US3237537A - Prestressed concrete highway - Google Patents

Description

c. H. HUTCHINGS PRESTRESSED CONCRETE HIGHWAY March 1, 1966 Filed Jan. 17, 1964 3 Sheets-Sheet 1 62ml afilmyg w BY (f a? ATTORNEYS March 1966 c. H. Hu'rcmucs 3,237,537

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INVENTOR I ATTORNEY 3,237,537 PRESTRESSED CGNCRETE HIGHWAY (Iarl H. Hutchings, 864 9th Ave. SE, Rochester, Minn. Filed Jan. 17, 1964, Ser. No. 340,850 8 Claims. (Cl. 948) This invention relates to improved highway construction, and particularly to such construction wherein the highway is formed of prestressed concrete, and this application is a continuation-in-part of my co-pending application Serial No. 21,979, filed April 13, 1960, entitled Prestressed Concrete Highway, now abandoned.

Prestressed concrete is being used in many ways in different fields of construction. Its general field of use, however, has been by means of structural members which are precast at a central plant and then transported to the place of construction. These are usually formed by stressing suitable cables and pouring concrete into a mold about the stressed cables. When the concrete has set, the cables are released so that the stressing force places the concrete in compression.

In highway construction, however, the concrete must be poured in situ. Therefore, the use of conventional prestressing methods and apparatus has not been feasible.

The general object of the present invention is to provide a prestressed construction which is suitable for use in laying concrete roadways, streets, etc.

A more specific object is the provision of such construction whereby the highway can be constructed in sections, and the stressing force can be carried through from one section of the highway to another.

A further object is to provide a construction of this nature wherein slabs of considerable length can be formed without need for expansion joints in the slabs.

Another object of the invention is to provide means for I stressing the highway transversely, using shoulder strips as the jacking heads, and using the shoulder strips as separators between longitudinally spaced, transversely extending jack heads for stressing the highway longitudinally.

Still another object is to provide means in the jack heads for permitting the cable stress of one slab to be imposed upon the next.

Yet a further object is to provide means for joining one cable length to another to attain continuity of force transmission throughout the highway length.

It is also an object of the invention to provide a highway of this kind wherein means are employed intermediate jack heads for slidably guiding the stressing cables to cause them to follow a rolling road bed, or to provide support means for pro-tensioned pavement slabs of less length than the distance between adjacent jack heads and reduce the number of jack heads required per unit length of roadway constructed.

It is an object of the invention to provide an improved highway construction which will result in a superior highway capable of rapid construction, at less cost than with present day constructions.

Other objects of the invention will become apparent from the following description of practical embodiments thereof when taken in conjunction with the drawings which accompany, and form part of, this specification.

In the drawings:

FIGURE 1 is a plan view, somewhat diagrammatic, of a highway constructed in accordance with the principles of the present invention, with intersecting highways crossing at right angles;

FIGURE 2 is a plan view of a section of highway including the basic construction unit of a pair of jackheads and intermediate slab, parts being broken away;

FIGURE 3 is a longitudinal section through the high- 3,237,537 Patented Mar. 1, 1966 way shown in FIGURE 2, and is taken on the line 3-3 of FIGURE 2;

FIGURE 4 is a transverse section through the highway taken on the line 4-4 of FIGURE 3;

FIGURE 5 is an enlarged section through one of the jackheads and adjacent structure, illustrating a joint between adjacent stressing cables;

FIGURE 6 is a section through a cable coupler, taken on the line 66 of FIGURE 5;

FIGURE 7 is a vertical section through one of the intersections shown in FIGURE 1;

FIGURE 8 is a longitudinal section through a highway having an undulating contour, illustrating a modified construction; and

FIGURE 9 is a transverse section through the highway shown in FIGURE 8, and is taken on the line 9-9 of FIGURE 8.

In general, the invention concerns a highway construction in which spaced jackheads are employed which permit stressing of cables between them prior to pouring concrete between the jackheads to embed the pre-tensioned cables. The highway is stressed transversely by means of shoulder strips which also form spacers between the longitudinally spaced jackheads. In the case of intersecting highways, the intersection forms a jackhead for stressing longitudinally of the highways in all four directions. Where the roadway is not flat, anchor blocks can be used to hold the cables to the contour of the road during tensioning of the cables and curing of the concrete.

