Civil Engineering Reference
In-Depth Information
h
1
)
h
01
−
x
−
h
1
+
f
y
A
s
(
h
01
−
a
s
)
Ne
f
cm
b
(
x
−
h
1
−
2
+0
.
9
f
cm
1
b
1
h
1
h
01
−
+
f
y
1
A
s
1
(
h
01
−
a
s
1
)
h
2
(3.57)
where,
f
cm
and
f
cm
1
are respectively the factored flexural compressive strength of the new
adding concrete and the original, which respectively equal 1
.
1
f
c
and 1
.
1
f
c
1
;
x
is the com-
pressive height;
h
1
is the thickness of adding concrete in compressive region;
b
and
b
1
are
respectively the section width of the original columns and the retrofitted ones;
A
s
and
A
s
1
are respectively the section area of tensile reinforcement in original and retrofitted columns;
f
y
and
f
y
1
are respectively the factored tensile strength of the tensile reinforcement in
original and retrofitted columns;
e
is the distance between action points of axial force and
reinforcement resultant force, which is:
e
=
ηe
i
+
h
2
−
a
h
01
is the distance from compressive edge to action point of tensile reinforcement resultant
force including the original and the new addition. When the two action points are close,
h
01
equals to the effective height
h
0
of original columns.
a
s
1
is the distance from the compressive
edge to the action point of the new adding tensile reinforcement resultant force.
a
is the
distance from the tensile edge to the action point of tensile reinforcement resultant force
including the original and the new. Meanings of the other symbols are shown in
Specification
for Retrofitting of Concrete Structures
and Eq. (3.55).
e
η
ei
f
y
1
A
s
1
f
y
A
s
f
y
1
A
s
1
f
y
A
s
h
1
a
st
h
1
x
a
h
0
Fig. 3.39
Calculation of column limits.
Calculation of the bearing capacity of single thickening columns could make reference to
Eq. (3.56) and Eq. (3.57).
By using surrounded outsourcing, calculation of the bearing capacity is complicated. To
simplify calculation, factored compressive strength of the new concrete equals the flexural
compressive strength
f
cm
of the original concrete, which means replacing the 0.9
f
cm
1
in
Eq. (3.56) and Eq. (3.57) with
f
cm
. This is based on the fact that the strength grade of
the adding concrete is one level higher than that of the original concrete. The simplification
indicates that 0.9
f
cm
1
is a little bigger than
f
cm
.
