The effect of multi-directional seismic inputs on the determination of modal parameters

A procedure for the identification of modal parameters of an instrumented building subjected to a multi-input excitation is described and discussed. The procedure is applied to identify modal parameters of a masonry structure subjected to a set of simulated earthquakes on a shaking table facility. The same experimental data are used to identify modal parameters by means of the traditional approach (considering only the base input acting in the direction of the response). The two sets of results thus obtained are then used to calculate the response at two locations of the system. Such responses are compared to the measured ones. The comparison shows that the traditional approach, requiring a lower computational effort, can satisfactorily evaluate modal parameters. However, the multi-input procedure, allowing the evaluation of "indirect effective participation factors", enables a more complete description of structural conditions with the evolution of damage.