Contents preface (VII) introduction 1—37

(viii) Other Miscellaneous Loads
In addition to the above-mentioned forces there may be thermal loads and vertical water loading too. If the contraction joints are grouted, the horizontal thrusts, caused by volumetric increases due to rising temperature, will produce load transfer across joints. This load transfer increases the twist effects and the loads at the abutments (3). Vertical water loading is exerted by the weight of the water on sloping upstream and downstream faces of the dam. The vertical component of the water flowing over the spillway is not included in the analysis as water tends to attain the spouting velocity which reduces pressure on the dam. Any negative pressure which may develop on the spillway crest is also neglected. However, any sub-atmospheric pressure developing on the downstream sloping surface of the spillway due to lack of aeration should be considered by treating them as positive load (acting in the downstream direction) applied on the upstream face.
The design of gravity dams must consider most adverse combination of probable load conditions (1). Combinations of loads whose simultaneous occurrence is highly improbable may, however, be excluded. Most load combinations can be categorised as usual, unusual, or extreme. For example, normal design reservoir elevation with appropriate dead loads, uplift, silt, ice, tail-water, and thermal loads corresponding to usual temperature make a typical usual type load combination. Unusual load combination considers maximum design reservoir elevation with the loads of usual type load combination. Extreme load combination results when the effects of maximum credible earthquake are included in the usual load combination.