ETL 1110-2-365
31 Aug 94
A-6. Evaluation of Results
significantly different than the conventional linear,
gravity turn-on analysis.
a. General. Current practice relies heavily on
d.
Cracking criteria.
engineering judgement to evaluate the results of a
NISA. The performance of a NISA is a means for
(1) Model. The potential for cracking at any
assessing MCS's with regard to thermal loading and
integration point is checked using an interactive
the potential for cracking. A NISA is not a linear
stress-strain cracking criterion. The cracking criterion
analysis with factors of safety and allowables, but it
is not explicitly time dependent which is why an
is a prediction of actual response under extreme con-
interactive stress-strain criterion is used. The time
ditions. Controlling the ultimate response will require
effects are accounted for through the age-dependent
require adjustments to those structures with potential
modulus as described in Annex 2, Appendix A. If
cracking problems. Adjustments might be made in
the cracking criterion is violated, a crack will be
construction procedures, materials, and/or geometric
introduced perpendicular to the direction of the maxi-
configuration to provide better ultimate performance.
mum principal strain. If a crack is introduced, the
These adjustments will ensure a more reliable
constitutive matrix is reformulated within ABAQUS,
product.
and a new stress state is developed based on zero
stress in the principal tensile strain direction. The
b. Verification of input and data. The design
new constitutive matrix and stresses are then used for
team must use every available means to verify the
subsequent calculations until another crack is indi-
correctness of the actual data and the input data for
cated by the criterion or the crack closes. The cracks
the NISA. NISA's require a considerable and widely
will close when placed in a compressive state, and
varied set of structural, material, and thermal input
the material will again be able to carry compressive
parameters. This variety of parameters, some of
loads. Depending on the severity of the crack, the
which are unfamiliar to structural engineers, require
shear resistance is reduced at the cracked integration
the utmost care in verification of units and magni-
points, but the crack will have limited shear resis-
tude. General guidelines for input verification for
tance due to friction and aggregate interlock.
finite element analyses are given in ETL 1110-2-332.
(2) Evaluation.
c. Verification of results. The design team
should use any means available to help verify the
(a) Concrete cracking. The cracking criterion is
validity of the results. Using the minimum specified
yes, the material has cracked, or no, it has not. This
parametric combinations provided in paragraph A-2,
yes/no crack prediction is necessary and correct when
coupled with the experience and judgement of the
finding the ultimate response of the structure, but it is
structural engineer, an initial check of the results can
not very useful in predicting reliability or potential
be made on a qualitative basis. Exploring previously
for cracking. Therefore, the ANACAP-U subroutine
analyzed NISA structures and their results, perform-
provides a percentage of the cracking criterion to
ing a simple ambient condition analysis (no creep,
evaluate the potential for cracking. A percentage
shrinkage, aging modulus, or adiabatic temperature
approaching 100 indicates an increasing possibility of
rise), and performing a simple gravity turn-on analy-
cracking. Any structure with a NISA that indicates
sis (typical linear structural analysis) are all possible
cracking should be evaluated for the severity of the
methods for providing confidence and a check on the
consequences of the predicted cracks. If the conse-
validity of the structural model, effects of ambient
quences are deemed detrimental with respect to safety
temperature load, and aging material properties.
or economics, the structure should be redesigned.
Material property combination 1 (paragraph A-2) is to
Possibilities for redesign include, but are not limited
be used for education, verification, and validation
to, the use of additional reinforcement, the revision of
regarding these parameters without performing
construction procedures, and/or the modification of
exhaustive parameter studies. Extensive parameter
the material constituents to alleviate or control the
studies have been performed in the past for several
cracking.
projects as outlined by Truman, Petruska, and Ferhi
(1992) and Garner et al. (1992). Engineering judg-
(b) Reinforcing. Resulting stresses in the rein-
ment must be used in all cases since the effects of
forcing bars should be monitored, reported, and
these parameters can produce results that are
A-21
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