US1410217A - Dam construction - Google Patents

Description

F. A. NOETZLI DAM CONSTRUCTION.

APPLICATION FILED JUNE 16, 1919.

' Patented Mar. 21, 1922.

2 SHEETSSHEET I- If: r 14 7" 55555 I [ZYl/E/YTOR lwwaww 'F. A. NOETZLI. DAM CONSTRUCTION.

APPLICATION FILED JUNE I6, 1919- I I I 1 410 211 Patented Mar. 21, 1922.

2 SHEETS-SHEET 2.

MTf/E'J 5: A INVENT R' av /swam must) STATES has.

aris FRED.A NOETZLI, OE OAKLAN'D, CALIFORNIA.

DAM CONSTRUCTION.

Specification of Letters Patent.

Patented Mar. 21,1922.

Application med Julie 1c, 1919. Serial ste m.

To all whom it may concern:

FRED A. Non'rzm, a

Be it known that I,

residin at Oakland,

citizen of Switzerland,

fornia, improvements which the following is a specification.

lilhis invention relates to improvements in dams and more particularly to masonry dams of the archltypel and it has for its object to build dams safer and more economi-cally. An arch clam may be considered either as an arch reaching from top to bottom, or as a plurality 'of superposed arches.

In the single or multiple arch dams which heretofore have been constructed, it has been shown that there is the tendency in the lower parts of the dam to produce open cracks either between foundation and masonry or higher up in the masonry itself and in more or less horizontal directions. Many among these curved dams also have developed vertical cracks in the upper portions due to shrinkage and temperature stresses. In no dam built thus far, to the best of my knowledge, exists an economical and harmonious cooperation between vertical cantilever and horizontal arches, the. Vertical cantilever in arching dams always being built'too stiff,

though not strong enough, to support its share of load. The result was thatthe cantilever cracked and deflected until the horizontal arches were able to get into action and relieve the cantilever, thus preventing ultimate failure; The objects of my invention are, first, .to provide an economical divisionof waterpressure between vertical cantilever and superposed horizontal arches by giving the cross section of the dam a special shape and varying the radius of the horizontal arches in a special way; second, to anchor the dam by means of steel bars to the rock'foundation or to a special foundation built of masonry third, to build single arch dams overhanging in a downstream.-

direction: and fourth, to construct arched dams with a core-of masonry stronger than concrete, and covered on one or both sides with a reinforced concrete slab.

Other objects of my invention will be hereinafter set forth and more particularly pointed out in the appended claims.

in the accompanying drawings, in which my improved dam is illustrated,

Figure 1 is a down-stream elevation of the improved arch dam;

Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3' is a section on line 3-3 of Fig. 1; Fig. t shows the deflection lines of vertical and horizontal arch slices in a vertical plane.

Fig. 5 IS a cross section of a dam showing the method of anchorage;

Fig. 6 shows in detailv one method of anchorage;

Fig. 7 shows asecond method of age;

Fig. 8 shows a third method of anchorage; -Fig. 9 is a horizo'nt-alsectionthrough a dam with special masonry was? Fig. 10 is a; horizontal section through a dam reinforced by concrete slabs cast against up and down-stream faces of said dam.

Similar letters and numerals refer to similar parts throughout the several views.

Referring now to Fig. 1, a curved dam A. is shown which rests on an enlarged case B and abuts sideways against the hillsides either directly upon the solid. rock or upon a continuation of the enlarged base B which provides a smooth and-uniform bearing for anchorthe arches without abrupt changes in the arch spans.

If the horizontal arch were subject radial water-pressure only, the thickness of an arch dam would have to be uniform in every horizontal plane Temperature and shrinkage forces produce additional stresses in every horizontal archslice and it can be proved that these secondary stresses are much greater near the arch abutments than near the crown. The thickness of the horizontal arch slices therefore has to be increased towards the abutments to obtain a structure of uniform strength. To obtain this, I choose the center 1 for the circular upstream face at a point farther down "earn than the center 2 for the circular townstream face, all as shown in Fig. .2.

Referring-now to Fig. 3, wherein is shown a cross section of the darn. on the line 3--3,

the arch A is supported by the enlarged base 33 and well anchored to said base it by means of the reinforcing bars 3 which may extend for any lengtlrup into the arch and suil iciently down into the base :8 to'insure a safe bond. The cross section of the arch is shown of about uniform thickness in the near 5 or even higher up would be too smalllower part 4 just above the base B, to provide for a flexible cantilever. Farther up near 5 the thickness of the arch is increased somewhat to provide for a very strong middle arching part.

