Experimental determination of structural damping of a full‐scale building with and without tuned liquid dampers

The theory of vibration absorbers is well established, but the literature lacks documentation of the actual performance of absorbers installed in tall buildings. This paper presents an experimental assessment of the dynamic characteristics of one of two identical high-rise towers of the European Court of Justice in Luxembourg, before and after the activation of tuned liquid dampers, tuned to the frequency of the first mode. The prime focus of this assessment is structural damping and the effect that the tuned liquid dampers have on this. Two different full-scale test methods were utilized: operational modal analysis, using ambient vibrations, and harmonic forced vibration tests using two centrifugal mass exciters. All three modes were excited at and around their natural frequencies of approximately 0.44, 0.57, and 0.82 Hz, respectively. To determine the damping, the free decays of the acceleration signals after shutting off the forces were studied. A clear and unambiguous increase in damping was found after the activation of the tuned liquid dampers, with damping increasing from 0.8% to 3.8% for the first mode. Also, the damping of the second mode was increased, although only from approximately 0.8% to 1%. The damping of the third torsional mode is approximately 0.6% and it is unaffected by the activation of the dampers. Thus, the tuned liquid dampers mainly affect the first mode as intended where the damping ratio increases with at least 500%. The results, finally, strongly suggest nonlinear behavior of the tuned liquid dampers, with higher damping at higher vibration levels.