Global vertical mode vibrations due to human group rhythmic movement in a 39 story building structure

In this paper, the field vibration measurement tests have been conducted for investigating the exact causes of the abnormal vibration accident which occurred on last July 5, 2011 in TechnoMart, a 39 story steel building structure. The vertical accelerations of the building floors were measured under the 4D movie-theater operation and human rhythmic movements in a fitness center which were estimated as ones of the vibration sources. From field tests, it could be identified that the building has global vertical vibration mode of 2.7 Hz natural frequency and human group rhythmic movements having frequency component mainly close to 2.7 Hz in a fitness center caused the resonance of the vertical mode. Especially, the fact that the identified damping ratio of the vertical mode by observing the free vibration response after the human group excitation was just 0.3%, implies that response amplification could be so significant that only 23 people could excite the 39 story building having the total mass of 30 thousands of metric ton move globally up and down. Tuned mass damper (TMD) is being considered as a measure for keep this resonance by adding damping to the building. The TMD design results shows that the acceleration level resulting from the same human excitation can be reduced to one fourth of that of the building without TMD.