Civil Engineering Reference
In-Depth Information
where
f
y
is design strength of additional reinforcement;
E
s
is elastic modulus of additional
reinforcement;
σ
s
0
is stress of reinforcements which lies at the side with lower stress level
for original part while retrofitting;
E
s
0
is the elastic modulus of original reinforcements;
δ
is the thickness of additional layer and could be taken as the average thickness of double
surfaces;
h
01
is the effective depth of original section.
b. When additional concrete is cast onto compressive surfaces of flexural members, loading
effect should be determined in accordance with the provisions of
Code for Design of Concrete
Structure
.
c. Regarding enlarging sections with additional reinforcements at tensile surface, design
strength of the reinforcements should be multiplied by strength utilization coecient 0.9 for
flexural calculation.
d. When calculating the shear capacity of inclined sections, the strength utilization coef-
ficient for additional concrete and additional reinforcement should be taken as 0.75 and 0.85
separately and the contribution of unanchored U-shaped stirrups for shear capacity should
be ignored.
3. Detail provisions
a. The minimal thickness of additional concrete should not be less than 40 mm for slabs,
60 mm for beams, and 50 mm for shotcrete construction.
b. Pebble and gravel may be used as coarse aggregate for their hardness and durability,
and the maximum particle size may not be more than 20 mm.
c. Diameter of the additional reinforcements may be 6
∼
∼
25 mm
for beams, and deform steel is preferred for longitudinal reinforcement of the beams. Also,
diameter of the enclosed stirrups may not be less than 8 mm and diameter of the U-shaped
stirrups may be the same as the original stirrups.
d. The net spacing between original reinforcements and additional reinforcements should
not be less than 20 mm and welded stub bars should be employed for their connection;
furthermore, enclosed stirrups or U-shaped stirrups should be adopted in accordance with
the
Code for Design of Concrete Structure
.
a) When stub bars are employed to connect additional reinforcements and original re-
inforcements (see Fig. 3.5(a)), it is suggested that diameter and length for the bars shall
not be less than 20 mm and 5
d
(
d
is the lesser value of the diameter for original reinforce-
ments and additional reinforcements) and the spacing between stubs shall not be more than
500 mm.
b) U-shaped stirrups should be adopted for double-surface retrofit as well as single-surface
retrofit (see Fig. 3.5(b)).
U-shaped stirrups may be welded to original stirrups and minimal weld length should reach
10
d
and 5
d
separately for one side welding and double side welding (
d
is the diameter of
U-shaped stirrups).
Also, stirrups could be anchored to anchor holes directly as well as be welded to steel bars
or anchor bolts which are anchored in existing members (see Fig. 3.5(c)). The diameter of
steel bars or anchor bolts should not be less than 10 mm and distance from centroids of the
bolts to the edges of members should not be less than 3
d
and 40 mm. Furthermore, anchor
depth of the bolts should not be less than 10
d
and epoxy mortar or epoxy grout should be
used to anchor the bolts to the holes drilled in existing beams. In addition, the diameter
of anchor holes should be 4 mm larger than that of anchor bolts, and anchor behavior,
especially at the longitudinal ends, should be validated for reliability.
e. Both ends of the added reinforcements should be anchored reliably.
8 mm for slabs and 12
4. Construction requirements
a. The procedures and provisions below should be followed in retrofit of RC structures.
