LOADING: CONCEPTS AND CRITERIA 123
(a) Primary loads
WATER LOAD
The external hydrostatic pressure, pw, at depth z 1 is expressed as
pw (^) wz 1 (3.1)
where (^) wis the unit weight of water, 9.81 kN m^3 ( g; symbol is
adopted here for unit weight to be consistent with the accepted soil
mechanics usage employed in Chapter 2, while gis used in subsequent
chapters in conformity with fluid mechanics usage).
The resultant horizontal force, Pwh, is determined as
Pwh (^) wz^21 /2 (kN m^1 ) (3.2)
acting at height z 1 /3 above plane X–X.
A resultant vertical force Pwvmust also be accounted for if the
upstream face has a batter or flare, as with the profile of Fig. 3.1,
Pwv (^) w(areaA 1 ) (kN m^1 ) (3.3)
and acts through the centroid of A 1.
Fig. 3.1 Gravity dam loading diagram. DFLdesign flood level;
NMLnormal maximum level, i.e. maximum retention level of spillweir;
TWLtailwater level