Month: July 2007

  • Uncategorized

    • Controventi innovativi del tipo «RSS»: regole di progetto ed affidabilità sismica

    Maria Teresa Giugliano, Alessandra Longo, Rosario Montuori

    In this paper, a new design methodology for concentrically braced frames is presented aiming at the control of the failure mode by means of a rigorous application of the capacity design principles. The design goal is the prevention of the out-of-plan buckling of columns. In fact, the use of the recommendations provided by Eurocode 8 /1/, which have been substantially adopted by OPCM 3431 /2/, leads to the design of structures which are not able to exploit all the possible dissipative zones due to the premature out-of-plan buckling of columns. Whith reference to three bay concentrically braced frames having only one brace element for each braced bay, the proposed design methodology is applied both including and without including the local weakening strategy (Reduced Section Solution or RSS). The behaviour of concentrically braced frames designed according to above methodologies is compared with the one resulting from application of Eurocode 8 design rules. To this scope, the Jalayer and Cornell approach leading to the evaluation of the mean annual frequency of exceeding a given limit state is applied, so that the obtained results accounts for the record-to-record variability.

    This paper is available in Italian only.

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  • Uncategorized

    • Un criterio per l’ottimizzazione vincolata dei Liquid Column Mass Dampers (LCMD) per la mitigazione degli effetti sismici sulle strutture

    Giuseppe Carlo Marano, Sara Sgobba, Michele Mossa

    Liquid Column Mass Damper (LCMD) devices offer an interesting solution to the problem of controlling structural vibrations. Even though a LCMD is less efficient than other passive systems, such as a Tuned Mass Damper (TMD), it is an extremely simple device, easy to install and economical. This paper presents a criterion aimed at optimizing the project parameters of the device. Unlike previous approaches proposed in literature, this criterion considers not only tre structural performance but also the simultaneous control of a constrained system of hydraulic protection. This means imposing that the best solution guaratees the maximum oscillation of the verti- cal liquid column without exceeding the column’s own stationary piezometric level in order to avoid jeopardizing the entire system by allowing air to enter the horizontal pipe section. The procedure is developed stochastically with the assumption that the seismic excitation is based on the Kanai Tajimi (KT) model of a white or coloured Gaussian stationary process. The structure to be protected is represented as a linear system with a single degree of freedom. The efficiency of the system of protection is evaluated by measuring the reduction of the horizontal movement caused at the base by seismic excitation. The solution, in statistical terms, regarding the non linear terms of the problem due to the loss of fluid viscosity in the pipe is evaluated by classical covariant analysis using the stochastic equivalent linearization technique. The matrix covariance elements, evaluated in the state space, are used both for the objective function (OF) and the constrained optimal solution to the problem which is represented by the maximum value of the vertical oscillation of the water column. The project vector used includes the hydraulic loss factor and the LCMD hydraulic frequency. A genetic hybrid algorithm is applied to obtain the desired effect of constrained optimal solutions independently from seismic intensity variations and some system parameters. An efficiency evaluation follows regarding the optimal project parameters for different conditions of operation.

    This paper is available in Italian only.

  • Uncategorized

    • Lo studio di interventi antisismici tramite analisi dinamiche con un modello ad elementi rigidi: il caso del Castello Maniace

    Siro Casolo, Vincenzo Petrini, Carlo Alberto Sanjust

    A specific numerical model is proposed for the in-plane dynamical analysis of a masonry monument, with particular attention to the design of interventions for seismic protection. In order to perform effective compu- tational analyses, the present model is conceived to operate at the macro-scale considering the energy dissipation capacity of the masonry material, as well as the effects of the masonry texture on the local damage mechanisms. In particular, the model was implemented according with a mechanistic point of view, in the spirit of the rigid body and spring model approach, RBSM. In the present application we describe the passage from the global three dimensional model of the Maniace Castle in Syracusae to the identification of the specific collapse mechanism that is more at risk, and that can be specifically described by means of a plane model. Then, the dynamics of a transversal cross-section of the hypostyle salon of the Castle is investigated with particular attention to the enhancement of the seismic response that can be achieved by an intervention of rebuilding and reshaping of the buttresses.

    This paper is available in Italian only.

  • Uncategorized

    • Analisi statica non lineare di edifici in muratura esistenti mediante modelli strut and tie

    Alessia Vanin, Paolo Foraboschi

    A strut and tie model for not reinforced and not confined masonry panel is defined. This model permits to estimate the behaviour of the wall both in the linear elastic field and after the peak load, that is in the cracked non linear field up to the mechanism state. This model constitutes the base of non-linear static analysis method for existing masonry buildings that can be utilized into the practice.

    This paper is available in Italian only.