Theory shows that an arch dain in the lower portion 4 acts mainly as'a vertical cantilever. This portion 4 thereforehas to -be rather-slender to produce enough deflection near 5 so that horizontal arch action may develop. Figure 3 showsthe cantilever part 4 subdivided into a plurality of substantially parallel walls; purpose of making thecantilever more flexible. Further, the thickness of the dam about midway between its to and base is increased somewhat thus provi ing suflicient strength for the arches. In the really arching portion of a curved dam, i. e. from 5 to the top of the dam, the lowest-portion 5 of these arches has to be the strongest. Therefore there exists the necessity of having a slender cantilever in the lower portion 4 of a dam and suflicient strength in a horizontal direction where arching starts to prevail. It is often of advantage to make portion 5 stronger than any other part of the dam' abox e the base.

If we would increase also the thickness of the cantilever part 3 of such a dam, this would have the undesirable effect of making the cantilever so stifi' that itsdeflection ator to allow appreciable arch-action to evelop. Thus more load would-be thrown upon the cantilever than it might be able to carry, unless it be made of-full gravity section as this alone enables a dam to sustain full water-pressure without 'material help from horizontal arching.

The up ermost portion 6 of a slender arch dam pre erably is made overhanging in a down-stream direction. .rangement the weight of the dam portion 6 will prevent the opening of shrinkage cracks. In most existing single arch dams vertical cracks occur due to excessive tensile temperature and shrinkage stresses. This greatdisadvantage is overcome successfully by making an arched dam sloping entirely or partially in a down-stream direction.

Referring now to Fig. 4, wherein are shown the deflection lines of vertical cantileverand horizontal arches in a vertical sectionfof a curved dam, it ma be assumed for the'purpose of stati'cal esign that an arch dam consists of a series of vertical dam slices, acting as cantilevers. and a series ofhorizontal arch slices. I

Let us consider asan example a vertical 1 section at the centerof the dam. Under the assumption that the horizontal arch slices have to carry all the load, andconsidering also that under the influence of a drop in temperature and the shrinkage in the con- This is for the.

With such an ar-'.

crete the arches are shortened, the arch crowns may come into the position given by the line a in Fig. 4. On the other hand, if the vertical cantilever without breaking were able' to .and really had to sustain without the help of the upper arches all the water-pressure which falls upon it on account of its stifl'ness near the bottom, where practically noarch action can develop, it would deflect elastically alongthe'line c. If the vertical cantilever "and the horizontal arches work together, the resulting real deflection line is about in the position of the line a. an deflections are plotted horizontally from a vertical axis 3)..

In designing an arched masonry dam, we have to assume that part of the water-pressure is supported by vertical cantilever action and part by horizontal arching. It can be, shown that in an economically designed arch dam cantilever action prevails inthe lower part 4 and arching in the upper part 6 of thedam. In 'no single arch dam, built there exists an ieconomicaldivision of the water-pressure between vertical cantilever and horizontal arches, the latter carrying .very little. or no load at the time of low temperature, unless the vertical cantilever be cracked. 'By varying in an arch dam the thickness of the dam. and the radii of curvature of the axis of the horizontal arch slices in such a way that the elastic cantilever deflection line 0 intersects the arch crown deflection line a, more economical conditions are obtained for the dimensions of such a dam. At the same time the vertical canti- L lever has to be anchored sufiiciently to the foundation that no cracks are produced at or near the base of the dam.

It can be proved, that all of the existing arched dams either do not develop any horizontal arch action at the time of low dam temperature, .or that they can do so only after the cantilever has cracked partially, in general in opening cracks between foundation and masonr Not to my knowledge has ever enough, i any, steel reinforcement been placed in these parts of excessive tension in a dam as, no method was known to compute those stresses. a V

5, 6, 7 and 8 illustrate alternative schemes how the base of a dam D maybe the vertical cantilever is able to carry its share of water pressure without breaking away from the base. Fig. 5; shows the -method of anchoring a dam of-"any shape. Fig. 6, shows a detail of Fig. 5. A hole 7 is drilled into the r'ock R- and a metalhar 8 introduced into said hole which is afterwards filled with cement -mortar. Fig. 7 shows the steel bar 8, set into the hole 7 and protected by a tube 9 of noncorrosive material, such as galvanized iron pipe, tar paper anchored to the rock foundation R so that .trench lO is excavated near the tip-stream or down-stream face of the dam, this trench being filled with masonry, into which metal bars 8 are anchored by bending them around other metal bars 8 which lie in the longitudinal direction of the trench.

