US2433878A

US2433878A - Stabilizing harness for suspension bridges

Info

Publication number: US2433878A
Application number: US576394A
Authority: US
Inventors: Merl R Wolfard
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-02-06
Filing date: 1945-02-06
Publication date: 1948-01-06
Anticipated expiration: 1965-01-06

Description

Jan. 6, 1948. M. R. WOLFARD STABILIZING HARNESS FOR SUSPENSION BRIDGES Filed Feb. 6, 1945 2 Sheets-Sheet 1 IN VEN TOR.

M erl R. Wolfard ATTORNEY Jan. 6, 1948. M. R. WOLFARD 2,433,873

STABILIZING HARNESS FOR SUSPENSION BRIDGES Filed Feb. 6, 1945 I 2 Sheets-Sheet 2 i I, g {v12 238 218 223 227 249 248 Fig.3

Fig. 6

Fig.7

Merl R. Wblfiil'd INVENTOR.

Fig. 8

ATTORNEY Patented Jan. 6, 1948 STABHJZING HARNESS FOR SUSPENSION BRIDGES Merl R. Wolfard, Cambridge, Mass.

Application February 6, 1945, Serial No. 576,394

20 Claims.

This invention relates to stabilizing harness for principal load-sustaining elements that hang with sag in suspension bridges.

More particularly it relates to the stabilizing of load-sustaining elements that hang with approximately parabolic sag to sustain dead load at many points between supports, and are'subject to intermittent live loadings which tend to produce undulatory movements of those elements, as in the cables of suspension bridges.

The invention provides a, stabilizing harness which is connected to a principal load-sustaining element at a plurality of spaced-apart points along that element. The harness, when the principal element is static, deflects that element upward at one harness-connected point and downward at an adjacent harness-connected point. There should be at least one such upward deflection and one such downward deflection of the principal element in each end-half portion of a span. Usually there will be not less than three spaced-apart harness-connected points in each end-half portion of the span of a principal element between its supports.

A principal element, in which the undulatory movement may occur, may have a degree of resistance to bending, indeed the large cables required for long suspension bridges have very substantial resistance to localized bending. Such stiffness may be sufiicient to resist localized deflections resulting from live loadings, without being sulficient to prevent the longer undulatory movements which intermittent windsand moving loads may produce. These longer undulations are transmitted to the bridge platform, and, if not arrested, become detrimental and even destructive. The currently accepted method of restricting such undulations is to add a stiffening girder. Such girders are both massive and expensive. The stabilizing harness of this invention, in comparison, is light and inexpensive, yet it arrests all such undulatory movements without the use of a stiffening girder. V

This unique effect depends upon the locations of the harness connections to the principal loadsustaining element, and upon the oppositeness of the directions in which the harness restrains movements of that element at those connections. The upward and downward deflections of the principal element at the harness-connected points need not be great. It is an outstanding discovery that the harness of this invention thus connected is eifective in arresting lengthwise travel of undulations along the principal element. Intermittent deflections resulting from localized live loadings do not become communicated to remote parts of the principal element. And the opposing restraints applied by the harness to that element are such that no single gust of wind is sufiicient to initiate a general travel of undulation along the principal load-sustaining element. Therefore successive gusts cannot build up large undulations of that element.

The stabilizing effectiveness of the harness has been established by an extensive series of experiments with models of difierent sizes employing materials having a high modulus of elasticity in various structural arrangements.

In the absence of a theoretical analysis adequate to explain fully the remarkable results obtained, the following observations are helpful for visualizing the nature and effect of the forces which may act, concomitantly or successively, at the harnessrestrained points.

In any vibrating structure forces resulting from resilience of the elements of that structure are factors that contribute to the building up of whatever large undulations occur. The high tension materials used in suspension bridges are particularly active resiliently. It seems probable that the separating of points at which restraining forces may act in opposite directions, concomitantly with resilient forces that are out of phase with at least one of those oppositely acting forces, is of vital import here, the resilient forces of the ties being in the directions of the lengths of those ties while the concomitantly acting resilient forces of the principal load-sustaining element are primarily crosswise of the length of that element. Furthermore, rhythmic undulations of the structure are inhibited by the lengthwise elements of the harness being loaded at fewer points than is the co-extensive lengthwise portion of the principal element.

In previous structures wher restraint has been applied at each of a series of points in an effort to reduce undulations, as in a truss, the restraint has been applied in more than one direction,

ing of restraint without making points readily available to become nodes prevents the developing of large detrimental waves in the bridge structure.

