will be used to develop the final design parameters to

conditions, and film coefficients. The material prop-

be used in evaluating the various monoliths.

erties must then be defined and should include the

conductivity, density, and specific heat of any materi-

(3) Final NISA. A final NISA should be com-

als used in the analysis. This will require properties

pleted late in the design process, using the design

for both the concrete and foundation and possibly air.

parameters selected in the initial NISA to verify the

The initial temperature of the concrete must be

selected designs. The analysis should be based on

defined and is typically assumed to be the placing

the final design layout and the parametric combina-

temperature. A definition of the air temperatures

tion which produced the worst condition in the initial

should be made as described in paragraph A-2*c*. Fin-

NISA studies. Should actual conditions during con-

ally, a definition of the time history must be made as

struction deviate from those assumed for the final

shown in steps 6 and 7 of Figure A-1. This includes

analysis, it may be necessary to perform another

defining the length of each step and its increment,

NISA using the actual field conditions.

changing the model as necessary, applying, removing,

and changing film coefficients as required, applying

the heat generation (paragraph A-5*a*(2)), and defining

composed of a heat transfer analysis and a stress

any required output. It is critical that a temperature

analysis. The heat transfer analysis is performed to

output file be defined properly to ensure that tempera-

determine how the temperatures within the structure

tures needed for the stress analysis are computed

change with time. The stress analysis is performed to

properly.

determine the stress and strain state of the structure

based on these changing temperatures, gravity loads,

(3) Stress analysis. A flow chart defining the

changing material properties, and the boundary condi-

steps in a stress analysis is presented in Figure A-2.

tions. A description of these two types of analyses is

The node and element data defined in the heat trans-

provided in the following paragraphs. Parametric

fer analysis for the concrete are typically used in the

studies are an important part of performing a NISA

stress analysis and these data can then be used to

and are used to assist the engineer in making the

identify the needed node and element sets. Input

proper decisions for design and construction parame-

parameters for the user material subroutine must be

ters. Use of parametric studies is discussed in para-

determined by calibrating the model for the concrete

graph A-2*g*. Once analyses are completed, it is

mixture being analyzed with the test results for that

necessary to evaluate the results as described in para-

mixture. If springs are used in place of continuum

graph A-6 to determine the effects of various

elements to model the foundation, then spring con-

parameters. Finally, the results, conclusions, recom-

stants must be determined and used as a definition of

mendations, and any cost savings should be reported

the spring properties. A definition of the initial

as described in paragraph A-7.

boundary conditions must be specified prior to begin-

ning a time-history analysis. As in the heat transfer

(1) General. To date, NISA's have been per-

analysis, the final process in the stress analysis is to

formed using the finite element (FE) code ABAQUS

define the time-history analysis to take place as

(Hibbitt, Karlsson, and Sorensen 1989). Since experi-

shown in steps 6 and 7 of Figure A-2. This includes

ence has been gained by using ABAQUS and its

defining the time of the steps and their increments,

associated user supplied subroutines (UMAT,

defining changes in the model, application of

DFLUX, and HETVAL), discussion will be based on

mechanical loads, accessing the temperature data

the methods used by ABAQUS for performing a

from the heat transfer analysis to define thermal

NISA as well as these user supplied subroutines used

loads, and definition of the output desired.

by ABAQUS.

(2) Heat transfer analysis. A flow chart defining

structural, materials, geotechnical, cost, and construc-

the steps in a heat transfer analysis is presented in

tion engineers should be established prior to perform-

Figure A-1. The first step is the basic step necessary

ing a NISA study. Interdisciplinary coordination is

for any FE analysis in which the structure and foun-

essential to ensure that the complex structural analysis

dation are discretized into a group of elements

is based on reliable concrete and foundation proper-

defined by nodes. Once the nodes and elements have

ties and realistic construction techniques. The struc-

been defined, it is necessary to define node and ele-

tural, materials, and construction engineers should

ment sets for items such as material properties, initial

predict an appropriate set of construction conditions

A-2

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