US2950517A - Method of making post-stressed reinforced cement-concrete structures - Google Patents

Description

Aug. 30, 1960 A. E. BRlcKMAN 2,950,517

METHOD 0F MAKING PosT-sTREssED REINFORCED CEMENT-CONCRETE: STRUCTURES 2 Sheets-Sheet 1 Filed June 6, 1955 ALAN E. BRICKMAN INVENToR BY UVW ATTORNEY Aug. 30, 1960 A E BRICKMAN 2,950,517

' METHOD OF MAKING POST-STRESSED REINF'ORCED CEMENT-CONCRETE STRUCTURES v 2 Sheets-Sheet 2 Filed June 6, 1955 ALAN E. BRICKMAN iNvEN'roR BY Gc ATTORNEY United States Patent C) par WTHOD OF MAKNG POST-STRESSED REIN- FORCED CEMENT-CGNCRETE STRUCTURES Alan E. Brickman, 85 Nlayfair, Williamsville 21, N.Y.

Filed June 6, 1955, Ser. No. 513,314

2 Claims. (Cl. 25-154) This invention is concerned with a method of making post-stressed reinforced cement-concrete structures of considerable length such as, for example, concrete highways, airport runways, and the like, and is directed in particular to the stressed metal reinforcement members embedded in such concrete structures. More especially, it has to do With a new method and means of applying tension to the metal reinforcement members in such structures.

The application of prestressed concrete, in which pretensioned steel or other reinforcement members are incorporated in a concrete element or structure, has been quite commonly used heretofore in the construction of various types of concrete structures such as bridge girders, beams, floor slabs, etc. In making such concrete structures the steel reinforcing or tension members, such as stranded wire structures, are stressed to a predetermined tension within the form, after which concrete is poured into the form or before the poured concrete has started any appreciable set. After the concrete has set the form is removed and the `bond of the concrete to the metal reinforcement members reacts on the concrete to place it under compression. The most common way of applying tension to the stranded wire structures is by means of a cone socket member secured to each end of the stranded wire structure by means of a wedge with the socket members having a threaded portion which can be drawn up in various ways to apply the tensile Stress.

To obtain the necessary prestress in the concrete, the stranded reinforcement is stressed initially under a tension on the order of 60% of its elastic limit values and in this condition applies compression forces to the adjacent concrete in a manner that puts the entire concrete structure in compression. In this state, stresses due to temperature changes and thermo-contraction which normally would cause cracking of the concrete are counteracted Aby the initial tension forces released by said reinforcing members and transmitted to the concrete thereby setting up compression therein and preventing occurrence of cracking or warping thereof.

Prestressing, however, has not been used extensively in cement-concrete highway construction because of the absence of a satisfactory means for applying tension to the steel or other metal reinforcement rods or wires which usually run lengthwise in the longitudinal direction of the pavement and are necessarily of a fixed length so that the pavement design therefore is not continuous but formed in slab units of a prescribed length which is considerable and would be so great as not to provide any practicable method of accomplishing the bringing of the individual metal reinforcement rods or Wires under a condition of tensile stress during the laying of the Wet pavement.

In accordance with the present invention, I have provided a practical method of tensioning, herein termed as post-tensioning, whereby each reinforcing tension member of a system of metal reinforcement consisting of steel or other metal rods or wires of uniform cross-Section is placed under tensile stress through an external pulling force applied to one end or to both ends of each rod or wire, the tensioning being carried out in conjunction with the laying of the wet pavement. The rods or wires in being placed under tension are secured to anchorage members temporarily aixed on the road forms. Both the `anchorage members and the reinforcing tensioning rods preferably are centered with respect to the thickness of the pavement or halfway of the height of the road forms. In my post-tensioning method, the ultimate tensile stress placed on the reinforcingI members is not applied until after the concrete has been poured and some initial set of said concrete has taken place. In the practice of my method, tension lis applied to each of the individual metal reinforcement members in one or more stages to lengthen them to a predetermined ex-V tent and to place them under prescribed tensile stress. For example, in the rst tensioning stage, a tensile `force is applied to the metal reinforcement rods or wires to securely fasten their ends within the limits of the method of anchorage of such tension members to the road forms. In the second tensioning stage, additional tension is applied to each metal rod or Wire after the concrete has been poured. Due to the combined weight of the wet concrete to that of the road forms it is possible to apply greater tension at this stage thereby bringing the reinforcing tension members into proper position in the center of the slab Where they properly belong. After the concrete has set for a short time, such as, for example, approximately 11/2 hours, full tension then is applied to the reinforcing tension members and they are so secured and maintained for the life of the pavement.

