US2690667A

US2690667A - Stressed concrete beam

Info

Publication number: US2690667A
Application number: US128937A
Authority: US
Inventors: Mauquoy Jean
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-11-29
Filing date: 1949-11-23
Publication date: 1954-10-05
Anticipated expiration: 1971-10-05

Description

Gct. 5, 1954 J. MAUQUOY STRESSED CONCRETE BEAM 4 Sheeis-Sheet 1 Filed NOV. 23. 1949 m M TUP Q NAM I M Z A E M 7 Y B ATTO RN EYS Oct. 5, 1954 J. MAUQUOY 2,690,657

STRESSED CONCRETE BEAM I Filed NOV. 25, 1949 Y 4 SheetsSheet 2 FIG. '4

INVENTOR JEAN MAUQUOY BY mxwiafld m ATTORNEYS 1954 J. MAUQUOY 2,690,667

STRESSED CONCRETE BEAM Filed Nov. 23. 1949 4 Sheets-Sheet 3 &

INVENTOR JEAN MAUQUOY BY mm, (Loam M ATTORNEYS Get. 5, 1954 J. MAUQUOY 2,690,667

STRESSED CONCRETE BEAM Filed Nov. 25. 1949 4 Sheets-Sheet 4 FIG. 9

INVENTOR JEAN MAUQUOY BY Ema, w M

ATTOR NEYS Patented Got. 5, 1954 UNI'EEE STATES ?ATENT OFFICE Claims priority, application Belgium November 29, 1948 2 Claims.

The present invention relates to reinforced concrete structures in which the reinforced concrete elements are compressed during and after setting by subjecting the reinforcements to tension during the fabrication of the structure and in the use of the finished structure.

Reinforced concrete beams which are fabricated under conditions which prestresses the concrete are well known and widely employed. The reinforcing elements of prestressed concrete beams serve to subject the concrete to an initial compression and to thereby partially equalize the tensile forces distributed on the beam under service loads. In order to tension the reinforcing elements, it has been necessary to use costly, heavy and relatively complex tensioning apparatus. The tensioning devices used in the prior art have included heavy jacks, locking devices, wedges, hooped cones, etc., and the use of these have required careful supervision and a high degree of skill. The advantages of prestressed concrete are well understood but the application of these structures to particular uses has been limited due to the high cost of fabrication and due to the difficulties involved in fabricating the structures on the job in rural areas at a point remote from the technical facilities which are commonly had in urban areas, Further, without recourse to special measuring instruments, it has been substantially impossible to obtain a ready verification of the tension required with variations of the distribution in service loads in structure already assembled and in use. There is a tendency for the reinforcing elements to flow and the distribution of the load is thereby changed. This contributes to a reduction in the load carrying capacity of the beam and further requires changes in design based upon this ex-- perience. Accordingly, the safety of the finished structure is affected, and it has been necessary to over-design in order to compensate for the diiiiculties which have been encountered.

These difficulties are obviated by the present invention by providing a plurality of abutments at intermediate spaced apart points along an elongated beam which serve to bear guiding means positioned on opposed surfaces of these intermediate abutments, and by providing end abutments which bear guiding means which are positioned on the external arcuate surfaces thereof, these aforementioned guiding means serving to confine a plurality of wire reinforcing elements looped about the end abutments, spliced between the ends, and tensioned by bearing'members' and gripping means. By virtue of the plurality of intermediate spaced apart abutments, controlled and separate tensioning is permitted along limited linear portions of the concrete structure. Thus, variations in the characteristic distribution of the load can be compensated by such tensioning in a reproducible and simple manner. The repair of broken reinforcing wires is also facilitated since shorter sections can be readily repaired without unduly stressing the weakest part of the structure, the concrete. The displacement of the abutments by means of the tensioning devices securely held in place by the guiding means effectively is directed in a plane perpendicular to the axis of the reinforcing means and thereby accords directly counter to the forces which are due to the service load.

