US3384395A

US3384395A - Anchorage for dynamically stressed steel wire and improved method for cold-upsetting an anchor employed in conjunction with the aforesaid anchorage

Info

Publication number: US3384395A
Application number: US371218A
Authority: US
Inventors: Brandestini Antonio
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-05-29
Filing date: 1964-05-29
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21

Description

y 1968 A, BRANDESTINI 3,384,

ANCHORAGE F0 YNAMICAL STRESSED EL WIRE AND IM V M OD F D-UPS TING A OR EM YED IN JUNG I N WI THE AFORESAID ANCHOR Filed May 29, 1964 2 Sheets-Sheet l INVENTOR ANTONIO BRANDESTINI ywM/dgw ATTORNEYS lOO- m (\1 E A 2 9s y 1968 A. BRANDESTINI 3, 3

ANCHORAGE FOR DYNAMICALLY STRESSED STEEL WIRE AND IMPROVED METHOD FOR COLD'UPSETTING AN ANCHOR EMPLOYED IN CONJUNCTION WITH THE AFORESAID ANCHORAGE Filed May 29, 1964 2 Sheets-Sheet 2 45 O as a K 8 0 45 88 I04 I20 140 I60 kg/mm FIG.6

FIGS INVENTOR ANTONIO BRANDESTINI BY aW/zZ/QM ATTORNEYS United States Patent 3,384,395 ANCHORAGE FOR DYNAMICALLY STRESSED STEEL WIRE AND IMPROVED METHOD FOR COLD-UPSETTING AN ANCHOR EMPLOYED IN CONJUNCTION WITH THE AFORESAID ANCHORAGE Antonio Brandestini, 60 Alte Landstrasse, Kusnacht, Zurich, Switzerland Filed May 29, 1964, Ser. No. 371,218 Claims. (Cl. 28720.3)

ABSTRACT OF THE DISCLOSURE An anchorage for dynamically high stressed steel wire of the type wherein the wire passes through a bore in a support and is supported thereon by means of an upset anchor head. To provide a high-quality anchorage resisting dynamical stress, i.e. variable traction, the anchorage uses a support with a bore which over a portion of its length is widened to form a suitable seat for the upset anchor head, which anchor head partly extends freely into the non-widened portion of the bore of the support.

The present invention relates to an improved anchorage for dynamically stressed steel wire of the type wherein the wire passes through a bore in a support and is supported thereon by means of an upset anchor head. The present invention also relates to an improved method for cold-upsetting an anchor head used in connection with an anchorage of the above-mentioned type.

The provision of a high-quality anchorage for high resistant wires or cables (diameter e.g. up to millimeters, resistance e.g. 120-200 kg./mm. is very important, especially with regard to its behavior during dynamical stress (variable traction), e.g. in suspension bridges, reinforced-concrete and mechanical engineering.

A number of solutions are already known to the art from actual practice:

1) Grouting-anchorage: the ends of the wires are anchored individually or conjointly in a metallic substance (suspension bridges) or in mortar or concrete (reinforcedconcrete engineering) and are held by adherence. This kind of anchorage is especially adapted for small wire diameters; for larger wire diameters it is necessary to use specially shaped wires and great anchorage lengths, resulting in relatively expensive constructions and, in reinforced-concrete engineering, in a most unfavorable initiation of the forces.

(2) Screw-anchorage: each end of the wires or cables, mostly steel-bolts or bars, is suitably threaded and then anchored by means of a screwed nut. For this kind of anchorage it is necessary that the wire possess a relatively large diameter. The threading of high resistant steel-bolts is difficult and for long span lengths also requires long threads. Furthermore, in this instance there is always a risk of damaging the thread.

(3) Key-anchorage: the wire ends are anchored individually or in bunches by means of keys. The disadvantages of key anchors are known; they do not permit a narrow arrangement of the different wires of a bunch and, furthermore, there is always a risk of an uncontrollable slipping of the wires.

(4) Presstube-anchorage: a steel tube is drawn up on the slightly spread wire ends of a wire bunch from the other wire ends. If the wires are suitably shaped it is possible to provide individual wires with an anchor in that a steel tube is pressed onto said wire. This method permits only to anchor specially shaped wires (mostly litz wire).

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(5) Warm-upset rivet-anchorage: the wire ends (especially rods and rivets) are heated and deformed to heads by means of a jumper. In the case of conical flush rivet heads, the heated rod end is pressed into a die. This method, known in steel and mechanical engineering, is not applicable for extreme resistant steel wires because the warm upsetting results in a considerable loss of resistance.

