Page 140 - Pressure Vessel Design Manual

120 Pressure Vessel Design Manual

PROCEDURE 3-3

SEISMIC DESIGN FORVESSELS 12, 31

Soil profile type (Table 3-9c)
Notation Seismic zone factor, Z
Numerical coefficient, RW
V = base shear, lb
Z = seismic zone factor (see Figure 3-8) For zone 4 only:
Zone 0: ............................................................ 0 Seismic source type
Zone 1: ...................................................... 0.075 Distance to fault
Zone 2A: ..................................................... 0.15 Near source factor, N,
Zone 2B: ..................................................... 0.20 Step 2: Determine or calculate seismic coefficients.
Zone 3: .......................................................... 0.3
Zone 4: .......................................................... 0.4 C, (Table 3-9a)
I =importance factor C, (Table 3-9b)
standard facilities .......................................... 1.0 Step 3: Determine period of vibration.
hazardous/essential facilities ..................... .1.25
R, = coefficient T=
self-supporting stacks ................................... 2.9 Step 4: Calculate the base shear, V.
vertical vessel on skirt .................................. 2.9
spheres and vessels on braced legs.. ........... 2.2 V is the greater of V1 or V,
horizontal vessel on pier .............................. 2.9 but need not exceed V3:
vertical vessel on unbraced legs ................. 2.2
C, =coefficient from Table 3-9b 1 Vi = 0.56C,IW0
C, = coefficient from Table 3-9a
S = site coefficient (1.0-2.0 based on soil profde)
W, = operating weight of vessel, Ib
w = uniform weight of vessel or stack, lb/ft
F, =lateral force applied at top of structure, Ib
Ft = 0.07TV or 0.25V
whichever is less, or 2.5C,IW0
=0, if T < 0.7 sec RW
H = overall height of vessel, ft !
D =outside diameter of vessel, ft For zone 4 there is the additional requirement that the
T =period of vibration, sec (see Figure 3-7) 1 ' base shear shall be at least equal to V4,
y = deflection, in.
N = number of column legs 1.6 ZNJW,,
A =cross-sectional area of leg braces, in.' v4=
g = acceleration due to gravity, 386 in./sec2 RW
I, = moment of inertia of pier, legs, stack, etc., in.4
E = modulus of elasticity, psi Step 5: Since the seismic design for pressure vessels is based
SA- SF = soil profile type from Table 3% on allowable stress rather than ultimate strength, the base
N,, N, =near source factor from Table 3-9d shear may be reduced by a factor of 1.4.
Seismic source type = from Table 3-9e

Design Procedure
1 Step 6: Determine if some percentage of the base shear
Step 1: Determine the following. needs to be applied at the top of the vessel, Ft.
For all zones: If T < 0.7 sec, Ft = 0
Weight, W, 1 For all other cases Ft = 0.07TV
Importance factor, I but need not exceed 0.25V =