Page 179 - Pressure Vessel Design Manual

Design of Vessel Supports 157

Notes 4. If reinforcing pads are used to reduce stresses in the
shell or a design that uses them is being checked, then
1. A change in location of the c.g. for various operating Bijlaard recommends an analysis that converts moment
levels can greatly affect the moment at lugs by increas- loadings into equivalent radial loads. The attachment
ing or decreasing the “L” dimension. Different levels area is reduced about two-thirds. Stresses at the edge
and weights should be investigated for determining of load area and stresses at the edge of the pad must be
worst case (i.e., full, half-full, empty, etc.) checked. See “Analysis When Reinforcing Pads are
2. This procedure ignores effects of sliding friction Used.”
between lugs and beams during heatinghooling 5. Stress concentration factors are found in Procedure 5-5.
cycles. These effects will be negligible for small- 6. To determine the area of attachment, see “Attachment
diameter vessels, relatively low operating temperatures, Parameters.” Please note that if a top (compression)
or where slide plates are used to reduce friction forces. plate is not used, then an equivalent rectangle that is
Other cases should be investigated. equal to the moment of inertia of the attachment and
3. Since vessels supported on lugs are commonly located whose width-to-height ratio is the same must be deter-
in structures, it is assumed that earthquake effects will mined. The neural axis is the rotating axis of the lug
be dependent on the structure and not on the vessel. passing through the centroid.
Thus equivalent horizontal and vertical loads must be 7. Stiffening effects due to proximity to major stiffening
provided rather than applying UBC seismic factors. See elements, though desirable, have been neglected in this
Procedure 3-3. procedure.

PROCEDURE 3-9

SEISMIC DESIGN-VESSEL ON SKIRT [ 1, 2, 41

V = base shear, kips
Notation V, = shear at plane x, kips
M, = moment at plane x, ft-kips
T =period of vibration, sec Mb = overturning moment at base, ft-kips
SI = code allowable stress, tension, psi D = mean shell diameter of each section, ft or in.
H =overall height of vessel from bottom of base E = modulus of elasticity at design temperature,
plate, ft lo6 psi
h, =height from base to center of section or c.g. of El =joint efficiency
a concentrated load, ft t =thickness of vessel section, in.
h, =height from base to plane under considera- Pi =internal design pressure, psi
tion, ft P, =external design pressure, psi
a, 6, y=coeffcients from Table 3-20 for given plane Aa, A y = difference in values of a and y from top to
based on h,/H bottom of any given section
W, =total weight of section, kips 1, =length of section, ft
W =weight of concentrated load or mass, kips aXt = longitudinal stress, tension, psi
W,, =total weight of vessel, operating, kips a,, = longitudinal stress, compression, psi
Wh =total weight of vessel above the plane under R, =outside radius of vessel at plane under consid-
consideration, kips eration, in.
w, = uniformly distributed load for each section, A = code factor for determining allowable com-
kips/ft pressive stress, B
F, =portion of seismic force applied at the top of B =code allowable compressive stress, psi
the vessel, kips F =lateral seismic force for uniform vessel, kips
F, =lateral force applied at each section, kips Ch =horizontal seismic factor (see Procedure 3-3)