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American Concrete Design
Section 3
3-14
2) Find an approximate arrangement of bars for the assumed
reinforcement.
3) Calculate PNMAX = 0.85 Po, where Po is the maximum axial load
capacity of the section. Ensure that the actual nominal load on the
column does not exceed PNMAX. If PNMAX is less than Pu/PHI,
(PHI is the strength reduction factor) increase the reinforcement
and repeat steps 2 and 3. If the reinforcement exceeds 8%, the
column cannot be designed with its current dimensions.
4) For the assumed reinforcement, bar arrangement and axial load,
find the uniaxial moment capacities of the column for the Y and
the Z axes, independently. These values are referred to as MYCAP
and MZCAP respectively.
5) Solve the Interaction equation
αα
ny
M
ycap
nz
M
zcap
MM
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
+
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
≤ 10.
where α =1.24
If the column is subjected to a uniaxial moment, α is chosen as 1.0
6) If the Interaction equation is satisfied, find an arrangement with
available bar sizes, find the uniaxial capacities and solve the
interaction equation again. If the equation is satisfied now, the
reinforcement details are written to the output file.
7) If the interaction equation is not satisfied, the assumed
reinforcement is increased (ensuring that it is under 8%) and steps
2 to 6 are repeated.
Column Interaction
The column interaction values may be obtained by using the design
parameter TRACK 1.0 or TRACK 2.0 for the column member. If a
value of 2.0 is used for the TRACK parameter, 12 different Pn-Mn
pairs, each representing a different point on the Pn-Mn curve are
printed. Each of these points represents one of the several Pn-Mn
combinations that this column is capable of carrying about the
given axis, for the actual reinforcement that the column has been
designed for. In the case of circular columns, the values are for