US3548432A

US3548432A - Suspension bridge cable anchorage

Info

Publication number: US3548432A
Application number: US614651A
Authority: US
Inventors: Jackson L Durkee; Frank W Neeld Jr
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1967-02-08
Filing date: 1967-02-08
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22
Also published as: FR1553466A; GB1216708A

Description

Dec. 22, 1970 DURKEE El AL 3,548,432

SUSPENSION BRIDGE CABLE ANCHORAGE Filed Feb. 8, 1967 4 Sheets-Sheet 1 INVENTQRS Jae/(son L. Our/fee Fran/f H4 lVee/o Jr.

Dec. 22, 1970 L. DURKEE A 3,548,432

SUSPENSION BRIDGE CABLE ANCHORAGE Filed Feb. 8, 1967 4 Sheets-Sheet 2 INVENTO/IS Jae/(son L. Dar/fee flan/r M lVee/a L/r.

Dec. 22, 1970 DURKEE ETAL 3,548,432

SUSPENSION BRIDGE CABLE ANCHORAGE Filed Feb. 8, 1967 4 Sheets-Sheet 5 Jackson L. Our/fee Fran/f M A/ce/a Jr.

INVENTORS Dec. 22-, 1970 ,DURKEE EIAL 3,548,432

SUSPENSION BRIDGE CABLE ANCHORAGE Filed Feb. 8, 1967 4 Sheets-Sheet 4.

. INVENTORS Jae/(son L. Dl/r/(ce Han/f M4 A ee/o L/r.

United States Patent O 3,548,432 SUSPENSION BRIDGE CABLE ANCHORAGE Jackson L. Durkee, Bethlehem, and Frank W. Neeld,

In, Riegelsville, Pa, assignors to Bethlehem Steel Corporation, a corporation of Delaware Filed Feb. 8, 1967, Ser. No. 614,651. Int. Cl. E0111 11/00 US. Cl. 1421 3 Claims ABSTRACT OF THE DISCLOSURE An anchorage for prefabricated strands of suspension bridge cables wherein a series of adjacent hollow cylindrical members are integrally attached to a heavy backing plate to form a unitary anchorage means which is then embedded in a concrete anchorage block. Individual strands of the suspension cable are passed through the cylindrical members and secured against the backing plate so that the tension of the strands is uniformly transferred throughout the anchorage block by the backing plate and the cylindrical members.

BACKGROUND OF THE INVENTION This invention is directed to simplified, more efficient and economical anchorages for prefabricated strands in suspension bridge cables.

In the past, suspension bridge anchorages for prefabricated strands have generally involved structural members partially embedded in concrete, to the protruding portions of which structural members the strands are secured in various manners. Typical of such anchorages are those shown in Pats. 1,852,683 to Sunderland and 2,178,147 to Moisseiif. While these anchorages have been found to adequately anchor the cable, they have certain disadvantages. The metal anchor bars stretch under load and there is a tendency for a progressive breaking of the bond with the concrete beginning at the point of entry of the bar into the concrete at the forward face and working towards the rear of the anchorage. This causes cracking of the concrete, and such cracks at the front face of the anchorage create points of water entry. In order to overcome these objections the prestressed type of anchorage has been developed and used. These anchorages, while effective, are considerably more expensive because of the complicated prestressing components and procedures, the complicated tension linkages at the front of the anchorage, and for other significant reasons.

Attempts have been made to provide a simpler anchorage for structural cables by passing the cable through an opening in an anchorage block and securing the cable at the rear of the block. A specialized form of such an anchorage arrangement is shown in Pat. 2,914,783 to Hoyden et a1. Such anchorages are not completely satisfactory, however, as they do not uniformly distribute the load throughout the anchorage concrete, and, depending upon the particular design, may also experience difficulty due to poor bond of metalwork with concrete.

SUMMARY OF THE INVENTION It is an object of this invention to provide a simplified bridge cable anchorage which distributes the load uniformly throughout the anchorage and preserves the integrity of the concrete, and which is, at the same time, cheaper, simpler, and faster to construct than anchorages heretofore known.

We have discovered that the foregoing object can be attained by providing a rigid prefabricated assembly comprising a plurality of hollow cylindrical members secured at their lower ends to a heavy bearing slab having openings therethrough in registry with the cylindrical mem- ICC bers, embedding the said assembly in a concrete anchorage block, passing the ends of the strands to be anchored through the orifices in the anchorage block provided by the hollow cylindrical members, and seating the strand end fittings against the bearing slab adjacent the lower end of each cylindrical member by any suitable means so that the tension in the strand is taken against the bearing slab and transferred uniformly in compression into the anchorage concrete.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional elevation of a bridge anchorage according to the present invention.

FIG. 2 is a detailed longitudinal section through the embedded portion of the anchorage shown in FIG. 1.

FIG. 3 is an end view of the embedded section along line 3-3 of FIG. 2.

FIGS. 4 and 5 are respectively elevations of an upper and a lower section of an anchorage assembly before embedment.

FIGS. 6 and 7 are respectively transverse sections along lines 6-6 and '77 of FIGS. 4 and 5.

