Page 206 - Pressure Vessel Design Manual

184 Pressure Vessel Design Manual

a Bending moment, M. minimum depth from the bottom of the wear plate
to the top of the base plate.
M = f&e 2. The full length of the web may be assumed effective
in carrying compressive stresses along with ribs. Ribs
0 Bending stress, fh. are not effective at carrying compressive load if they
are spaced greater than 25 times the web thickness
MC2
fh = - apart.
I
3. Concrete compressive stresses are usually considered
0 Combined stress. to be uniform. This assumes the saddle is rigid enough
to distribute the load uniformly.
4. Large-diameter horizontal vessels are best supported
fh
fa
-+-e1
Fa Fb with 168" saddles. Larger saddle angles do not effec-
tively contribute to lower shell stresses and are more
I difficult to fabricate. The wear plate need not extend
Notes beyond center lines of vessel in any case or 6" beyond
saddles.
1. The depth of web is important in developing stiffness 5. Assume faed saddle takes all of the longitudinal
to prevent bending about the cross-sectional axis of loading.
the saddle. For larger vessels, assume 6 in. as the

PROCEDURE 3-12
DESIGN OF BASE PLATES FOR LEGS 120, 211

A, =total cross-sectional area of bolts in tension, in.'
Notation a = coefficient
T, = shear stress
Y = effective bearing length, in.
M =overturning moment, in.-lb
Mb =bending moment, in.-lb
P =axial load, Ib
ft =tension stress in anchor bolt, psi Calculations
A = actual area of base plate, in.2
A, = area required, base plate, in.2 Axial loading only, no moment.
f: =ultimate 28-day strength, psi
f, =bearing pressure, psi Angle legs:
fi =equivalent bearing pressure, psi
P
Fb = allowable bending stress, psi f --
Ft = allowable tension stress, psi '-BD
F, = allowable compression stress, psi L = greater of m, n, or n'
E, = modulus of elasticity, steel, psi 3f,L2
E, = modulus of elasticity, concrete, psi t=&
n = modular ratio, steel-concrete
n' =equivalent cantilever dimension of base plate, in.
B, = allowable bearing pressure, psi Beam legs:
K1,z.s = factor
P
T =tension force in outermost bolt, lb A, = -
C =compressive load in concrete, lb 0.7fk
V=base shear, lb
N =total number of anchor bolts
Nt =number of anchor bolts in tension D - 0.95d
Ab = cross-sectiond area of one bolt, in.z m= 2