ETL 1110-2-365
31 Aug 94
contains the material model for the time-dependent
desirable to perform 3-D analyses on all structures,
properties for creep, shrinkage, and the aging modu-
the complexity associated with performing 3-D analy-
lus of elasticity. Other parameters used within the
ses is such that this approach is not yet practical.
UMAT subroutine are Poisson's Ratio, the cracking
Therefore, 2-D analyses of transverse strips should be
strain, the coefficient of thermal expansion, band-
used for most investigations. Additionally, behavior
width factors for creep and shrinkage, the time of set,
of the structure in the out-of-plane direction may be
and the 3-day compressive strength of the concrete
determined using 2-D strips in the longitudinal direc-
(Annex 4, Appendix A, is a complete list of input
tion and/or a 3-D analysis. The primary purpose of a
parameters required for a NISA). Curves contained
3-D analysis should be for cases where 2-D analysis
in the material model must be fitted for the concrete
is inappropriate because of geometrical configuration
mixture which is expected to be used at the project
or loading conditions.
site. This curve fitting is currently performed by
CEWES-SC, but efforts are in progress to implement
c. Mesh generation and refinement. Conven-
a procedure which will allow curve fitting to be
tional FE modeling techniques should be applied to
accomplished by others. The material model used in
develop an FE mesh for a NISA (ETL 1110-2-332,
UMAT was developed by ANATECH Research Corp.
"Modeling of Structures for Linear Elastic Finite
and is contained in the ANACAP-U software
Element Analysis," and Technical Report ITL-87-8,
(ANATECH Research Corp. 1992). The mathemati-
"Procedure for Static Analysis of Gravity Dams
cal relationships adopted for the material properties
Using the Finite Element Method - Phase Ia" (Will
contained in the subroutine are contained in the
1987)). In addition, consideration should be given to
ANACAP-U Theory Manual (ANATECH Research
the items discussed below.
Corp. 1992). In addition, ANACAP-U uses a
smeared crack model (discussed in further detail in
(1) General. Typically, the mesh developed for
paragraph A-5e(4), Appendix A) where cracking
use in the heat transfer analysis will be used in per-
occurs at the integration points. The cracking criteria
forming the stress analysis. Using the same mesh for
is based on an interaction curve between stress and
both analyses ensures that each node in the stress
strain (ANACAP-U Research Corp 1992). There is a
mesh has a temperature associated with it from the
brief description of the cracking model in Annex 2,
heat transfer mesh. In addition to items discussed in
Appendix A.
subsequent paragraphs, the designer should attempt to
include at least two elements through the thickness of
(4) Units. The ABAQUS code does not provide
any member.
an input option for different units for different param-
eters, therefore the user must ensure that all of the
(2) Foundation. For soil-founded structures, the
input parameters have consistent units. The preferred
soil elements used in the heat transfer analysis are
units are:
usually replaced by springs in the stress analysis to
save computing time. A similar approach may be
Length - inches
used for rock foundations but may require some
investigative analysis since, to date, no NISA's have
Weight - pounds
been performed on rock-founded structures. Another
possibility for rock foundations is the use of superele-
Stress - lb/in.2
ments which allows for the stiffness of a large num-
ber of discrete elements to be lumped into a single
Time - days
region which is the superelement. Despite the
method used, a rock foundation should model an area
Temperature - oF
1.5 times as deep and 3.0 times as wide as a struc-
ture's base as established in "Static Analysis of
Heat - Btu
Gravity Dams Using the Finite Element Method,
Foundation Effects - Phase Ib" (Jones and Foster in
preparation).
b. 2-D versus 3-D analysis. There are many
MCS for which a 2-D analysis of a monolith will be
(3) Inclusion of lift joints. Development of an
sufficient. However, any structure undergoing tem-
FE mesh for a NISA study must account for the
perature loadings exhibits some 3-D behavior, even
locations of the construction lift joints and vertical
traditionally 2-D type structures. While it may be
A-17
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