EP 1110-2-12
30 Sep 95
increases in this zone, performance requirements may
a. General performance requirements. Both
still be satisfied. Thus, the structural criteria for the
new RCC dams and existing dams shall be capable of
MCE, when using linear-elastic analysis, are set by
surviving the MCE without a failure of a type that
limitations of the method of analysis rather than on
would result in the loss of life or significant damage
criteria that relate to an acceptable level of structural
to downstream property caused by an uncontrolled
concrete damage.
release of the reservoir pool. Nonlinear behavior
with associated damage is permissible, but the post
c. Allowable tensile stresses. The allowable
earthquake damaged condition of the dam shall allow
for controlled lowering of the pool to facilitate repair.
tensile stress ft (allowable) for the MCE is established
below. DTS = Dynamic Tensile Strength, and f ′t =
b. Structural criteria. The upper limit of linear
the direct tensile strength.
elastic analysis is considered to be that point on the
ft (allowable) = 1.33 DTS = 2.000 f ′t
straight stress/strain line corresponding to a linear
stress level of 1.33 f ′t (see Figure 4-7). When tensile
strains exceed the strain associated with this linear
d. Damping. The linear-elastic analysis for the
stress limit, macrocracking occurs and the RCC will
MCE shall utilize a damping ratio equal to 7.0 per-
be subject to some degree of structural damage. As
cent of critical damping for the concrete dam struc-
the strain level increases well into the tensile soften-
ture only. The increase in the damping ratio from
ing zone, response becomes markedly nonlinear and it
5 percent for the OBE to 7 percent for the MCE
is clear that a linear-elastic analysis no longer approx-
helps account for some additional nonlinear behavior
imates the response. Although crack damage
while using a linear-elastic approach.
4-2
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