Bentley 2006 Manuel D’Utilisation

 

American Concrete Design 

 Section 3

 

 

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 

α

α

ny

M

ycap

nz

M

zcap

M

M

 

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟ +

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟ ≤ 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. 

 

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