Impact of Seismic Uplift and Soil Support on the Acceleration Distribution of a Liquid Storage Tank

Abstract

A rigid base is assumed in most seismic studies of liquid storage tanks. Additionally, recent studies have shown that permitting uplift can significantly reduce the damage to tanks. Uplift is the transient partial separation of the tank base from the supporting foundation. However, uplift of storage tanks is still not well studied and a rigid base is assumed in numerical studies. In this work, the simultaneous effect of uplift and a soil foundation are utilised to evaluate experimentally the effect of these two factors on the acceleration in the tank wall. A low-density polyethylene tank and a shake table were employed. Stochastically generated seismic excitation is employed based on the New Zealand design standard, NZS 1170.5, for medium soil, classification B. Three base conditions were considered: 1) fixed-base tank on a rigid support, 2) freebase tank on a rigid support and 3) free-base tank on a flexible support. To simulate the rigid support condition, the tank is resting on a steel plate rigidly attached to the shake table. A laminar box infilled with sand is utilised to represent a flexible soil condition. Results revealed that the highest acceleration at the tank top occurred when the tank is resting freely on a rigid supporting base. Furthermore, for this case the maximum uplift occurred at the same time as the maximum acceleration. However, for the case of a flexible support, the maximum acceleration occurred at the tank base and did not coincide with the time of maximum uplift. The maximum uplift occurred for a flexible supporting base and is not related to the maximum acceleration at the tank top. Thus, the distribution of the maximum acceleration, and hence uplift, depends significantly on the support condition.

Lid induced sloshing suppression and evaluation of wall stresses in a liquid storage tank including seismic soil‐structure interaction

“…Normalised power spectral density of four strain gauges during the free vibration of the tank on a rigid-supported case and free sloshing Table 4 suggests the three first frequencies may belong to the convective modes, while the remainder are associated with the impulsive modes. The first theoretical impulsive frequency 𝑓 𝑖𝑚𝑝 ., that is 36.67 Hz calculated using Equation (15), is not present in the results of the pulse test for the tank supported either on a rigid base or supported by sand. In contrast, the first theoretical convective frequency 𝑓 𝑐𝑜𝑛 ., that is 1.43 Hz estimated employing Equation ( 16), agrees with the first free-vibration frequency in both the rigid and sand-supported cases.…”

“…The shear wave velocity was measured following the same impulse test described in. 15 In this case, the shear wave velocity was a constant value of 𝜈 𝑠 = 214 m∕s, independent of strain. The soil is assumed to behave elastically during the tests and the Poisson's ratio is 𝜈 𝑠 = 0.3.…”

“…The aspect ratio was chosen because sloshing has enough space to develop freely, that is the sloshing effects on wall stresses can be assessed without contamination of the data from the water contacting the lid. The first impulsive period was calculated using Equation (15). The tank can be modelled as a single degree-of-freedom (SDOF) system.…”

“…In contrast to the vast number of numerical studies in the literature, limited experimental research has been reported considering the effects of SSI on tank response. Hernandez-Hernandez-Hernandez et al [13][14][15][16][17][18] experimentally explored the simultaneous effects of uplift and SSI on a tank-water system response. It was found that for tanks with an aspect ratio ℎ∕𝑟 ≥ 2, uplift is more likely to be experienced with increasing stiffness of the supporting medium.…”

Evaluation of the adequacy of a spring‐mass model in analyses of liquid sloshing in anchored storage tanks

“…The characteristics of the seismic excitation, for example, frequency content, amplitude, and duration 13–16 The interaction between the soil and tank (soil‐structure interaction SSI) 17–20 …”