FIG. 8 is a detail of the bearing end of a portion of the anchorage assembly.

FIG. 9 is a section of the bearing assembly of the anchorage of the present invention, along line 99 of FIG. 8.

FIG. 10 is a detail of the splay end of a section of the anchorage assembly.

FIG. 11 is a detailed longitudinal section through the embedded portion of an anchorage having diverging anchorage cylinders.

FIG. 12 is an end view of the embedded section of FIG. 11 along line 1212 of FIG. 11.

FIG. 13 is a detail of the bearing end of a portion of the anchorage of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the draings, as shown in FIG. 1 a suspension bridge cable 11 formed from a plurality of prefabricated strands, which strands may be either the wellknown helical-wire strands or the more modern shopfabricated parallel-wire strands, passes through an anchorage saddle 13 supported on a portion 15 of the bridge structure, from which saddle 13 the individual component strands 17 diverge from each other at predetermined splay angles to anchorage block 19. Anchorage block 19 may be part of anchorage foundation 21 of the bridge. Hollow anchorage cylinders 23 are embedded in anchorage block 19 to provide tubular orifices passing from one end of anchorage block 19 to the other. Strands 17 pass through anchorage cylinders 23, and sockets 25 on the ends of the strands are abutted against a heavy bearing slab 27 firmly secured to the rear of anchorage cylinders 23 and partially embedded in anchorage block 19. Referring to FIG. 2, tension on strands 17 is taken in compression through shims 29 and bearing assembly 31 into bearing slab 27, and also into anchorage cylinders 23, which components then transfer the strand forces into the concrete of anchorage block 19.

Anchorage cylinders 23 are secured not only to bearing slab 27 but also to an intermediate embedded diaphragm plate 56 and a front diaphragm plate 53 which together with the bearing slab 27 tie the entire fabricated assembly together into a rigid structural unit. (Refer to FIGS. 3, 4 and 5). Other suitable structural members may be secured to the anchorage cylinders as may be necessary to tie them together in a unit, either in addition to or in place of plates 53 and 56. It is important that bearing slab 27 be present, however, to transfer the initial bearing of the strands uniformly into the rear face of the anchorage concrete as well as into anchorage cylinders 23. Various concrete engaging means may be welded as may be necessary to the anchorage cylinders or provided as an integral part of the outer surfaces thereof in order to increase the interlocking of the cylinders and the assembly as a Whole with the concrete of the anchorage.

In FIG. 2, which shows a detail of the anchorage as sembly, it is seen that end fittings or sockets are spaced from hearing slab 27 by slotted shims 29 which seat on bearing assembly 31 shown in detail in FIGS. 8 and 9. Bearing assembly 31 is made in two

halves

33 and 35 each comprising a flat plate 39 each with a cutout section defining, when placed around strand 17 as shown in FIG. 9, a tight fitting round hole 40 through which the strand passes. To each plate is attached a half section of a tubular element 37 concentric with hole 40.

Strands 17 will normally have end fittings 25, of any suitable kind such as poured-zinc-type sockets, already secured on the ends before they are transported to the bridge site. When the strands 17 are erected the ends with fittings 25 are pulled through anchorage cylinders 23, the two

halves

33 and 35 of bearing assembly 31 are placed around each strand 17, and each assembly is placed against bearing slab 27 with the small tubular elements 37 positioned inside the slab orifice. A fairlead 43 of nylon, zinc, or other suitable material is inserted in the opposite or upper end of the anchorage cylinder 23 and adjusted radially to support and direct strands 17 toward the splay point at anchorage saddle 13.

After the full dead load of the bridge is in place and the strands are fully tensioned, a stopper plug 45 of a suitable caulking material such as rubber may be cast or placed near the upper end of anchorage cylinder 23, and a filling 47 of a moisture excluding material such as chloride-free cement grout or plastic foam forced into anchorage cylinders 23 through access pipes 48 and taps 48B to provide a seal around the strands 17. Stopper 45 limits the flow of filling 47 near the upper end of anchorage cylinder 23. Lastly, special sealing plug 41 of rubber of other suitable dense material may be cast-in-place at the upper end of the anchorage cylinder as a means of preventing any water entry.

FIGS. 4 through 7 show an anchorage assembly before it is embedded in anchorage block 19. This assembly may be fabricated in portions such as two

halves

49 and 51 for convenience in shipping and erection. Anchorage cylinders 23 in both sections are welded to heavy bearing slab sections 27A or 27B at one end by means of welds 28, and to

diaphragm plate sections

53A and 53B at the other end by welds 54 with a small section of anchorage cylinders 23 protruding through

plates

53A and 53B so that any moisture that may subsequently run down the front face of the anchorage housing will be deflected away from the strands in the completed anchorage. Stiffening webs 55 are welded between anchorage cylinders 23 to provide additional rigidity to the entire assembly. One or more intermediate diaphragm plate sections 56A and 56B secured by welds 52 to cylinders 23 may be used to give the assembly portions additional rigidity.