Apparatus embodying the present invention includes anchorage members adapted to be temporarily supported by the road forms inside the area in which the wet pavement is to be poured, and additionally includes a number of detachable tension-applying means externally operated outside of the form and connectable through the forms to end `couplings provided with step portions for stretching the rods or wires to a predetermined extent and placing them under a precalculated or known tensile stress. Upon prestressment of the rods or Wires to the ultimate required tensile stress, the externally-operated tension-applying means are detached from the stepped couplings` on one or both ends of the reinforcing rods or Wires and the latter then remain so tensioned by being securely held by their anchorage members to the road forms. The anchorage members are initially attached to the inside face of the road forms and are demountable therefrom so that they stay permanently in the concrete after the road forms are stripped from the finished pavement.

It therefore is an object of my invention to provide a method of making pretensioned reinforced concrete structures of considerable length for use as pavements in concrete highways, airport runways, and the like, in which the individual metal reinforcement members are brought under a condition of predetermined tensile stress by tension applied in two or more stages.

Another object of the invention is to provide a practical method of making a prestressed reinforced concrete structure of considerable length in which the pavement will be continuous in both longitudinal and transverse directions and devoid of longitudinal joints and the numerous transverse expansion joints that characterize such concrete structures made in accordance with the present practice.

These and other objects will be more apparent after referring to the following specification and accompanying drawings, in which:

Fig. 1 represents a top plan view of a length of concrete highway during construction in accordance with my invention with a portion of the pavement being shown 2,95o,517 I o brokenV away to disclose the stressed diagonal tension members for reinforcing the concrete, and also showing the manner in which such metal reinforcement members are placed under tension and so maintained anchored to the various anchorage saddles therefor temporarily carried by the road forms during this stage of the highway construction;

Fig. 2 is a fragmentary plan view, on enlarged scale, showing a side edge portion ofthe highway of Fig. 1 including two adjacent anchorage members each having a pair of diagonal oppositely-inclined tensioned reinforcement members secured thereto in various stages of tensioning, and the means associated with both anchorage saddles for tensioning the reinforcement members thereof;

Fig. 3 is aV side elevation of the fragmental pavement portion of Fig. 2, as viewed from outside of a road form with the tensioning means for one of the anchorage membersv removed to show the slotted opening in the form side through which said tensioning means is inserted into the anchorage saddle for alternate connection to the ends of the two diagonal reinforcement membersV thereof for tensioning the same;

Fig. 4 is a fragmentary cross-sectional view of the concrete .pavement shown in Fig. 1 and taken along the line 4-4 of that figure, looking in the direction of the arrows;

FigA 5 is an enlarged fragmentary plan View, partly in section, of one of the numerous anchorage saddle members for initially securing the tensioned reinforcement members to the road forms and which, subsequently, is detached therefrom and embedded in the concrete, and including a pair of tensioned reinforcement members in place, one being Yshown secured in the position assumed in the rst stage of tensioning thereof and the other being shown secured in its nal tensioned position; and also showing one of the tension-applying means associated with the anchorage saddles in alternate positions thereto for tensioning said reinforcement members respectively into their above-mentioned stressed positions;

Fig. 6 is an enlarged end elevat-ion of the anchorage saddle with attached road form of Fig. 5 taken substantially on line 6-6 and showing the road form partly in section;

Fig. 7 is an end view of one of the stepped-wing tensioning coupling members as viewed from the threaded (open socket end thereof;

Fig. 8 is a side elevational view of the coupling member shown in Fig. 7 and as viewed from the right side thereof;

Fig. 9 shows an end portion of one of the metal reinforcement members to be stressed and having secured thereon a swaged tting which is to be received within the socket portions of the coupling members of Fig. 7; and

Fig. 10 is a view of a reinforcement or tension member having swaged fittings on both its ends.

