EP 1110-2-12
30 Sep 95
Chapter 2
ground shaking combined with cracking due to
foundation fault displacement could propagate to an
Seismic Design Criteria
extent where a failure mechanism is formed thus
impairing the ability of the dam to contain the pool.
Criteria defining an acceptable response of the dam to
2-1.
Stability
design earthquakes are based on initiation and
propagation of tensile cracking within the RCC.
a. Resultant location and sliding. RCC dams
shall satisfy the overturning and sliding stability
c. Analyzing response to ground shaking. The
requirements for gravity dams using inertia forces
process of cracking and the propagation of the cracks
calculated by the seismic coefficient method as set
result in nonlinear behavior of the dam. There are
forth in EM 1110-2-2200 and ETL 1110-2-256. The
also nonlinearities associated with dam-foundation
seismic coefficients shall be as shown on the seismic
interaction and dam-reservoir interaction which are
zone maps provided in ER 1110-2-1806.
difficult to assess. Approximate linear relationships
account for some of the nonlinear dynamic behavior
b. Extreme stability conditions. When intense
and allow the response of the dam to the design
ground shaking causes serious tensile cracking at the
earthquake ground motion to be determined using a
dam-foundation interface, a nonlinear time history
linear-elastic analysis method. Tensile stresses can
analysis shall be performed to evaluate cracking,
then be evaluated based on tensile strength parameters
potential permanent displacements, and the effect
adjusted to be compatible with linear-elastic analysis
these have on sliding stability. Certain stipulations
methods.
regarding nonlinear analyses are covered in
paragraph 2-2g.
d. Analysis methods. The simplest of the linear-
elastic methods uses a response spectrum to define
the ground motion as outlined in Chapter 5. Most
2-2.
Response to Ground Shaking
RCC dams will be found adequate using this method.
For the few exceptions, the next level of refinement
RCC dams shall be capable of resisting the strong
in determining the dynamic response is the linear-
motion ground shaking associated with design
elastic time history method, and in rare cases a
earthquakes within the allowable tensile stress design
nonlinear time history finite element analysis may be
criteria specified in Chapter 4. Dynamic stress
required.
analysis methods and procedures are described in
Chapter 8. The dynamic analyses shall incorporate
e. Allowable tensile stress. The tensile strength
the dynamic characteristics of the dam, foundation,
of the RCC is the single concrete material property
reservoir, and backfill or silt deposition when
used to evaluate cracking, and to establish acceptable
applicable.
response. Allowable tensile stresses are defined in
paragraph 4-2c and paragraph 4-3c for the OBE and
a. Defining ground motion. The free field
MCE, respectively.
ground motions are used to define the ground motion
that would be felt at the site due to two design
f. Evaluating time-history response. When
earthquakes. Free field ground motion associated
dynamic response is determined by the linear-elastic
with each shall be represented by design response
time-history method, the allowable tensile stress is the
spectra and, when required, design acceleration time
principal criterion for evaluating acceptable response,
histories. The design earthquakes are operating basis
but additional criteria are also required to qualify
earthquake (OBE), and maximum credible earthquake
other response characteristics such as the number of
(MCE). Both are discussed in detail in Chapter 4.
stress cycles approaching or exceeding the allowable
stress, and the magnitude and pattern of these
b. Propagation of cracks in RCC. Most dams
excursions beyond the specified limits.
with earthquake resistant provisions will probably
survive the most severe earthquake shaking possible
g. Evaluating nonlinear analyses. When
at the site with little or no damage, although high
dynamic response is determined by the nonlinear
dams located near major faults have experienced
time-history method, criteria for evaluating acceptable
extensive cracking during major earthquakes (Chopra
response are based on the theory of fracture
and Chakrabarti 1973). Concrete cracking due to
2-1
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