ETL 1110-2-365
31 Aug 94
(e.g., time between lifts, lift heights, type of form-
accounted for by performing parametric studies using
work, formwork removal, construction start date,
combinations of the upper and lower bounds
insulation requirements, etc.) which will approximate
described in paragraph A-2b.
actual field conditions and which can be adequately
modeled. The materials engineer and structural engi-
(b) Start times. Variations in behavior will
neer should develop a set of time-dependent curves to
occur due to construction of a monolith beginning at
be used in the analytical model for the aging
different times of the year and these variations should
modulus, adiabatic temperature rise, creep, and
be accounted for. Assuming construction starts at
shrinkage based on the results of laboratory testing.
different times of the year may identify additional
These curves will be banded to reflect the typical
critical areas of the structure. Minimum requirements
variations specified in paragraph A-2b(2) and the
for analyses with different start times are presented in
confidence level the materials engineer has with the
paragraph A-2d.
local site conditions. Other concrete properties (e.g.,
tensile strain capacity, the coefficient of thermal
(c) General. Variations in other parameters may
expansion, thermal conductivity, specific heat, dens-
also be accounted for by varying the parameter of
ity, and Poisson's ratio) should be provided for the
interest while other parameters remain constant.
proposed concrete mixtures by the materials engineer
General guidance on performing a parametric study is
through results of test data. The geotechnical engi-
given in paragraph A-2g. This approach can be used
neer and structural engineer should develop appropri-
to identify and confirm cost-saving construction tech-
ate values for the thermal conductivity, coefficient of
niques and to increase the structural designer's confi-
thermal expansion, specific heat, density, and
dence in the results that are being produced. For
Poisson's ratio for the foundation material, and the
cases when cracking appears to be imminent for a
pile-subgrade reaction moduli. The structural engi-
given set of conditions and the variation of some
neer should obtain the monthly average ambient air
other parameter could induce crack initiation, a para-
temperatures as described in paragraph A-2c. It will
metric study may be valuable in assessing the design-
be the structural engineer's responsibility to ensure
er's confidence in the satisfactory behavior of the
that the specified parameters are properly modeled for
structure.
the numerical analysis. When modeling assumptions
must be made, the structural engineer should consult
(2) Methods of analysis. Two-dimensional
with other design team members as necessary, but the
NISA's of entire monolith cross sections are currently
final decision on how to implement the various
practical. Three-dimensional (3-D) NISA's are typi-
parameters will be made by the structural engineer.
cally performed on isolated portions of structures, or
sometimes entire monoliths may be modeled, pri-
e. Assumptions, simplifications, and limitations.
marily to determine the 3-D behavior of the structure
This guidance is based on proven methods of FE
in all directions. Three-dimensional NISA's may also
analysis, on NISA's performed on Corps of Engineers
be used to confirm 2-D results. Most structures
projects, and from independent parametric studies.
should be modeled using a plane-stress approach.
The past experience has highlighted the following
Plane-strain modeling may also be considered, but
points.
studies have shown that differences between the plane
stress and plane strain approach are minimal for the
(1) Variations in input data. The analysis
results in the plane being evaluated (Truman,
requires reliable, but not exact, input data for mean-
Petruska, and Ferhi 1992 and Garner et al. 1992).
ingful results. Since exact data are not available,
The selection of an appropriate approach is a matter
parametric studies are valuable in predicting the
of engineering judgment with consideration given to
trends in behavior that can be expected in a given
factors such as the volumetric change which may
structure.
occur in the out-of-plane direction, the ability of the
ends of the monolith to move with respect to each
(a) Material properties. Variations in material
other, and the length of the monolith. For example,
properties due to scatter of test data, differences in
if volume changes are small, the selection between
behavior of the material between actual and that
plane stress and plane strain will create little differ-
predicted by the numerical model, and expected dif-
ence in the results, but if these volumetric changes
ferences between the laboratory mixture and the
are large the length of the monolith may be the deter-
actual mixture used during construction can be
mining factor for which model to use. The longer a
A-7
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