US3673624A

US3673624A - Suspension bridge

Info

Publication number: US3673624A
Application number: US64725A
Authority: US
Inventors: Ulrich Finsterwalder; Klemens Finsterwalder; Hans Stefaniak
Original assignee: Dyckerhoff and Widmann AG
Current assignee: Walter Bau AG
Priority date: 1969-08-18
Filing date: 1970-08-18
Publication date: 1972-07-04
Anticipated expiration: 1989-07-04
Also published as: JPS4827028B1; CA921211A

Abstract

Wide span suspension bridge having a strengthening or reinforcing girder in the form of a streamlined solid walled box girder, which box girder is suspended by vertical trusses or supports from a supporting cable disposed in the vertical central plane of the bridge with which supports it is articulately connected.

Description

I United States Patent 1151 3,673,624

Finsterwalder et a1. July 4, 1972 SUSPENSION BRIDGE [56] References Cited,

[72] Inventors: Ulrich Finsterwalder, Munich-Obermenz- UNITED STATES PATENTS swung; 3,132,363 5/1964 Roberts ..14/1s Stelaniak, Freising-Weihenstephan, all of Germany FOREIGN lATENTS 0R APPLICATIONS [73] Assignee: Dyckerholl 8: Widmann Kommandit- 1,176,170 8/1964 Germany ..l4/18 Mumch' Germany OTHER PUBLICATIONS [22] Ffled' 1970 Engineering News-Record, Dec. 19, 1964 page 130 [21] App1.No.: 64,725 Popular Mechanics Sept. 1953 page 137 l Primary Examiner-Jacob L. Nackenofi' [30] Poms 'Apphcamn Pmmy Attorney-Robert H. Jacob Aug. 18, 1969 Germany ..P 19 41 977.3 Aug. 18,1969 Germany ..P 19 41 978.4 [57] ABSTRACT Wide span suspension bridge having a strengthening or rein- [52] U.S.C1. ..l4/l9, 14/21 forcing girder in the form of a streamlined solid walled box [51] Int. Cl ..I:01d 11/00 g r r, whi h x gir r is suspended y er i l trusses or [581 Field of Search 14/1 8, 19, 22, 20, 21, 73 pp from a supporting cable disposed in the vertical tral plane 01' the bridge with which supports it is aniculately connected.

7 Claims, 1 Drawing Figure PATENIEDJuL "4 m2 sum u or 5 3,673 624 INVENTORS:

SUSPENSION BRIDGE BACKGROUND OF THE INVENTION The invention relates to bridge structures and is particularly concerned with suspension bridges where the reinforcing girder is in the form of a box girder with solid walls of streamlined shape.

The problem of aerodynamic stability has been known since the construction of the first wide span suspension bridges. It has been found that the supporting cables of suspension bridges are subject to oppositely directed oscillations caused by the effects of wind. In this connection, essentially two different systems of oscillations are observed and considered, namely on the one hand pure bending oscillations and pure torsion oscillations of fixed amplitude, and on the other hand combined bending and torsion oscillations. Since the combined bending and torsion oscillations are the more dangerous ones, attempts were made after the collapse of several bridges, to reduce or entirely eliminate these oscillations by means of a stiffening girder which carries the runway.

At first, the stiffening or reinforcing girder was constructed as a hollow box girder having truss or frame-like walls in order to impart to it great torsional stiffness or strength. In some cases also the runway was made permeable to permit the passage of wind, for example, by means of a grid covering to reduce the attacking wind forces.

Considerable progress was made in the construction of suspension bridges with the construction of the Severn bridge across the Severn River in Great Britain, where for the first time, a solid walled box girder of relatively small structural height was used as stiffening girder, which has the same torsional rigidity as the truss frame girders that are about three times as high as those used formerly. To this solid walled stiffening girder streamlined form was imparted so that it has less air resistance; due to its torsional strength, it was able to center besides the stabilization of the cables that oscillate in opposite directions under the influence of wind, also the loads that act from one side on the axis of the bridge and thus transfer the torsion moments that result therefrom to the area of the pylons.

In order to avoid the danger of oppositely acting oscillations of the two supporting cables of this suspension bridge, obliquely disposed hangers were used alternately within their vertical planes. Due to this type of suspension of the stiffening girder on the supporting cables a dampening of the oscillations induced by the wind is to be obtained by a stretching of the hangers. That, however, has the serious shortcoming that the oblique hangers, in order to justify their task, must be consecutively subjected -to load between zero tension and the maximum value; a load which the steel bars or steel rods available are not able to withstand due to their limited resistance to oscillations.

