·     

Load due to wind acting in the upper portion of the vessel.

P_uw = K₁ K₂ p₂ h₂ D_o

Where,

P_uw – total force due to wind load acting on the upper part above 20 m.

D_o - outer diameter of the vessel including the insulation thickness

h₂ – height of the upper part of the vessel above 20 m

K₂ – coefficient depending upon the period of one cycle of vibration of the vessel

(K₂ = 1, if period of vibration is 0.5 seconds or less; K₂ = 2, if period exceeds 0.5 seconds)

Stress due to bending moment: Stress induced due to bending moment in the axial direction is determined from the following equations.

1. (i)  M_w = P_bw h₁ /2 ;                          h₁ ≤ 20m

(ii)  M_w = P_bw h₁ /2 + P_uw (h₁ + h₂ /2 ) ;                          h₁ ≤ 20m

Therefore, the bending stress due to wind load in the axial direction

 

                                                  (6.15)

Where,

f_w - longitudinal stress due to wind moment

M_w - bending moment due to wind load

D_i – inner diameter of shell

t – corroded shell thickness

 

6. THE STRESS RESULTING FROM SEISMIC LOADS

 

The seismic load is assumed to be distributed in a triangular fashion, minimum at the base of the column and maximum at the top of the column. It is a vibrational load, it produces horizontal shear in self supported tall vertical vessel (Figure 6.4).

 

Figure 6.4a : Seismic forces on tall column

Figure 6.4b : Seismic forces on tall column