US3158959A

US3158959A - Prestressed concrete

Info

Publication number: US3158959A
Application number: US136311A
Authority: US
Inventors: Jr George D Ratliff
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-09-06
Filing date: 1961-09-06
Publication date: 1964-12-01
Anticipated expiration: 1981-12-01

Description

United States Patent 3,158,959 PRESTRESSED KIGNCRETE George D. lltatliti, Jan, 1365 Hialeah Piaee,

Fiorissant, Mo. Filed Sept. 6, 1961, Ser. No. 136,311

17 flaims. (Cl. 50-431) This invention relates to a new and improved prestressed concrete beam construction wherein the beam is supported by tension elements extending longitudinally exterior of the beam.

A characteristic of concrete is the gradual shortening of its length during aging. This shortening causes steel cables or similar tension elements to lose a portion of their intial stress, since they are generally attached to the ends of the concrete structure. If the tension elements are not sufficiently stressed, they may lose all of their initial prestress over a period of time. The shortening of present day prestressed concrete structures is generally a constant amount, being about /2 in, per hundred feet of length after the structure has attained an age of approximately one year. By making the total strain relatively large, as for example, 3 in. per hundred feet, the resultant loss of strain becomes a small part of the total; however, to strain the steel to such an extent without breaking the same, the use of high-strength steel is necessary. 7

While it is not a general practice, it has been shown that prestressed concrete can be suspended from steelcables in such a way that the loss of strain is not a constant amount, but more likely a constant proportion of the initial strain, as for example, 0.2 of the initial strain.

In the French Patent 1,015,745, there is provided a span construction having tension elements which transmit the vertical support from the pier to a roll atop the pier, through the tension element, through additional roller and rocker devices at predetermined distances from the pier, and finally, to the concrete beam. In this arrangement, the cable unwinds from a curved surface, thus shifting the point where the cable changes from a straight to a curved configuration, i.e., as the cable unwinds from a drum or curved surface, the point of sharp bending progresses along the cable.

According to my invention, a new and improved prestressed concrete beam construction is provided which includes a hinge strut wherein the point of flexing is fixed, the tension elements thereby bending substantially less than the prior art of the character described. Thus, instead of progressing to a new point and straightening at the old point, the tension elements bend only slightly at the same point.

Another significant object oftthis invention is to provide a prestressed concrete beam arrangement wherein ordinary strength bars or rods may be used in lieu of cables or high-strength bars or rods.

Another object of this invention is to provide a new and improved suspended prestressed concrete structure which obviates the requirement for a roller on top of the supporting pier wherein a hinged strut is substituted for the roller at a predetermined distance from the pier.

A further object of this invention is to provide a new and improved prestressed concrete beam construction which includes a means for substantially reducing the local bending stress of the cable which is otherwise present their adjacent ends to the hinge.

ice

when rollers or similar devices are utilized. By virtue of eliminating or materially reducing this localized bending in the tension elements, a notably superior and unexpected improvement in prestressed concrete structures is realized, i.e., ordinary strength stel may be used for the tension elements instead of high-strength steel. This is rendered possible because the tension element loses a portion of the initial prestress no matter how small the degree there: of; whereas, with ordinary prestressed concrete, the tension elements may lose all their prestress if they are not sufiiciently stretched. Ordinary steel bars cannot be used in such prior art suspended prestressed concrete structures because of the flexing inherent when steel passes over the rollers which necessitates cables or other flexible highstrength tension elements.

A further object of this invention is to provide a new and improved prestressed concrete beam construction wherein there is provided a concrete beam carrying hinge means intermediate the ends thereof, tension elements extending longitudinally of the beam and joined to the ends thereof in any convenient manner, these tension elements engaging the hinge means and also engaging the pier so that the tension elements are placed under tension by engagement with the pier, and the beam is wholly supported by the tension elements at this pier.

This invention further contemplates a novel hinge construction for a concrete beam wherein the tension ele ments are divided into segments and pivotally joined at The localized bending of the tension elements is thereby reduced to any desired level, as the hinges may be used where the tension elements contact the pier, or the ends of the beam.

There further is provided according to this invention, means for changing the effective length of the tension elements, which permits the vertical movement and the amount of the prestress of the beam to be controlled during the life of the structure.

These and further objects, advantages, and novel features of the present invention will become apparent in the specification and claims taken in connection with the accompanying drawings.