Referring in detail to the drawings, and more specifically to Figure 1 thereof, the stressed reinforced elongated body or structure of cement-concrete constituting one embodiment of my invention is shown in the form of a concrete highway and is generally indicated by the reference numeral 11i. As indicated -at the lefthand end portion of Figure 1 where the concrete section is broken away, there are exposed a number of stressed metal reinforcement members 12 consisting of steel or other metal rods or wires of uniform cross-section, which rods or wires are tobe stretched and brought under tensile stress through the application of yan external force, as will be explained more in detail later. These reinforcement members are placed approximately 12 to 15 inches apart within the side forms 13 and are arranged in oppositelyV inclined groups diagonally with respect to the pavements length for substantially the full width of the pavement, and they lare in contact with each other where they cross, as'indicated at 14. It is to be understood that there may be provided conventional supporting chairs 4 A i (not shown) at the intersections of crossing reinforcements to eliminate the catenary sag thereof prior to the pouring of the concrete. Such a system of metal reinforcements permits the use of rods or wires of relatively short length whose ends are readily accessible to accomplish the bringing of the rods or wires under various conditions of tensile stress during laying of the wet pavement and without interruption of the continuity of the latter.

The road forms 13 are arranged at opposite sides of the pavement during construction thereof and are provided at uniform intervals -along their inside faces with a series of demountable anchorage saddle members 15 to each of which are anchored two oppositely inclined diagonallyextendingreinforcement members 12 which `are brought into an ultimate condition of predetermined tensile stress in a manner and by means as will be hereinafter described. As shown in Figst 2, 3 and 4, the road forms 13 are held in place during construction of the highway by means of form stakes passing through apertures in a series of brackets 16, as presently will be described, these brackets being disposed at uniform intervals longitudinally along the outer faces of each of the road forms. Accurate spacing between the -road forms is accomplished by means of plates 17 arranged for longitudinal sliding movement on the bottom of the form between suitable transversely spaced labntments 13 and 19, the plates 17 each being formed with an angular slot 20 through which is driven the usual form stake 21 which passes through a central transverse slot 22 of the web 23 of the bracket 16 and like underlying transverse slot 23 in the base of form 13 (see Fig. 3) thus xedly anchoring the form to the subgrade. By driving the plates 17 lengthwise of the forms, in either direction, the opposed road forms 13 may be moved in or out whereby the spacing between them may be accurately adjusted to a prescribed dimension. Y

As illustrated in Figs'. 3 and 5, the vertical sides of the road forms 13 at each location of an anchorage saddle member 15 is provided with lsuitable -apertures 24 for the fastening bolts 24 which support the anchorage saddle members 15 `in initial assembly on the inside face of the side forms' 13, and a slotted opening 25 for passing of a tension-applying dev-ice 26 temporarily associated with each anchorage saddle, as will be hereinafter described in detail. The same slotted opening 25 serves for passing the tension-applying device 26 for alternate connection with a pair of socketed tensioning coupling members 23 connected with the ends of the reinforcing rods 12 associated with each of the anchorage saddles 15 and having step-by-step interlocking engagement therewith as the rods are placed in tension, `as will be hereinafter described. The slotted openings 2S and the anchorage saddle members 15 on opposite sides of the road forms are in alignment transversely of the pavement, as represented in Fig. l.

