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

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.

Giuseppe Carlo Marano, Sara Sgobba, Michele Mossa