ETL 1110-2-365
31 Aug 94
the cracks that form which are important as well as
in Figure B-5 was created due to ambient conditions
areas where there is a high potential for cracking. If
and the stresses in the reinforcing are low, it would
a NISA shows that only a few integration points
be reasonable to allow the construction parameters to
exceed the cracking criteria (discussed in Annex 2,
remain unchanged.
Appendix A) and the analysis shows that the cracking
has stopped, then measures to reduce the cracking
(3) Figure B-6 shows the cracking which has
may not be necessary, particularly if reinforcing is
begun to occur on the land wall half of the slab.
present. If it is shown though that the cracking
Three integration points have cracked initially and do
extends through the depth of a member, then con-
not extend beyond the top lift. Figure B-7 shows the
sideration must be given to making changes to reduce
final crack pattern in this portion of the slab at day
the cracking regardless of the fact that reinforcing is
183 and only one additional integration point has
present. This section will discuss cracking potentials
cracked. As with the cracking which occurred in the
and crack plots and how to use this information. The
other portion of the slab, the crack indicated by the
chamber monolith shown in Figure B-1 is used for
plots does not continue to propagate. If stresses in
this presentation. It should be noted that the cracking
the reinforcing are evaluated, they are low, so as
criteria was reduced by one-half in the following
before, changes in the construction parameters to
analyses so that cracking would occur.
reduce or eliminate the cracking shown do not appear
to be necessary.
b. Crack plots.
c.
Crack potential plots.
(1) Figures B-2 through B-5 are crack plots of
the middle wall and one-half of the chamber and
(1) Figures B-8 through B-14 are crack potential
Figures B-6 and B-7 are crack plots of the land wall
contour plots of the middle wall half of the model,
and one-half of the chamber. As can be seen in
while Figures B-15 through B-18 are crack potential
Figure B-2, no cracks have formed at 81.5 days (time
contour plots of the land wall half of the model. The
of the analysis is designated by the AMP parameter
contours shown in these plots provide information
located at the top of the plot). Figure B-3 is a plot at
about how close to cracking various parts of the
85.75 days and as can be seen, an integration point
structure are in the form of percentages of the crack-
above the top left corner of the culvert has cracked.
ing criteria, i.e., a 50 percent contour indicates that
It can be seen by looking at Figures B-4 and B-5 that
the level of stress and strain is one-half the cracking
the crack does not extend beyond this initial cracking.
criteria. These plots can be used to identify areas
Such a crack would typically not require taking mea-
that are near the cracking level.
sures to eliminate the crack, particularly for a rein-
forced structure.
(2) Figure B-8 is a crack potential plot of the
left half of the model at day 81.5 which is just a few
(2) Figure B-4 is a plot at 143 days and an inte-
days prior to the crack occurring at the top left corner
gration point has cracked at the lower left hand cor-
of the culvert. As can be seen in the figure, high
ner of the culvert and six integration points have
cracking potentials are developing at this corner. An
cracked approximately one-third of the way across the
enlarged view of the culvert is shown in Figure B-9
slab. As can be seen in Figure B-5, 20 days after the
and in this figure it can be seen that the potential for
condition shown in Figure B-4, the crack at the bot-
cracking at the corner in question is approximately
tom corner of the culvert has not grown, but the
70 percent. Figure B-10 is the enlarged view of the
crack in the slab has extended further into the slab.
culvert again, but it is shown at day 85.75, which is
The crack as shown in Figure B-5 is as far as the
the step after the crack has formed at the corner. As
crack advanced. As with the crack at the top of the
can be seen, the cracking potential near the corner
culvert, no additional steps should be needed at the
has been reduced, and the potential for cracking of
bottom of the culvert. The crack in the slab may
66 percent is occurring more toward the center of the
need to be evaluated further. The design team should
culvert.
evaluate a crack such as the one seen in Figure B-5.
Then, based on the load causing the crack and the
(3) Figure B-11 again shows the left half of the
stresses in the reinforcing, a decision should be made
model at day 103. The potential for cracking near
as to whether steps should be taken to reduce or
the top left corner of the culvert continues to build to
eliminate the crack. Since the crack seen in the slab
a level of 88 percent. In addition, the top of the slab
B-3
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