A new alternative is presented for the estimation of modal mass, in order to scale the vibration modes obtained from operational modal analysis tests, using optimization techniques, in the frequency-independent proportional damping situation (structural or hysteretic), achieving optimal results even with the presence of a high level of noise in the signal.
After a brief exposition of the theoretical foundations, and the limitations in the current state of the art, the determination of modal parameters is analyzed in a coupled dynamic system, using optimization techniques.
To illustrate the procedure, two examples of application are presented: first, for the case of an elementary beam model of small dimensions; and then, to confirm the capacity of the proposed method to be applied to real civil structures, said capacity is illustrated by a numerical simulation, on a very slender bridge currently in service, and with a very complex internal geometry of its main beam.
Abstract A new alternative is presented for the estimation of modal mass, in order to scale the vibration modes obtained from operational modal analysis tests, using optimization techniques, [...]
Specific computer programs for identification in modal analysis of structures are not economical, and they may not always be available. This paper presents a technique for simple optimization, getting fast and quality results, in the estimation of the damping ratios for each separate mode, and that can be resolved with a demo version (downloadable for free from the internet) of commercial optimization software. It is suitable for low levels of structural damping (or non-frequency-dependent damping), which are those that appear in large structures. Likewise, it is not necessary for the modes to be separate, or even that the magnitude of the near modes be less than that of those with which we are working; within the algorithm movable residual complements optimize their position according to the frequency and vertical axes (the response magnitude), to take into account the influence of the modes outside the considered range. In addition, it is not very sensitive to the presence of noise in the signal.
Abstract Specific computer programs for identification in modal analysis of structures are not economical, and they may not always be available. This paper presents a technique for [...]
The consideration of the assumption of viscous damping as a starting hypothesis in the dynamic analysis of structures can introduce a substantial error in the calculations. This is due to the energy dissipated by the structure in its oscillation being frequency dependent under that premise, while experimentally the opposite becomes apparent, when structural or hysteretic damping is taken into account. The modes of vibration obtained in the operational modal analysis are not scaled, since the magnitude of the excitation on the structure is unknown. For this reason it is necessary to resort to additional calculation procedures, such as the mass change method, to determine the scale factors of each mode. However, all variants of this method, in the current state of the art, have been deduced in the undamped situation. In this paper we analyze the influence of the deviation of the results for the scale factors, obtained by means of a viscous damping analysis, compared to that same deviation determined under the consideration of hysteretic or structural damping, independent of the frequency, whose results align much better with the experimental behavior of the structure.
Abstract The consideration of the assumption of viscous damping as a starting hypothesis in the dynamic analysis of structures can introduce a substantial error in the calculations. [...]
In the present paper, the application of optimization techniques –via FRF– is developed for determining modal parameters by means of the identification method that are exclusively limited to: systems with viscous damping, low levels of damping, and methods that work within the frequency domain. Decomposition techniques are proposed for working with complex magnitudes that allow the real and imaginary parts to be treated separately (which can, in this way, be implemented in commercial optimization programs), even in matrix product operations. The influence of high and low modes is rigorously taken into consideration via the selfsame optimization algorithm. To illustrate this work we have analyzed a structure unique in its slenderness, La Cartuja Bridge (Seville, Spain), which also constitutes a very light structure with very little damping. Its design contributed in its day a new structural framework of complicated geometries through the use of a new material: high yield strength steel.
Abstract In the present paper, the application of optimization techniques –via FRF– is developed for determining modal parameters by means of the identification method [...]
Determinación de la masa modal en estructuras civiles mediante el acoplamiento de un sistema dinámico oscilante en la situación de amortiguamiento proporcional independiente de la frecuencia 