Referring to the drawings in detail, and first adverting to the basic principle as illustrated in FIGURES 2 to 5, inclusive, there is shown a highway 1 which includes piertype jackheads 2, shoulder strips 3 extending between the jackheads, and slabs 4, which fill the area outlined by the jackheads and shoulder strips and form the major portion of the highway surface.

The jackheads 2 are in the form of piers, having a base leg 5 which extends in any event below the frost line, and suificiently deep to provide the stability necessary for the piers to withstand the required stressing force. The formation of the earth (rock, gravel, soil, sand, swamp, etc.) will determine the depth of the pier leg and the spacing between piers. The upper portion of the pier flares outwardly, as at 6, giving increased bearing surface against the ground and a widened base portion. The jackhead proper, 7, rises vertically from the widened base and extends the full length of the pier. The jackhead is narrower than the base, and rises centrally of the base, leaving a shoulder 8 on either side which will form a ledge upon which the slab 4 may rest. These shoulders, or ledges, extend the full length of the piers.

In forming the piers, the earth will be trenched to proper depth and width and the concrete poured into the trench. Suitable forms may be used for the upper structure. If the pier is set upon rock, the rock is drilled, a pin 9 set in the rock and the concrete poured to embed the pin. The shoulders 8 will be flush with the graded roadbed, and the jackhead will project above the shoulders at distance equal to the desired thickness of the slab 4.

The jackhead 7 will be provided with a plurality of openings extending from the face adjacent one shoulder of the pier to the face adjacent the opposite shoulder. These openings are preferably formed by means of pipes It), horizontally positioned, and cast into the concrete of the jackhead. The pipes end at the vertical faces 11 of the jackhead.

Shoulder strips 3 are poured upon the graded roadbed bridging the space between the ends of a pair of piers. Trenches may be provided to form downwardly extending legs 12 so that the strip will be of channel cross-section. Suitable forms may be used to define the shape of the upper structure. The tops of the shoulders will be at the level of the top of the jackheads and, with the jackheads will form an outline, or border for the central slab 4. Horizontally laid pipes 13 will traverse the shoulders, with the pipes of one shoulder strip being in vertical alignment with the pipes of the opposite strip. The pipes 13 will be at a different level from the pipes through the pier jackheads. The pipes 13 may continue completely through the shoulders, or they may terminate in enlarged rings 14 which will form abutments for temporary anchoring of the transverse stressing cables during pouring and setting of the central slab.

In order to hold the shoulders in their parallel relation to one another during tensioning of the cables, and to prevent them from buckling and cracking under the strain, spacers 15 are placed at intervals between the shoulders. These are elongated members which lie in the roadbed and span the space between the shoulders. The distance between spacers will be determined by the need for bracing between the shoulders in a particular installation. The spacers will abut the depending legs of the shoulders, and will have their top surfaces at the level of the roadbed.

After the piers and shoulders have been poured and the concrete has been set, the stressing cables will be put in place. If the openings 13 are at a lower level than the ones in the pier jackheads, the transverse stressing cables will be put in position first. These cables, 16, are threaded through the shoulderopenings 13 so that they will extend across the roadbed from shoulder to shoulder, through the shoulders, and have their ends project beyond the outside edges of the shoulders at the sides of the roadway. One end of the cable will be welded, or otherwise affixed, to the ring 14 of one shoulder, and conventional jacking (not shown) will be secured to the opposite end of the cable and positioned to bear against the outside of the shoulder. The jack means will then be operated to tension the cable the desired amount, using the shoulder as a jack-head, When the desired tension has been applied the cable adjacent the jack means may be welded to the adjacent shoulder ring to anchor it to its tensioned condition. All transverse cables can be similarly tensioned and anchored.

The longitudinal cables 17 will be threaded through the openings 10 in the pier jackheads, and through clamping members 18 which are positioned on each side of each jackhead. The clamps may have feet to rest upon the pier ledges 8 to hold them in alignment with the jackhead openings, and each has a hole 20 through which the cable will pass. A set screw 21 is threaded through the clamp for movement transversely into the hole to clamp the cable against the opposite side of the hole. The clamps are designed to bear against the vertical faces 11 of the pier jackheads when clamped to a cable and the cable is under tension. When the cables are strung between a pair of piers, the clamp 18 adajcent a cable end, that is, at the outside face of a pier with respect to the pair of piers involved, will have its set screw tightened to fix the clamp to the cable so that any pull upon the opposite end of the cable will result in the fixed clamp being drawn tightly against the jackhead face to anchor the cable end. lacking means will then be attached to the opposite cable end with the jack bearing against the jackhead face, and the cable tensioned to the desired degree. When the cable is tensioned, the clamp adjacent the jacking means is tightened upon the cable while in abutment with the jackhead face, and the jack released. This will hold the cable under tension as the clamps which are fixed to it are at the opposite outside faces of the jackheads and held against movement toward one another by contact with the jackhead faces.

