Seismic vulnerability assessment of clustered historical centers: fragility curves based on local collapse mechanisms analyses

open5noProtection and preservation of minor historical centres against earthquakes effects are not trivial tasks, particularly in the cases, quite common, of complex aggregate buildings. The paper aims at evaluating the seismic vulnerability of historical clustered buildings on a urban scale, through the analysis of local collapse mechanisms, carried out with a parametric approach. This procedure is applied to four historical centres of L’Aquila province struck by the 2009 earthquake. The identification of the significant parameters is related to the definition of representative typologies within the city centres. Each typology is characterized by recurring features, mainly recognizable with a survey performed outside the buildings. After the identification of the relevant aspects, local mechanisms of collapse analyses are carried out, by varying the parameters between defined range of values, in order to take into account possible uncertainties in the data collection. A set of fragility curves for each identified typology is defined and the obtained results are compared to the damage data gathered in the post-earthquake phase for the buildings. This approach allows for possible extensions to buildings that may be included in the typology categories here defined.openTaffarel, S.; Caliman, M.; Valluzzi, M.R; da Porto, F.; Modena, C.Taffarel, Sabrina; Caliman, M.; Valluzzi, MARIA ROSA; DA PORTO, Francesca; Modena, Claudi

Seismic vulnerability assessment on a territorial scale based on a Bayesian approach

Italian historical centres are mostly characterized by aggregate buildings. As defined by the Italian codes (Norme Tecniche per le Costruzioni 2008 and Circolare n. 617), the analysis of the most representative local mechanisms of collapse must be performed in order to assess their vulnerability. In this article, the out-of-plane local mechanisms of collapse analysis is implemented by applying a new method of analysis based on a probabilistic approach. Usually information which are necessary for the implementation of the local mechanisms analyses are affected by uncertainty or are missing, therefore in lots of cases it is only possible to hypothesize them on the basis of the other buildings information collected during the on-site survey. In this context, the implementation of a Bayesian approach allows to deduce buildings lacking information (i.e. wall thickness and interstorey height) starting from certain collected data (i.e. facades height). The historical centre of Timisoara (Romania) is selected as the case study for the implementation of this new method of analysis, given the extension of the on-site survey already carried out in the area (information about more than 200 structural units have been collected) and the seismic vulnerability assessment on an urban scale already performed by applying a traditional method. Results obtained by adopting the two approaches are then compared and a validation and a calibration of the new one is carried out

The application of a Bayesian approach to assess the seismic vulnerability of historical centers

The seismic vulnerability of historical centers at a territorial scale cannot be assessed performing detailed analysis which are usually adopted at the single building scale. In fact, a traditional complete survey would be extremely time-consuming and not sustainable for this purpose. The approach described in this paper is based on the idea that it is possible to infer quantities which cannot be directly detected from buildings outside inspection starting from parameters that can be measured. In order to achieve this purpose, a Bayesian approach is applied, updating initial hypotheses when new data become available. In this context, the procedure herein proposed aims at applying a probabilistic approach instead of a deterministic one to define facades inter-storey height starting from buildings height knowledge. In order to validate the method, for out of plane local mechanisms of collapse (walls overturning), horizontal loads multiplier \uf0610 values are calculated and compared to results obtained by using data collected on-site

Fragility curves for Italian residential masonry buildings with retrofit interventions

The earthquakes of the last decades have shown that the Italian residential masonry built her-itage has high seismic vulnerability, in particular when considering structures built before 1919. For this reason, it is necessary to develop effective large-scale risk mitigation strategies in order to reduce the huge losses that could occur in the aftermath of an earthquake. In this paper some retrofit interventions applicable mainly to old buildings are presented, explaining their advantages and potential. These interventions are then implemented, through Vulnus 4.0 software, on a database of 205 buildings built before 1919, previously analyzed in their as-built state. Fragility curves are then developed for each building, and are processed in order to create a vulnerability model for different construction periods that takes into account the possible ret-rofit intervention strategies. Therefore, this procedure allows a comparison between pre and post retrofit intervention fragility, and the results in terms of curves can be used for large scale damage and risk simulations

