31 Dec 93
Seismic analysis can be accomplished in static
be critically evaluated throughout the dynamic analy-
(pseudostatic) or dynamic terms. Dynamic analysis
methods can be separated into two types: response
spectrum analysis (RSA) and time history analysis
(3) Water modeling. Water loads due to seismic
(THA). Generally, initial designs should be based on
forces are normally modeled in dynamic analyses
pseudostatic analyses. Depending on seismological
relative to the Westergaard formulation of hydrody-
recommendations, a RSA may be required during the
namic forces. In pseudostatic analyses the hydrody-
preparation of the design memorandums. A THA
namic distribution of pressure can be applied as a
may not be required and should not be done on a
distributed static load. In dynamic analyses this
preliminary basis, but may be chosen to be performed
distribution is applied usually through the use of
during the preparation of the design memorandums.
added mass attached at node locations along the
With computational capabilities improving constantly,
perimeter of the water location. Sloshing must be
THA has become less formidable and can yield more
taken into account. Usually calculated using
efficient designs, especially when used in combina-
Housner's method, sloshing is applied as a static load
tion with a complete soil structure interaction model.
in pseudostatic analyses and as an added mass in
dynamic analyses. Hydrodynamic water loads also
affect the miter gate reaction loadings on the walls.
b. Geological and seismological investigations.
The first step in performing a dynamic analysis is to
obtain potential ground motion response through a
8. Special Considerations
geological and seismological evaluation at the site.
This may yield actual site-specific motions or syn-
8-1. Monolith joints.
thetic motions generated analytically based on site-
specific geological data. Specific results from these
a. Independent monoliths. Generally, U-frame
investigations should yield definitions of the opera-
tional basis earthquake (OBE) and the maximum
lock monoliths are designed to act independently.
credible earthquake (MCE) in terms of the peak
Isolation simplifies the analysis and is a reliable basis
for predicting performance.
synthetic (or both) time histories and corresponding
response spectra should be obtained.
(1) For pile-founded locks, it may be necessary
for adjacent monoliths to act together to resist applied
(1) Damping. Foundation and structural damping
lateral loads. For example, resistance to the thrust on
coefficients are described in other guidance. There
miter gate monoliths could be supplemented by adja-
are normally different damping values used for the
cent monoliths through the use of proper joint detail-
OBE and MCE conditions.
ing (see paragraph 9-7).
(2) Backfill modeling. Modeling of backfill on
(2) For soil-founded locks, it may be necessary
lock walls is a complex issue. Generally, in pseudo-
to key or dowel the monoliths together to minimize
static simplified analyses, traditional lateral earth
coefficient methods are used to compute backfill
forces. For finite element models, modeling is nor-
mally accomplished with linear springs attached to
(1) Details of connections and transmitted loads
the structure with stiffnesses based on the calculation
from adjacent structures must be thoroughly investi-
of dynamic or pseudostatic backfill pressure. How-
gated. Poor detailing at these connections could
ever, in actuality, during an earthquake motion the
result in localized failures and/or serviceability prob-
earth pressure coefficients are varying from passive to
lems. Some areas to look at are: cofferdam tie-ins,
active values. Analytical models do not normally
abutting dam piers and their joint treatment, and
have the capacity for nonlinear springs, or if they do,
guidewall tie-ins. The load for designing sheet pile
they are analytically complex and computationally
tie-in connections should consider the interlock force
expensive. Therefore, engineering judgment on the
of the piles as referenced in EM 1110-2-2503.
value of the spring coefficients is required and must