An object of the present invention is to provide a reinforced concrete structure comprising an elongated beam having abutments with planar and arcuate surfaces at each end of said beam and having a plurality of intermediate spaced abutments in alignment with the end abutments, all of the abutments projecting from a common side of said beam. Guiding means which are positioned on opposed surfaces of the intermediately spaced abutments, guiding means positioned on external arcuate surfaces of the end abutments, a plurality of wire reinforcing elemerits which are looped about the ends of the abutments and which bear on both of said guiding means, splicing means for connecting overlapping, non-continuous ends of the wire elements, and tensioning devices which comprise a pair of bearing members on opposite sides thereof, gripping means which include a pair of opposed channel shaped elements to engage the wire on opposite sides of the beam between the abutments, and a threaded rodfitted with a tensioning nut interconnecting the pair of channel shaped elements, said tensioning nut engaging said rod to draw the channel elements toward each other against the resistance of the reinforcing wire elements to thereby impart the necessary tensile stresses to said reinforcing eiemerits and to impart the desired stresses to said concrete structure.

A further object of the invention is to provide the structural modifications hereinabove described to an elongated substantial linear beam or an arcuate beam such as an arch and to improve the tensioning. action of the wire reinforcing elements by interposing suitable lubrieating surfaces, such as zinc sheets between the channel shaped elements of the gripping means and between the wire and the guiding means,

3 whereby the distribution of tension along the wire is more readily facilitated.

Other and further objects of the present invention will appear from the more detailed description set forth below, it being understood that such detailed description is given by way of illustration and explanation only and not by way of limitation, since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

In connection with that more detailed description, there is shown in the drawings, in

Figs. 1 and 1A, sectional views of abutments, guiding means and reinforcing elements for post stressing the top and sides of a rectangular unitary concrete structure;

Fig. 2, a sectional view of a modification of a detail for the gripping means of Fig. 1;

Fig. 3, a sectional view of a cone locking embodiment for fixing the wire reinforcing elements at the ends thereof to obtain a firm anchorage of these with respect to the concrete beam;

Figs. 4 and 5, sectional views respectively of the detail of splicing;

Figs. 6 and 7, a face view and a sectional view respectively of the gripping means of the present invention;

Figs. 8 and 8A views in perspective of a straight beam and lubricating sheet in accordance with the invention; and

Fig. 9, a view in perspective of an arch in accordance with the invention.

Figs. 1-3 illustrate the use of wire transverse reinforcing elements 4 such as cables, the ends of which are embedded in the sides of the rectangular concrete beam 2 and said cables disposed in an undulating or zig zag trajectory to cross-tension the longitudinal reinforcing elements which are also embedded at their ends in the sides of the reinforced concrete beam 2. The transverse reinforcements 4 pass through and are secured at their upper and lower ends by the guiding means 6, comprising a metal sleeve to which is welded the projecting metal portion 6 as shown in Fig. 1A and said guiding means 6 likewise serves to guide and restrain the longitudinal reinforcing elements. The guiding means 6 are disposed in alignment with abutments which are integral with and project downwardly from the top of the reinforced concrete beam. The upper pair of guiding means 3 shown in Fig. 1 are mounted integrally with these intermediate abutments. The gripping means 24 shown in Fig. 1 comprises a rod threaded at the ends and fitted with nuts, which rod is inserted between the longitudinal reinforcing elements to tension these in a vertical direction. The rod and nuts 24 also join the transverse reinforcements 4 which serve to cross brace the longitudinal reinforcements to the common guiding point of engagement of guiding means is. In Fig. 2 the rod and nuts 25 are applied to the cross or transverse reinforcements 4 and thereby tension the horizontal reinforcements at the point of engagement of these with the guiding means 6. Thus, there is illustrated various ways of tensioning the sections of the reinforcing elements between the guiding means 6 which may be disposed directly from the abutments integral with the top of the beam or may be disposed through the connection of the tensioning nuts along reinforcing elements which are disposed below the upper horizontal tensioning wires. The three pairs of horizontal ten- 4 sioning wires provide a control of both vertical and lateral tension as shown in Figs. 1 and 2, whether the tensioning rod and nuts serve to vertically tension the horizontal rows of wires together with the transverse wires (Fig. 1) or whether the rod and nuts serve to tension the transverse \vires only as in Fig. 2.

The trajectories of the reinforcing elements shown in Figs. 1 and 2 may be varied in known manner to provide for a wide range of tensions in application to concrete structures of various size. The ends of the tensioning elements are shown to be embedded in Figs. 1 and 2, but in certain cases, one may use hollow sheaths 1, of metal or concrete, which are encased in the concrete beam and which are provided with metal cones 8. The cones may be made of concrete or of other hard material, if desired, as long as the necessary strength characteristics required for anchoring the reinforcing wire or cable are setisfied.

