Papers by stefano podesta
Progettazione Sismica, 2013
Gli effetti traumatici che si susseguono dopo ogni evento sismico fanno emergere con assoluta chi... more Gli effetti traumatici che si susseguono dopo ogni evento sismico fanno emergere con assoluta chiarezza quanto sia vulnerabile il nostro costruito esistente. Alle costruzioni storiche, più o meno antiche, realizzate senza il rispetto di criteri che tengono conto della pericolosità sismica del sito -criteri imposti oggi dalla Normativa o governati dalle regole dell'arte nel passato -si aggiunge la continua constatazione dell'inadeguatezza degli strumenti che utilizziamo per cautelarci dal rischio sismico. L'evoluzione dell'ingegneria sismica è d'altronde basata, in maniera quasi duale, sugli eventi più o meno importanti che si sono verificati nel mondo industrializzato, alimentando la ricerca della comunità scientifica. Ogni evento, infatti, rappresenta un test che permette di valutare la bontà dei modelli di calcolo, delle soluzioni tecniche, permettendo di proporne di nuovi quando i risultati non sono stati congruenti a quanto teoricamente preventivato. Fa parte ovviamente del consueto sviluppo della ricerca che ha l'obbligo di stare sulla frontiera della conoscenza, modificare i metodi di verifica, aggiornare i parametri che entrano in gioco. Più complessa è però l'applicazione sulle costruzioni, monumentali e non. Gli interventi che progettiamo sono episodi che condizionano il comportamento strutturale (la risposta sismica) per un lasso temporale molto lungo, che male si coniuga con gli aggiornamenti normativi che la ricerca accademica può determinare. Le motivazioni sono abbastanza ovvie: da un lato la difficoltà a traghettare sul mondo professionale i risultati della ricerca rende lento questo aggiornamento continuo, dall'altro le disponibilità economiche limitate, completamente assorbite per gestire l'emergenza del momento non consentono di pianificare in termini preventivi una riduzione del rischio sismico. In questo panorama l'evento dell'Emilia rappresenta una situazione emblematica. L'azione sismica che si è verificata sia in termini di accelerazione massima sia come contenuto in frequenza evidenzia un evento con una probabilità di eccedenza minore di quella presa normalmente come riferimento per lo stato limite di salvaguardia della vita. La ridotta profondità dell'evento sismico ha determinato accelerazioni verticali comparabili a quelle orizzontali. Valori così elevati della componente sussultoria, sottolineano la necessità di una diversa interpretazione del loro effetto in termini di spettro di risposta, rispetto a quanto ad oggi normato. Si fa ad esempio riferimento all'invariabilità degli spettri verticali previsti dalle Norme Tecniche per le Costruzioni (D.M. 14 gennaio 2008) per le diverse classi del sottosuolo. Da questo punto di vista la possibilità di cautelarsi preventivamente può sembrare quasi inutile, consci delle conoscenze in nostro possesso. In questo lavoro, invece, si è provato a dimostrare tramite lo studio di alcuni manufatti storici, come sia possibile operare in un'ottica preventiva, cercando di capire come anche la "limitata conoscenza" attuale sul fenomeno terremoto avrebbe potuto salvaguardare molte costruzioni, oggi irrimediabilmente compromesse. Lo stato di danneggiamento oggi rilevabile sulle costruzioni monumentali emiliane non può unicamente essere imputato ad una non esaustiva conoscenza della pericolosità sismica di quelle zone: la totale mancanza di agire in un ottica culturale di prevenzione è, ancora una volta, la prima causa della perdita nostro patrimonio culturale.
