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    • Seismic performance of a mixed rc-masonry building strengthened with fiber composites

    Massimiliano Ferraioli, Gennaro Di Lauro

    In this paper the performance-based assessment of a masonry building strengthened with fibre re- inforced polymers to improve seismic resistance is carried out. At first, a specific procedure was used to calibrate the finite element model according to the experimental dynamic properties. Then, pushover analysis was carried out with an adaptive load pattern which allows for the redistribution of load as an effect of non-uniform yielding. A homogenous and isotropic smeared cracked model was used for non linear modelling of masonry. An incremental non-iterative procedure, that is an adaptive extension of the capacity spectrum and the inelastic demand response spectra method, was used for the displacement-based seismic assessment of the building. The proposed procedure was validated by comparison with the results from seismic response testing on a scale model. The final objective of the paper is the assessment of the effectiveness of retrofit as far as the safety not only at collapse but also at the other limit states.

    For this paper is available an extended abstract after the text in Italian

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    • An index for a timely seismic damage detection

    Maria Pina Limongelli

    This paper presents a new seismic damage index feasible for automatic damage detection approaches. The definition is based on a new approach to damage detection based on the comparison between the accuracy of a given shape function in interpolating the response of a structure, in the damaged and the undamaged (reference) states. The comparison is carried out in terms of an error function defined as the difference between responses recorded on the structure and responses calculated via the spline interpolation. The variations of the error with respect to the reference value report the existence of damage in the region of the structure close to the locations where the higher changes occur. The method has been tested on the numerical model of a multistorey frame where damage has been simulated as a storey stiffness reduction. Results relevant to several damage scenarios show that the method allows both the detection and the localization of damage with a level of accuracy that increases with the intensity of damage. The application of the method requires a densely instrumented structure and the availability of responses recorded before and after a damaging event. The main advantages of the proposed method are that it does not require a numerical model of the structure nor heavy post-processing of recorded data. Hence, after a damaging earthquake, it can provide, nearly in real time, reliable information about the location of damage. These characteristics make the method a potentially useful tool for automated post-earthquake damage assessment.

    For this paper is available an extended abstract after the text in Italian

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    • Railway station of underground line under seismic action

    Bruno Cavagna, Angelo Arienti, Michela Chiorboli, Alberto Castellani , Francesco Calvetti, Marco Valente

    The dynamic behaviour of a railway station of the Underground line of Milan is analysed under the effects of an earthquake defined according to Eurocode 8, with peak ground acceleration of 0.07g.
    The analysis requires the preliminary knowledge of the state of stress and strain in the soil surrounding the tunnel. It depends on the geometry and on the mechanical properties of the soil layers, which are generally non-homogeneous and non-isotropic. Besides, the state depends on excavation and construction procedures. The computer code FLAC, 2004 version, is proved to be capable of representing this state fairly, the main limitation resting on the knowledge of the constitutive law of the soil and on the representation of excavation and construction procedures. In this paper this state of stress and strain is briefly reviewed. It will be referred to as the relaxation state of stress. If the ground is exposed to seismic excitation, the resulting state of stress in the surrounding soil and the sheet-piling is computed by integrating the equilibrium equations during the earthquake duration, with reference to the non-linear behaviour of the soil. Starting from the relaxation state of stress, the program executes the integration step by step, updating the soil properties according to the total strain amplitude. The sheet-piling and the vertical wall of the station are not linked by steel bars and are kept in contact by the earth pressure. The gap between the two structures may be open during the seismic event, depending on the conditions of the tendons. In the model this element is represented by apposite gap elements, able to follow the contact condition. The reinforced concrete structures remain in the linear elastic realm, in practice. Severe damage to this type of structures, although small in number, was caused in Kobe, Japan, by the disastrous Hygo-Ken Nanbu (Kobe) earthquake of 1995. The worst damage to the large-scale underground facilities was the collapse of the Dakai Underground Station in Kobe, pertaining to the underground railway (Kobe Rapid Transit). Other damages have been reported for railways station in occasion of the Athens Earthquake of 1999.

