2.2　Symbols

2.2.1　Action and action effect

Ft——design value of hoop tension per unit height of ringwall；

Ft0——design value of hoop tension per unit height of outside ringwall；

fa——modified characteristic value of subgrade bearing capacity；

Fk——vertical force transferred to foundation top surface from the upper structure corresponding to nominal load combination；

Gk——combined self-weight of foundation and weight of soil on foundation；

gk——nominal value of the vertical linear distributed load transferred to ringwall top from bottom of tank shell；

MR——Sliding resistant moment；

Ms——Sliding moment；

Pk——average pressure value at foundation bottom surface corresponding to nominal load combination；

P0——additional pressure at the calculation bottom surface of tank foundation corresponding to quasipermanent combination of load effects；

S——final settlement of subgrade；

ΔSi′——settlement of No.ith stratum soil layer within the range of calculated depth；

ΔSn′——Calculated value of deformation for the soil stratumΔZ，which is taken upward from the calculated depth.

2.2.2　Calculation indicators

Esi——compression modulus of No.ith soil layer under the bottom of tank foundation；

Es0.1-0.2——compression modulus of subgrade soil under pressure at 100kPa-200kPa；

fak——characteristic value of subgrade bearing capacity；

fy——design value of tensile strength of ordinary steel rebars；

γc——gravity of ringwall；

γL——gravity of service fluid stored in tank；

γm——average gravity of the packing material of each layer inside ringwall；

γw——Gravity of water.

2.2.3　Geometric parameters

A——tank foundation bottom surface area；

As、As0——sectional area of circumferential rebars per unit height respectively of ringwall and outside ringwall；

b——width of ringwall；

b1——distance from the inner side of outside ringwall to the inner side of tank shell wall；

Dt——inner diameter of tank bottom shell；

H——height from tank bottom to outside ringwall bottom；

h——height of ringwall；

hL——height from ringwall top to the maximum fluid（medium）level in tank；

hw——height from ringwall top to the maximum water level in tank；

i——slope；

R——radius of center line of ringwall or outside ringwall；

Rh——inner radius of outside ringwall；

Rt——inner radius of tank bottom shell.

2.2.4　Calculation coefficients and others

K——lateral pressure coefficient at ringwall；

α-i——coefficient of average additional stress；

β——coefficient of the width extended from tank shell into ringwall top；

γ——component coefficient of self-weight of tank；

γ0——Importance factor；

γQm——component coefficient of the packing material self-weight in each layer inside ringwall；

γQw——component coefficient of water self-weight；

ψs——empirical coefficient for settlement calculation.