Abstract. The article analyzes the requirements of national and international regulatory documents for allowable dimensions of local subsidence (immersion) of the central part of the vertical storage tank (VST) bottom in order to establish more realistic requirements for tank steel structures that will reflect the real character of the VST bottom central part deformation. Analytical solutions for the problem of elastic deformation of a flexible membrane on the subsoil base and numerical simulation based on finite elements methods for solid deformable body mechanics were used. Based on the results of the analytical and numerical calculation the dependence was established between the limit depth value in the local tank bottom subsidence area and its radial component. The results obtained consist of stress values acting in the center of the local subsidence area for bottoms of 6 and 9 mm in thickness. Analysis of the calculations results showed that requirements of the RF regulatory documents concerning the depth of local subsidence areas are significantly inflated and require changes in the size of the allowable limits of local tank bottom subsidence and differentiation depending on the thickness of the VST bottom sheet.

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Abstract. The paper is aimed at determining the possibility of applying the simplified method proposed by the authors to calculate the tank seismic resistance in compliance with current regulations and scientific provisions. The authors propose a highly detailed numerical model for a common oil storage tank RVSPK-50000 that enables static operational loads and dynamic action of earthquakes to be calculated. Within the modal analysis the natural oscillation frequencies in the range of 0-10 Hz were calculated; the results are given for the first ten modes. The model takes into account the effect of impulsive and convective components of hydrodynamic pressure during earthquakes. Within the spectral analysis by generalized response spectra was calculated a general stress-strain state of a structure during earthquakes of 7, 8, 9 intensity degrees on the MSK-64 scale for a completely filled up, a half-filled up to the mark of 8.5 m and an empty RVSPK-50000 tank. The developed finite element model can be used to perform calculations of seismic resistance by the direct dynamic method, which will give further consideration to the impact of individual structures (floating roof, support posts, adjoined elements of added stiffness) on the general stress-strain state of a tank.

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