US1933092A - Dam - Google Patents

Description

0d- 31, 1933- E. H. BURROUGHS m' AL 1,933,092

DAM

Filed April 30, 1930 2 Sheets-Sheet l n E 'TOR B/YM? ATTORNEYS CCL 31, 19.33- E. H. BURRoUGHs Er AL 1,933,092

DAM

Filed April 30, 1930 2 Sheets-Sheet 2 BY 5792 W4/waff t heel to toe.

the toe of the dam is more severely stressed than Patented Oct. 31, 1933 UNITED STATES PATENT euriesN bursen Construction Company, Inc., New York, N. Y., a corporation of New York Application April s, 1930.` serial No. 448,503

14.v Claims.

This invention relates to a novel and improved form of dam, the novel features of which Vwill be best understoodk from the following description and the annexed drawings, in whichare shown selected embodiments ofthe invention and in which:

Fig. 1 is a vertical sectional 'View through a dam constructed according to vourinvention Fig. 2 is a down-stream elevation of the dam shown in Fig. 1.

Fig. 3 is a section on the lines 3-3 of Fig. 1 but showing a slight modification.

Fig. 4 is a section on the line 4-4 of Fig. 1.

Fig. 5 is a section on an enlarged scale, on the line 5-5-of Fig. Land showing the distribution of stresses at the bearing surface between an upstream slab and one of the buttresses upon which it rests. Y

Fig. 6 is a view similar to Fig. 3 but showing a. different form of rip-stream construction.

Fig. 7 is a diagrammatic vertical cross-section through a dam of the general type covered by this application. n

Fig. 8 is a diagram showing the distribution of I foundation pressures in a dam of the type shown in Fig. '7.

Fig. 9 is a diagram showing the distribution of principal stresses in a dam of the type shown in Fig. 7.

Referring now to Figs. 7, 8 and 9, Fig. '7 shows a dam of the so-called buttress type, having an up-stream deck i supported by buttresses 2 which extend upand down-stream. In such a type of dam the vertical pressure exerted by the darn,

as constructed according to present practice, is

shown in Fig. 8, the amount ofthe pressure beingY measured by the vertical ordinates of the diagram. From this diagram it will be seen thatthe pressure at 3, which is the pressure at the upstream end or heel of the dam, is a minimum,

while the pressure at 4 which represents the,

down-stream or toe of the dam is a maximum, the pressure varying substantially uniformly from This means that the foundation near that portion near the heel or 11p-stream side. The ressures lare obtained from the following formula:-

P (max) =P (avkigyj-r P (min) l in which P (max) and P (min) Athe maximum and minimum pressures at the toe and heel respectively.

(ci. (s1- 30) P (av) the average of maximum `and minimum pressures. A L

Mf: the moment about the horizontal section or the product oi the resultant vertical load by the y eccentricity -or distance between the point of application and the center of gravityof the section. f .f

Y the distance from the center ci gravity of the horizontal section to the most remote fibre. y While the ,pressuresron horizontal planes is 65 determined from the above `formula, as shown on the diagramof Fig. 8, andare the critical ones f' which, govern foundationfdesign, they dol not govern the design of the superstructure. In ,this part of the dam the critical stresses are those known as principal or maximum inclined stresses. In dams of Vthe type under discussion, these principal stresses in the superstructure are distributed as .indicated in Fig. 9, this diagram showing the distribution on the line 5y of Fig. 75 7. The maximum stress is represented by the vertical ordinate 6 which represents the stress approximately at the point 6 in Fig. 7. From this diagram it will be seen that the maximum stress in the superstructure occurs near the upstream side of the dam.

In the usual prior art construction which is under discussion the buttresses 2 are usually of uniformthickness substantially throughout their length upand down-stream, and the water bear- S5 ing surface of the dam is formed by slabs supportedon brackets or short cantilever beams projecting from the sides of the buttressesand this invention relates particularly to an improvement upon this type. In thistypev of construction the U0 bracket or cantilever beam must be designed to take care of stresses caused' by moment, shear, and diagonal tension, all of which requires a. large amount of reinforcing steel which, in turn, makesit diiiicult to obtain a sufficiently dense concrete in thisv portion of the dam. It` should be rememberedthat this. portion is that which forms the water bearing surface and thus the concrete must be absolutely water-tight, sound and durable. Placing of concrete about reinforcing steel increases the liability of the formation of pockets and provides a chance for poor workmanship..

With the above discussion of the prior art lin mind, this invention aims to provide a dam hav-l 105 ing a substantially uniform distribution of stresses yin both the foundation and superstructure, at the same time providing for maximum economy and safety of the entire'structure. This object `is achieved in this embodiment by the structure which will now be described in detail.

Referring first to Figs. 1 to 5 inclusive, the invention is shown herein as embodied in a dam having a plurality of buttresses '7 extending upand down-stream. In this application we shall refer to the dam as if it were built across a stream, although of course by that language we do not intend to limit the structure to one which must necessarily be built across a water course.