FIGURE 1 is a side elevation view of the structure according to this invention;

FIGURES 2, 3 and 4 are sectional views taken along lines 22, 33, and 4-4, respectively in FIGURE 1;

FIGURES 5 and 6 are enlarged views of modified hinge constructions according to this invention; and

FIGURE 7 is an enlarged fragmentary end view taken 7 along the line 7 7 of FIGURE 1.

Reference is now made to the accompanying drawings wherein there is shown a prestressed concrete beam construction Iii which includes spaced apart first and

second piers

12 and 14, respectively, carrying a beam 16 of concrete. The second pier 14 carries a roller 18 and the adjacent end of the beam 16 carries a bearing plate 20 in engagement with the roller.

' any suitable means, there being shown an end bearing plate 24, carried within an end recess in the beam 16. The

rods

22, 22 are joined to the respective edges of the plate 24 by welding or the like. The opposite ends of rods 22, 212' are threaded, in turn, engaging a turnbuckles 26. Threadably carried by the opposite end of the turnbuckles and extending towards the opposite end of the beam to adjacent the pier 14 are second tension elements, e.g., rods 27, 2'7 which are fixed to this end of the beam 16, as by welding to a transverse plate 28.

Passing transversely through the beam 16 intermediate the piers 12 and 14- is a rod 3% positioned relatively close to the first pier i2. Carried at the ends of the rod (FIGURES 1 and 3) are

hinge plates

32, 32. The first pier 12 is positioned inwardly of the adjacent end of the pier i l and is of U-shaped construction so as to receive the leg of the T-shaped beam. The rods 22, 22' are in engagement with the bottom surface of the respective hinge plates 32, 32' and the upper surface of the

upstanding legs

34, 34* r" the first pier 12. Thus, the beam 16 is supported adjacent the pier 12 solely by the rods 22,

22 which are to be placed under tension to impart the desired stress to the concrete below the neutral stress plane thereof.

Turning now to FIGURE 5, a slightly modified construction is shown wherein the rod 22 (and 22') is divided adjacent the respective hinge plate 32 (and 32') and the ends thereof joined as by welding thereto.

In the embodiment of the invention shown in FIGURE 6, the hinge 32 (and the hinge 32;) carry two pins 38, which, in turn, pivotally carry opposed tie plates lil and 4-2, joined as by welding to the respective ends of the rod 22.

Also, similar pins and tie plates may be added to the connection by the rod 22 and the first pier i2; and, in place of the connection of the ends of the rods 22, 22' to the respective

transverse end plates

24 and 28. As will beappreciated, the localized bending occurs in varying'degrees in each of the connections, and hinges may be desired at any one or any number of them depending upon the degree of localized bending which is to be tolerated.

Conveniently, the rod 34) may be positioned within the beam during the formation thereof and the

respective hinge plates

32, 32 pivotally connected thereto at the free ends. Numerous alternative means will be apparent to those skilled in the art for positioning the hinge plates 32, 32' along the beam, e.g., without passing the rod 3% transversely through the beam. For example, a bent or split plate conforming to the cross-sectional configuration of the beam 16 may be fixedly positioned therealong as by welding the ends to one another, the surrounding plate operatively carrying the hinges by rods extending therefrom.

Further, the suspension system described may be utilized in both piers shown in FIGURE her in more than two piers as required to support the beam. As is the case with most beam constructions of this type, the roller 18 is required on all but one. pier; however, it may be placed on the piers below the suspension system, i.e., at the top of the pier 12 instead of the arrangement as shown in FIGURE 1.

Still further devices may be used such as a hinge mounted near the bottom of all but one pier or column to permit predetermined horizontal movements for the purpose of 'ielieving stress inherent when there are no rollers, hinges, or other translation means.

Also, while the beam 16 is shown to be of T-shaped cross-sectional configuration with the rods 22, 22' and the rods 27, 27' extending along the outer side walls thereof, it will be appreciated that this arrangement may be conveniently varied depending upon the particular beam in configuration utilized. For example, the beam 16 may be of inverted U-shaped configuration and the top of the pier 12 of mating rectangular configuration, so

that the tension elements may be carried within the sidewalls of the inverted U-shaped beam, the hinge mem- 4i ber 32 being thereby positioned within the recess of the inverted U-shaiped beam.

As will be appreciated, while the tension elements are shown to be rods of ordinary strength steel, cables may be substituted therefor, as desired. In this regard, the significant problem of reducing localized bending stresses is effectively obviated in either instance.