(6) Cold-upset wirehead-anchoragez the wires are upset at their ends to form balls and are laid upon a fiat steel surface. This method has proven to be particularly successful in reinforced-concrete engineering. This anchorage has a support provided with at least one bore for the passage of the steel-wire, such wire being supported on the support by an upset anchor. The present invention also starts from such type of anchorage. In the case of a steel wire which is dynamically high-stressed, only an insufficient anchorage is possible if, as in well known methods, the bore at the support is cylindrical over its whole length and if the upset anchor is a ball head having. a flat contact surface extending at right angles with respect to the axis of the wire.

The anchorage for a dynamically stressed steel wire in accordance with the present invention is characterised by the features that, the bore of the support widens outwardly in funnel-shaped manner over a portion of its length, to thereby form a seat for the upset anchor head which is substantially conically widened towards its free end, and that a portion of said anchor head extends freely into the non-widened portion of the bore of the support.

Due to the fact that the substantially conically widened anchor head extends into the portion of the bore which is not widened, there exists relatively great play between the actual wire and the aforesaid non-widened portion of the bore. Thus, any contact between the wire and the wall of the bore is avoided. Furthermore, since the smallest cross-sectional area of the wire, i.e. the transition location between anchor head and cylindrical wire, is not in contact with the seating surface, the aforesaid transition location is only subjected to tensile stress. Greater and non-pure tensile stresses are encountered within the zone of the seating surface, so that the most loaded cross-section is greater than the effective crosssection of the wire.

In a preferred form of the invention the axial length of the anchor head is at least twice the length of the seating surface of the support, whereby the support contacts the anchor head within the outer portion thereof and at an axial distance beneath its greatest cross-sectional area. The angle of inclination of the seating surface relative to the bore axis is at maximum 30, but at maximum equal to the greatest angle of inclination of the anchor head relative to the wire axis. The gener-atrix of the anchor head surface may be an S-curve. This results in an improved distribution of the load acting upon the anchor head.

The present invention is also concerned with an improved method for cold-upsetting an anchor head employed in connection with an anchorage provided in accordance with the teachings of the invention. This method is generally characterized by the features that, the wire is engaged and clamped in a clamping guide between two clamping jaws, the guide being progressively widened towards its end portion on the side of a jumper, with the wire end projecting past the jaws over a predetermined length, the jumper is then pressed down over a predetermined length thereby pre-upsetting the projecting wire end without coming in contact with the wall of said guide, the thus pre-upset wire then is withdrawn into its initial position and this is followed by a second pressing down of the jumper over the same length to give the final shape to the wire end, the guide portion of the clamping jaws serving as a die for this second upsetting operation.

It is therefore, an important object of the present invention to provide an improved anchorage for dynamically stressed steel wire ensuring for a highly reliable and safe anchoring between the Wire and its support.

A further important object of the present invention pertains to an improved method for cold-upsetting an anchor head employed in conjunction with the improved anchorage of the present invention.

Other features, objects and advantages of the invention will become apparent by reference to the following detailed description and drawings describing illustrative embodiments of anchorages produced according to the teachings of the present invention as well as to the inventive method for cold-upsetting an anchor head employed in conjunction with the improved inventive anchorages, wherein like reference numerals denote similar or analogous elements, and in which:

FIGURE 1 is an axial sectional view depicting the upsetting of an anchor head for an anchorage fabricated in accordance with the teachings of the present invention;

FIGURE 2 is a cross-sectional view taken along lines IIII of FIGURE 1;

FIGURE 3 illustrates in axial sectional view a first embodiment of anchorage produced according to the invention, using a wire having an anchor head which has been made in accordance with the method shown in FIG- URE 1;

FIGURE 4 is an axial sectional view of a second embodiment of anchorage manufactured in accordance with the teachings of the invention, using a wire with a conical anchor head;

FIGURE 5 shows an anchor head produced in accordance with FIGURE 1; and

FIGURE 6 is a diagram graphically illustrating different dynamic tension tests.

Referring now to the drawings, it will be appreciated that the upsetting or jumping of an anchor head upon a wire 1 shown in FIGURE 1, said wire being, by way of example, a cold-drawn steel wire of highest resistance (140-180 kg./mrn. dependent upon the diameter of the wire), is carried out by means of two clamping jaws 2 and a jumper 3. The clam ing guide 4- of the two clamping jaws 2 is formed by two recesses or grooves 401 each possessing an approximately semi-circular cross-section and is progressively widened towards its end portion a at the side of the jumper 3. The clamping jaws 2 are not completely in contact with one another whenthe wire 1 is clamped, so that fins 5 are formed on the surface of such wire in the remaining slot means 5a. The wire 1 is engaged, prior to the upsetting operation, between the clamping jaws 2 in such a manner as to project past the clamping jaws 2 through a predetermined amount or length, as generally indicated by reference numeral 111 in FIGURE 1. The working surface 3a of the jumper 3 is in the same plane E as the end face 1e of the wire 1.

