Simplified 3D model for the uplift analysis of liquid storage tanks

A methodology is proposed to enable state-of-the-art record selection using ground motion components in all three principal loading directions. Relying on the well-established Conditional Spectrum approach, its fundamental concepts are extended to ensure hazard consistency when the vertical ground motion component is considered along with the horizontal ones. To this end, different record selection techniques are employed, spanning sets of ground motion records with and without vertical motions, as well as with and without vertical ground motion hazard consistency. To demonstrate the effect that each record set can potentially have on a structure, an unanchored liquid storage tank is adopted as a case study, because of the vertical uplift motion it can exhibit, even under the application of horizontal loading only. A reduced-order structural model is employed to generate the numerical output via multi-stripe analysis, thus enabling the evaluation of the pertinent record selection approaches. Focusing on uplift and compressive meridional stress, response ratios and response hazard curves are extracted. It is shown that although the vertical ground motion component only mildly affects uplift, its effect on compressive meridional stress, on average, amplifies the response by a factor of 1.8 for moderate intensities and 2.8 for higher ones.

Section: Case Study Structurementioning

confidence: 99%

Hazard consistent record selection procedures accounting for horizontal and vertical components of the ground motion: Application to liquid storage tanks

Kohrangi¹,

Bakalis

Triantafyllou³

et al. 2023

“…The effect of uplift on the tank‐water response has been added to the spring‐mass model proposed by Housner, for example Refs. 53–55. This more versatile spring‐mass model can also incorporate SSI, for example Refs.…”

Section: Nonlinear Spring‐mass Model Of Liquid Storage Tanksmentioning

confidence: 99%

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

Hernandez‐Hernandez

Larkin

Chouw

2022

Aboveground liquid storage tanks are often found on weak compressive soil due to their proximity to harbours and rivers. These soil conditions lead to a high probability of significant soil‐structure interaction (SSI) under earthquake loading. In strong earthquakes, the transient partial separation of the tank base from the supporting medium (uplift) and chaotic liquid sloshing often cause damage to the tank wall. This experimental research determines the simultaneous effects of SSI and the restriction of sloshing on the development of hoop and axial stresses in the tank wall. A low‐density polyethylene tank with two different supporting foundation conditions, that is rigid and flexible, was tested using a shake table. A high‐density foam floating lid was utilised as a barrier to the development of sloshing enabling evaluation of the contribution of sloshing to wall stress development. The maximum experimentally determined stresses are compared with those from a nonlinear elastic spring‐mass model. The results reveal that a flexible supporting medium reduces the development of stresses by increasing the occurrence of uplift compared to that when the tank lies on a rigid supporting medium. Furthermore, restricting chaotic sloshing decreases both the maximum stress and uplift. The spring‐mass model predicts the maximum stresses with more accuracy when the tank is on a flexible than on a rigid supporting medium.

“…The natural vibration period of unanchored tanks is always larger than that of anchored tanks due to relaxed vertical constraint. When uplift happens, the contact area between the base plate and the foundation reduces and the stress of tank shell far from the uplifting side increases, resulting in its elephant's foot buckling at the tank base 6,7 . The compressive meridional stress and its distribution of uplift tanks around the circumference are much different.…”

Section: Introductionmentioning

confidence: 99%

Seismic response of column supported tanks considering uplift effect and soil‐structure interaction

Liu

Zhao

Zhou

2023

In this paper, the seismic responses of column supported tanks under horizontal earthquake are obtained by finite element method. Two types of structures are discussed including the anchored tank with columns fixed on the ground and the resilient tank whose columns can uplift. The uplift effect is realized by the contact algorithm to allow the column move upwards in a vertical direction and the soil‐structure interaction (SSI) is considered by equivalent soil springs. Different soil types and hard ground condition are adopted to study SSI effect on natural frequencies of tanks and seismic responses of the anchored tank, as well as coupling effect (both uplift and SSI effects) on seismic responses of the resilient tank. The structural displacement and acceleration, the stress of tank walls and columns, the base shear and the overturning moment, the uplift displacement of columns are discussed. The results of tanks in different conditions are compared with each other, which show that SSI has a significant impact on seismic responses of column supported tanks. As the stiffness of soil decreases, the tank has larger displacement, smaller natural frequency, and stress level of structural members especially when it is sited on softer soil type. Compared to the anchored tank, due to the combination of both uplift effect and foundation deformation, the resilient tank has smaller displacement to prevent its overall collapse and lower responses such as the base shear and the overturning moment. The resilient tank has better seismic performances regardless of soil conditions.