From the foregoing description of the various embodiments of this invention, it is evident that the objects of this invention, together with many practical advantages are successfully achieved. While preferred cmbodimen of my invention have been described, numerous further modifications may be made without departing from the scope of this invention;

Therefore, it is to be understood that all matters herein set forth or shown in the accompanying drawings are to be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. Prestressed concrete span comprising: a concrete beam; spaced apart first and second pier means for operatively supporting said beam; tension means joined to the end regions of said beam and extending along the outside of the wall surface thereof; hinge means carried by beam intermediate the ends there-of between said pier means in laterally extending relationship beyond the beam walls and in operative engagement with said ten sion means; said first pier means supporting the respective end of said beam wholly by operative engagement with said tension means to impart tension thereto.

2. Structure defined in claim 1 wherein said hinge means includes a rod extending transversely from said beam, said hinge means depending from said rod, an: said tension means includes opposed rods extending along the sidewalls of said beam in engagement with said hinge means.

3. Structure defined in claim 1 wherein said tension means includes cables extending along the outer wall surface of said beam.

4. Structure defined in claim 1 wherein the one end of said beam extends beyond said first pier means.

5. Structure defined in claim 1 wherein said tension means is dis-posed below the neutral plane of stress of said beam.

6. Structure defined in claim 1 including translation support means between said beam and said second pier means.

7. Structure defined in claim 6 wherein said translation support means includes a roller carried by the upper end of said second pier means.

8. Structure defined in claim 1 including means carried by said tension means for changing the length thereof.

9. Structure defined in claim 8 wherein said means include a turnbuckle.

10. Structure defined in claim 1 wherein said tension means is fixedly secured to said hinge means.

11. Structure defined in claim 10 wherein said tension means is in parts along each side and the adjacent ends of said parts are welded to said hinge means.

12. Structure defined in claim 10 including tie plates pivotal ly secured to said hinge means and said tension means is joined at adjacent ends of segments thereof to said tie plates.

13. Structure defined in claim 1 including plate means secured to the ends of said beam and joined to the respective ends of said tension means.

14. Prestressed concrete span comprising: a concrete beam having sidewalls; spaced apart first and second pier means for operatively supporting said beam; hinge means carried by said beam intermediate the ends thereof between said :pier means in laterally extending relationship beyond the walls of said beam; first tension elements joined to one end of said beam and extending adjacent the outside of the sidewalls thereof and in engagement with said hinge means; second tension elements joined to said beam at the opposite end thereof extending along the outside walls of said beam and joined to said first tension elements, said finst pier means supporting the respective end of said beam wholly by supportive engagement of said first tension elements therewith.

15. Structure defined in claim 14 wherein said tension elements include rods of ordinary strength steel.

16. Structure defined in claim 14 wherein said tension elements include cables.

17. Structure defined in claim 14 including turnbuckles joining each of :said first and second tension elements to one another.

References Cited in the file of this patent UNITED STATES PATENTS Mortenson Feh. 24, 1920 Sahlberg Nov. 6, 1934 Finsterwalder Apr. 18, 1939 Dubassofi Aug. 7, 1945 Coil June 13, 1950 FOREIGN PATENTS Germany Feb. 5, 1953 Great Britain June 14, 1961 France of 1952

Claims

14. PRESTRESSED CONCRETE SPAN COMPRISING: A CONCRETE BEAM HAVING SIDEWALLS; SPACED APART FIRST AND SECOND PIER MEANS FOR OPERATIVELY SUPPORTING SAID BEAM; HINGE MEANS CARRIED BY SAID BEAM INTERMEDIATE THE ENDS THEREOF BETWEEN SAID PIER MEANS IN LATERALLY EXTENDING RELATIONSHIP BEYOND THE WALLS OF SAID BEAM; FIRST TENSION ELEMENTS JOINED TO ONE END OF SAID BEAM AND EXTENDING ADJACENT THE OUTSIDE OF THE SIDEWALLS THEREOF AND IN ENGAGEMENT WITH SAID HINGE MEANS; SECOND TENSION ELEMENTS JOINED TO SAID BEAM AT THE OPPOSITE END THEREOF EXTENDING ALONG THE OUTSIDE WALLS OF SAID BEAM AND JOINED TO SAID FIRST TENSION ELEMENTS, SAID FIRST PIER MEANS SUPPORTING THE RESPECTIVE END OF SAID BEAM WHOLLY BY SUPPORTIVE ENGAGEMENT OF SAID FIRST TENSION ELEMENTS THEREWITH.