A preferred way for tensioning the concrete beam and the construction which results thereby is illustrated in Figs. 5, 8 and 9.

Fig. 4 shows a looping of the wire reinforcing elements about the arcuate surface of end abutments it), which end abutments project from a common side of the beam. The ends of the cable are spliced by means of splicing elements shown as S in Fig. 4. The overlapping and non-continuous ends of the loop are spliced together by means of the splicing means 9 and each of the splicing devices consists of a pair of U-shaped metal elements 21 joined to each other by nuts 28 and bolts 29, the nuts and bolts being alternately vertical and horizontal as is shown in the detail of Fig. 5. The alternation of the bolts in a vertical and horizontal arrangement as in Fig. 5 effectively constrains the reinforcing wire or cable so that the cable will periodically undulate in both the vertical and horizontal plane and the tendency for the splicing device to twist under tensioning is thereby reduced.

The reinforcing members fixed to the concrete (as in Figs. 1-3), are maintained in a spaced apart relationship at intervals by means of guiding means 6 the function of which is to keep the reinforcements spaced apart at the places where the latter are in contact with the end fixing means.

As shown in Figs. 8 and 9, the ends of the reinforcements may be suitably and securely attached to stress the concrete beam by attachment to abutments rigid with the beam itself. In Fig. 8, a linear beam I4 is shown which is formed with abutments ID at the ends thereof, these abutments having planar and arcuate surfaces with intermediate spaced abutments, 3 and 3, these in alignment with the end abutments ill and all of the abutments projecting from a common side of said beam.

In Fig. 9 the elongated concrete beam is an arch and the end abutments [0 of the arch are the respective ends of the arch itself. The reinforcing wires I are looped around the arcuate outer surfaces of the straight beam or arch in Figs. 8 and 9 so as to provide no sharp corners which will tend to bend or set the wire reinforcements in the stretched position. The longitudinal surfaces of the end abutments :0 may be planar or arcuate (see elements ill in Fig. 9). It is necessary that the respective end and longitudinal surfaces of the abutment I0 satisfy the requirement that the abutment provide no acute angle which would adversely affect the tensioning of the wire.

To further assist the tensioning of the reinforcing wires I, it is of value to lubricate the areas of engagement of the intermediate abutments 3 and the end abutments It! with the r inforcing elements I by means of suitable lubricating sheets 25, such as zinc sheets. This facilitates the uniform distribution of tension along the entire length of the reinforcing wire. Accordingly the arcuate surfaces of the end abutments It in'Figs. 8 and 9 provide the means which fix the loops of the tensioned reinforced wires to the beam and the opposed surfaces of the intermediate abutments 3, with or without the lubricating sheets 26, provide the guiding means to provide a substantial horizontal alignment of the reinforcing wires I with the loops of the wire under tension on the end abutments I 0.

As shown in Figs. 8 and 9, the tensioned wires are alternately looped about and guided on the intermediate abutments 3, each of these intermediate loops in horizontal alignment to the other and these further tensioned by gripping means II which serve to tension cable pairs between the intermediate spaced abutments and preferably on opposite sides of at least one of these abutments.

The gripping means I I consists of two channel bars, preferably of metal, which are secured to each other by means of a screw threaded rod and nut I2 and lock nuts I3 (Figs. 6 and 7). The pair of opposed channel shaped elements H engage the wire on opposite sides of the beam between the abutments. The screw threaded rod and nut I2 and lock nuts I3 serve to tension the wires on opposite sides of the beam by action of the tensioning nuts which engages the rod I2 to draw the channel elements I I toward each other against the resistance of the reinforcing wire elements I. The engagement of the rod I2 in the central hole of the channel bars II is shown in Fig. 6. However, the channel elements need not be necessarily completely detached from the rod, since one of the channel elements may be fixed to the rod at its base and the other may be removable with respect thereto.

Under certain circumstances, it may be appropriate to replace one of the two channel elements with an eyelet which is securely attached to or integral with the rod. The gripping means II are suitably retained as a permanent part of the reinforced concrete structure. However, if they are to be removed, equivalent means for holding the tensioned cables in substantially the same relationship must be provided and the gripping means may then be removed.