With both the longitudinal and transverse cables stressed, the slab 4 is poured. The shoulder strips 3 will serve as side forms in pouring the slab, and any suitable abutment may be used at the pier ledges to form the end of the slab spaced from the faces 11 of the pier jackheads. The ends of slab 4 will overlap, and rest upon, the ledges 8 of the adjacent piers. A layer of grease, or separators can be put upon the ledges of the piers before pouring the slabs so that the slab will be free from the pier so that it may move under load and during expansion and contraction with temperature changes. As soon as the concrete of the slab has set, the clamps 18 on the longitudinal cables will be released and the transverse cables cut free from the rings 14-. This will release the cable tension to the slab to stress the slab. The cable ends will be free to move through the openings 10 and 13 so that the entire stress can be imposed upon the slab.

The next section of highway can now be laid, and the longitudinal cables for that section will be connected to the ends of the cables of the section just laid. The cable ends can be coupled in any suitable manner. One coupling that might be used consists of a pair of cablegripping anchors 22 attachable to the cable ends and held against separating movement by being seated in a yoke 23. The yoke is simply a rectangular frame having holes 24 in its end walls 25. The anchors comprise a tubular housing having tapering inner walls 26, and being threaded on its outer surface at the end having the larger internal opening. A pair of arcuate tapered jaws 27 are mounted within the housing for sliding contact with the housing walls and closing motion when moved toward the smaller internal end of the housing. A cap 28 is threaded on the end of the housing, and a spring 29 bears against the cap and the jaws to urge the jaws toward closing position. When a cable end is threaded through the opening 24- in the yoke and into the small end of the anchor, the spring will urge the jaws to gripping relation with the cable. With two anchors attached to the ends of two cables and bearing against opposite ends of the yoke, the two cables will be effectively tied together.

The second slab will be laid precisely as the first, and after it is set the cables will be released from the jackheads to stress the slab. After there is no further need for access to the clamps 13, the space between. the pier jackhead faces 10 and the ends of the slabs 4 may be filled with grout to form expansion joints 30.

Under this system of laying the highway, successive prestressed slabs will be tied together, due to the continuity of the cables, and the cable lengths between adjacent slabs will be free for endwise movement in the openings in the pier jackheads. The slabs will be highly resistive to bending under load, and will serve as spans between successive piers to carry the load even though the roadbed may be on swampy or other soft ground. It will be obvious that pier spacing, cable stressing, and the number of both transverse and longitudinal cables will depend upon conditions for the particular highway to be constructed.

In some installations, it will be advantageous to have the several slabs of the highway entirely separated, in which case the longitudinal cables may be severed at the jackhead joints after the concrete has set, to release the cables to stress the slabs. After this is done, the piers serve simply as support mmebers for the slab end.

The construction just described lends itself ideally to highway construction where there are intersecting roads, or to construction of city streets. Where this arrangement occurs, the intersection itself forms the jackhead for stressing the cables which extend longitudinally in the four directions leading from the intersection.

Such an arrangement is shown in FIGURE 1 and the intersection pier is illustrated in cross-section in FIGURE 7. In this particular arrangement, the only interest is in the upper, or jackhead section of the intersection membet, and only that part is illustrated in detail. It will be understood that the footing, or foundation, of the member may take any necessary form.

The intersection member 31 is substantially rectangular, having the four edges 32, 33, 34 and 35 confronting the streets, or highways, 36, 37, 38 and 39. The corners of the member are notched, as at 40, to receive the several shoulder strips 41. The member will have ledges 42 upon which the edges of the several slabs 43 will rest. The member will have a plurality of horizontal openings 44 extending through it in one direction opening to the faces, or edges 32 and 35, and a similar plurality of openings 45 at right angles to the first group, lying at a different level, and opening to the faces 33 and 35. Thus, in effect, the intersection member functions as two of the pier jackheads previously described, where the jackheads are normal to one another, for the longitudinal cables for the four directions can be stressed from the one member. It will be understood that a clamp 18 will be used upon each cable end to bear against the face or edge of the member opposed to the direction of cable extent. In this way all of the cables can be stressed, and the several road slabs poured one at a time.

