US1592685A - Suspension bridge - Google Patents

Description

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W. SCHACHENMEIER SUSPENSION BRIDGE Filed NOV. 2, 1921 2 Sheets-Sheet 2 mmm/ 7 Mum mSC/MCHE/VHE/ER ,4 TTORNEYS experienced in providing a satisfactory ar .v with by means of horizontal struts, thus'- Patented July 13, 1926.

` ,1,592,635` FicE.

WILHELM SCHACHENMEIER, 0F MUNICH, GERMAN Y.

4 SUSPENSION BRIDGE.

i Application led November 2, 1921, Serial No. 512,220, and in Germany April 25, 1921.

My invention relates to suspension bridges and has for its object to provlde a novel and 4e-iiicient construction whereby wind pressure is effective] resisted and deflections of the bridge in orizontal, transverse directions is materially diminished and substantially" eliminated. lDitlculty has heretofore been rangement for adequately resisting wind pressure against suspension bridges, which pressure, generally speaking, is principally in horizontal directions. In many casespa wind-bracing has been arranged below the floor of the bridge to function in the manner of a horizontal beam-girder- Cables running over all of the spans and located in the floor for effectin a horizontal rigidity and stiffness in the utilized but have proved insufficient for the intended purposes because of the small camber of the cable deflection. `The hitherto cxistin arrangements are especially ineiicient or long spans because thewidth of the floor, in such cases, in proportion4 to the length of span, is too small to provide a suficient stiffness in the wind-bracing. In such cases, it hasbeen attempted to take up and counteract the force of the wind by means of cables which project laterally beyond the floor of the bridge and are connected thereforming a horizontal suspension-girder. With such arrangements it is impossible to extend thel cables sufficiently to prevent sagging thereof by their own Weight, so that the forces of the wind are resisted only when the slack ofthe cables has been taken up,

which .results in a considerable horizontal deflection of the whole superstructure. The arrangements in' question are, therefore, very unsatisfactory and are used V1n practice only in rare instances. The present invention overcomes all of the disadvantages of 'isting arrangements and provides an imp Aved construction in which wind-cables ar employed -in bridges in such a manner thattheir etlciency has been increased tol a hivhde ree. The invention will be fully; e-

scribed hereinafter and the featuresjof fnov elty will be pointed out in the a'ppended claims.

In the accompanying drawings, 'which dias., grammatically illustrate examples of the invention without defining its limits, Figure 1 is an elevation of n bridge cmbodylngthe invention; Fig. .2 is a plan View thereof ridge have also been Figs. 3'and 4 are cross-'sections taken respectively neai a pier and near the centre' of the bridge, and F igf5 is a 'diagrammatic crosssection illustrating one method whereby' the wind-cables may be rendered taut.

, Referring more particularly to Figs. 1 to 4 inclusive of the drawings, a represents the wind-cables and b 'are cross-bars or struts whereby said cablesare stretched or renderedgtaut; in the preferred arrangement the two wind-cables a cross each other by about the width ofthe bridge at approximately the centre of theV inner span of the bridge and also near the outer end of each end span, as shown in Fig. 2. The Windcables are anchored in any convenient man-` ner, preferably near the anchorages of the main cables e, which are operatlvely combined with the piers in the well known way. The floor c of the bridge is suspended from the main cables eby means ofA suspension' members d while the Wind-cables a are connected with each` other and with the main girders of the bridge through the medium of horizontal members f; the wind cables a-are suspended from the main cables e by means of suspension `members g which are located in relatively close relation to each other.

The wind-cables a are located in`a plane which corresponds as nearly as possibleto the central plane of the effective wind forces.

'The required and adequate initial stress or pull in the wind-cables 'a whereby the latter are rendered taut for resisting the force of thewind, is produced by shifting "each cross-bar b transversely outward relatively to the bridge. This may be done in any suitable 'manner as, for instance, by

means of a hydraulic jack or other convenient mechanism or, as shown diagrammatically in Fig. 5, the dead-load of the superstructure may be utilized fomadjusting said crossbars b. In such case ylons or osts h and i siipportthe main ca les e an carry the whole dead-load of the superstriicturey lim wardly in opposite directions whereby the cables a are rendered taut and placed under a stress; by redetermining the inclination or slope of t e struts k and Z the pull or resistance against the wind forces exerted by said cables a may be adjusted to just the degree required in each structure. T he roller bearings m and n facilitate the adjustment or shifting of the cross-bars b and bear thever'tical component of the strut pressure; these bearings, as well as the struts .1c and Z may be removed from the structure after` the wind-cables a have been properly .put in stress. The cross-bars b may be temporarily secured in their finally adjusted positions in any suitable manner, as by means of splicing and are permanently and rigidly connected with the whole pylon construction, for instance, by riveting or bolting.

