Browsing by Author "Di Matteo, Alberto"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Evolutionary power spectral density estimation using energy spectrum equation(IASSAR, 2021) Spanos, Pol D.; Di Matteo, Alberto; Zhang, Hanshu; Yue, Qingxia; Pirrotta, AntoninaIn this paper a novel approach is developed for the determination of evolutionary power spectra (EPS) of non-stationary random processes that can be used as models of earthquake accelerograms. Specifically, the spectra are estimated by considering the statistical moments of the energy of lightly damped linear systems (filters) excited by the stochastic seismic process. In this manner, an estimate of the EPS of the seismic input is derived by varying the frequency of the linear system. For this purpose, an appropriate smoothing procedure is also incorporated, relying on the use of the so-called Savitzky-Golay moving average filter. This is done for obtaining reliable spectra based on a relatively small number of available records. Further, a possible refinement of the approach is investigated introducing a polynomial representation for the mean energy of the filter output. Finally, several examples involving both simulated data with known target spectrum, and measured data are used to show the usefulness and reliability of the proposed approach.Item Nonlinear rocking of rigid blocks on flexible foundation: analysis and experiments(Elsevier, 2017) Spanos, Pol D.; Di Matteo, Alberto; Pirrotta, Antonina; Di Paola, MarioPrimarily, two models are commonly used to describe rocking of rigid bodies; the Housner model, and the Winkler foundation model. The first deals with the motion of a rigid block rocking about its base corners on a rigid foundation. The second deals with the motion of a rigid block rocking and bouncing on a flexible foundation of distributed linear springs and dashpots (Winkler foundation). These models are two-dimensional and can capture some of the features of the physics of the problem.Clearly, there are additional aspects of the problem which may be captured by an enhanced nonlinear model for the base-foundation interaction. In this regard, what it is adopted in this paper is the Hunt-Crossley nonlinear impact force model in which the impact/contact force is represented by springs in parallel with nonlinear dampers. In this regard, a proper mathematical formulation is developed and the governing equations of motion are derived taking into account the possibility of uplifting in the case of strong excitation. The analytical study is supplemented by experimental tests conducted in the Laboratory of Experimental Dynamics at the University of Palermo, Italy. In this context, due to their obvious relevance for historical monuments, free-rocking tests are presented for several marble-block geometries on both rigid and flexible foundations. Numerical vis-à-vis experimental data are reported, supporting the usefulness and reliability of the proposed approach.