; Lippi, F.; Nardini, L.; Salvatore, W.; Dall'Asta, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/82240

Identificazione dinamica e modellazione numerica del ponte pedonale sul fiume Esino
Atti dell’A.N.I.D.I.S. – 13° Convegno Nazionale – L'ingegneria sismica in Italia
Autore/i: Chellini, G.; Lippi, F.; Nardini, L.; Salvatore, W.; Dall’Asta, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/82247

Influence of abutment restraints on the seismic response of multi-span continuous bridges
Proceedings of the 14th World Conference on Earthquake Engineering
Autore/i: A., Dallasta; Ragni, Laura; E., Tubaldi
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46353

A design method for steel frames equipped with buckling restrained braces
Proceedings of the 14th World Conference on Earthquake Engineering
Autore/i: A., Dallasta; Ragni, Laura; A., Zona
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53519

Validation of a HDR-based device model by experimental tests on a steel-concrete composite frame
Proceedings of the 14th World Conference on Earthquake Engineering – 14 WCEE
Autore/i: A., Dallasta; Dezi, Luigino; G., Leoni; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52329

Mitigation of seismic effects by means of dissipative braces based on high damping rubber and elasto-plastic buckling restrained devices: experimental campaign on a real scale mock-up
Tecnologie per l’Isolamento ed il Controllo di Strutture ed Infrastrutture
Autore/i: Dall'Asta, A.; Dezi, Luigino; Leoni, G.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72360

Seimic behaviour of continuous composite bridge with aboutment restrains
Atti del "VII Workshop Italiano sulle Strutture Composte"
Autore/i: Tubaldi, E.; Dall'Asta, A.; Ragni, Laura
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72363

Design methods for existing r.c. frames equipped with buckling restrained braces and dissipative braces based on high damping rubber
Tecnologie per l’Isolamento ed il Controllo di Strutture ed Infrastrutture
Autore/i: Dall'Asta, A.; Ragni, Laura; Tubaldi, E.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72357

A design method for steel frames equipped with buckling restrained braces
Proceedings of EUROSTEEL 2008
Autore/i: Ragni, Laura; Duca, C.; Zona, A.; Dall'Asta, A.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/58500

Dissipative braces based on high damping rubber: analysis and design
Proceedings of the 14th World Conference on Earthquake Engineering
Autore/i: A., Dallasta; Ragni, Laura; E., Tubaldi
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46352

Nonlinear behavior of dynamic systems with high damping rubber devices
ENGINEERING STRUCTURES
Autore/i: Ragni, Laura; A., Dall'Asta
Classificazione: 1 Contributo su Rivista
Abstract: The High Damping Rubber (HDR) is widely used in seismic engineering and, more generally, in the passive control of vibrations. Its constitutive behaviour is quite complex and is not simply non-linear with respect to strain but also shows a transient response during which material properties change (Mullins effect). A number of recent works were dedicated to analyzing and modelling the material behaviour. The present work intends to study the consequences of such non-linear behaviour in the dynamic response of S- DoF systems where the restoring force is provided by dissipative devices based on the HDR (structural system with dissipative bracings and isolated systems). Preliminary analyses under harmonic forces and impulsive excitations were carried out in order to separately characterize stable and transient responses. Finally, the response under seismic inputs with different intensities was studied. Results show that the Mullins effect may play an important role in the seismic response and the dynamic properties of the system change significantly for seismic events with different intensities.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/37869

Dynamic systems with high damping rubber: Nonlinear behaviour and linear approximation
EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS
Autore/i: A., Dall'Asta; Ragni, Laura
Classificazione: 1 Contributo su Rivista
Abstract: High damping rubber (HDR) shows a quite complex constitutive behaviour, which is nonlinear with respect to strain and is dependent on the strain rate. In addition, it exhibits a transient response during which the material properties change (scragging or more generally the Mullins effect). A number of recent works were dedicated to analysing and modelling material behaviour. This paper studies the nonlinear dynamics of systems with restoring force produced by HDR-based devices in order to propose a procedure to define equivalent linear models considering both transient and stationary behaviours. The reliability of these linear models is tested by evaluating the upper and lower bounds of the seismic response of a structural system equipped with HDR-based devices (structural system with dissipative bracings and isolated systems).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/37870