Giacomo Navarra

THE TLCD PASSIVE CONTROL: NUMERICAL INVESTIGATIONS VS EXPERIMENTAL RESULTS

Very recently the tuned liquid column damper (TLCD) is receiving an increasing interest from researchers concerned with vibration control, to be considered an alternative device with respect to the tuned mass damper (TMD), since the former has low cost, easy adjustment, flexible installation.However, in recent studies the authors [1] have pointed out that for TMD the analytical formulation provides results that are in good agreement with the experimental ones, while for TLCD it has been deducted that the analytical formulation needs further investigation.In fact using the classical formulation of the problem, numerical results are very different from the experimental results obtained by the authors using the facilities at the experimental dynamic laboratory of University of Palermo.In particular it has been shown that the total liquid length should be corrected in an effective one, but in a different way from what has been done in literature, where only the variation of section of the vessel has been taken into account. On the other hand, from experimental investigations it is seen that the liquid moves more in the central area of the tube and less in the area in contact with the side walls. This aspect plays a fundamental role for capturing the real performance of TLCD. In fact, being the TLCD a special type of auxiliary damping device which relies on the inertia of liquid column in a U-tube to counteract the forces acting on the structure, then it is necessary to identify the effective moving liquid mass. To aim at this, in this paper the authors differentiate the total liquid mass into a liquid dead mass and a liquid dynamic mass, then introducing these values into a properly modified mathematical formulation numerical results match the experimental ones for all tests.© 2012 ASME

A Novel Mathematical Model For TLCD: Theoretical And Experimental Investigations

In this paper a novel mathematical model for the Tuned Liquid Column Damper (TLCD) is presented. Taking advantages of fractional derivatives and related concepts, a new equation of motion of the liquid inside the TLCD is obtained. Experimental laboratory tests have been performed in order to validate the proposed linear fractional formulation. Comparison among experimental results, numerical obtained using the classical formulation and numerical with the new linear fractional formulation are reported. Results in frequency domain show how the new linear fractional formulation can predict the real behavior of such a passive vibration control system, more correctly then the classical mathematical model, widely used in

Amplification of Interstory Drift and Velocity for the Passive Control of Structural Vibrations

Mitigation of structural damage due to earthquake ground motion may be performed by inserting dampers in the structure. In order to enhance the damping effect various toggle brace configurations have been recently proposed. In this paper these equipments are analyzed in detail and compared with a new one here proposed. The analysis is performed by taking into account the inherent nonlinearities of the damper by means of stochastic analysis and validated by using time histories of recorder accelerograms and by the stochastic analysis using spectrum consistent power spectral density.

Impulsive Tests on Historical Structures: The Dome of Teatro Massimo in Palermo

Cultural heritage is the set of things, that having particular historical cultural and aesthetic are of public interest and constitute the wealth and civilization of a place and its people. Sharpen up methodologies aimed at safeguarding of monuments is crucial because the future may have in mind the historical past. Italy is a country that has invested heavily on its historical memory returned in large part by the historical building or the monuments. Furthermore, culture represents a fundamental indicator of the growth of the culture of a country. Consider a monitoring project of one of the most Impressive theater in the world, like “Teatro Massimo” in Palermo (Italy), means to add value to both of the issues mentioned above. Among several methods providing useful information about the conservation status of the structures, dynamic monitoring techniques are suitable to check and restore the global behavior of the buildings. The anomalous features diagnosis of the structural dynamic response is an index of alterations of the material state and, in the worst cases, is related to the presence of damaged structural elements. The present paper assesses, through a real investigation, the importance of dynamic tests on historical buildings. In particular impulsive tests return the main structural characteristics describing the current behaviour. Such tests are then crucial for updating numerical evaluation and check the need of restoring original main features or not, suggesting a strategy of restoration as well.

A NOVEL ANALYTICAL MODEL OF POWER SPECTRAL DENSITY FUNCTION COHERENT WITH EARTHQUAKE RESPONSE SPECTRA

In the most advanced seismic codes earthquake loads are often defined by means of pseudo-acceleration Response Spectra (RS) and the use of modal superposition analysis method is strongly encouraged. The effectiveness of the design procedures is thus limited by the underlying hypotheses, such as the linearity of the system and the reliability of the modal correlation coefficients used to combine the modal responses for MDOF systems. On the other hand, linear systems response statistics could be easily computed by using stochastic analysis tools, once a stochastic characterization of the seismic action is provided. In this paper a few-parameters analytical model for the definition of Power Spectral Density functions (PSD) coherent with Response Spectra is proposed. Closed-form relationships between the parameters involved in the definition of the PSD and the RS defined by several international seismic codes are provided. The reliability of this tool is assessed by means of a numerical campaign by comparing stochastic analysis and Monte-Carlo simulations. By using the proposed approach, the seismic action can be defined both in terms of RS and in terms of PSD, and, therefore, the engineer can choose the most appropriate analysis tool for his purpose.

Dynamic characterization of fractional oscillators for Fractional Tuned Mass Dampers tuning

A novel formulation for Fractional Tuned Mass Damper (FTMD) devices is proposed in this paper. The FTMD is realized by connecting an oscillating mass to the main structure using a viscoelastic link, realized through elastomeric rubber bearings with fractional derivative constitutive model. A new function, labeled Damped Fractional Frequency, is defined for the fractional oscillator as the analogous of the damped frequency for classic single oscillators. Then, a critical value for the fractional order derivative involved in the damper constitutive law is defined as the limit value for which the DFF is real. It is shown that prevalent elastic or viscous dynamic behaviours are observed for the fractional oscillator when the fractional order derivative assumes values smaller or greater than the critical value, respectively. Finally, the DFF concept is utilized to opportunely tune the FTMD to its main structure, analogously to classic Tuned Mass Damper devices. Applications to a system excited by stochastic loads are presented, using the classic tools of stochastic analysis to determine the system response statistics and measure the performance of the FTMD.

Exact Closed-Form Fractional Spectral Moments for Linear Fractional Oscillators Excited by a White Noise

In the last decades the research community has shown an increasing interest in the engineering applications of fractional calculus, which allows to accurately characterize the static and dynamic behaviour of many complex mechanical systems, e.g. the non-local or non-viscous constitutive law. In particular, fractional calculus has gained considerable importance in the random vibration analysis of engineering structures provided with viscoelastic damping. In this case, the evaluation of the dynamic response in the frequency domain presents significant advantages, once a probabilistic characterization of the input is provided. On the other hand, closed-form expressions for the response statistics of dynamical fractional systems are not available even for the simplest cases. Taking advantage of the Residue Theorem, in this paper the exact expressions of the spectral moments of integer and complex orders (i.e. fractional spectral moments) of linear fractional oscillators driven by acceleration time histories obtained as samples of stationary Gaussian white noise processes are determined.