Int. J. Chem. Sci.

: 12(1), 2014, 265-271

ISSN 0972-768X
www.sadgurupublications.com

CALCULATION AND DESIGN OF THE LARGE VOLUME

TANKS EXPOSED TO SEISMIC LOADS
B. K. KUMAR, А. E. OSPANOVA, J. J BAZYLOV and
E. B. MAKASHEV*

Kazakh National Technical University after K.I. Satpaev Institute of Geology and Oil Gas Business,
ALMATY CITY, REPUBLIC OF KAZAKHSTAN

ABSTRACT

The widespread use of vertical cylindrical tanks puts the question of their sustainable design.
Snow load brings the greatest contribution to the stress-strain state of the supporting structures of vertical
tanks spherical domed coatings. The coefficients of the external pressure on the walls and coating of the
wind were also determined. The obtained results can be used to develop effective design solutions for
domed coatings of the oil tanks.

Key words: Seismic load, Cylindrical tank, Stress-strain state.

INTRODUCTION

In the recent time, a clear tendency to build large volume tanks of 50,000 to
100,000 m3 with double-deck floating roofs has been traced. Most frequently the construction
areas of such tanks are critical both from climatic (snow, wind, ice storm) and seismic point
of view.

During the design stage of the double-deck floating roof two alternative engineering,
fabrication and installation concepts are implemented1:

(i) Standard solution using plate-by-plate method when the greater part of the roof
assembly and welding works is performed on site. The roof consists of two
decks: upper and lower decks interconnected by a number of concentric rings
that form ring cells. The external cell is separated by radial partition walls to
form leak-proof boxes (Fig. 1).
________________________________________
*
Author for correspondence; E-mail: makasheve@mail.ru
266 B. K. Kumar et al.: Calculation and Design of the….

Fig. 1: Structural layout of floating roof

(ii) New solution using installation method of the factory-assembled rectangular

boxes. The boxes are radially oriented towards the centre of the tank. The
spaces between the boxes are covered with plate-by-plate panels on the upper
and lower decks during the installation (Fig. 2).

Thus the main difference between these design layouts of the roofs is the division
principle into ring or radial cells.

In accordance with the design rules the tank roof shall be stable, floating and robust
when at least two adjacent cells are no more leak-proof and the outside load equally or
non-equally distributed acts on the upper deck (Fig. 3).

Distinguishing design characteristic of the vertical cylindrical tanks of the large

volume is that as the diameter of the structure increases curvature of the cylindrical wall and
hence its rigidity significantly decrease2.

When such tanks are constructed in the seismic regions and in the high wind/snow
areas reliability of the structural design and engineering is of great importance3.
Int. J. Chem. Sci.: 12(1), 2014 267

Fig. 2: Settlement scheme of a roof

Design combination 1 dead weight of the Design combination 2 dead weight of the
roof (pr + pw), snow (ps = 3.20 kPa) roof (pr + pw), snow (ps = 3.20 kPa)
uniformly on the entire surface uniformly on the entire surface, 2 flooded
boxes of external cell
Cont…
268 B. K. Kumar et al.: Calculation and Design of the….

Design combination 3 dead weight of the Design combination 4 dead weight of the
roof (pr + pw), snow (ps = 3.20 kPa) roof (pr + pw), snow (ps = 3.20 kPa)
uniformly on the entire surface, 1 flooded uniformly on the entire surface, snow bag
box of external cell and flooded sec. cell (SNiP 2.01.07-85)

Fig. 3: Design combinations of the effects on the floating roof

Development and testing of the tank calculation methods that meet the latest global
requirements of the engineering science are also essential.

Experience with various software products has shown that application of ANSYS
computer system is the most effective for the calculation of the tank structures. Basic
software package for calculation of the tank wall, fixed and floating roofs, individual
assemblies such as tie-ins, etc was launched in the last several years within ANSYS
computer system. This software is provided with the strength and stability control units.
Software programs have coded representation, that is to say letters, which do not require
re-programming and ensure fully automatic calculations when initial data are measured.

This reduces design period significantly. The example and calculation results of the
floating roof are shown below.