    For this paper is available an extended abstract after the text in Italian

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    • Analysis of the seismic risk of major-hazard industrial plants and applicability of innovative seismic protection systems Part II: Steel liquid storage tanks with floating roof

    Maurizio De Angelis, Renato Giannini, Fabrizio Paolacci, Leonardi G. Luccone, Sergio Di Cave, Mariano Ciucci

    In this paper the main results obtained within different research projects, developed about the applicability of seismic passive control of major-hazard industrial installations are shown. The work has been subdivided into two papers; in this second part the results relating to big steel tanks equipped with floating roof are presented. After a brief discussion about the seismic vulnerability of tanks and the study of the equations of motion of fixed and isolated base tanks, the main results of a series of shaking table tests, carried out on a steel tank with diameter of 4 m and filled with water up to 1m, are presented. The tank has been tested both in fixed base configuration with floating roof and seismically protected with elastomeric and elasto-plastic isolation devices. The results have confirmed the reliability of the simplified models and the high effectiveness of the base isolation systems in reducing the pressure on the tank wall and the relative stresses, also with floating roof. On the contrary, a low increasing of the oscillation amplitude of the liquid surface has been observed, partially compensated by an increasing of damping, which drastically reduces the number of the free oscillations of the floating roof, in the post-earthquake phase.

    For this paper is available an extended abstract after the text in Italian

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    • A proposito della legge Magnitudo-frequenza

    Giuseppe Grandori

    Let F1 and F2 be two competing models proposed for the interpretation of the seismic catalog regarding a given site. Which one is more reliable than the other?
    If the test bench is the consistency of the models with the catalog, the scarcity of data prevents meaningful comparisons. In what follows it is shown that a different test bench (however interesting from the engineering point of view) opens new statistical perspectives. A few methods aiming at a reduction of the epistemic uncertainty in the choice between F1 and F2 are described.

    This paper is available in Italian only.

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    • Analisi sismica non lineare di telai piani in c.a.: verifica delle previsioni del metodo pushover tradizionale per mezzo del confronto con l’analisi time history non lineare

    Andrea Onasini, Andrea Vignoli

    In the work, after a brief state of the art about push over method, the most interesting results are presented on comparison between two methods of analysis nonlinear proposed to the OPCM 3274 and his modi- fications /1/, on looms plans in ca of various heights, are presented. The comparison has focused on aspects of maximum displacement at the top and interstory, base shear and distribution of inelastic inelastic. It has been extended to frames designed with the old legislation, D.M. 16/1/96 /2/, and others frames designed with linear methods proposed to the OPCM. All designed frames were divided into three classes of height (2, 7, 12 floors) to cover several parts of the spectrum and were considered regular and irregular frames second point 4.3.1 of the OPCM said. The most clear result of this comparison is that the push over method seems to give acceptable forecasts in all aspects to chassis height not over 4 plans for those irregular and 5 plans for regular. Beyond this limit interstory drift prediction becomes unacceptable and the same fate touches to the inelastic demand forecast for 7 floors structures. A 12-storey goes into crisis also the base shear forecast, while maintaining acceptable that the maximum displacement in the summit.

    This paper is available in Italian only.

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    • Il cambiamento di scala delle strutture per la verifica sismica su tavola vibrante: un telaio in c.a. progettato per carichi verticali

    Igor Lanese, Francesco Marazzi, Roberto Nascimbene

    The work presented here is one of the fundamental phases of a research programme on seismic evaluation of existing buildings, funded by the Department of Civil Protection and developed at the European Centre for Training and Research in Earthquake Engineering (Eucentre). The present article contains a brief summary of the general theory on scaling: this concepts are then specialised for RC structures to be tested on shaking tables. These ideas are finally applied to the numerical model of the studied building and actually under testing on the Eucentre shaking table.

    This paper is available in Italian only.