EP 1110-2-12
30 Sep 95
computer. However, it takes less time and effort to
equivalent mass system model as a common attribute.
perform a simple 2-D analysis using a general pur-
These methods use any one of several proven general
pose finite element program on a personal computer
purpose finite element computer programs to perform
(PC) and the results of the finite element analysis will
the dynamic analysis. Examples are ANSYS, SAP6,
be more accurate. Also, comparative studies have
GT-STRUDL, and STAAD III. The material behav-
indicated that as the flexibility of the foundation
ior attribute for most of the general purpose programs
increases, the response calculated by the simplified
is linear-elastic; however, some programs such as
method tends to diverge from the response deter-
ANSYS and ADINA have nonlinear capability.
mined by more refined methods, and the simplified
method is not always conservative.
(1) Primary advantage. Attribute flexibility is
the primary advantage of the general purpose finite
(3) Recommended use. Because of the limita-
element methods. Except for the common attribute
tions of the simplified method, it should be used only
mentioned above, design methods are possible which
for preliminary design work as described in para-
feature most of the other possible combinations of the
remaining attributes. This allows the dynamic analy-
graph 8-4a. However, appropriate equations and
sis phase to start with a simple method such as the
design figures used in this method are helpful in
2-D, linear-elastic, response spectrum method. If the
checking the results from other more refined analyses
results of the simple analysis or the project conditions
and to prepare the computer input for these methods.
indicate the need of a more refined analysis, the
procedure may transition conveniently into a more
b. EAGD-84 Analysis Method. EAGD-84, A
refined analysis by modifying or adding to the input
Computer Program for Earthquake Analysis of Con-
to the same general purpose program.
crete Gravity Dams (Fenves and Chopra 1984), is a
specialized computer program that allows the founda-
(2) Other advantages. The general purpose finite
tion and the reservoir effects to be characterized by
element programs discussed above are large, compre-
the substructure model described in
hensive programs developed for main frame com-
paragraph 8-1d(2).
puters. In addition to these programs are several
smaller general purpose finite element programs
(1) Other attributes. Other attributes that define
specifically developed for PC's. Since these desk-top
the EAGD-84 analysis method include 2-D represen-
PC's are now a standard item in most design offices,
tation, linear-elastic material behavior, and time-
a considerable amount of the dynamic analysis phase
history ground motion definition of the design
may be completed without the need or expense of a
earthquake. All attributes of EAGD-84 are fixed and
large main frame computer.
cannot be changed.
(2) Advantages and limitations. When compared
8-3.
Dynamic Analysis Procedure
to either a standardized model or a finite element-
equivalent mass system model, the EAGD-84 sub-
The dynamic analysis procedure described hereafter is
structure model is a better representation of the
derived with the objective of arriving at a reasonable
foundation and reservoir, as long as the project condi-
and economic design of a new dam, and evaluating
tions properly fit the program requirements. Also,
the seismic resistance of existing dams using an anal-
the time-history definition of ground motion is a level
ysis method with the simplest attributes possible. In
of refinement beyond response spectrum definition.
general the procedure is to perform a dynamic stress
Therefore, the EAGD-84 method is capable of pro-
analysis and evaluate the results to determine if the
ducing the most accurate response, and the time-
RCC dam response to the design earthquakes is
history response output provides additional
acceptable. If not acceptable, the design of a new
information often needed to evaluate acceptable per-
dam may be modified and reanalyzed, or a more
formance. The biggest disadvantage of EAGD-84 is
refined analysis method may be employed when
the lack of attribute flexibility.
analyzing either new dams or existing dams.
c. General purpose finite element program
a. Evaluating acceptable response. The
analysis methods. This comprises a number of
response is judged acceptable for a linear-elastic
methods each with a different combination of
analysis when the tensile stresses are within the
attributes, but all having the composite finite element-
8-4
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