Each buttress is shown as flared at its upstream edge as indicated at 8, and at its downstream edge as shown at 9, these flared portions being connected by a portion 10 ofyreduced thickness. The flared ends 8 and 9 arepreferably joined to the reduced portion 10 by rtapered portions of gradually varying thickness ratherthan by abrupt changes. We have found that by constructing the buttresses in'this manner, both the principal stresses in the superstructure and the stresses in the foundation are more uniformly distributed. This is probably because of the fact that the up-stream flaring portion `8 is beneath the water bearing up-stream face of the dam, thus'providing a larger section of masonry directly under the application of the load, than would bethe case if the buttresses were of the usual uniform thickness throughout their lengths. This arrangement therefore appears to reduce the intensity of the principal stress at the point of application of the loading and by properly ldesigning the transition or intermediate portion between the maximum and minimum widths of a buttress, nearly equal intensities of stress may be attained-throughout the portions 8 and l10 of the buttress, 'that is to say, for approximately the up-stream half of the buttress. The downstream rlare 9 of the buttress will of course decrease the intensity of any principal stress occurring therein and serves to draw the center of gravity of the buttress section down-stream or nearer the point of application of `the resultant loading. 'This' in turn reduces the eccentricity ofthe resultant loading, thus tending to'equalize the foundation'pressure -as well as-the stresses in the superstructure.

Aside from the above advantages, the flared buttress construction makes'it possibleto space the buttresses further `apart than under present practice andto span the space betweenthe upstream rlares by slabs or beams 11, or by larches '12, as shown in Fig. 6. The relative spacings of `the different portions of the buttresses may conveniently be defined' by stating that the clear span between the narrowr portions 10 of the buttresses ls greater than or at least as great as the lengths of the members 11 or," in other words, as the distance between the portions of the buttresses with which the ends of the membersll contact. This construction is plainly shown inFig. 3.

'Th wider spacing makes it possible to decrease the number of buttresses, thus saving a large expense for form work. Moreover, the placing of a relatively thick or massive section of concrete near the up-tream portion of the dam, adds a stabilizing eiectagainst overturning of the dam and makes it possible to place less dependence on the water load acting on the water bearing upstream surface of the dam. This,in1turn, allows the placing of this up-streaxn water bearing sur- 'face more nearly perpendicular than would otherwise be possible, thereby saving masonry and forms.

If desired, the rigidity of the structure may be greatly increased by connecting the adjacent down-'stream ared portions of thefbuttresses by Walls 18, as shown in Fig. 3, although these walls may be omitted if desired. These walls may be placed between each two buttresses or between alternate buttresses or at other selected locations as desired.

The vlip-stream edge of each buttress is provided with a 'tongue portion 14 extending lengthwise of the buttress and having on opposite sides thereof recesses l5 to interlock with projections on the slabs, in order to form expansion joints. As a measure of the relative dimensions of the buttress, it may be noted that the width of a tongue 14 between adjacent slab` ends is greater than or at least as'great as the minimum thickness of the buttress at vthe reduced portion 10. At the downstream end of each portion 14 is provided a bearing surface 16 here shown as cylindrical in form and adapted to contact with a corresponding cylindrical surface on a slab 1l. It will be noted 'that this portion 16 is inclined down-stream with respect to the Water bearing surface A1'7 of the slab, and this inclination is to lsuch an extent that the'linesl of pressure on the surface 16 all intersect the center line 18 of the buttress and when the surface 16 is cylindrical, as isthe preferred construction, all of these lines intersect as at a point' 19. It will be noted that-the lines of pressure fallentirely within the dared portion 8 of the buttress.

The arrangement just described provides in eifect rocker bearings for the slabs 1l and, consequently an even distribution of pressure throughout the entire surface-16, the distribution of pressure being indicated by' the diagram 20 in Fig. 5. Thus, we avoid concentration of loading on the outer edge of the bearing for the slab, '.'hic'n has been objectionable in: the prior art construction of the type referred to above. As before pointed out, .such construction requiresk a great amount of reinforcement which tends to create rock pockets and to give a porous and unsatisfactory concrete at the very part ofthe structure which ought to have the densest and most reliable concrete.

The use of a cantilever beam or bracket is thus entirely eliminated and the loads are transmitted directly to the buttress from the slabs in compression, bending moments and diagonal tension being eliminated, thereby eliminating the'neces- 'sity for reinforcing steel in this part of the structure. The ared portion 8 is designed as an integral part of the buttress and does not take any stresses corresponding to those carried by the brackets or cantilever bear/ns of the prior art. The expansion joints which include the recesses l5 may be nrade water-tight by any suitable means, :and preferably the bearing surface 16 is also made water-tight by being coated with suitable asphaltic material or the like.

While we have shown the invention as embodied in certain specic forms, it is to be understood ythat various changes in details may be made without departing from the scope of the invention, and we therefore do not intend to lirnit ourselves except by the appended claims.

We claim:

x1. In a dam, a plurality of buttresses extending up-.and down-stream, and an upstream face comprising members extending between adjacent buttresses and Abearing thereon, with the bearing surfaces on the buttresses extending laterally of the buttresses and the distance of each surface from thev plane of the upstream edge of the buttress increasing from a minimum at the edge of the surface nearest the center of the buttress vso and extending laterally of the buttresses and the p distance of each surface from the plane of the upstream edge of the buttress increasing from a minimum at the edge of the surface nearest the center of the buttress to a maximum at the edge remote from said center.