Assembly half 51 has three I-beams or support members 57 secured to it to provide attachment means for supporting it on supporting frameworks 59, as shown in FIG. 1, prior to the time that the concrete of anchorage block 19 is placed. Holes 60 for lifting the assemblies are supplied in

plates

27A and 27B, and 53A and 53B, reinforced with plates 58 as may be required. Bearing slabs 27A and 27B and

diaphragm plates

53A and 53B conveniently serve as partial concrete forms for the anchorage block 19 during its formation.

Splice plates 62 attached to the upper portion of hearing slab section 27B provide attachment means between slab sections 27A and 27B following assembly at the bridge site. Stiffened bearing and connecting

angles

63 and 64 provide a bearing surface and attachment means between

diaphragm plates

53A and 53B. Aligned bolt holes, not shown, through

angles

63 and 64 facilitate connection of the assemblies. A small bearing bar 65 at the top of intermediate diaphragm plate 56B provides support for matching diaphragm plate 56A following erection at the bridge site. It may be desirable at times to securely Weld the two

halves

49 and 51 of the anchorage assembly together at the bridge site in order to provide a rigid unitary whole.

The entire anchorage is customarily enclosed in a weather structure 61 as shown in dotted outline in FIG. 1, with a sealing hood 66 provided to prevent water access into the achorage.

If a larger anchorage block 19 and

anchorage assemblies

49 and 51 are not detrimental, the anchorage members 23 instead of being assembled in parallel relationship to each other may be assembled in diverging relationship, at the same angle as the splay angles of the respective strands 17 which pass therethrough. In this manner fairleads 43 to direct a change in direction of the strand may be eliminated and the strands 17 directed in a straight line from the splay point or anchorage saddle to a curved or stepped bearing surface at the rear of the anchorage, which surface would have to be suitably equipped with bearing slab means to transfer the stress into the concrete.

FIGS. 11, 12 and 13 show such a diverging anchorage assembly. The parts are designated by the same numerals as used in FIGS. 1 through 10. A stepped bearing surface is provided at the rear of the anchorage by the use of beveled bearing assemblies 31 composed of

half sections

33 and 35 which bearing assemblies 31 are, as seen in FIG. 12, arranged so that the bevel of each assembly compensates for the various diverging angles of the anchorage cylinders 23 with respect to the flat bearing plate or slab 27. For convenience of fabrication the ends of the anchorage cylinders 23 are cut off square and welded at an angle within the orifices in bearing plate or slab 27. As an alternative the anchorage cylinders could also be cut on a bevel and butted directly against the bearing slab 27 as shown in FIG. 8.

By the arrangement of this invention there is provided an economic and convenient bridge anchorage wherein the tension of the suspension strands is taken in direct compression on the rear surface of the anchorage and is dispersed uniformly throughout the anchorage block to secure the strength and safety of a prestressed embedded type anchorage without the expense and complications of such anchorages.

We claim:

1. An anchorage for bridge strand in a suspension bridge comprising:

(a) a concrete anchorage block at one end of the bridge span,

(b) a plurality of hollow cylindrical members arranged in a pattern adjacent to each other in a substantially parallel relationship embedded in said anchorage block,

(c) a perforated bearing slab mounted against one end of said concrete anchorage block,

(d) the end portions of said cylindrical members being secured to said bearing slab in registry with the perforations in said bearing slab,

(e) a plurality of bridge strands extending through said cylindrical members,

(f) means secured to the ends of said bridge strands and bearing against said bearing slab, and

(g) a fairlead at the upper end of each hollow cylindrical member on the inside of any curvature of the strand leaving the hollow member to direct the strand to a splay point where the strands are brought together to form a bridge suspension cable comprised of the said strands.

2. An anchorage for bridge strand in a suspension bridge comprising:

(a) a concrete anchorage block at one end of the bridge span, said block having a lower face,

(b) a perforated metal bearing plate bearing against the lower face of the anchorage block,

(c) a perforated metal support plate spaced from said bearing plate,

(d) a plurality of rigid hollow metal cylindrical members arranged in a pattern adjacent to each other, embedded in said anchorage block, and fixedly secured at their outer ends to the bearing plate and the support plate in registry with the perforations therein;

(e) a plurality of bridge strands extending through said cylindrical members, and

(f) means secured to the ends of said bridge strands and bearing against said bearing plate.

3. A prefabricated anchorage assembly for embedment 15 in a concrete anchorage block of a bridge comprising:

(a) a perforated metal bearing plated adapted to bear against a lower face of said anchorage block, (b) a perforated metal support plate spaced from said bearing plate,

(c) a plurality of rigid hollow metal cylindrical members arranged in a pattern adjacent to each other and fixed secured at their outer ends to the bearing plate and the support plate in registry with the perforations 5 therein.

References Cited UNITED STATES PATENTS 2,914,783 12/1959 Hoyden et a1 1421 3,156,169 11/1964 Finsterwalder 948 10 3,225,499 12/1965 Kourkene 52-230 FOREIGN PATENTS 892,046 1/1944 France 14-21 906,940 3/1954 Germany 14-21 JACOB L. NACKENOFF, Primary Examiner US. Cl. X.R. 52-230.