Finite element calculation pattern of the floating roof is illustrated in Fig. 4.

Two consecutive tasks shall be solved for structural calculations:

• Floatability control, in other words determination of the roof equilibrium

position in the liquid under the snow load with the account of possible leakage
in several cells;
Int. J. Chem. Sci.: 12(1), 2014 269

• Strength control of the roof structural elements at the equilibrium position

obtained.

а) calculation pattern b) segment

Fig. 4: Model engineering of the floating roof using finite element method

a) b)

Fig. 5: Determination of the roof static equilibrium position: (а) Static equilibrium
position; (b) Calculation pattern for determination of the roof static
equilibrium position using deflection method

Task solving gets complicated since there are no external bracings in the floating
roof, and such structure is considered unstable from the structural mechanics point of view.
It is commonly known that application of the computer systems is no longer possible in this
case4. Universal special technique has been developed which allows for application of this
calculation method. It is based on the iterative approach and enables determination of the
roof depth rate Δ, roof swing α (Fig. 5) and all components of the stress and strain state for
any design variant for the roof or pontoon. Widely recognized deflection method forms the
270 B. K. Kumar et al.: Calculation and Design of the….

basis of this technique. Two additional bracings are introduced into the calculation pattern,
one of the bracing prevents from vertical movement, and the other bracing does not allow
the roof to turn (Fig. 6).

Fig. 6: Calculation results of the floating roof (а) travel of the lower deck;
(b) equivalent stresses of the lower deck elements

The bracings introduced make the system stable and allow for various calculation
methods, including finite element method5.

Based on the software developed the calculations have been made for the double-
deck floating roofs of different geometrical dimensions under the wide range of snow loads.
Researches demonstrate that when the tank diameter increases the advantage of the floating
roofs versus fixed roofs becomes undeniable even if snow bags occur. Large diameter fixed
roofs require additional supports to be installed inside the tank which reduce snow load on
the tank wall during static loading, however are ineffective under horizontal seismic loads.
Increase of the floating roof diameter up to 70 m is a favourable factor since it enhances roof
floatability and load-carrying ability; when diameter is greater than 75 m these parameters
remain unchanged6.

Application of the corrected calculation patterns throughout the design stages of the
tanks allows for detailed research and true and reliable evaluation of the structural stability
and strength. The calculations performed have confirmed the possibility to install steel
cylindrical tanks of 100 000 m3 in the seismic areas with high snow and wind loads.

СONCLUSION
Today in the territory of Kazakhstan more than 10 thousand tanks for storage of oil
and oil products are located, and the tendency to increase in their quantity is observed. Now
normative documents recommend touse spherical and conic domes of various constructive
schemes as stationary coverings of cylindrical tanks. Thus norm don't forbid to use as
stationary coverings of tanks of a roof and other forms.
Int. J. Chem. Sci.: 12(1), 2014 271

REFERENCES

1. V. A. Kucherenko, Recommendations on the Snow Load Determination for the

Certain Surfaces, M.L. (1983).
2. E. Ya, Yelenitskiy Best Calculation of the Strength for the Vertical Cylindrical Steel
Tank Walls, Structural Theory and Structural Analysis, No. 1 (2009).
3. E. Ya, Yelenitskiy Seismic Protection of the Vertical Cylindrical Steel Tanks,
Antiseismic Construction, Safety of Constructions, No. 5 (2006).
4. I. I. Goldenblat and N. A. Nikolaenko, Structural Analysis of the Seismic and
Impulsive Forces, М: State Publication for Construction (1961).
5. B. K. Kumar, A. E. Zhazylbekova and A. G. Moldaganapova, Desing of Vertical Steel
Tanks for Storage of Oil and Oil Products at Natural Loadings, Collection of Materials
of the International Scientific and Practical Conference, Construction, Architecture,
Desigh: Integration Processes in Modern Conditions, Volume 1-Almaty City, Kazakh
State Academy of Construction and Architecture (2012).
6. I. A. Poryvaev, M. N. Saifullin and A. A. Semenov, Oil and Gas Business, No. 4
(2011).

Accepted : 15.11.2013