The design criteria presented herein apply to either
will be somewhere between the values for the
cantilever or singly guyed stacks.
All stacks
fundamental and the appropriate higher mode of a
designed under the provisions of this paragraph must
similar cantilever stack. An illustration for a single-
have a constant moment of inertia. Stacks having a
guyed stack is shown in Figure 10-10. The design of
slightly varying moment of inertia will be treated as
guyed stacks is beyond the scope of this manual.
having a uniform moment of inertia with a value
equal to the average moment of inertia.
1. Stacks on the ground. Where stack
foundations are in contact with the ground and the
(1). Stacks on buildings. Stacks that extend
stack is not supported by the building, the stack will
more than 15 feet (4.6m) above a rigid attachment to
be considered to be a non-building structure
the building will be designed according to the
governed by other agency documents.
criteria for cantilever stacks prescribed below.
Stacks that extend less than 15 feet (4.6m) will be
2.
Anchor bolts.
Anchor bolts for
designed for the equivalent static lateral force
moment-resisting stack bases should be as long as
prescribed in Section 6.3.11 of FEMA 302.
possible. A great deal more strain energy can be
absorbed with long anchor bolts than with short
(a) Cantilever stacks.
ones. The use of these long anchor bolts has been
demonstrated to give stacks better earthquake
1. The fundamental period of the stack
performance. In some cases, a pipe sleeve is used in
will be determined from the period coefficient (i.e.,
the upper portion of the anchor bolt to ensure a
C = 0.0909) provided in Figure 10-9, unless actually
length of unbonded bolt for strain energy absorption.
computed.
When this type of detail is used, provisions will be
made for shear transfer (e.g., shear keys). The use of
2.
The dynamic response may be
two nuts on anchor bolts is also recommended to
calculated from the appropriate base shear equations
provide an additional factor of safety.
for
the
Equivalent
Lateral
Force
procedure
g.
Bridges, Cranes, and Monorails.
prescribed in Chapter 3.
In
addition to the normal horizontal loads prescribed by
(b) Guyed stacks. The analysis of guyed
the various other applicable government criteria, the
stacks depends on the relative rigidities of the
design of bridge cranes and monorails will also
cantilever resistance and the guy wire support
include an investigation of lateral seismic forces and
system. If the wires are very flexible, the stack will
deformations as set forth in this paragraph.
respond in a manner similar to the higher modes of
vibration of a cantilever, with periods and mode
(1) Equivalent static force. A lateral force
equal to 0.5SDS aP times the weight of the bridge
shapes similar to those shown on Figure 10-9. The
fundamental period of vibration of the guyed system
crane of monorail will be statically applied at the
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