16 Effects of Seismic Retrofit on the Dynamic Properties of a 4-Storey Parking Garage 127 Fig. 16.12 Mode 2: 1st torsion at 3.82 Hz Fig. 16.13 Mode 3: 1st torsion and 1 E–W transversal at 4.58 Hz Fig. 16.14 Mode 4: 2nd torsion at 5.94 Hz 16.5 Conclusions As a result of the Ambient Vibration Test, six modes have been identified up to a frequency of about 8.5 Hz. The fundamental mode occurs at 3.05 Hz and corresponds to a first bending mode in the N–S longitudinal direction. The results obtained with the different techniques in frequency and time domain agree reasonably well with each other. The presence of the mode shapes identified before the structural interventions was also confirmed by the second test.
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