Investigations on inter-storey seismic isolation as a technique for adding upper storeys

The inter-storey seismic isolation technique is becoming increasingly attractive for the seis-mic risk mitigation of buildings, also as alternative strategy to base isolation. The reasons for applying this technique can be various and of different nature, such as: architectural con-cerns, feasibility of construction, and performance benefits. An interesting application of this technique concerns its use for adding upper storeys to existing buildings, avoiding the in-crease of seismic forces on the substructure, or even reducing them. Therefore, this technique could also be effective for seismic retrofit applications, using the mass of the superstructure as a nonconventional TMD for controlling the dynamic response of the substructure. Among the main issues concerning this application, there is the need to control the relative displacement between the two structural parts and the acceleration of the superstructure, while improving the seismic performance of the substructure. In this paper, a multi-objective optimization method for the dynamic characteristics of the ad-ditional superstructure is presented, which uses a TMD approach and considers the perfor-mances of the substructure, isolation system and superstructure. A 3-storey (3 DOF) case study structure was taken as a reference, analysing a wide range of isolated masses, isolation periods and damping ratios. Time-history analyses are finally performed, based on the opti-mization results, in order to assess the effectiveness of both the optimization method and the isolation technique, also considering the structural non-linearity

Danneggiamento e recupero degli edifici storici: l\u2019esperienza dell\u2019Aquila

La salvaguardia del patrimonio architettonico, la cui fragilit\ue0 \ue8 stata messa in evidenza dai r ecenti eventi sismici, sta diventando sempre pi\uf9 un problema sociale ed economico in molti paesi. Occorr e particolare cura nel definire il livello di sicurezza accettabile, i materiali utilizzabili e le tecniche di r ecupero che rispettino i valori culturali e storici. Inoltre, devono essere stabilite regole di buona pratica applicabili nei centri storici, caratter izzati da edifici complessi e interconnessi tra lor

Effectiveness of load-level isolation system for pallet racking systems

Recent Italian earthquakes have shown the high seismic vulnerability of pallet racking systems. In the down-aisle direction and in the absence of bracing systems, these structures are very flexible moment-resisting frames. Instead, in the cross-aisle direction they consist of slender trusses, stiffened by various bracing systems; the latter, although necessary for lateral stability, attract significant seismic accelerations, which can cause the stored goods to fall, posing a threat to human safety. To reduce this risk while increasing the rack structural performance, some mitigation systems were proposed, based on specific base-isolation or dissipation devices. In this paper, an innovative passive control system is investigated, i.e., the Load-Level Isolation System (LLIS), which consists of applying isolators to the load level to control the movement of pallets in the cross-aisle direction. The LLIS is based on the Tuned Mass Damper (TMD) strategy and exploits the high payload of these structures. Among the major uncertainties of this system are the amount of isolated mass and its position within the structure. Therefore, for a case study rack, the LLIS parameters (isolation stiffness and damping ratio) are optimized for various arrangements of this system, considering cases with one or two isolated levels. The applied optimization procedure is an extension of the classical TMD approaches. The effectiveness of the optimized LLISs is then investigated through bidirectional Time-History analyses on 3D Finite Element rack models. The results show that using the LLIS, even on a single load-level, can greatly reduce the upright stresses and the cross-aisle displacements and accelerations, and that the optimal position of the LLIS is in the upper part of the rack

Seismic vulnerability maps of Timisoara historical center based on fragility curves

The seismic vulnerability assessment on a territorial scale requires the application of simplified procedures. Data collection is usually carried out by adopting external inspections; for this reason the knowledge gained for the considered buildings is usually not complete and lack of information has to be managed. The definition of a methodology which takes into account these aspects is one of the aims of this paper. Another goal is the extension of the obtained results to buildings not directly surveyed on site, whose characteristics are similar to those of the analyzed buildings. The case study of Timisoara (Romania) is presented. A rapid survey of the historical center is performed and recurring typologies are identified. Analyses of the most significant local mechanisms of collapse are implemented, taking into account possible parameters variation. Fragility curves for each typology are then obtained allowing the definition of vulnerability maps for the whole historical center