Then, the jumper 3 is pressed down until its working surface 3a is moved from the plane E to the plane E As a result, the projecting wire end la (without coming in contact with the wall of the enlarged wire guide a of the clamping jaws 2) is pre-upsetted to a form as shown at 112 in FIGURE 1. Thereafter, the pre-upsetted wire is released from the clamping jaws 2 and drawn forwardly until its end face 1e is again in the plane E, as shown at 1c in FIGURE 1. On the following, second upsetting stroke of thejumper 3, the wire end is again pressed back into the plane E In so doing, the widened guide portion a of the clamping jaws 2 serves as a die which imparts to the anchor head, together with the partly free upsetting operation, the form shown at id in FIGURE 1.

In FIGURE 5 there is illustrated a wire anchor head In produced in accordance with the aforedescribed method. Its generatrix is an S-curve having a turning point A at about /5 of the total anchor head length I), as viewed from the free end side of the anchor; at A the S-curve which is concave at this location, continuously changes or transforms into the paraxial surface line of the wire.

FIGURE 3 depicts a first embodiment of anchorage provided by means of the wire anchor head 1d. A support 6 in the form of a flat plate is provided with a cylindrical bore 7 allowing the wire 1 provided with an anchor head 1a to pass therethrough. On the supporting side 6a of the support 6, the bore 7 is conically widened over its end portion to provide a conical seat 7a for the anchor head 1d. The dimensions are such that the concave contact surface of the anchor head 1d, formed inside of the half portion adjacent point A and between the points A and A comes into contact with the seat 7a of the support 6, and that the turning point A of the generatrix of the surface of the anchor head 1d lies outside of the aforesaid support 6. At the same time, the greatest portion of the contact surface of the anchor head extends freely into the bore 7 of the support 6, thereby ensuring that the wire 1 can pass with relatively great play (about 10-15% of the wire diameter) through the bore 7 of support 6.

Thus, the Wire 1 cannot positively engage or contact the wall '70 of the bore 7. Furthermore, the smallest cross-sectional area of the wire 1, i.e., the section at the connection or transition location between anchor head 1d and cylindrical wire I will not come into contact with the seating surface 7a and, therefore, said section and the actual or effective wire are only subjected to tensile stress. Greater and non-pure tensile stresses are produced within the zone of the seating surface 7a, so that the most loaded or stressed cross-section lies somewhere in the anchor head In? and is thus greater than the effective cross-section of the wire. Such an anchorage is, therefore, of higher quality than known anchorages, wherein the smallest cross-section is simultaneously the most loaded or stressed section.

The support 6, in the present instance, is formed of a material which is softer than that of the wire It, so that the fins 5 are pressed into the seat 7a of the support 6 upon stretching the wire, and that the conical seating surface 7a of the'support 6 accommodates itself to the slightly convex contact surface of the anchor head 1d. The length of the seating surface 7a should likewise be taken into consideration when selecting the material for the support 6, because with a predetermined tension or pull upon the wire 1, and the smaller the length of such seating surface, the greater the specific surface tension. In order to ensure for a good pressing-in or embedding of the fins 6 both the length and the material of the seating surface 7a must be considered. In order to guarantee for a satisfactory seat of the anchor head at the conical seat 7a of the support 6, the angle of inclination a of the seating surface 7a relative to the bore axis is equal or slightly less than the greatest angle of inclination B of that portion of the contact surface of the anchor head 1d which lies completely within the seating surface 701 relative to the wire axis; the value of the angle a is at maximum 30, yet at least amounts to 8.

In the heretofore described embodiment the seating surface 7a of the support 6 is conical, however the seating surface could also possess a curvature corresponding to the contact surface of the anchor head.

Another embodiment is shown in FIGURE 4. In this case, the anchor head 10:! of the wire 10 and the seating surface 7a have also a maximum inclination of 30, but at least 8, with respect to the wire axis. As best seen from FIGURE 4, the surface 10 lying between the points B and B of the anchor head 10d also projects somewhat past the support 6, but abuts against the supporting surface 7a inside of its half-portion which is nearer the point B Therefore, the conical anchor head 10d extends over at least half of its length freely into the cylindrical bore 7 of the support, ensuring for a relative large play between the bore 7 and the wire 10. The connection or transition between the conical anchor head 10d and the cylindrical wire 10 could also be in the form of a continuous curve.