First European …, 2006
In autumn 2002 two moderate energy earthquakes (31 October, 10:32 GMT, M W = 5.4, and 1 November,... more In autumn 2002 two moderate energy earthquakes (31 October, 10:32 GMT, M W = 5.4, and 1 November, 15:08 GMT, M W = 5.0) struck the provinces of Campobasso and Foggia (southern Italy). The earthquakes attained an intensity VII (Modified Mercalli scale) throughout the epicentral area, except for the village of San Giuliano di Puglia, that suffered an intensity VIII-IX. Damage and vulnerability surveys on monuments (churches) suggested that the geomorphological site conditions greatly affected the damage level. In particular we found that, for a comparable intrinsic vulnerability of the building, the structural damage level is directly correlated to local amplification phenomena related to the different morphological and lithological characteristics of each church site. The assessment of damage increase related to local amplification of the ground shaking is made possible by evaluating the damage and seismic vulnerability of each church (e.g., the lack of antiseismic protection, the presence of vulnerability indicators). The damage increase was compared to the morpho-lithological characteristics of each site, schematized with a few simplified parameters. This methodology allowed us to evaluate separately a morphological hazard, related to the topographic characteristics of the site and the building location, and a lithological hazard, evaluated on the basis of the Italian Seismic Code. Our research goal was to set up an expected damage evaluation method, that considers not only the building vulnerability, but also the additional vulnerability related to the morphological conditions of the church site. The methodology can be effectively used in preventive analyses, targeted to define a priority list of historic buildings and monuments at high seismic risk.
The evaluation of structural safety derives from the knowledge of material properties. In case of... more The evaluation of structural safety derives from the knowledge of material properties. In case of existent masonry building, the definition of reliable mechanical parameters could be a very difficult task to be achieved. For this reason, an estimation of these values is useful, for example it is the first phase of the knowledge process, for simplified mechanical model or when NTD test is the only possibility.The transversal connection in masonry panels is a technological detail that affects the static and seismic behavior and could significantly increase the strength of the element.In this paper the effect of transversal connection in double-leaf brickwork masonry panels is evaluated by diagonal compression tests. To achieve this goal, a new set-up was designed to load each leaf independently.The results have shown an increment of about 20% in strength if transversal connection is present. If the leaves have very different mechanical parameters, the tests highlight an unexpected beh...
Bulletin of the New Zealand Society for Earthquake Engineering, Sep 30, 2009
The seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on t... more The seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on the characteristics of wooden floors and, in particular, on their in-plane stiffness and on the quality of connection between the floors and the URM elements. It is generally well-recognized that an adequate inplane-stiffness and proper connections can significantly improve the three-dimensional response of these buildings, obtaining a better distribution and transfer of forces to the lateral load resisting walls. However, the extensive damage observed during past earthquakes on URM buildings of different types have highlighted serious shortcomings in typical retrofit interventions adopted in the past and based on stiffening the diaphragm. Recent numerical investigations have also confirmed that increasing the stiffness of the diaphragm is not necessarily going to lead to an improved response, but could actually result to detrimental effects. The evaluation of the in-plane stiffness of timber floors in their as-built and retrofitted configuration is still an open question and a delicate issue, with design guidelines and previous research results providing incomplete and sometimes controversial suggestions to practicing engineers involved in the assessment and/or retrofit of these type of structures. In this contribution, the role of the in-plane stiffness of timber floors in the seismic response of URM buildings is critically discussed, based on the relatively limited available experimental and numerical evidences. A framework for a performance-based assessment and retrofit strategy of URM buildings, capable of accounting for the effects of a flexible diaphragm on the response prior to and after the retrofit intervention, is then proposed. By controlling the in-plane stiffness of the diaphragm, adopting a specific strengthening (or weakening) intervention, the displacements, accelerations and internal force demands can be maintained within targeted levels. This will protect undesired local mechanisms and aim for a more appropriate hierarchy of strength within the whole system.
