A COMPARISON OF MEASURED AND PREDICTED EARTHQUAKE BEHAVIOR OF SUPPORT STRUCTURES FOR LARGE INDUSTRIAL EQUIPMENT

摘要

The results from microtremor measurements obtained on steel support structures for large industrial boilers are used to identify the parameters that control the dynamic response of the structure-equipment system (vibration frequencies, mode shapes and damping ratios). These results are then compared to results obtained from analysis procedures used in engineering practice for this type of structures. The comparison shows that the frequencies identified from the microtremor measurements correspond to a situation where the heavy hanging masses in the structure are not active in the dynamic response, thus failing to identify the true frequencies of the system under earthquake excitation (large amplitude). When the actual earthquake response measured in one of this structures is compared with the analytical results the errors, in terms of maximum accelerations at the top level platform are found to be within 12% for one of the directions of movement, but go up to 50% in the other direction. A major source of uncertainty is the mass distribution, in height and in plan, that is used in the models.