Strengthening of Columns for Confinement - Strengthening Design of Reinforced Concrete with FRP - page 195

7.3.3.2 Contribution of Steel
The following computation steps are taken in general:

1. The depth of each bar layer measured from the top extreme fiber is

d

bar

d = clear cover + d +

_,1 bar tie

2

+ −× −

dd

_,1 bar

d = d ( ) j (7.9 0)

_ barj _ bar ,1

No.oflayers1 −

2. The strain and stress in the steel bar layer j is

ε= −

cd
c

_ barj

ε

sj ccu

f =ε≤ E f

sj s j y

ε

(7.91)

f is obtained fromEquation (7.3) by substituting ε for.

cj sj c

3. The axial force ( P sn ) and the bending moment ( M sn ) contribution of steel are

∑

P = ( f − f ) × A

sn sj cj s barj ,

j

h

∑

M = ( f − f ) × A × − d

(7.92)

sn sj cj s barj , _ barj

2

j

The axial force and bending moment capacity of the section is the
simple sum of the contribution of concrete and steel:

PP P =+

n cn sn

(7.93)

MM M =+

n cn sn

7.3.4 i interaCtion D iagramS For r eCtangular
C olumnS u Sing kDot C olumn e xpert
As shown in the previous section, the effective confining pressure ( f l ) in the case
of the two eccentric points (Point B and Point C) is lower than that of pure axial
compression (Point A), where the section is fully confined. In KDOT Column
Expert software, this issue of partial confinement is modeled more consistently
throughout the range of eccentricities that are correlated to the ratio of the com-
pression zone to the entire section. While the case of pure axial compression
has zero eccentricity and full confinement, the pure bending case has infinite