Civil Engineering Reference
In-Depth Information
According to Eq. (3.67), section resistance moment could be computed by:
f
cm
bx
h
01
−
2
+
f
y
A
s
(
h
01
−
x
a
s
)+0
.
9
f
y
A
s
(
h
a
s
)
−
a
s
0
−
565
+ 310
136
.
4
2
=11
×
400
×
136
.
4
×
−
×
1256
×
530
+0
.
9
×
215
×
1428
×
(600
−
30
−
20
.
3)
10
8
N
10
8
N
=6
.
67
×
·
mm
>Ne
=5
.
67
×
·
mm
3.3.4
Replacing Method
1. Introduction
Concrete columns need to be retrofitted because of deficiency of bearing capacity due to
fire or construction error.
2. Calculation
a. Bearing capacity of axial compressive members using partial replacing can be computed
by:
φ
(
f
c
A
0
+
α
0
f
cj
A
j
+
f
y
A
s
)
N
(3
.
70)
Using whole section replacing method, it can be computed by:
φ
α
0
f
cj
A
j
+
f
y
A
s
N
(3
.
71)
where
N
is factored axial force after retrofitting;
φ
is stability coecient according to
Code
for Design of Concrete Structure
;
f
c
is the factored strength of remaining concrete;
f
cj
is
the factored strength of new concrete;
A
0
is the section area of remaining concrete;
A
j
is
the section area of new concrete;
α
0
is the utilization coecient of new concrete,
α
0
=0
.
8
when without construction supports;
α
0
=1
.
0 when using construction supports.
b. Bearing capacity of eccentric compression concrete members using replacing method
to retrofit can be calculated as the following two situations:
a) When the replacement depth of compressive concrete
h
n
>x
n
, its bearing capacity
can be computed according to
Code for Design of Concrete Structure
using the strength of
new concrete.
b) When the replacement depth of compressive concrete
h
n
x
n
, its bearing capacity
can be computed by:
h
n
)+
f
y
A
m
−
N
f
cm
bh
n
+
f
cm
0
b
(
x
n
−
σ
m
A
m
(3
.
72)
a
m
) (3
.
73)
where
N
is factored axial force after retrofitting;
f
cm
is factored flexure compressive strength
of new concrete, equal to 1
.
1
f
c
;
f
cm
0
is factored flexure compressive strength of concrete in
original members, equal to 1.1 times the factored axial compressive strength;
x
n
is the height
of concrete compressive region after replacement;
h
n
is the concrete replacement depth;
h
0
is the distance from resultant force center of tensile reinforcement to the edge of compressive
region;
h
0
n
is the distance from resultant force center of tensile reinforcement to centroid of
replacement concrete;
h
00
is the distance from resultant force center of tensile reinforcement
to centroid of original concrete;
A
m
and
A
m
are respectively the section area of longitudinal
reinforcement in tensile region and compressive region;
b
is the width of rectangle section;
a
m
is the distance from resultant force center of compressive reinforcement to the edge
of compressive region;
f
y
is the factored compressive strength of longitudinal compressive
reinforcement;
σ
m
is the stress of longitudinal tensile reinforcement.
h
n
)
h
00
+
f
y
A
m
(
h
0
−
Ne
f
cm
bh
n
h
0
n
+
f
cm
0
b
(
x
n
−