The single rods or wires, of uniform cross-section 'employed `as the reinforcement or tension members 12 in accordance with the practice of my invention are preferably of cylindrical form as shown in Figs. 6, 9 and 10, and made of a steel with elastic limits in therange of from l90,QGO-220,000 pounds per square inch. The words rod-s or wires of uniform cross-section as herein used, are intended Ito specify a standard rod or wire which is commercially smooth and whose'circular crosssection is `approximately uniform to such a degree as shall be readily and commercially feasible in the process `of manufacture. A rod or wire of hard drawn steel of approximately 5%; inch in diameter and a tensile strength of 195,000 pounds per square inch is found to be advantageously suited Afor this purpose in practice. Also, -a G inch diameter steel wire having a tensile strength on the order ofV between 200,000-216,000 pounds per square inch also would be practicable. It is Ifound that when a 3/s inch steel rod of the type hav- .5 ing the above-mentioned tensile strength Value is stressed under a tension on fthe order of 60% of its elastic limit value, the elongation for `a 48 foot length will be on the order of 2.4 inches which would be the ultimate elongation or extent to which each reinforcing tensioning rod has been stretched at the completion of the final tensioning stage when the tensioning force is applied to one end only of the reinforcing rod. If the reinforcing tension rods or wires 12 are placed under the required tensile stress through an external pulling force applied to bo-th ends of each rod or wire, then for a rod of the above-stated diameter and elongation characteristics the extent `of stretch or elongation obtained when stressed under a tension on the order of 60% of its elastic limit value would be 1% inches and, therefore, the socketed tensioning coupling members 28 then would be only half the length required when tensioning is effected at only one end of each of the rod or wire reinforcements.

In Figs. 9 and l0 I have shown a reinforcing tension member 12 which consists of a rod made of high tensile eel having athxed a predetermined distance apart thereto a pair of swaged ferrules 30 with the ends 31 of the rod extending through and projecting a short distance beyond Ithe ferrules. Distance L between the opposed inner ends of the ferrules 30 must be accurately determined for the particular type and size of steel rod employed so that `a prescribed initial tension will be applied to each tension member prior to pou-ring of the wet concrete within the side forms 13. Prior to swaging the ferrules 3o on the ends of each of the reinforcing rods 12 the rod is inserted through the socketed coupling members 2S. The portion of the rod 12 on which the ferrules 30 are swaged have been prepared with surface indentations into which ferrule metal cold ows under swaging and so develops the required stripping strength.

The anchorage saddle members 15 are of identical construction so that the description of one will suiiice for the others, and as shown in Figs. and 6, each comprises an open-sided hollow casting having oppositely inclined oblique end walls 33 and 34 connected by an inwardly curved front wall 35. The end walls 33 and 34 as well as the top and bottom walls 36 and 37 respectively terminate in a vertical plane at the open back of the casting whereby the latter may be mounted in at seating engagement with the inside face of the road forms 13 when attached thereto by the fastening bolts 24 which have threaded connection with suitable web portions 38 cast in the anchorage saddles. Suitable top and bottom stabilizing iianges 39 and 40 may be provided bordering the open side of the casting, if desired. As shown in Figs. 5 and 6, the end walls 33 and 34 of the anchorage saddle casting have a butterfly-shaped opening 41 and an elongated `slotted opening `42 therethrough. Mounted within the butterfly-shaped openings 41 of each anchorage saddle for both longitudinal adjustment therein and slight 4axial rotation thereof vare two of the socketed tensioning coupling members 28 provided for connecting the tension-applying device 26 to the ends of the pair of diagonally-extending reinforcing rods 12 during tensioning thereof and for securing them in their various tensioned states to their particular anchorage saddle members 15. As best shown in Figs. 7 and 8, the tensioning coupling members 2S are alike in their structure in which each has an elongated body portion 44 formed with an enlarged axial bore 45 extending inwardly from one end and adapted to accommodate the ferrule 30 of a reinforcing rod 12 and having a central hole '46 at the other end for insertion therethrough of the main rod portion of the reinforcing member 12. The entrance end of the bore 45 is internally threaded as indicated yat 47 for connection with the tension-applying device 26 as will be hereinafter described. The body portion 44 is of partially cylindrical formation as shown in Fig. 7, and -it is provided exteriorly on opposite sides thereof with wing extensions 4S and 49 each having a series -of lip steps 50, 51 land 52 for locking, in turn, behind the back edge of portions of the end walls 33 and 34 bordering the circular portions of the butterfly-shaped openings 41 thereof through which pass the cylindrical body portions 44 of the coupling members 28. The positions of the lip steps 50, 51 land 52 are determined by the elongation characteristics of 4the particular rod or wire structure employed for the reinforcing tension members 12. The lip steps 50, 51 and 52 respectively are situated at identical positions but on reversed faces of the wing extensions 44t; and 49 so that at the completion of each tensioning stage the corresponding flip steps of both Wing extensions will be interlocked at the same time with the end walls 33 and 34 of the anchorage saddle members 15.

