fore now applied only to smaller and less vulnerable concrete dams, or for
purposes of preliminary analysis. For high dams, or dams in situations
where seismicity is considered critical, more sophisticated procedures are
necessary. In such circumstances seismological appraisal of the dam site
should be followed by a comprehensive dynamic response analysis, as dis-
cussed in Chopra (1988).PSEUDOSTATIC ANALYSIS
Pseudostatic inertia and hydrodynamic loads are determined from seismic
coefficientshandvas detailed below.INERTIA FORCES: MASS OF DAM
Horizontal force isPemh hPm (3.14a)and vertical force isPemv vPm. (3.14b)As with self-weight load, Pm, inertia forces are considered to operate
through the centroid of the dam section. The reversible direction of the
forces will be noted; positive is used here to denote inertia forces opera-
tive in an upstream and/or a downward sense, as indicated in Figs 3.1 and
3.4.HYDRODYNAMIC INERTIA FORCES: WATER REACTION
An initial estimate of these forces can be obtained using a parabolic
approximation to the theoretical pressure distribution as analysed in
Westergaard (1933).
Relative to any elevation at depth z 1 below the water surface, hydro-
dynamic pressure pewhis determined bypewhCeh (^) wzmax(kN m^2 ). (3.15)
In this expression zmaxis the maximum depth of water at the section of
dam considered. Ceis a dimensionless pressure factor, and is a function of
z 1 /zmaxandu, the angle of inclination of the upstream face to the vertical.
Indicative values of Ceare given in Table 3.1.
The resultant hydrodynamic load is given by
Pewh0.66Cehz 1 w(z 1 /zmax)1/2 (3.16)