Referring now to FIGURES 8 and 9 of the drawings, there is shown a highway which follows an undulating ground contour. A roadbed of this pattern presents special problems, for the stressing cables, when tensioned, tend to rise from the concave sections of roadbed and be supported only at the tops of the rises. Therefore, some means must be employed to hold the cables to the roadbed contour. The arrangement shown in FIGURES 8 and 9 solves this problem.

The roadbed 46 is not flat, but rolling, having bills, or rises, 47 with intermediate valleys, or depressions, 48. Piers 49, similar to those previously described, will be located along the roadbed at approximately the same distance spacing as would be the case with a flat road. In the concavities of the roadbed contour, anchor blocks 50 are embedded, where required, to hold the stressing cables at the proper height above the bed.

Blocks 50 may be pre-stressed concrete and extend the full width of the roadbed. Each one will have a row of loops 51 projecting vertically above its upper surface and extending the width of the roadbed when the block is in place. The loops may be provided singly, or may be formed by partially embedding a serpentine rod 52 in the concrete block to leave the upper bights of the rod exposed.

When piers 49 are formed and anchor blocks 50 are laid, stressing cables 53 will be threaded first through the openings 54 in the jackheads 55 of one pier, then through the loops 51 of successive anchor blocks, and lastly through the openings in the jackhead of the next pier. After the cables are in place, they may be tensioned as previously described, and the concrete poured to form slab 56. When the concrete is cured, cables 53 may be cut at the piers, as described to free the slab, or they may be left intact to maintain the tie from one slab to the next. By employing separators at the plane of the loops 51, the roadway may be divided into a plurality of relatively short slabs, each bridging the space between a pair of anchor blocks, on a pier and anchor block. When the separators are removed, the cables may be cut if desired, to separate the slabs. In any event, the joints 57 will be filled with grout and provideadditional expansion joints.

While in the above practical embodiments of the invention have been disclosed, it will be understood that the details of structure shown and described are merely by way of illustration and the invention may take other forms within the scope of the appended claims.

What is claimed is:

1. A method of constructing a concrete highway comprising, grading a roadbed, digging transverse trenches therein at longitudinally spaced locations and erecting forms about and above the trenches, placing openingforming mandrels horizontally across the forms above the roadbed level and extending longitudinally of the roadbed, pouring concrete into the trenches and forms and about the mandrels to form footed piers with raised jackheads having openings therethrough, threading cables through the openings and spanning the space between piers after the concrete has set, tensioning the cables by jacking against the jackheads, anchoring the tensioned cables to the jackheads, pouring a concrete slab upon the roadbed between the piers and embedding the cables, and releasing the anchored cables after the concrete slab has set.

2. A method of constructing a concrete highway as claimed in claim 4 wherein before pouring the concrete slabs concrete shoulder strips having openings transversely of the roadbed therein are fonmed along the sides of the roadbed between the piers, threading cables through the shoulder strip openings and across the roadbed after the concrete has set, tensioning the shoulder strip cables, anchoring the shoulder strip cables to the shoulder strips, then pouring the slabs embedding both sets of cables, and after the slab has set releasing the anchors of the shoulder strip cables.

3. A concrete highway upon a graded roadbed comprising, a plurality of concrete piers with each pier extending transversely across the roadbed and the piers spaced from one another longitudinally of the roadbed, each pier having a downwardly extending legembedded in the roadbed to anchor the pier against lateral pulls longitudinally of the roadbed, and a jackhead at the top of each pier projecting above the surface of the roadbed, the jackheads having openings extending horizontally therethrough longitudinally of the roadbed, stressing cables threaded through the openings and strung under tenston between the piers, releasable means for abutment with the jackheads to clamp the cables and hold them tensioned between the jackheads, and a concrete slab extending each two piers in which the cables are embedded and bonded, each pier having a widened base at the top of the leg and beneath the jackhead, the base extending horizontally outward beyond the leg longitudinally of the roadbed to provide a stabilizing member to bear against the earth and prevent movement of the pier longitudinally of the roadbed under the pull of the tensioned cables.