In the described embodiments the anchor heads 1d and 100 are provided with a flatend face 1e and 10a respectively. Such respective end face may be curved inwardly, at and 21, or outwardly at 22 and 23 as shown in dotted lines in FIGURES 3 and 4 respectively. Since the behavior of such anchorages with dynamic and swinging or vibratory loads gives a certain insight into its quality, the dynamic tension test (high-frequency pulsator) serves as a basis for the technical evaluation of the anchorage. In these tests, with a given lower stress limit, the upper stress limit is reached after two million load alternations, the factor of quality being the swinging or oscillation amplitude reached by this techinque.

In view of the herein considered range of application (suspension bridges, mechanical and reinforced-concrete engineering) a wire material of the best quality and of highest resistance is preferred, e.g. cold-drawn wires of a strength of 140-160 kg./mm. (dependent upon the diameter). In known anchorages an amplitude of oscillation of about 5-15 kg./mm. is reached, dependent upon the load range and on the anchor type. However, for many constructions these values are not sufficient and the engineer is interested in a considerable increase of the same.

The steel Wire anchorage according to the present invention has been especially developed for high dynamical loads. The results of the tests, shown diagrammatically in FIGURE 6 for diiferent load ranges, indicates that there are reached amplitudes of oscillation of -30 kg./mm. ie more than double those of the prior art anchorages noted above. In this figure:

S: denotes amplitude of oscillation under different stress limits for: 1: wire 2: wire anchorage in accordance with the invention,

and 3: well-known prior art wire anchorages.

The range up to about 90 log/mm. is used for suspension-bridge engineering, while reinforced-concrete engineering works with higher values.

While there is shown and described present preferred embodiments of the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. An anchorage for dynamically high stressed steel wire comprising a support provided with a bore through which is adapted to pass a wire, a wire passing through said bore, and including an upset anchor head which is substantially conically widened towards its free end, said bore being widened outwardly substantially funnel-shaped over a portion of its length to provide a seating surface for said upset anchor head, said bore further including a non-widened portion, a portion of said anchor head extending freely into said non-widened portion of the bore of said support, the axial length of said anchor head being at least twice the length of the seating surface of said support, said support contacting said anchor head at the outer portion thereof and at a distance below its greatest cross-section.

2. An anchorage for dynamically high stressed steel wire comprising a support provided with a bore through which is adapted to pass a wire, a wire passing through said bore, and including an upset anchor head which is substantially conically widened towards its free end, said bore being widened outwardly substantially funnel-shaped over a portion of its length to provide a seating surface for said upset anchor head, said bore further including a non-widened portion, a portion of said anchor head extending freely into said non-widened portion of the bore of said support, the angle of inclination of said seating surface with respect to the axis of said bore at most amounts to 30, but at maximum is equal to the greatest angle of inclination of the anchor head with respect to the axis of the wire.

3. An anchorage for dynamically high stressed steel wire comprising a support provided with a bore through which is adapted to pass a wire, a wire passing through said bore, and including an upset anchor head which is substantially conically widened towards its free end, said bore being widened outwardly substantially funnel-shaped over a portion of its length to provide a seating surface for said upset anchor head, said bore further including a non-widened portion, a portion of said anchor head extending freely into said non-widened portion of the bore of said support, the shape of the surface of said anchor head and the seating surface of said support is the same.

4. An anchorage for dynamically high stressed steel wire comprising a support provided with a bore through which is adapted to pass a wire, a wire passing through said bore, and including an upset anchor head which is substantially conically widened towards its free end, said bore being widened outwardly substantially funnel-shaped over a portion of its length to provide a seating surface for said upset anchor head, said bore further including a non-widened portion, a portion of said anchor head extending freely into said non-widened portion of the bore of said support, the generatrix of the surface of the anchor head is substantially an S-curve, the diameter of said anchor head passing through the turning point of said S-curve being greater than the largest diameter of the widened portion of said bore, said seating surfaces of said support being conical.

5. An anchorage for dynamically high stressed steel wire comprising a support provided with a bore through which is adapted to pass a wire, a wire passing through said bore, and including an upset anchor head which is substantially conically widened towards its free end, said bore being widened outwardly substantially funnel-shaped over a portion of its length to provide a seating surface for said upset anchor head, said bore further including a non-widened portion, a portion of said anchor head extending freely into said non-widened portion of the bore of said support, said anchor head having at least two diametrically opposed axially extending fins which are pressed into the material of said support, said support being formed of a material which is softer than the material of the wire.

References Cited UNITED STATES PATENTS 2,698,193 12/1954 Kennison 277-187 2,867,884 1/1959 Brandt 14-22X FOREIGN PATENTS 476,889 12/1952 Italy.

EDWARD C. ALLEN, Primary Examiner.

CARL w. TOMLIN, RICHARD w. COOKE, Examiners. WAYNE L. SHEED, Assistant Examiner.