Civil Engineering Reference
In-Depth Information
d
120
120
Stub bars
Added reinforcement
Added reinforcement
500
(a) Detailing of stub bars
10
d
(one side welding)
U-shaped
stirrups
5
d
(double side welding)
Weld length
U-shaped
stirrups
Anchor bolt
Welding
Stub bars
Added reinforcement
U-shaped stirrup
U-shaped stirrups
(b) Welding U-shaped stirrups to existing stirrups
(c) Welding U-shaped stirrups to anchor bolts
Fig. 3.5
Details of connection between additional reinforcements and existing member.
a) Chisel off plaster layer until the structural layer is reached and toughen the surfaces
or notch grooves for certain spacing. As to the grooves, depth may not be less than 6 mm
and spacing may not be larger than 200 mm as well as the spacing of additional stirrups.
Furthermore, concrete edges of existing members should be filleted and dregs should be
removed as well.
b) Flush the roughened surface of existing members thoroughly and cover it with fresh
cement paste or interfacial agent before casting additional concrete.
b. The next procedure is to remove the rust on reinforcements. Also, it is suggested that
such a measurement as unloading or set bracing shall be executed after derusting and then
reinforcement shall be welded rebar after rebar, region after region, section after section,
layer after layer gradually to reduce the effects of the created heat as much as possible.
c. In addition, the procedures including supporting formwork, banding reinforcement,
casting concrete, and curing concrete should meet the Code for Acceptance of Constructional
Quality of Concrete Structures.
5. Calculation example
Example 3.1
A cast-in-situ multi-stories RC frame, which is used as a parking garage
for the first floor and an oce above the second floor, carries live load 2 kN
/
m
2
.Asaresult
of renovation, the live load of the second floor increases to be 4 kN
/
m
2
.Asaresult,itis
found that floor slabs are insucient with regard to bearing capacity and should be prepared
to retrofit by the strategy of enlarging section.
Solution:
a. Known data: The concrete has grade C20 and the steel has grade 235. Structural
thickness of the existing slabs is 70 mm and cover thickness of the cement plaster is 20 mm;
Specific dimension and steel configuration appear in Fig. 3.6.