Structural control & health monitoring, 2008
The impossibility of adjusting the monumental buildings to the protection levels adopted for newl... more The impossibility of adjusting the monumental buildings to the protection levels adopted for newly conceived buildings brings about the need to accept lower safety levels. In such case, the potentiality of dynamic monitoring by means of periodic checks on the dynamic characteristics of the structure (its own frequencies and vibration modes) would allow, at least theoretically, one to check globally that there are no changes to the boundary conditions that would further diminish the structural safety level. To this end, the dynamic analyses of a masonry triumphal arch of a medium-sized church are reported in this paper. The dynamic identification campaign was carried out at the ELSA Laboratory, studying the in-plane behaviour of the structure in undamaged and damaged conditions. The dynamic identification campaign, which lasted more than 6 months, allowed us to test the reliability of different acquisition systems, of different typologies of excitation and above all of evaluating the influence of environmental conditions on the dynamic parameters that may be identified. Indeed, variation of the environmental factors (e.g. temperature, insolation, humidity) may determine a change of the structure's own frequencies that must be taken into consideration just so as to be able to recognize the variations that may be correlated to a structural change due to the presence of damage.
International Journal of Architectural Heritage, Jan 30, 2019
The effectiveness of tie-rods is widely stressed in past earthquakes and they are still used toda... more The effectiveness of tie-rods is widely stressed in past earthquakes and they are still used today as reinforcement intervention, given that their use is a low-invasive and low-expensive technique. However, the earthquake design of these devices is not so simple since the main feature of a tierod derives from its ductility and that should be preserved as was done in the past. In this article, some considerations about static and seismic design of tie-rods are made, highlighting the main failure modes of the system. To assess seismic vulnerability of I-mode mechanism, displacement-based methods are usually used, requiring high elongation capability of the tie-rods. For this reason, an experimental campaign was carried out to define clearly the maximum elongation of tie-rods and to investigate the influence of bar length on ductility. The results have shown a good displacement capacity that decreases with the increase of steel strength. A simplified formulation, obtained from nonlinear kinematic analysis, is derived to evaluate quickly the seismic vulnerability of I-mode mechanism with tie-rods and to design this common retrofitting intervention in existing buildings.
Spinotto: barra cilindrica a sezione circolare, usualmente di acciaio, inserita in una sede prefo... more Spinotto: barra cilindrica a sezione circolare, usualmente di acciaio, inserita in una sede preforata ed usata per trasmettere carichi perpendicolari all'asse dello spinotto. Umidità del legno: la massa dell'acqua contenuta nel legno, espressa come percentuale della massa anidra di quest'ultimo. Umidità di equilibrio del legno: valore di umidità al quale il legno non assume o perde umidità in un dato ambiente. Punto di saturazione: stato di un elemento di legno nel quale le pareti cellulari sono sature di umidità, ma non vi è acqua nelle cavità cellulari. Dimensione geometrica: ai fini strutturali la dimensione geometrica è quella netta degli elementi alle condizioni di umidità specificate e al grado di finitura superficiale previsti a progetto. Ad essa vengono riferiti gli scostamenti, che idealmente devono essere uguali a zero. Classe di resistenza: profilo unificato di valori caratteristici e/o medi di resistenza, moduli elastici e massa volumica. Categoria: suddivisione cui vengono assegnati i segati classificati secondo la resistenza, conformemente ad una determinata norma. Tipo di legname: materiale al quale si applicano i valori caratteristici. Esso è definito da parametri quali la specie, la provenienza e la categoria.
This paper presents the main results concerning mechanical approach for seismic vulnerability ass... more This paper presents the main results concerning mechanical approach for seismic vulnerability assessment obtained during a recent research project, having as objective the creation of risk maps at the urban territory of the cities of Sion and Martigny, highest seismic zone of Switzerland. It focuses on validation and improvement of Risk-UE LM2 capacity curves for unreinforced brick masonry (URM) buildings, with stiff floors and reinforced concrete (RC) shear wall buildings. Given that the standardized Risk-UE capacity curves have been mainly developed for building stock of southern European cities, their reliability for different building features is validated. Within the framework of the development of seismic scenarios for the two cities, a detailed survey was performed for a sample of 500 buildings. Individual capacity curves were determined for all buildings, following the DBV simplified approach. Specific typological classification has been proposed for the Swiss built environm...
