Experiments on Large Structures - Dynamic Behavior of Concrete and Seismic Engineering - page 210

Figure 6.5. Frequency response of the higher floor in the slanting tower
Four torsion modes including the fundamental mode, and four bending modes
were identified over the frequency range used. Three other coupled modes could
also be observed. Ambient responses were also measured under the effect of wind,
and the results were correlated to the dynamic properties obtained under harmonic
vibrations. Vibrations due to the motion of the outer panoramic lift were recorded,
both to estimate the amplitude of the resulting accelerations and to identify the
specific modes excited when it is operating.
In total, 11 experimental modes were identified, among them the first torsion
mode at 1.02 Hz and the second bending mode at 1.35 Hz. This enabled a three-
dimensional finite element model, including the interaction with the flexible roof, to
be constructed. It predicted a fundamental bending mode and a second torsion mode.
Modal damping was identified for all modes, and this enabled calibration of
Rayleigh's damping on the first mode (1.29%) and the eleventh mode (2.55%) to be
calculated.
6.4.2. Reinforced concrete building
A real-size reinforced concrete building was constructed at the Sherbrooke
University structure laboratory, as part of a project to assess the performance of very
high efficiency concrete structures under seismic loads. The building was subjected
to increasing seismic load levels using the pseudo-dynamic test method presented in
this topic. Here we only discuss the second objective of that study, which was to
measure the damage caused by dynamic testing. The signature of the undamaged
building was obtained and used as a reference to determine the damage.