1,721,104 research outputs found
Multimodal galloping of dense spectra-structures
No full textNonlinear interaction phenomena among galloping modes of slender structures having several frequencies contained in one or more bands are analyzed. Due to nonlinear modal coupling associated with aerodynamic forces, all the modes of a band are in internal resonance. By referring to a nearly-periodic system consisting of weakly coupled beams and using the multiple scale perturbation method, a system of nonlinear differential equations in the amplitudes and phases of the interactive modes is obtained. Numerical results relative to a two-beam system are presented. In particular, the conditions under which steady-state solutions can occur are determined and their stability is investigated, while the occurrence of periodic motions involving exchanges of energy among the interactive modes is also remarked upon. Attention is given to the influence of small imperfections causing asymmetry of the structure
Nonlinear Tuned Mass Damper for self-excited oscillations
No full textThe effects of a class of nonlinear Tuned Mass Dampers on the aeroelastic behavior of
SDOF systems are investigated. Unlike classical linear TMDs, nonlinear constitutive laws of the internal
damping acting between the primary oscillator and the TMD are considered, while the elastic properties
are keept linear. The perturbative Multiple Scale Method is applied to derive a set of bifurcation equations
in the amplitude and phase and a parametric analysis is performed to describe the postcritical scenario of
the system. Both cubic- and van der Pol-type dampings are considered and the dependence of the limitcycle
amplitudes on the system parameters is studied. These new results, compared with the previously
obtained bifurcation scenario of a SDOF aeroelastic oscillator equipped with a linear TMD, show a
detrimental effect on the maximum limit-cycle amplitude reduction of the nonlinear TMD. However, the
analyses evidence that in the parameter region away from the perfect tuning condition the nonlinear
connection can be used to tune the system with an enhancement of the limit-cycle amplitude reduction
A simplified method for seismic assessment of unreinforced masonry buildings
No full textThe paper presents a simplified vulnerability assessment method for unreinforced masonry buildings based on the evaluation of a few structural parameters, which can be determined from visual inspection and a geometry survey. The authors proposed an empirical approach with the aim to assess the in-plane vulnerability quickly by predicting the damage failure of bearing masonry walls. Field observations reveal different behaviours: out-of-plane and in-plane seismic responses. Several simplified assessments focus on out-of-plane behaviour. Few studies deal with in-plane seismic behaviour, which is also the expected response for more masonry buildings. The proposed seismic method provides a vulnerability index, which is evaluated as the weighted sum of 10 parameters markedly affecting the in-plane seismic performance. The reliability of the method is investigated through an application on buildings located in Central Italy, damaged by the 2016 earthquake. The mean damage and damage probability distributions were predicted for each building using the proposed method. Then, fragility functions were estimated from the results of non-linear static analysis, and the damage probability distributions were derived. The capability of the simplified method to foresee the damage probabilities was confirmed by a comparison between different approaches, confirming the reliability of the method in large-scale seismic assessment
1:1 resonant Hopf bifurcations in slender space structures with tuned mass dampers
No full textThe effects of a tunable added mass on the aeroelastic stability of a SDOF bluff body exposed to a steady flow are investigated. The model captures the essential aspects of the behavior of flexible structures equipped with Tuned Mass Dampers orbiting at low position in the rare atmosphere. The system exhibits simple as well double Hopf bifurcations, of nonresonant and 1:1 resonant type. The occurrence of different types of bifurcations in the parameter space is discussed, and the Multiple Scale Method is employed to obtain a bifurcation equation in the complex amplitude of motion. Preliminary numerical results are drawn by numerically integrating this evolution equation. Steady solutions are compared with extract numerical results and asymptotic solutions previously obtained
Retrofitting effects on the dynamic behaviour of S.Maria di Collemaggio
No full textThe Basilica S.Maria di Collemaggio has recently been subjected to some small-scale repair work required after a recent earthquake in Central Italy; the structure has also been moderately strengthened. As preliminary step, a numerical analysis to predict and frame the effects of the work was performed by finite element models. Experimental research was also conducted to help calibrate the parameters of numerical models and, at the same time, to verify the actual behaviour of the church before and after reinforcement. The numerical and experimental analyses compared in this paper allow us to assess the consequences of the reinforcement and to appreciate the effectiveness of dynamic tests
Modelli di previsione del comportamento a lungo termine di travi prefabricate in calcestruzzo normale ed SCC
No full textLong-term behaviour of typical precast, prestressed double T concrete beams made of SCC and ordinary concrete was compared. Increase in deflection under load was registered in both elements for a year. Creep and shrinkage were monitored on laboratory concrete specimens as well. Data shown that concrete elements made of SCC rather than ordinary concrete perform substantially the same. Predictions of the long-term behaviour of the concrete structures was made according to different international Codes (Eurocode 2, ACI and JSCE Guidelines for Concrete) and the analytical results compared to the experimental ones
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