Referring now to Fig. 9, wherein is shown a partial horizontal section of an arch dam, the fact that the temperature stresses in an arched structure increase with the third power of the thickness of the arch, makes it very desirable to buildarched dams as thin as possible. it is therefore often of advantage to use a better quality of arch material than common concrete,to give a structure suficient strength in direct axialcompression'. Well coursed masonry of granite, etc., is very suitable for this purpose and the material in general is readily available near every dam site. Nevertheless, in first class masonry arches, tension is liable to occur at certain places, due to temperature deformations. Masonr other than concrete cannot very well be reinforced by steel bars to take care of tensile stresses. l prefer to carry out this feature of my invention b casting concrete slabs 11 against the lai masonry 12, and embedding safely into said concrete slab any number of steel bars 13 and in any 'direction that maybe found desirable. To provide a good bond between said concrete slab 11 and the masonry core 12, I introduce additional steel bars 14 in more or less radial direction passing throu h or part through the masonry core 12 ah well anchored into the concrete slabs 11, or fastened to the bars 13. Before casting the concrete slabs 11 against the masonry core 12, I cover the exterior of said masonry core 12 with a thin watertight layer 15 of mortar, applied with a cement gun.

Referring now to Fig. 10, wherein is shown a partial horizontal section of an arch dam, many arch dams through incor rect design or construction have .developed cracks, which under the influence of temperature changes and the varying waterpressure open and close periodically. This endangers the stability of the structure. I improve the strength of such a dam by casting concrete slabs 11 against the faces 16 of the existing dam 17 and embed in said slabs 11 sufiicient metal reinforcement '13 to take care of the tensile stresses occurring in the arch under pressure. To insure a good bond between the existing masonry core 17 and the new concrete slabs 11, I drill holes 18 into said existing core 17 and anchor steel bars 19 into the holes 18', said bars extending well into the slabs 11, being fastened eventually to the slab'reinforcement 13.

I am aware that prior to my invention dams have been built which possess certain. features in part similar to the ones described above. I therefore do not claim such combinations broadly; but

1 'claim 1. A single-archdam having preponderantly cantilevering I and preponderantly arching parts, the thickness of said dam in horizontal planes being greater near the abhtments than near the crown.

2. An archdam of such a shape that horizontal planes out both upstream and downstream faces of said dam along lines which areisubstantiallycircular in form, the centers of these circles being non-coincident,

the center of the down-stream circle lying further rip-stream than the center of the up-stream circle.

3. An arch dam of varying radii of curvature, said dam being thicker at upper elevations than at lower-ones, substantially as described.

4. An arch dam comprising a plurality of superposed arches, the thickness of such arches being larger in upper horizontal planes than in lower ones, such, arches in the upper portion of said dam projecting out in varying amounts beyond other arches below.

5. A reinforced arch dam comprising superposed arches, the thickness, reinforcement and strength against axial compression of such arches being larger in upper horizontal planes than in lower ones substantially as described. 7

6. An arch dam comprising a preponderantly cantileveriiig and a preponderantly arching part, said cantilevering part being subdivided into a plurality of walls substantially parallel to the axis of the dam.

7. A reinforced concrete arch dam comprisingsuperposed arches and a plurality of vertical cantilever slices, the thickness of such arches being larger in upper horizontal planes than in lower ones, said cantilever slices deflecting elastically under their share of the water load at any elevation of the dam substantially as much as said arches at that same elevation, if said arches have to support the full water load and also are shortened by a decrease of temperature at the dam crest of not less than 15 Fahr. be-

low the closin temperature of the darn, substantially as escribed.

8. An arch dam comprising a pre onder antly cantilevering and a prepon erantly arching part, said arching part comprising superposed arches, the thickness of such arches being larger in upper horizontal planes than in lower ones, the cantilevering part of said dam being anchored to the rock foundation by means of metal bars.

9. In an arch dam the combination of an enlargedbase of masonry and a plurality of superposed arches, the thickness of such arches being larger in upper horizontal planes than 1n lower ones, said arches being anchored to said enlarged base by means of metal bars.

10. An arch dam comprising a plurality of superposed arches, the thickness of such arches being larger in .upper horizontal planes than in lower ones, said arches having a core of rubble masonry, concrete slabs placed against said core, said concrete slabs being reinforced by metal bars.

11. An arch dam havin both faces inclined in a down-stream direction, the said dam being thickest in vertical planes at a point intermediate its top and base and having its base portion subdivided into' a plurality of vertical parallel planes.

12. An arch dam having both faces inclined in a down-stream direction, the thickness of said dam in any "horizontal plane being greatest adjacent the abutments and the thickness of said dam in tvertical planes being greatest at .a point intermediate its 4 Witnesses.

FRED A. N OETZLI. \Vitnesses H. E. LINDEN, IvAR BULL LMoN-TE.

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