Патент USA US3084492код для вставки
April 9, 1963 3,084,481 W. J. SILBERKUHL ETAL PRESTRESSED CONCRETE BODIES Filed Deo. 18, 1959 2 Sheets-Sheet 1 NÓE Wllhelm Johannes Silberkuhl Uwe Kosîl Erns’rHoeussler INVENTORS‘. BY AGENT. April 9, 1963 w. J. slLBERKUHL ETAL 3,084,481 PEEsTREssED CONCRETE BODIES Filed Dec. 18, 1959 2 Sheets-Sheet 2 @ä wäâ Ñ. .EN N m m „ë Näë ê ëä„.ì_ë. Ñ... .m äwää„ Wilhelm Johannes Silberkuhl Uwe Kastl Ernsm` Hoeùssler INVEN TOR-f. BY WE AG1/EN T. f. 3,084,48l ECC Patented Apr. 9, 1953 2 erally along a fiber subjected to maximum tensile stress 3,084,481 PRESTRESSED CÜNCRETE BOBIES Wilhelm Johannes Silberknhl, Uwe Kastl, and Ernst Haenssler, all of Brunuenstrasse 29, Essen (Ruhr), Germany Filed Dec. 1S, 1959, Ser. No. 860,579 Claims priority, application Germany Dec. 19, 1953 4 Claims. (Cl. Sti-129) Our present invention relates to prestressed elongated concrete bodies, such as girders or slabs, adapted to be employed in load-bearing structures (eg. bridges, over passes, elevated highways and the like). It is an object of our invention to provide a light-weight, structurally rigid prestressed concrete body of exceptional strength. Another object of our invention is to provide a hollow load-supporting concrete slab adapted to span sizable dis tances and having a relatively large strength-to-weight in the unprestressed structure. rIhus, the pitch may be greatly lengthened in the unsupported intermediate re gion of the span, where a major part of the moment line passes underneath the girder axis, so that the prestressing element extends nearly horizontally and «axially in that region. . We have found that a concrete girder of annular cross section, provided in this manner with imbedded sheaves of oppositely wound, generally helically extending pre stressing elements (eg. steel wires), is under sufficient axial and peripheral compression to withstand large and varying live loads without requiring additional, unpre stressed reinforcements; this results in a further saving 15 of weight and cost. The above and other objects, .features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying `drawing in which: 20 FIG. 1 is a side-elevational Iview of a bridge according ratio. A further object of the invention is to provide a con `to our invention; FIG. 2 is a fragmentary sectional top view of the struc crete span adapted to support a large load while obviating ture of FIG. l, showing the disposition of the reinforcing the disadvantages of great bulk and high cost encountered elements therein, taken generally along line Il-II of in conventional bridge and road construction. A known type »of prestressed concrete members used 25 FIG. 1; FIG. 3A is a cross-sectional View taken along line for single-span or continuous structures are lin the form IIIA-IIIA of FIG. l; of hollow girders of generally rectangular cross-section, FIG. 3B is a cross-sectional View taken along line which may be extended sideways at the level of their upper IlIB-IIIB of FIG. 1; and flanges to »form a road bed,the lateral webs of these gird ers being usually of considerable width to accommodate 30 FIG. 3C is a cross-sectional view taken along line IIIC-IIIC of FIG. >1. sheaves of prestressing cables or rods extending generally horizontally therewithin while following a wavy line in ÁIn the ydrawing we show a continuous, prestressed con crete bridge comprising a tubular girder 2 supported, via `the region of maximum tensile stress. Thus, each pre stressing element rises and falls in a given vertical plane, anti-friction bea-rings 10, by longitudinally spaced pairs reaching its zenith a‘bove the supports and its nadir sub 35 of pillars 1, 1’. The girder 2 has its upper wall portion stantially midway therebetween. Since the wall thickness integrally extended laterally at -both sides to »form a road way-supporting slab 3- bounded by curbstones 3". The of the aforementioned webs greatly exceeds Athat required inner cavity 7 of the hollow girder structure 2 is of by static considerations, it is a more particular object of the instant invention to provide an improved hollow girder roughly elliptical cross-section (best seen in FIGS. 3A of this general type in which this Wall thickness, and 40 3C) and extends longitudinally along the bridge axis. The girder 2 is provided with prestressing rods which are therefore the overall weight of the structure, is consider ably reduced for a predetermined load-bearing capacity. arranged in two sheaves 4a, 4b imbedded in its shell. As In accordance with the present invention we imbed a lbest shown in FIG. 2, the sheaves 4a, 4b define fiat sheets sheaf of prestressing elements in the shell of a hollow which are helically wound about the girder axis and concrete girder in such manner that at least the sloping 45 whose major faces are substantially parallel to the wall portions of these elements, extending between the high of cavity 7 throughout their length. It will be apparent and low points thereof, are -relatively staggered in axial that, as viewed in the direction of the section plane direction of the girder so as to be substantially equidistant denoted by line IIIA-IIIA in FIG. 1, shaft 4a is Wound from the girder axis. These sloping portions, accordingly, in a clockwise direction about the axis while sheaf 4b is define a sheet Whose thickness dimension generally coin cides with that of »the girder webs so that the latter may be made much narrower than heretofore. Preferably, we wound in the opposite sense. The rods forming `the sheaves 4a, 4b are individually anchored under suitable tension to the concrete at the extremities of the structure, provide two such sheaves extending around the girder at the piers (not shown) forming the outermost supports, axis in opposite directions so as to intersect at their high in the usual manner. axis, its