Civil Engineering Reference
In-Depth Information
for retrofit design to calculate the stress of reinforcements in retrofitted members and make
sure it is lower than code-specified requirement during service. Service stress of the tension
reinforcement of retrofitted members is given by
σ
s
=
σ
s
1
+
σ
s
2
0
.
9
f
y
(3.7a)
where
σ
s
1
is reinforcement stress due to moment
M
1
before additional concrete active, and
can be determined below:
M
1
A
s
η
1
h
0
σ
s
1
=
(3.7b)
σ
s
2
is reinforcement stress due to moment
M
2
after additional concrete active and can be
determined below:
σ
s
2
=
M
2
(1
β
)
A
s
η
2
h
01
−
(3.7c)
where
A
s
is sectional area of the tensile reinforcement;
η
1
and
η
2
represent internal lever
arm coecient at the cracked section and both may be taken as 0.87 approximately;
β
is
composite characteristic parameter and may be taken in accordance with Eq. (3.7d), which
indicates the effect of load prestressing and the ratio of
h
1
/h
.
β
=0
.
5
1
h
h
1
−
(3.7d)
f
y
denotes design strength of tension reinforcement;
h
and
h
0
are sectional depth and ef-
fective depth of the section for original members; also,
h
1
and
h
01
are sectional depth and
effective depth of the section for retrofitted members respectively.
(3) Calculation of bearing capacity
In the retrofit by section enlarging method, the estimation of bearing capacity should
conform to the provisions of the
Code for Design of Concrete Structure (GB50010—2002)
in China and much attention should be given to the interaction between additional concrete
and original concrete.
When the strategy of section enlarging method is adopted for retrofit of bent members, the
retrofit design should conform to the provisions of the
Code for Design of Concrete Structure
(GB50010—2002)
and
Technical Specification for Strengthening Concrete Structures (CECS
25:90)
in China.
a. The depth of compression zone of relative boundary value
ξ
b
could be determined as
follows with regard to enlarged section.
a) As to enlarging section on one side of additional steel at tensile surface
0
.
8
1+
f
E
s
1+
2
δ
h
01
ξ
b
=
(3
.
8)
σ
s
0
E
s
0
1
0
.
0033
+
·
b) As to enlarging section at compressive surface
0
.
8
ξ
b
=
(3
.
9)
f
y
0
.
0033 +
1+
2
δ
h
01
1+
σ
s
0
E
s
0
E
s
0
c) As to enlarging section at both surfaces and neglecting discrepancy on thickness for
both surfaces
0
.
8
0
.
0033 +
1+
2
δ
h
01
σ
s
0
E
s
0
1+
2
δ
h
01
ξ
b
=
(3
.
10)
f
E
s
+2
σ
s
0
E
s
0
0
.
0033 +