A further problem in the application of oblique hangers and of the exploitation of their stretching for dampening wind induced oscillations resides in that this function of the hangers is changed considerably by changes in temperature and traffic load strains. Thus, it must be considered that with temperature changes of i 35 C a plurality of oblique hangers is completely eliminated approximately along the center half of the bridge span so that the stiffening efiect no longer exists. That part of the bridge then acts as if only vertical trusses were present.

SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a form of construction for a suspension bridge which as far as its exterior shape is concerned, as well as also the choice of the materials, that offers the possibility of reducing the effects of the combined bending and torsional oscillations on the stability of the bridge.

In accordance with the invention, this problem is solved in connection with a suspension bridge having a wide span by a stiffening girder in the form of a streamlined solid walled box girder in that the stiflening girder is suspended by vertical hangers from a supporting cable arranged in the vertical central plane of the bridge and connected pivotally with the hangers.

The dampening of the oscillations caused by the wind is obtained in accordance with the invention by applying a new method, namely the discording or detuning of the frequencies of the oscillating parts. The essential structural elements of the suspension bridge in accordance with the invention comprise the combination of the torsion resistant hollow box of streamlined construction with a single carrying cable arranged in the central plane of the bridge together with vertical hangers which extend also vertically in their plane and are connected in articulated or flexible fashion to the stiffening girder,'so that it can also eflect rocking movements about its longitudinal axis.

Additional advantages can be obtained in that when the stiffening girder in the form of a solid walled hollow box with a top and bottom cover plate disposed parallel relative to one another along a continuous edge withinwardly buckled side walls, where ledges extend from the edges formed by buckling the side walls, vertical bands are arranged for preventing oscillations caused by winds at the outer border of the two ledges, which in their'regions adjacent the longitudinal borders of each band are more penetrable, and in their inner regions adjacent the ledges are less penetrable for air whirls that emanate from the edges of the hollow box.

These bands may be connected with the ledges approximately at their longitudinal center axis. The width thereof may be approximately one-half of the structural height of the hollow box and the bands may be so arranged that their upper sides are disposed approximately in the plane of the runway.

The arrangement of these bands and of their penetrability for the air moved by wind that decrease from the outside inwardly and increase again toward the opposite border results in that the whirls that break away in cadence or in harmony are disturbed so that they come out of step and lose their oscillation inducing effect. As a result, the pure bending and torsion oscillations to which known suspension bridges are subjected are eliminated completely, so that only the combined bending and torsion oscillation remains, which will be control lable in its effect upon the stability of the suspension bridge by the manner of suspension of the hollow box.

,A- preferred embodiment of the suspension bridge in accordance with the invention is furthermore characterized in that the pylons are A shaped with struts disposed on both sides of the stiffening girder, are made of reinforced concrete, and are anchored proximate the ends of the bridge by retaining or guy cables, which extend steeper in the projection to the vertical central plane than the carrying or supporting cable, preferably less than 45 relative to the horizontal, that the supporting cable and the retaining cables are made of tensioning elements which are disposed closely together embedded in concrete which cross over one another and are anchored in the head. of the pylons and that between each pylon and the stiffening girder a connection is provided which absorbs a bend and torsion.

Advantageously two retaining cables are provided which extend approximately through the oblique planes defined by the struts of the pylons.

In the suspension bridge constructed in accordance with the invention the retaining cables reach back into the land area less than supporting cables of conventional suspension bridges that are placed over pylons. This in turn makes it possible to locate the pylons more closely to the banks or shoreline,

jacent tensioning members embedded in concrete, the weight of the cables is increased. As a result the deformation of the bridge under traffic loads is decreased. Furthermore, the structural elements essential for the durability of the bridge are protected against corrosion by the embedding in concrete and require no maintenance.

The choice of material of different strength for the carrying cables in the inner area of the bridge and the retaining cables in its outer area provides the advantage that the material in the inner area of the bridge which is of better quality provides for greater elasticity and softness of the bridge in connection with smaller weight, while the arrangement of material of poorer quality for the retaining cables effects greater rigidity there, which results in that the pylon with the retaining cables constitutes, in a way, a stiff anchoring support or trestle for the carrying cable.

