EP 1110-2-12
30 Sep 95
method is acceptable for all preliminary designs and
Method may be either hand-calculated or done by a
for final designs under noncritical seismic conditions.
computer program. Some computer programs, such
Since the modal frequencies are fairly well separated
as the general purpose finite element programs, allow
in gravity dams, the simpler SRSS method produces
the attribute options to be changed so that one of
adequate results which are in balance with the general
several possible methods may be employed for the
level of precision required for preliminary or
dynamic analysis. This often allows a transition to a
noncritical analyses.
more refined method without necessarily abandoning
all the previous computer model input effort. Other
computer programs, such as the EAGD-84 program,
d. Seismic zone map. The seismic zone map,
and Chopra's Simplified Method are single method
Figure 5-1, shall be used in the dynamic stress
programs since they have fixed attributes. Chapter 8
analysis phase of the seismic design. The peak
discusses dynamic analysis methods in more detail.
ground accelerations for use in scaling standard
design response spectra are contained in Table 5-2
c. Preliminary and final design. The two-
and are based on the zone map. The seismic zone
maps and the seismic coefficients contained in
dimensional, linear-elastic, response spectrum method
ER 1110-2-1806 shall be used only in the stability
shall be used for the preliminary design analysis.
analysis phase of seismic design.
Either Chopra's Simplified Method or a general-
purpose finite element program shall be employed
depending on the design conditions. The simplest
1-9.
Analysis Methods and Procedure
final design analysis utilizes a composite finite
element-equivalent mass system model and general-
In general a dynamic stress analysis shall be
purpose finite element program.
performed, and the results shall be evaluated to
determine if the response of the RCC dam to the
1-10.
Coordination
design earthquakes is acceptable. If the response is
not acceptable, the design of a new dam may be
modified and reanalyzed using the same analysis
A fully coordinated team of structural engineers,
method, or a more refined analysis method may be
geotechnical and materials engineers, geologists, and
employed. For an existing dam, progressively more
seismologists should ensure that all factors relevant to
refined methods of analysis are employed.
the dynamic analysis are correct and that the results
of the analysis are properly evaluated. Some of the
critical analysis and design aspects requiring coordi-
a. Method attributes. There are four attributes
nation are discussed below.
that characterize a particular dynamic analysis
method.
a. Design response spectra. Developing site-
(1) Material behavior. Options are (a) linear-
specific design response spectra when required.
elastic or (b) nonlinear behavior.
b. Tensile strength of RCC. Obtaining
(2) Design earthquake definition. Options are
representative cores from test-fill placements for new
(a) design response spectrum or (b) time history
dams or from the in-place concrete for existing dams
ground motion record input.
for use in determining the direct tensile strength and
dynamic tensile strength of both the lift joints and the
(3) Dimensional representation. Options are
parent RCC.
(a) two-dimensional representation or (b) three-
dimensional representation.
c. Foundation properties. Obtaining explora-
tory corings and evaluating tests to determine the
(4) Model configuration. Options are
foundation deformation modulus and other foundation
(a) Chopra's "standardized" model, (b) composite
properties.
finite element-equivalent mass system model, or
(c) finite element-substructure model.
d. Foundation fault displacement. Evaluating
geoseismic conditions at the site to determine if
b. Computer programs. Various computer
foundation fault displacement is possible, and to map
programs are available which are identified with
the location, strike, and dip of the potential faults.
certain analysis methods. Also, Chopra's Simplified
1-3
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