4. A concrete highway upon a graded roadbed comprising, a plurality of concrete piers with each pier extending transversely across the roadbed and the piers spaced from one another longitudinally of the roadbed, each pier having a downwardly extending leg embedded in the roadbed to anchor the pier against lateral pulls longitudinally of the roadbed, and a jackhead at the top of each pier projecting above the surface of the roadbed, the jackheads ha ving openings extending horizontally therethrough longitudinally of the roadbed, anchor blocks embedded in the roadbed at spaced points intermediate the piers, cable-receiving eyes carried at the tops of the anchor blocks, stressing cables threaded through the openings in the pier jackheads and the eyes on the anchor blocks and strung under tension between the jackheads, releasable means in abutment with the jackheads to clamp the cables and hold them tensioned between the jackheads, and a concrete slab extending between each two piers in which the cables are embedded and bonded.

5. A concrete highway upon a graded roadbead as claimed in claim 4 wherein, the concrete slab is divided into a plurality of slabs separated at the anchor block eyes.

6. A concrete highway upon a graded roadbed as claimed in claim 4 wherein, the anchor blocks extend transversely of the roadbed the width of the roadbed.

7. A method of constructing a concrete highway comprising, grading a roadbed, digging transverse trenches therein at longitudinally spaced locations and erecting forms about and above the trenches, placing opening-forming mandrels horizontally across the for-ms above the roadbed level and extending longiutdinally of the roadbead, pouring concrete into the trenches and forms and about the mandrels to form footed piers with raised jackheads having openings therethrough, digging additional trenches transversely of the roadbed spaced apart longitudinally of the roadbed intermediate the piers, setting anchor blocks having eyes on their tops in the additional trenches to a depth to place the eyes at approximately the same level above the roadbed at the openings through the jackheads, after the concrete has set threading cables through the openings in the jackheads and the eyes on the anchor blocks and spanning the space between piers, tensioning the cables by jacking against the jack heads, anchoring the cables to the jackheads, pouring a concrete slab on the roadbed between the piers and embedding the cables, and releasing the anchored cables after the concrete slab has set. v

8. A concrete highway upon a graded roadbed comprising, a pair of concrete piers each extending transversely across the highway and with the piers of the pair spaced longitudinally of the highway, a portion of each pier projecting above the surface of the roadbed to provide a jackhead, the jackheads having openings horizontally extending therethrough longitudinally of the highway, stressing cables under tension threaded through the openings and strung between the piers, releasable clamp means in abutment with the jackheads clamping the cables and holding them tensioned between the jackheads and a concrete slab extending between the piers in which the cables are embedded and bonded, the piers each having a ledge projecting horizontally beneath the jackhead portion toward the opposite pier, and said slab having its ends rest ing on the ledges.

References Cited by the Examiner UNITED STATES PATENTS 1,201,452 10/1916 Fitzgerald 942 2,116,033 5/1938 Malone 94-4 2,655,846 10/1953 Freyssinet 94--8 FOREIGN PATENTS 799,825 4/ 1936 France.

290,091 5/ 1928 Great Britain.

561,135 5/1944 Great Britain.

36,955 12/ 1935 Holland.

CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, Examiner.

Claims (1)

1. A METHOD OF CONSTRUCTING A CONCRETE HIGHWAY COMPRISING, GRADING A ROADBED, DIGGING TRANSVERSE TRENCHES THEREIN AT LONGITUDINALLY SPACED LOCATIONS AND ERECTING FORMS ABOUT AND ABOVE THE TRENCHES, PLACING OPENINGFORMING MANDRELS HORIZONTALLY ACROSS THE FORMS ABOVE THE ROADBED LEVEL AND EXTENDING LONGITUDINALLY OF THE ROADBED, POURING CONCRETE INTO THE TRENCHES AND FORMS AND ABOUT THE MANDRELS TO FORM FOOTED PIERS WITH RAISED JACKHEADS HAVING OPENINGS THERETHROUGH, THREADING CABLES THROUGH THE OPENINGS AND SPANNING THE SPACE BETWEEN PIERS AFTER THE CONCRETE HAS SET, TENSIONING THE CABLES BY JACKING AGAINST THE JACKHEADS, ANCHORING THE TENSIONED CABLES TO THE JACKHEADS, POURING A CONCRETE SLAB UPON THE ROADBED BETWEEN THE PIERS AND EMBEDDING THE CABLES, AND RELEASING THE ANCHORED CABLES AFTER THE CONCRETE SLAB HAS SET.

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