Engineering and Contracting . sus-ceptible of mathematical treatment: and yetengineers were not afraid ot making rivetedjoints. It may be said, with equal truth, that engi-neers will not be afraid to continue buildinggravity dams on the middle-third theory, or archdams on the cylinder theory, and no disaster willfollow, always provided that there is due rec-ognition ot the conditions of the foundation andabutments which nature provides. The futility of attempting a pure mathemat-ical determination of the stresses in a dam iswell exemplified by the measurements of theactual deflections of an ar
Engineering and Contracting . sus-ceptible of mathematical treatment: and yetengineers were not afraid ot making rivetedjoints. It may be said, with equal truth, that engi-neers will not be afraid to continue buildinggravity dams on the middle-third theory, or archdams on the cylinder theory, and no disaster willfollow, always provided that there is due rec-ognition ot the conditions of the foundation andabutments which nature provides. The futility of attempting a pure mathemat-ical determination of the stresses in a dam iswell exemplified by the measurements of theactual deflections of an arch dam at BarrenJack. New South Wales. The structure Is of concrete with a light ver-tical reinforcement (against temperature stress-es) ot 20-lb. steel rails, 10 ft. from center tocenter and 1 ft. from the face. As the steel areais only of the area of the concrete at thebase, and at the top of the dam, its pres- ?<u\f ft Ioii Rc««rvoiremptyAirT« g v ^Fop of Dmm o O-J Inch —Down-Str«»nr-. Fig- 1- cnce Is negligible, as far o« bending stresses oreconcerned. The deflections of the Barren Jack Dam, whichare shown In the diagram. Fig. 1. were takenunder varying conditions of tempeniture andwater depth. The ol)servatlon8 made when therisorvoir was empty and the olr temperature57, which approximates the closest of the ob-servations to mean temperature, are drawn asa straight line, and tho other observations oreplotted In regard thereto. The curves drawnthrough tho various observed points are broughtfor convenl-n^e to one common point of originon the base. This Is not strlolly cor-rect, for It makes the Impossible assumption thiitthe base Is rigid, and that the rockon which the ilaiii stands Is Incapable of elasticdeformation under tho stresses transferred to Itby the dam and by tho weight of water support-ed by the rock bed Immediately above tho of tho rock undoubtedly takesplace, and, such being tho case
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