For stretching and initially tensioning the reinforcing tension members 12 so as to draw up the coupling members 28 in the iirst stage of tensioning of the rods or wires, Ia hand lever device 55 may be used of a type such as depicted in Figs. l and 5, said device having a fulcrum arm 56 one end of which is provided with a lug 57 adapted to be fulcrumed on the anchorage saddle casting 15 through the aperture 42 so' that when the coupling 28 is forced inwardly of the saddle casting 15 by the pad 57 on the operating handle of the device 55 the iirst lip step 50 will engage behind the inside edges of the butterfly slots of the openings `41 in the end Iwalls 33 and 34 of the casting and be held thereby after the individual coupling members 28 are given a little twist about their axes, as depicted in Fig. 6. The tension- -applying devices 26 are attached to each socketed coupling member 28 to effect the slight twisting movement thereof above-mentioned, and before pouring of the concrete, to assure not losing the first stage hitch in the tensioning operation as well as for drawing it up in the remaining two stages -of tensioning. As shown in Fig. 5, this tension-applying device 26 comprises a long draw screw 58 having threaded connection at its lower end with the internally threaded socket portion 47 of a coupling member 28, this draw screw passing through the slotted opening 25 in the road form 13 and a suitable aperture in la transverse web member 59 of the saddle casting 15.

A nut 60 having threaded connection with the outer end v of the draw screw 58 bears against the outer end of a metal sleeve member 61 which is loosely mounted on the draw screw and has its inner end seated against the confronting face of the web member 59. Manual turning of each of the nuts 60 by suitable ratchet wrenches in an `appropriate direction operates to draw up the socketed coupling members 28 into the anchorage saddle members 15 'to a point where the lip steps 50 of the Wings 48 and 49 can shoulder seat by being engaged behind the buttery slots 41 and locked thereby upon slight axial twisting movement of the couplings by means of a wrench applied to the squared head 58' of the draw screw 58.

In the second stage of tensioning, tension is applied to the reinforcement members 12 after the concrete has been poured betw'een the road forms 13 but before appreciable setting of the concrete has started, the socketed coupling members 28 at this time being further drawn into the anchorage saddle members 15 until the intermediate lip steps 51 of the wings 48 and 49 can shoulder seat by being engaged behind the butterfly slots 41 and locked thereby upon being turned into a twisted position by wrench turning the squared head 58'. After the concrete has further set on the order of an hour or more, additional tension is applied to the reinforcement members 12 by the draw screw tensioning device 26 to further draw up the socketed coupling members 2S in the anchorage members 15 to their third step 52 following which they are twisted into locking engagement with the end walls 33 and 34 of the anchorage saddle members 15. Obviously there will be no restraint to the torsional reaction ofthe coupling members 2S during twisting `by the draw screw 58 by wrench turning its head 58' in the first or initial stage of tensioning of the reinforcement members 12. However, in the second stage of tensioning of the reinforcement members 12 it is found necessary to subject the couplings 28/to torsional force suicient to twist the wings 4S and 49 in the Wet concrete Yto bring about second stage locking of the couplings by meansrof the step lips 51. To assure this second stage locking of the couplings 28 I effect the requisite additional torsional reaction on the draw screw 58 through use Vof the wrench on the squared end 58 thereof. This procedure also is employed for securing additional torsional force to effect third stage locking of the couplings 2-8 to their respective anchorage saddle members 15 by means of the step lips 52, in which instance the wings 48 and 49 of the coupling 28 will have been drawn substantiallyV completely inside of the saddlercastings and, consequently, do not form a restraint to twisting which otherwise would be impossible in hardened concrete.