It will be understood that instead of the struts k and Zland roller bearings m and n other means, such as a s stem of hinged struts, may be utilized or bringing the cables ato the desired and adequate degree of tautne. r

In sus ension bridges which do not include si e spans and have only a middle span and a proaches, the wind-cables a may be arrange -in a manner similar to that described hereinbefore. In such constructions special anchorages may be provided for anchoring said cables or those anchorages -wherebv the main cables are fastened may be used` for the purpose. The above described wind-bracing by cables may, under certain conditions, be applied also to other types of bridges, especially if the width of the bridge is extremely small in proportion tothe length of span. The arrangement may be incor orated in arch-bridges with particularly e cient results as in such cases the horizontal arch pressure will be partially neutralized by the horizontal pull of the wind-cables upon the end abutments of the brid ge.l

In kthe improved arrangement the windcables run continuously over all the spans of the bridge and are anchored within the same supports in which the main girdercables are anchored, so that they project considerably beyond the floor as well as beyond the masonry piers. In this way the requisite depth of oth wind-cables` necessary for the lateral bearing ca acity of the bridge is secured, the outer en s of the iron cross-bars b servingas points of support for said wind-cables. The wind-cables are 4given an artificial initial stress to an adequate extent by forcing the cross-bars b apart. In this way the two cables are connected to form a statica] system in which both cables, instead of acting separately, one for one direction of Wind and the other for lanother direction of wind, are forced to cooperate in v a manner similar to the two chords 'of a beam girder. With this arrangement, any wind load causes tension -to exist coincidentally with full wind loading will not cause a slackening or loosening of said cables. The system being stable only for an equally distributed total Wind rload over the whole length of the bridge, it

is connected 'Withr a horizontal stilening girder, the chords of which are at the same time chord-members of the two vertical main stifening girders The wind-cables, as welll as the cross-bars, are 'suspended from the main cables of the bridge by means of inclined tension members whereby said wind-cables are forced to remain Within the plane ofthe wind-bracing in all parts of the bridge including those parts of the span where said cables roject outside of the planes of the main glrders.

Thorough investigation has proved that the iarrangements erein shown and described provide ver essential advantages over existing metho s of wind-bracing and that these advantages increase as the span of the bridgev increases. For instance, in a bridge having a middle span of 3300 feet and a total length of 6600 feet, the result was a gain in steel construction of 6000 tons, which means about 7% ofthe total deadload of the bridge. In addition to this, the elasticdefleetions of the bridge in horizontal directions are diminished to a very considerable extent.

Various changes in the specific form shown and described may be made within the scope of the claims without departing from the spirit of my invention.

I claim:

l. The combination of a bridge including panels and piers, horizontal overlapping cables anchored in the main abutments, rods connecting said cables at every panel and extensible sectional cross-bars connecting said cables' at every ier, the sections of said crossbars bein fldrced apart and anchored to said bri ge whereby said cables comprising a statical system and being un der an initial tension stress which prevents sagging'of said cables in consequence of wind pressure, temperature increases or their own dead wei ht.

'2. The combination of ,a bridge, wind bracing cables extending horizontally over said bridge, cross-bars extending transversely of the bridge and connected with said cables, and meanswhereby the dead load of the bridge is eiectivel uion said crossbars to place said cables un initial stress. 0

3. The combination of a bridge, wind er an adequate lbracing cables extending horizontally over said brid e, and means for placing said cables un er an adequate initial stress by the action of the dead load of said bridge.

4. In a bridge, transversely extensible struts connected with said bridge, cables eX- tending longitudinally between the outer ends of said struts, said cables being under l' initial tension and lying in substantial curves in a common horizontal plane, said curves intersecting each other at two points intermediate said struts, and means for con-A necting said cables to the girders of the *pair of cables extending longitudinally of said bridge in a horizontal plane, said cables having their ends anchored to the main abutments of said bridge, extensible crossbars connected with said bridge and engagin said cables intermediate the ends thereo and said crossbars being extended under a compression stress to yplace said cables under an initial artificially produced, predetermined tension.

In testimony whereof I have hereunto set my hand.

WILHELM SCHACHENMEIER.

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