The straight beam of Fig. 8 may be cast on its base and provided with the end abutments Ill and intermediate abutments 3 in a single casting operation whereafter the tensioning wire elements I, gripping means II, splicing means 9 and lubricating sheets 26 may be arranged to provide a substantially longitudinal alignment of the tensioning and reinforcing elements after the concrete has hardened. The lubricating sheet 26 as shown in Fig. 8A comprises a zinc metal outer facing 26' on the backing. The guiding of the tensioning loops of the reinforcing elements I may be facilitated by providing notches in the abutment (not shown) and the beam is readily removed from its base after the necessary tension has been applied by means of the tensioning devices.

As is shown in Fig. 9, the concrete arch is provided with intermediate steel abutments 15 which are embedded in and integral with the concrete arch. The lower ends of the intermediate abutments I5 are fitted with suitably dimensioned enlarged rectangular end portions so as to maintain the alignment of the tensioned loops constituting the wire reinforcing elements I, as this alignment is determined by the engagement with the end abutment portions it? of the arch. lhe guiding means 3 of Fig. 9 may be retained on the elements I5 by means of a screw thread connection of the latter to engage corresponding threads of the former. The fitting of the guiding means 3 by means of screw threads with elements i5 provides for the separate adjustability of the height of each of the guiding means along each of the intermediate abutm nts, and this further facilitates the simplicity of aligning the loops of the reinforcing cables or wires.

When the concrete has hardened, the cables I, which are of special steel, are placed in position as previously described, and are subjected to tension by means of the gripping appliances II, I2, I3.

Owing to the tensioning of the tie, the arch rises slightly from its centering, and the removal of the centering is then easily effected without any special precaution.

This method of procedure renders it possible to produce reinforced concrete arches of wide span resting upon columns. The uncertainty with respect to the spacing of the supports is eliminated.

The reinforcements may themselves be subsequently encased in concrete, or may be protected by anti-rust agents.

This procedure enables the pull or the tensions of the reinforcements to be measured, and, should occasion arise, to be modified and thereby corrected. It also renders it possible to establish a regular distribution of the tensions in all the elements of the reinforcement. In the event of fiow of the concrete or of the reinforcement it is possible to correct the losses of tension and the increases of rise, and to correct cracks by a fresh gripping of the cables. It is also possible to replace successively any elements of the reinforcement that might happen to deteriorate.

Finally, in the event of the work being required to support a supplementary load, it is possible to add further reinforcements.

It is thought that the invention and its advantages will be understood from the foregoing description and it is apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing its material advantages, the forms hereinbefore described and illustrated in the drawings being merely preferred embodiments thereof.

Having thus disclosed the invention what is claimed is:

l. A reinforced concrete structure comprising an elongated beam having abutments with planar and arcuate surfaces at each end of said beam and having a plurality of intermediate spaced abutments in alignment with the end abutments, all of the abutments projecting from a common side of said beam, said structure fitted with guiding means, said guiding means being positioned on opposed surfaces of the intermediately spaced abutments, other guiding means positioned on the external arcuate surfaces of the end abutments, a plurality of wire reinforcing elements looped about the ends of the abutments and bearing on all of said guiding means, splicing means connecting overlapping ends of the wire elements and forming said elements into continuous loops, a plurality of tensioning devices disposed between the spaced abutments and engaging said continuous loops, each tensioning device including gripping means and a threaded rod having a nut threadedly engaged therewith, said gripping means comprising a pair of opposed channel-shaped elements having the flanges thereof disposed toward each other, and the webs thereof engaging the continuous loops on opposite sides of said concrete structure, said threaded rod passing through the webs of said pair of opposed channel-shaped elements and said nut drawing the opposite sides of said loops toward each other against the resistance of said wire and thereby imparting substantial tensile stresses to the wire.

2. A reinforced concrete structure as recited in claim 1 and including zinc lubricating material on the wire engaging surfaces of said guiding means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 293,427 Dibble Feb. 12, 1884 455,687 McCarthy July '7, 1891 460,213 McCarthy Sept. 29, 1891 852,898 Owens et al May 7, 1907 946,211 Flagg Jan. 11, 1910 2,155,121 Finsterwalder Apr. 18, 1939 FOREIGN PATENTS Number Country Date 144,193 Great Britain June 10, 1920 338,934 Great Britain Nov. 25, 1930 413,109 Great Britain July 12, 1934 464,361 Great Britain Apr. 16, 1937 541,160 Great Britain Nov. 14, 1941