3. In a dam, a plurality of buttresses extending upand down-stream, and with the upstream edge of each-buttress forming part of the Water bearing surface, the remainder of said surface being formed of slabs bearing on `said buttresses, with the bearing surface between each buttress and a slab supported thereon being so disposed that all lines of pressure normal to the bearing surface intersect the center line of the buttress.

4. In a dam, a plurality of buttresses extending upand down-stream, with the up-streain end of each buttress forming part of the water bearing surface, the Yremainder of said surface being formed or" slabs bearing on said buttresses, with the bearing surface betweeneach buttress and a slab supported thereon being so disposed that all lines of pressure normal to the bearing surface intersect the center line of the bnttress, and with the water bearing surface of the slab fiush with the water bearing surface of the buttress.

5. A dam comprising a plurality of buttresses extending upand down-stream, slabs extending between said buttresses and presenting 'water bearing surfaces, and bearing surfaces between s said slabs and buttresses, said surfaces being approximately cylindrical with the center of the cylinder within the butt-rese.

6. A darn comprising a plurality of buttresses extending upand down-stream, slabs extending between said buttresses and presenting water bearing surfaces, and bearing surfaces between said slabs and buttresses, said surfaces being approximately cylindrical with the center of the cylinder within the buttress and on the center line of the buttress.

7. In a darn, a plurality of spaced buttresses extending upand down-stream, and an upstream face comprising members extending between adjacent buttresses and bearing thereon, with the bearing surfaces on the buttresses extending laterally of the buttresses, said buttresses being so proportioned and constructed with-relation to the bearinU surfaces that all pressures exerted on said bearing surfaces follow lines entirely within the buttresses.

8. In a dam, a plurality of spaced buttresses extending upand down-stream, and an upstream face comprising members extending between adjacent buttresses and bearing thereon, with the bearing surface on the buttresses extending laterally of the buttresses, said buttresses being so proportioned and constructed with relation to the bearing surfaces that all pressures exerted on said bearing surfaces follow lines entirely within the buttresses and intersecting the longitudinal center lines of said buttresses.

9. In a dam, a plurality of Vspaced buttresses extending up and down-stream, :an upstreamlaterally of the buttresses and Vso constructed l with reiation'thereto that all pressures exerted on said 'surfaces follow Vlines entirely i within the buttresses, said buttresses having tonguesextending between said members, and said tongues for atleast -a substantial portion of the height of the dam beingv greater in thickness than the minimum thickness ofthe buttresses.

10.- In a dam,V a plurality of spaced buttresses extending upand down-stream, said buttr'esses having relatively narrow portions intermediate their lengths and having relatively wide portions adjacentA their up-stream ends, said up-stream ends of the buttresses having laterally extending bearingsurfaces and inclined down-stream from the centers of the buttresses to cause substantiallyall pressures exerted on said surfaces to follow lines substantially` entirely within the buttresses,

and water bearingy members supported on said surfaces, the clear span between said narrow portions` of two adjacent buttresses being at least as great asia parallel overall distance between the ends of the water bearing member supported by said two buttresses.

11.;In a dam, a plurality of spaced buttressesv extending upand down-stream, and an upstream face comprising membersv extending between adjacent buttresses and bearing* thereon, with the bearing surfaces on the buttresses extending laterallyof. the buttresses and inclined down-stream from-the centers of the outtresses to cause substantially all pressures exerted onsaid surfaces to follow lines substantially entirely!v within the buttresses, said buttresses gradually decreasing in width down-stream from said bearing surfaces at such a rate as to render the intensity of principal'stressin one of said buttresses jacent buttresses and bearing thereon, with the` bearing surfaces on the buttresses extending laterally of the buttresses and inclineddownstream from the centers of the 'buttresses to causesubstantially all pressures exerted on said surfaces to followy lines substantially entirely within the buttresses, said buttresses gradually decreasing in width down-stream from said bearing surfaces at such a rate as to render the intensity of principal stress in one of said buttresses` approximately uniform along its upand-down; stream axis for a substantial distance downstream from said face and gradually increasing in width adjacent the down-stream end thereof.

13. In a dam, a plurality of spaced buttresses extending upand Vdown-streanl, and an upstream face comprising members extending between adjacent buttresses and bearing thereon, with the bearing surfaces on the buttresses extending laterally of the buttresses and inclined down-streamfrom the centers of the buttresses to cause substantiallyy all pressures exerted on- I said surfaces to follow lines substantially en- 1 tirely within the buttresses, said buttresses `being so proportioned as to render the intensity of stress therein approximately uniform --for approximately the up-stream half thereof.

14. Ina dam, a plurality ,of spaced buttresses tirely within the buttresses, said buttresses being so proportioned as to render the intensity of stress therein approximately uniform for approximatelythe up-stream half thereof and to approximately equalize the foundation pressure throughout the length thereof.

EDGAR H. BURROUGHS.

CALVIN V. DAVIS.

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