The reinforcing tensioning members 12 may be provided throughout their eiective length with a coating of grease, asphalt, or similar material, or may be jacketed with a vinyl or simiiar plastic, so as to break bond with the concrete .as-may be necessary in the final tensioning step. After the concrete has hardened and set, the draw screw 53 of the tension-applying device 26 then is unscrewed from the socket portion of the coupling member 2S and the bolts 24 which hold the anchorage saddle members 15 in assembly with the road forms 13 are removed so that the road forms can be stripped from the iinished pavement for installation and use in the construction of subsequent pavement laying operations. The anchorage saddle members 15 with the socketed coupling members 28 left inside remain embedded in the concrete after stripping of the road forms 13.

A particular advantage in stressing reinforced concrete structures of the class described in accordance with my invention, is that the pavement slab can be made considerably thinner to withstand the same loading as a pavement slab having the common fabric type of reinforcement. The design and proper arrangement of the pretensioned diagonal reinforcing-tension members permit compression of the concrete thereby in two directions at the same time, viz., laterally and longitudinally, with the complete elirnination of all tensile stress in the concrete body. Furthermore, in making the pavement in accordance with my method, all joints can be eliminated so that continuity of the pavement may be obtained. Thus, a dual lane highway may be poured, two lanes at a time, omitting the center longitudinal joint as Well as the usual transverse joints commonly used in a non-prestressed construction.

The term concrete as used herein comprehend's mixtures of Portland cement, or other hydraulic cement, with water Vand any other suitable material such as sand and/ or crushed stone.

It is to berunderstood that stranded Wire structures can be substituted for the rod or wire reinforcing members and jacketed in the manner above-explained for the purpose of breaking bond ywith the concrete.

While one embodiment of my invention has been shown 3 and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims. 1

What is claimed is:

l. The method of making a prestressed reinforced concrete structure of considerable length and considerable width, which comprises placing spaced apart longitudinal non-rigid side forms in position, anchoring said side -forms to the ground without rigid connection therebetween, connecting oppositely inclined groups of diagonally-extending reinforcing tension members having a bondpreventing sheath thereon to said forms, then pouring wet concrete around said tension members between said side forms, tensioning each of said tension members after the Wet concretehas been poured but While it is still plastic so as to stretch the tension members into final position, and further tensioning each of said tension members after the concrete has reached its initial set so as to stretch the tension members to a position where they are held in a condition of tensile stress to maintain theconcrete in a continual state of compression.

2. The method of making a prestressed reinforced concrete structure of considerable length and considerable Width, which comprises placing longitudinal non-rigid side forms in spaced apart relationship, anchoring said side forms to the ground without rigid connection therebetween, providing anchorage members on the inner side of said forms, connecting oppositely inclined groups of diagonally-extending reinforcing tension members having a bond preventing coating to said anchorage members, then pouring wet concrete around said tension members between said side forms without substantial bond between the concrete and tension members, tensioning each of said tension members after the wet concrete has been poured but while it is still plastic so as to stretch the tension members in their anchorage members rwhere they are held in their `final position while thus stressed, and further tensioriirvy each of said tension members after the concrete has reached its initial set so as to stretch the tension members to a position where they are held in said anchorage members in a condition of tensile stress to maintain the concrete in a continual state of compression.

References Cited in the iile of this patent UNITED STATES PATENTS 1,640,739 Trester Aug. 30, 1927 2,371,882 Freyssinet Mar. 20, 1945 ,2,408,149 Miller Sept. 24,k 1946 2,413,990 Muntz Jan. 7, 1947 2,554,755 Sechaud et al. May 29, 1951 2,590,685 Coi Mar. 25, 1952 2,609,586 Parry Sept. 9, 1952 2,637,889 Dulleck May 12, 1953 2,655,846 Freyssinet Oct. 20, 1953 2,695,754 Karig Nov. 30, 1954 FOREIGN PATENTS .1,097,089 France Feb. 9, 1955 OTHER REFERENCES Engineering News-Record, Apr. 12, 1951, page 37.

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