ETL 1110-2-536
31 Dec 94
described in the following paragraph, will define the
nearly the same. However, there is a notable differ-
element mesh.
ence in the rate of coding. The two-dimensional
elements do not have the capability to conduct heat in
(3) The mesh sizes for the two models were
the out-of-plane direction. With convection being
established by the equation provided in the ABAQUS
modeled along the top surface only, of the longitudi-
user manual and restated in ETL 1110-2-234. Results
nal model, the elements sustain a higher thermal
from this equation were found to be very restrictive
gradient over a much longer period of time.
on the element size. Instead, a simple parametric
study was performed to determine if a larger element
(4) Discussion of stresses for both models should
size could be used without creating numerical insta-
be limited to principle tensile stresses. However,
bilities in the thermal model. The results of the para-
software developed for plotting stress histories is only
metric study indicated that the maximum length of
capable of plotting stress in orthogonal directions and
the element in the direction of heat flow could be
for shear stresses. Because Zintel Canyon Dam nor-
48 in. For both models, 48 in. was the maximum
mally has no pool and experiences a very short
size of element used in any direction for a 6-hr time
duration reservoir impoundment, cracking posed no
interval. A 6-hr time interval was chosen based on
concerns related to seepage. Of concern are the
production rate of RCC and because it satisfied the
orientation of cracks that will compromise the stabil-
maximum time interval required to compute early
ity of the structure. A feature of the ABAQUS-based
heat gain in the concrete. Results of the parametric
NISA that sets it apart from others is that it allows
study are shown in Appendix B. Mesh size was then
material properties and relationships to be user-
correlated with the RCC placement schedule of the
defined. UMAT is the subroutine that provides a
dam and was designed to capture heat gains at the
time-dependent cracking material model. The subrou-
early ages of construction. Appendix A, Figure A-1
tine allows input of specific material properties and
represents a time history for construction and the
calibration of the model-predicted properties against
analysis for the transverse and longitudinal model
actual observed material performance. While some
respectively, as well as the initial conditions, bound-
material testing had been done for Zintel Canyon
ary conditions, and input values used. Boundary
Dam, extensive evaluation of time-dependent proper-
conditions include the insulating effects of upstream
ties and creep performance had not been determined.
precast facing panels, free surface convection, soil
Consequently, calibration of the UMAT material
(rock) conditions, downstream stilling basin slab,
model could not be performed. The material model
average daily temperatures for preconstruction, during
generated for Olmsted Locks and Dam was used
construction, and postconstruction. Initial conditions
except that the material constants were replaced with
include RCC placement temperatures, and initial
actual or estimated values for Zintel Canyon Dam
foundation temperatures. The user subroutine
RCC materials. This means that the UMAT predicted
DFLUX was used, in conjunction with ABAQUS, to
performance for Zintel Canyon Dam was based on
generate time-dependent heat fluxes for the thermal
Olmsted material relationships. No data were avail-
analysis. Parameters used in DFLUX included adia-
able to shift the relationship curves. Without actual
batic heat gain (time and temperatures) for the RCC
data to calibrate the material model, changes would
mix as well as initial placement times for each lift.
be arbitrary and not necessarily an improvement over
Adiabatic heat gain curve is plotted in Figure A-1.
using the Olmsted data. To perform a reliable NISA,
Results of the thermal analysis for both the transverse
these material properties need better definition. More
and longitudinal model are represented in contour
complete definitions of the development of the modu-
plots in Appendix A, Figures A-2 to A-11 and time
lus of elasticity and creep are critical to accurate
history plots of maximum nodal temperatures in
results. For smaller scale projects, standard relation-
Appendix A, Figures A-12 and A-13. The maximum
ships for a range of materials should be developed so
temperature reported in the transverse model is
that the analyst can select the performance relation-
represented by node 2330, Figure A-12c, and in the
ship that most likely models the materials being eval-
longitudinal model by node 3213, Figure A-13c.
uated. Only the larger projects will have the funding
Maximum temperatures and temperature differential
to perform a complete battery of laboratory evalua-
correlate well with predicted temperatures calculated
tions. For the longitudinal model, the maximum
by using approximate computational methods for
principle stress occurred at the foundation/RCC inter-
Zintel Canyon Dam. As stated previously, effects of
face at element 1796 and are presented by stress
maximum heat gain between the two models were
contour plots in Appendix A, Figures A-14 to A-19
A-4
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