GNGTS 2014 - Atti del 33° Convegno Nazionale

442 GNGTS 2014 S essione 2.3 obtained by using theoretical relations provided by the regulations have been compared with the results of the single station top – bottom tests carried out on the structure. It was not possible to perform the test while the tank was full, since it is a buffer tank, while the coefficients used in the Malhotra approach are valid for H/R value higher than 0.3. In the Paluzza tank, instead, the actual H/R value is 0.18. As a side note, speculating over the possibility of extending the relations until 0.19, the results of the comparison between theoretical and experimental periods would be quite promising. However, to be more accurate, it has been decided to perform the same test on a fire protection water tank located in Trieste, since that one was full at the moment. In the test performed, the diagram representing the ratio between horizontal components acquired at the top and at the bottom of the structure shows a peak at about 4 Hz. This is very close to the impulsive frequency calculated with the EC formulations (4.97 Hz). Additionally, the experimental data show the beginning of a peak below 0.3 Hz: it wasn’t possible to investigate below this frequency, due to instrumental limitations, however that peak likely represent the convective one calculated with the formulations, which is equal to 0.2 Hz. The consistency of the data in this test suggests that the period estimated according to Eurocode reports provides acceptable results in this situation. Conclusions. Both single station and multichannel surveys have been carried out to define a stratigraphic model. This representation has then been used to estimate the spectra amplification due to site effects. The spectra with different values of damping ratio (2% and 0.5%) have been calculated through the use of strong motion data. In order to obtain the base stress and the overturning moment values through the Malhotra simplified approach suggested by EC8 part 4, the convective and impulsive periods have been considered. Single station top – bottom tests have been performed on the structure in order to validate the theoretical formulations. In conclusion, the shear stress, the overturning moment (above and below the base plate) and the sloshing wave height calculated are, respectively: Q = 6.15·10 7 N M above =4 .21·10 7 Nm M below = 6.1·10 7 Nm d= 7 – 20 cm In order to better validate through experimental evidences the relations used in the codes, further tests, both in Paluzza and Trieste sites, will be performed. Tab. 2 - Convective and impulsive periods calculated with EC8 part 4 formulations and comparison with the experimental data. T imp [s] T conv [s] f imp [Hz] f conv [Hz] Exp.f imp [Hz] Exp.f conv [Hz] Water tank (full) 0.20 4.9 4.97 0.20 4 <0.3 Oil tank (full) 0.24-0.26 5.59 3.85-4.14 0.18 / / [Oil tank (empty)] ≈ 0.05 ≈ 8.47 ≈ 19 ≈ 0.12 ≈ 10 <0.3 Tab. 3 - Theoretical parameters used in the computation of shear stress, overturning moment and maximum sloshing height at the Paluzza storage tank. R(m) H(m) C i C c (s/m 1/2 ) T imp (s) T conv (s) F imp (Hz) F conv (Hz) D(m) Oil tank (full) 13.72 16.00 6.35 1.51 0.26 5.59 3.8 0.18 0.07 Water tank (full) 10.668 14.325 6.3 1.5 0.20 4.9 4.97 0.20 0.06 [Oil tank (empty)] 13.72 2.58 ≈ 10.14 ≈ 2.28 0.05 8.47 19.63 0.12 /