Journal of Earthquake Engineering, 2019
This article addresses seismic vulnerability assessment at an urban scale using mechanical method... more This article addresses seismic vulnerability assessment at an urban scale using mechanical methods, more specifically potential improvements by involving typological curves instead of standard capacity curves and by using accurate displacement demand determination for reliable building damage prediction. The impact in terms of damage grades is computed for two typical Swiss cities. In Europe, seismic-vulnerability assessment is usually performed using the Risk-UE methodology, which involves an empirical approach (LM1 method) and a mechanical approach (LM2 method). The LM2 method contains standard capacity curves of conventional building types for computation of the corresponding damage grades. These capacity curves have been developed for southern Europe and are not optimal for describing features of other building stocks. New specific refined capacity curves are developed for northern Europe. Eurocode 8 prescribes the computation of displacement-demand for seismic assessment of existing building through a process based on the N2 method. However, the inaccuracy of the N2 method in certain conditions has already been studied. Therefore, modifications of N2 method have been proposed to improve the reliability of displacement-demand determination. In this study, the impact of typological capacity curves and the modified N2 method are investigated independently. Results show that both refinements contribute to improve the damage-grade distribution assessment.
Bulletin of Earthquake Engineering, 2016
This paper addresses seismic vulnerability assessment at an urban scale and more specifically the... more This paper addresses seismic vulnerability assessment at an urban scale and more specifically the capacity curves involved for building damage prediction. Standard capacity curves are a function of predefined building typology and are proposed in the Risk-UE LM2 method for computation of the corresponding damage grades. However, these capacity curves have been mainly developed for building stock of southern European cities and the accuracy of their application with different building features, such as the ones of cities of northern Europe should be assessed. A recent research project of seismic scenarios for the cities of Sion and Martigny in Switzerland provided the opportunity to check the capacity curves of Risk-UE LM2 method. Within the framework of this project, a detailed analysis was achieved for more than 500 buildings. These buildings were typical Swiss buildings and were composed of both unreinforced masonry buildings with stiff floors and reinforced concrete buildings. The construction drawings of each building were collected in order to have the most accurate information about their main structural characteristics. The typological classification that has been adopted was developed in a recent research project. Based on the individual features of the buildings, individual capacity curves were defined. Results of the seismic assessment applied to the 500 buildings compare very well with those obtained by using Risk-UE LM2 method for unreinforced masonry buildings with stiff floors. A slight improvement may be proposed for buildings with three stories through their introduction to the category of low-rise instead of mid-rise buildings. By contrast, accuracy for reinforced concrete buildings with shear walls is very poor. Damage prediction using related capacity curves of Risk-UE LM2 method does not correspond to reality. Prediction is too pessimistic and moreover damage grades increase with the height category (low-rise, mid-rise and high-rise) of these buildings which is in contradiction with the observed damages for this type of buildings. Improvements are proposed to increase the accuracy of the seismic vulnerability assessment for northern European building stock. For unreinforced masonry buildings, a slight modification of the limits of the height category of buildings using the ones defined for RC buildings improves the damage prediction. For reinforced concrete buildings with shear walls improved capacity curves derived from the typological curves of the specific typology C are proposed.
Proceedings of the VI International Conference on Structural Analysis of Historic Construction, SAHC08, 2-4 July 2008, Bath, United Kingdom, 2008
In order to evaluate the seismic vulnerability of ancient bell towers, the simplified mechanical ... more In order to evaluate the seismic vulnerability of ancient bell towers, the simplified mechanical model proposed into Italian document "Guidelines for evaluation and mitigation of seismic risk to cultural heritage" was applied to a sample of 31 bell towers damaged by the 1976 Friuli (Italy) earthquake. The seismic safety level has been evaluated taking into account the seismic input of the 1976 seismic event, in order to compare the forecast obtained by this simplified model with the observed damage. The comparison has highlighted some limits of the proposed methodology, based on the hypothesis of a tower with cantilever behaviour, constrained at the base that collapsed to axial compression and bending action. Such behaviour is not often confirmed by the damage observation. The crack patterns put in evidence the development of local collapse mechanisms ruled mainly by the equilibrium loss of masonry portion instead of crushing phenomena. The bell towers are not frequently able to develop an overall behaviour for the lack of interlocking corners or of steel tie-rods or of well-connected diaphragms. In the paper the authors proposed a new simplified method to evaluate the seismic risk of towers, based on the analysis of the constructive characteristics of the structure.
