Civil Engineering Reference
In-Depth Information
c) Set U-shape screw between stay bars and frap two reinforcements. Therefore pre-
stress is established in reinforcements.
1
4
3
2
5
1
Fig. 3.12 Stretching prestress by transverse frapping method by manpower:
original beam;
retrofitted reinforcement;
U-shape screw;
brace stay bars;
high strength friction grip blot.
c. Vertical stretching includes stretching by manpower and by jacks.
The method by manpower is shown in Fig. 3.13. Fig. 3.13(a) shows vertical frapping;
hooked frapping blot is clawed to the reinforcements after drilling through the deep
floor (the initial shape of tie rod can be a straight line or curved line); when screwing the
cap of frapping blot, reinforcements move downwards, which makes them become curved
from straight or adds curvature; consequently, prestress is established. Fig. 3.13(b) shows
vertical stretching by jacks, in which is steel plate fixed at the bottom of beam, is
the lower-steel plate with nut welded on the reinforcements; when screwing the puller blot
, the space between upper and lower steel plate is enlarged, reinforcements are forced to
move down; consequently, prestress is established.
2
1
B
B
2
7
8
1
5
6
3
1
5
2
4
(b)
(a)
Fig. 3.13
Vertical stretching by manpower:
original beam;
retrofitted reinforcement;
frapping blot;
steel plate;
high strength friction
grip blot;
puller blot;
upper steel plate;
lower steel plate.
Fig. 3.14 shows prestressed reinforcements of roof truss by jacks.
The techniques of
retrofitting are:
a) Anchor two ends of reinforcements
on plank.
b) Hang jacks
on the reinforcements by hooked stretch device
(oblique wedge is on
the end of jack).
c) Start jacks, pull reinforcements apart from bearings , and insert steel pads into the
gaps of reinforcements and bearings after stretching is qualified.
d. Electric heating stretching method. Apply large electric current at low electric pressure
to the reinforcements, which can make them heat and elongate; cut off the current when
the elongate quantity is qualified, and then anchor two ends immediately. After that, return
material to room temperature and produce shrinkage distortion; consequently, prestress is
established in reinforcements.