A further advantage of the bridge in accordance with the invention resides in its outward appearance. The appearance of the bridge exists in that the heretofore unavoidableunattractive intersections of the two cables and of the trusses are avoided. By the arrangement of the struts or hangers in the center plane of the bridge free view toward the outside is provided for the traveler, while the runways proper are separated by the struts.

Further features and advantageous characteristics of the invention will become apparent from the following description of the bridge illustrated in the drawings, in which FIG. 1 is an elevational view of the suspension bridge in accordance with the invention;

FIG. 2 is a cross-section, drawn to a larger scale, taken along line 11-11 in FIG. I centrally of the bridge;

FIG. 3 is a side view in the direction of the arrow III in FIG.

FIG. 4 is a cross-section taken along line IV-IV in FIG. 1,

FIG. 5 is a cross-section taken along line VV in FIG. 1,

FIG. 6 is a section illustrating details of the supporting or carrying cable and the arrangement of the suspension or hanger bars;

FIG. 7 is a further detail illustrating the disposition of the threaded steel bars of the cable in groups;

FIGS. 8 and 9 illustrate the manner in which the individual tensioning members of the carrying cable are fanned out and crossed over by the tensioning members of the retaining cables and anchored in the pylons; and

FIGS. 10, 1 1 and 12 are a side view, a transverse section and a section taken along line XII-XII in FIG. 10, respectively, of the suspension or hanger arrangement.

In the suspension bridge in. accordance with the invention the supporting cable 2 extends between the two pylons l, and on it the stiffening or reinforcing girder 4 is suspended by means of verticalhangers 3.

The supporting cable 2 in the embodiment shown consists of a large number of closely adjacent tensioning members of a quality of steel such as is conventional in reinforced or prestressed concrete construction, which are encompassed on all sides by concrete and arranged inside of a box-like structural element from sheet metal, plastic material or the like. The carrying cable 2 runs generally centrally into the head 5 of the pylons 1 (FIG; 4) where the tensioning members are individually fanned and anchored. The tensioning members of the carrying cable are crossed over in the head 5 of the pylons l by tensioning members of the retaining cables 6 which are constructed inthe same manner as the carrying cable 2 entering from the side, which are likewise anchored there individually. in a manner known from prestressed concrete con struction. These retaining cables 6 transmit the cable tension forces of the carrying cable 2 into the ground of the foundation along a short path. They define a trestle with the pylon that extensively prevents movements thereof which could cause bending loads.

The same purpose is also served if higher quality steel is used for the carrying cable and steel of lesser quality for the retaining cable. The retaining cables 6 are suitably disposed in the two oblique planes defined by the struts 7 of the pylons 1 in order to insure that the stresses of the pylon struts are applied as close to the center as possible.

The reinforcing or stiflening girder 4 is in the form of a closed box girder; it has a top deck plate 8 which supports the runway 9 as well as a lower cover plate 10; the side walls 11 extend in their upper region obliquely outwardly and are buckled inwardly above an edge 12 which extends throughout the full length of the reinforcing girder. Along the edge 12 ledges 13 are arranged that cantilever out to form walkways. A bending and torsion absorbing connection 4a is disposed between each strut 7 and the adjacent side portion of the girder 4.

At the outer edge of the ledges 13 bands 14 are connected substantially at the height of their center axes, whose height that-depends from the height of the hollow box is approximately half as great as that of the hollow box. In order to reduce the resistance to wind the bands 14 are provided with perforations 15 which are larger in the areas proximate the longitudinal borders or edges of the bands than in the inner areas, which results in different permeabilities. The perforations 15 of the bands are substantially circular, as indicated in FIG. 3. However, they may also have a difl'erent outline, as long as it is ascertained that the permeability in the outer areas is greater than in the inner area.

The runways per se are limited laterally and at thecenter by guide rails or baffle plates 16, which in order to decrease the air resistance may be made of steel cables. The hangers 3, which are suspended in an articulated manner from the carrying cable 2 of the bridge, support the reinforcing girder 4 in order to oppose the turning of the reinforcing girder as a result of torsion as little as possible.