Figura 1. Profilo topografico passante per il sito della chiesa di S. Pietro in Vincoli a Castell... more Figura 1. Profilo topografico passante per il sito della chiesa di S. Pietro in Vincoli a Castellino del Biferno (CB). Tabella 1. Campione di chiese analizzato (su sfondo grigio sono riportate le chiese danneggiate dal terremoto del 1984). Comune Denominazione H [m] α [°] I mcs
The damage and vulnerability survey of the monumental buildings, damaged by the 2002 earthquake i... more The damage and vulnerability survey of the monumental buildings, damaged by the 2002 earthquake in the Molise Region, has allowed singling out of a correlation between the observed damage of the churches and their morphological site conditions. The vulnerability model connected to the survey methodology provides an evaluation of the expected mean damage. Comparison with the observed damage determined the
In questo lavoro sono descritte le attività svolte nell'ambito del Progetto Europeo Strategico RI... more In questo lavoro sono descritte le attività svolte nell'ambito del Progetto Europeo Strategico RISKNAT riguardanti l'analisi di microzonazione di Sant'Agata Fossili (AL). Sono in particolare descritte tutte le indagini ed analisi numeriche condotte al fine di ottenere una microzonazione sismica di livello 3 secondo quanto previsto nelle recenti linee guida nazionali degli. Al fine inoltre di valutare le ricadute di tipo applicativo di una corretta microzonazione sismica del territorio, sono state realizzate delle simulazioni di scenario adottando come riferimento gli spettri di risposta ottenuti dall'analisi di microzonazione. Le valutazioni di scenario ottenute sono state infine confrontate con le previsioni di scenario realizzabili a priori sulla base dell'adozione degli spettri di risposta definiti nelle Norme Tecniche per le Costruzioni.
This paper describes the new methodology used to assess seismic damage in the churches of Molise ... more This paper describes the new methodology used to assess seismic damage in the churches of Molise damaged by the 31 st October 2002 seismic event. In the paper the first results of the statistical reelaboration of the data collected with the new survey form are presented, which is based on the method used after the 1997 earthquake in Umbria and The Marches (Lagomarsino ). The possibility of having a vulnerability survey of the churches through a subdivision into vulnerability indicators and a-seismic devices has allowed us a more accurate evaluation of the seismic behaviour of this kind of building that showed considerable damage, despite the low magnitude of the two main seismic events. The high intrinsic vulnerability of churches, , has, in fact, in many cases been increased by not so effective retrofitting interventions. The new detailed form has allowed us to identify these specific aspects and to give meaningful suggestions for the successive reconstruction phase.
An overview of the available methodologies for the vulnerability analysis of the monumental build... more An overview of the available methodologies for the vulnerability analysis of the monumental buildings is proposed. If the analysis has to be developed on the monumental buildings at a territorial scale, the vulnerability models have to be referred to a typological classification and the approaches mainly belong to two different categories: observational and mechanical. In case of the most important monuments, more detailed models may be defined. Thus the methodology is organised in: a) Level 1, based only on typological studies on the observed vulnerability; b) Level 2, analysing a single part of the fabric (macroelement), considering simplified mechanical models suitable at the territorial scale; c) Level 3, defined on a more detailed analysis of the whole building or of a macroelement. In the level 1 model, the seismic input is represented in terms of intensity. On the other hand, the mechanical approach is based on the Capacity Spectrum Method that requires the definition of the Capacity Curve of the macroelement or of the whole building.
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Papers by stefano podesta