Civil Engineering Reference
In-Depth Information
37.1
37.0
Acceptance
criterion
(1 mm)
36.9
36.8
36.7
36.6
36.5
36.4
0.36 mm
36.3
36.2
1-10 minutes
36.1
36.0
Figure 12.13
Results of creep test showing measured
elongation over 10 minutes test period compared
with acceptance criteria of 1 mm elongation.
0
1234
Log time (minutes)
56
10
provides acceptance criteria for each of the four
tests, and it is necessary that each anchor meets
all the acceptance criteria.
The results of a performance test shown in
Figure 12.12(a) are used to calculate the elastic
elongation
δ
e
of the head of the anchor. The
total elongation of the anchor during each load-
ing cycle comprises elastic elongation of the steel
and residual
δ
r
(or permanent) elongation due
to minor cracking of the grout and slippage in
the bond zone. Figure 12.12(a) shows how the
elastic and residual deformations are calculated
for each load cycle. Values for
δ
e
and
δ
r
at each
test load, together with the PTI load-elongation
acceptance criteria, are then plotted on a separate
graph (Figure 12.12(b)). For both performance
and proof tests, the four acceptance criteria for
tensioned anchors are as follows:
Second
, the total elastic elongation is less
than the theoretical elongation of the unbon-
ded length plus 50% of the bond length—this
ensures that load in the bond length is con-
centrated in the upper part of the bond and
there is no significant shedding of load to the
distal end.
Third
, for the creep test, the total elonga-
tion of the anchor head during the period
of 1-10 minutes is not greater than 1 mm
(Figure 12.13), or if this is not met, is
less than 2 mm during the period of 6-60
minutes. If necessary, the duration of the
creep test can be extended until the movement
is less than 2 mm for one logarithmic cycle
of time.
Fourth
, the lift-off load is within 5% of the
designed lock-off load—this checks that there
has been no loss of load during the operation
of setting the nut or wedges, and releasing the
pressure on the tensioning jack.
First
, the total elastic elongation is greater
than 80% of the theoretical elongation of the
unbonded length—this ensures that the load
applied at the head is being transmitted to the
bond length.
The working shear strength at the steel-grout
interface of a grouted deformed bar is usually