pitch corresponding to the spacing of adjacent span supports. The girder proñle is, for this purpose, preferably rounded into broadly elliptical shape, with the major axis of the ellipse or ovoid extending horizontally, a relatively long lay so as to extend substantially hori zontally and more nearly parallel to the axis of the so that each prestressing element describes an elliptically gered relationship, as `shown at 5 and `6. As best illus and low points in the upper and ythe lower Wall portion 55 The two sheaves. are crossed within the lower girder of the girder, respectively. wall at a single intermediate location ‘8 and within the Advantageously, each sheaf of prestressing elements upper wall portion, above the pillars 1 and 1', at 9. In deñnes a sheet wrapped with a long lay about the girder their lower reaches the sheaves 4a, 4b are wound with girder 2. Between the crossings 8 and 9, the prestressing elements of sheaves slope up and down in axially stag deformed helicoidal line. The pitch of this deformed trated in FIGS. 3A-3C, the wall of girder 2 is thickened helicoidal line may be varied throughout the length of 65 somewhat in the region above the pillars 1, 1’ to absorb the girder so ythat the prestressing element follows more the added compressive forces there. Since at all loca or less closely the curvature of a line whose vertical po tions each of the sheaves 4a, 4b defines a curved sheet sition in the structure is in accordance with the magni hugging the cavity 7, the entire girder shell may be of a tude of the moments along the girder, and which there 70 minimum thickness while manifesting full load-bearing fore may be referred to as a moment line and the av er-age direction of all of these elements extends gen strength. The curved configuration of the girder, whose cross-sectional outline rises arcuately upwardly from the 3,084,481 3 magnitude of the bending moments along the length of said fgirder. median zone 8 (FIG. 3A) along an approximately el liptical are at least in the middle region between sup ports 1 and 1', is maintained over the major part of the length `of the girder between these supports, as will be apparent «from FIGS. 3A and 3B, and in particular will -be seen to exist beyond the points of intersection 2. A structure according to claim 1 wherein said lower wall portion has a cross-section whose outline substan >tially extends along an arc of an ellipse with horizontal major axis at least in the region of said intermediate lo cation. 3. A structure according to claim 1 wherein said ele of the prestressing elements 4a, 4b with the plane of FIG. 2 which approximately corresponds to the horizon tal mid-plane of the girder; it will be noted that these points vof intersection lie closer to the piers 1, 1’ than to the intervening midpoint 8. In the erection of the structure, the rods 4a, 4b may be post-tensioned in the usual manner against the hard ened concrete after having `been imbedded therein with ments are wound with relatively short pitch in the upper part of said girder and with relatively long pitch in the lower part thereof, thereby traversing the horizontal mid plane of said girder at points closer to said supports than to the mid-point therebetween. 4. A structure according to claim 1 wherein said girder is provided with roadway-supporting lateral extensions in tegral and level with said upper flange, said girder being suitable bond-breaking means known per se, such as sheathing or asphalting. Although the invention has been specifically described of lgreater lateral -wallthickness above said supports than at said intermediate location, said girder extending be with reference to a bridge structure, it will be readily apparent that many modifications and variations may be made without departing from the spirit and scope of our _yond said supports, said prestressing elements continuing substantially helicoidally beyond said supports after in Vtersecting in said spaced locations. invention except as further limited by the appended claims. We claim: 1. A load-bearing structure comprising at least two hori References Cited in the tile of this patent UNITED STATES PATENTS zontally spaced-apart supports, a tubular concrete girder with an upper wall portion forming a roadway~support- 1,060,922 ing slab, said girder resting substantially horizontally on said Isupports and being provided with a lower wall por~ tion of reduced wall thickness whose outer surface rises Ligonnet _____________ __ Aug. 17I 1926 2,303,394 2,414,011 Schorer _______________ __ Dec. 1, 1942 Billner ________________ __ Ian. 7, 1947 arcuately upwardly from a median zone at least over FOREÍGN PATENTS the major part of »its length between said supports, said girder having lan interior surface generally paralleling said outer surface over said major part of the length of said' girder, and two sheaves of elongated prestressing ele -ments extending under tension along lgenerally helicoidal 386,108 822,090 725,826 566,308 ,lines of opposite pitch within the rgîrder wall, said sheaves intersecting at two spaced locations in said upper wall portion above said supports, respectively, and at a single intermediate location in said lower wall portion substan tially midway between said supports, said sheaves de scending from said two spaced locations to said inter mediate location substantially along a line whose ver tical position in the structure is in accordance with the Luten ________________ __ May 6, 1913 1,596,669 Great Britain ______________ __ Germany _________________ __ Great Britain ______________ __ Belgium __________________ __ of of of of 1933 1951 1955 1958 OTHER REFERENCES O Engineering News-Record, June 10, 1948 (pages 80, 81). Engineering News-Record, September 1, 1949 (pages 183~-187). Civil Engineering, January 1953 (pages 42, 43). .