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 (4) Continuous spiral reinforcing must enclose all longitudinal bars
in compression to insure their full development. The required area of
spiral reinforcement, Asp, is given by:
D2
f'c
EQUATION:
Asp = 0.1125 s Dsp ( - 1)
(79)
D2sp
fy
where,
Asp
=
area of spiral reinforcement, in2
s
=
pitch of spiral, in
D
=
overall diameter of circular section, in
Dsp
=
diameter of the spiral measured through the
centerline of the spiral bar
The spiral reinforcement must conform to the following:
(a) Spiral column reinforcement shall consist of evenly spaced
continuous spirals composed of continuous No. 3 bars or larger. Circular
ties are not permitted.
(b) The clear spacing between spirals shall not exceed 3 inches
nor be less than 1 inch.
(c) Anchorage of spiral reinforcement shall be provided by 1-1/2
extra turns of spiral bar at each end.
(d) Splices in spiral reinforcement shall be lap splices equal
to 1-1/2 turns of spiral bar.
(e) Spirals shall extend from top of footing or slab to level of
lowest horizontal reinforcement in members supported above.
(f) In columns with capitals, spirals shall extend to a level at
which the diameter or width of capital is two times that of the column.
g. Design for Rebound. To account for rebound forces acting on a tied
or spiral column, the longitudinal reinforcement must be properly anchored
into the foundations and into the members supported above. The anchorage
lengths used must provide for the full tensile strength of the bars.
5.
DYNAMIC DESIGN OF EXTERIOR COLUMNS.
a.
Introduction.
(1) Exterior columns may be required for severe loading conditions.
These columns could be monolithic with the exterior walls and as such would
be subjected to both axial and transverse loading. The axial load results
from the direct transfer of floor and roof beam reactions while the
transverse load is due to the direct impact of the blast load.
2.08-104
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