126 I. Capraro and C.E. Ventura 0 −50 −40 −30 −20 −10 0 10 20 dB 4 8 Frequency [Hz] Singular Values of Spectral Densities of All Test Setups 12 16 1.0 Fig. 16.10 Singular values of the spectral densities, 2014 results (before seismic upgrade) Fig. 16.11 Mode 1, 1st N–S longitudinal at 3.05 Hz 16.4 Comparison with the Results Before Seismic Retrofit Another Ambient Vibration Test was carried out in March 2014, before the seismic upgrade interventions. Details on the test and the results can be found in literature [3, 4]. The results in terms of natural frequencies are summarized and compared in Table 16.2. After the structural upgrade, the increase in frequency is found to be around 10% for the fundamental mode. This pattern does not hold for the higher modes, where a clear trend cannot be recognized and the results of the second test do not differ significantly from the ones obtained during the first test. The two ambient tests were planned according a similar method, the only condition that changed was the traffic volume experienced by the Parkade. The first test was conducted during a weekday, when the operational condition is higher level of traffic, while the second test was performed on a Saturday and less vehicles were present in the structure. Provided that a common trend for the change in values cannot be determined, the difference in frequency is expected to be the result of the seismic upgrade interventions only, or however, that the traffic conditions do not represent a significant variable in this study.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==