The heavy suspension cable 2 shown in FIG. 6 comprises in the present example a number of groups 17, each of which has seven tension members 18 that are arranged in honeycomb fashion. They are held together by an enclosure 19 and are separated from one another by spacers 20. The bars in the groups 17, as well as the groups in the cable 2, are enclosed by an outer casing 21 made of plastic. v

The hangers 3 pass through the cable 2 in perpendicular direction, and they are anchored at the top by means of nuts 22. The plate 23 between the nuts 22 and the casing 21 is of elastic material such as rubber or neoprene.

The anchoring for the tension members 18 of the supporting cable 2 is illustrated in FIGS. 8 and 9. The retaining cables 6 are anchored in a similar manner.

FIGS. 10-12 illustrate how the hangers 3 pass through an aperture 24 of the top deck plate 8 and are anchored at the lower end of a bridge member 27, defined by two lateral metal sheets 25 and a bottom plate 26. The anchoring is the same as atthe upper end of the supporting cable 2 by means of nuts identified here as 28 and, if desired, by interposing a plate of elastic material such as rubber, identified here as 29. The hangers 3 are disposed on both sides of transverse supports 30.

Having now described our invention with reference to the embodiment illustrated in the drawings, what we desire to protect by letters patent is set forth in the appended claims.

We claim:

1. Wide span suspension bridge having a streamlined stiffening girder in the form of a box girder having solid walls, a supporting or carrying cable disposed generally centrally of the bridge, vertically disposed suspension elements each suspended at one end from said cable and supporting said girder at the other end, articulated connections between the other ends of said suspension elements and said girder, pylons supporting said cable, said pylons being generally A-shaped and having struts on both sides of said girder and being made of steel embedded in concrete, anchoring or retaining cables extending rearwardly of said pylons and being anchored in the ground at the shorelines, said anchoring cables being disposed at angles steeper than the projection of the carrying cable relative to the vertical central plane of the bridge, preferably less than 45 with respect to the horizontal, said carrying cable and said anchoring cables being in the form of tensioning members placed closely together and embedded in concrete, said tensioning members crossing over one another and being anchored in the heads of said pylons, and a bending and torsion absorbing connection extending between said stiffening girder and each pylon.

2. Suspension bridge in accordance with claim 1, where said stiffening girder has an upper and a lower cover plate extending parallel to one another and side walls extending obliquely outwardly, said side walls being buckled inwardly proximate the upper regions thereof to form a continuous edge, a ledge extending outwardly from each said edge each defining an outer edge, and vertical bands disposed along the outer edges of said ledges and having outer borders, said bands having perforations proximate said outer borders of greater permeability and perforations of less permeability along their inner areas proximate said ledges for air whirls breaking in the areas of the edges of said stiffening girder.

3. Suspension bridge in accordance with claim 2, where said bands are connected with said ledges substantially at the center axes of said bands.

4. Suspension bridge in accordance with claim 2, where the width of said bands is approximately one-half the height or thickness of said stiffening girder.

5. Suspension bridge in accordance with claim 2, comprising a runway on top of said girder and where the upper borders of said bands are disposed substantially in the plane of the top of said runway.

6. Suspension bridge in accordance with claim 1, including two anchoring cables extending generally in the oblique planes defined by said pylon struts.

7. Suspension bridge in accordance with claim 1, where said supporting cable is made of higher quality steel than said anchoring or retaining cables. Y

l I 1 k h

Claims

1. Wide span suspension bridge having a streamlined stiffening girder in the form of a box girder having solid walls, a supporting or carrying cable disposed generally centrally of the bridge, vertically disposed suspension elements each suspended at one end from said cable and supporting said girder at the other end, articulated connections between the other ends of said suspension elements and said girder, pylons supporting said cable, said pylons being generally A-shaped and having struts on both sides of said girder and being made of steel embedded in concrete, anchoring or retaining cables extending rearwardly of said pylons and being anchored in the ground at the shorelines, said anchoring cables being disposed at angles steeper than the projection of the carrying cable relative to the vertical central plane of the bridge, preferably less than 45* with respect to the horizontal, said carrying cable and said anchoring cables being in the form of tensioning members placed closely together and embedded in concrete, said tensioning members crossing over one another and being anchored in the heads of said pylons, and a bending and torsion absorbing connection extending between said stiffening girder and each pylon.

7. Suspension bridge in accordance with claim 1, where said supporting cable is made of higher quality steel than said anchoring or retaining cables.