In suspension bridges having long spans the required size of each cable provides stiifness which is sufficient to resist local deflections that result from intermittent live loadings; and so undulations of thekshorterilengths are prevented- In shorter spans, where the requisite size of the cable does not make the cable be stiff enough, the invention provides a special cross-sectional dis-- tribution of area for the load-sustainingtelernentr: i

which stiifens that element in those regions of its length which are between the harness-connected.

points. eliminated from such spans. that are shorter than have heretofore been Furthermore;.spans and has anchorages at each end which are Thereby, the usual stifiening girder'is substantially"belowthe respective anchorages I4 LOf the "cable.

Th stabilizing harness comprises this upper tension element combined with a lowertensiomelement 22 extending along a mid- ,znportionrof-the' span,-at the middle of which is a deemed feasible for suspension bridges canbe built, with much less material and with greater stability-"th equal leng. sp

were used.

In this special distribution "of cross-sectional. area th e lowertension -carrying area is manyxx 1;. times larger'than its upper area which carries. compression. This saves much material income.

parisonwith theusing of a'n l-bearnri uss type oi'structure having- For cases where it is desirable-that theianchor ages of the principal element should benot beyond the end of tlie span, a.compression..nie1nbermay be provided extending from one supportedend of the principal element'to the'other. n The prin' cipal load-sustaining 'element preferably the special cross-sectional "area mentioned above- It is intended that thepa'tent shall cover bysuitableex'pression in the appended claimswhah ever features of patentable novelty exist in the invention -disclosed.-

The accompanying drawings are diagra'mmatic, and the proportions oi some par-tsare distorted,

for co'ncisesh'owing,

Figure l is a side elevation showing'thehar ness 0f-the invention applied to' a suspension..-.

the upper-tension element 20.

i..tension element '22 upwardly,

clamp 26 to prevent endwise slipping relative to The lower element 22 extends lengthwisedownwardly to the 1 :cable :Hi .to whichit .is connected at points 23 within the middle-half-portion of the span. In-

. .tervening between clamp 26 and each point 23 there "is .a strut 2 i'between the lower tension element 22:and.the.cable Hi. This strut bends the and applies a downwardi'deflection to the cable at the point 25 at the bottom of the strut. This provides an upward deflection of the cable at 23 at each end of the; tension element 22 and a downward defiec-. ;.tion ofcthercable atieach point 25 which is at the 1 bottom. of a strut 2e onleach side of the center of the span.

The harnesscillustrated in Figure 1 also com- "r prisesr ties. 23,: one in each end-quarter-portion of the span, causing a downward bend in the upper tension element 20 which applies an upward bridge-of; usual type in which the principal load-' sustaining element is a cable, and thereflis an upper tension elementof the harness extending c0-' extensively with the cable; 1

Figure-2. is aside'elevation 01 another suspension bridge; iii-which theload-sustaining element is of inverted-T cro-ss-section, and in which the upper tension elements of the harness are not co-' extensive with the -p-rincipalelement but extend only from .one-harness-connected point 'to a remote 'harnessconnected pointy Figure 3t-is aside elevationof the central span of still anotherrsuspension bridge. in which the invention isiembodied. in a harness of very few part5 1 I defiection'to' the cable It! at the point 29 of connection. In Figure l the harness also has a tie 36 .in each side span which applies a downward bend to. the side-span portion of the upper tension element 29 and applies an upward deflection to the cable Ii] at 3|.

Between this point 3! and the anchorage M of the cable the upper tension element 20 of the harness crosses the cable Iii, in each side span at a distance from its anchorage l5 which is substantially-lower than the anchorage M of the cable i8; and at the point 33 near the crossing there is a tie 32. Thereby an upward bend is provided in the upper tension element 20, which produces a downward deflection of the cable l0 at y the point 33.

In Figure 1 the harness also has a plurality of ties extendingvfrom appropriate points in each tower IE to points-in the side spans and in the adjacent end-quarter-portion of the center span.

Figure 4 is a side elevation of asuspensionz. r

structure, invwhich there is-a compression member between' theiends of theload-sustaining element; 1.12;...

Figures 5'land: Stare respectively a side eleva-.

tion and amend elevationin:cross-section .of an."

I-beampwith. descriptive reference lines; '3.

Figure .7;.is; an end. elevationashowingfa. pret- 1.1;

In thisparticular illustrative dia ram there are four Ofi'thGSe ties, 34, 36, 38 and ill, connected to the cable i0. respectively at

points

35, 31, 39 and ii, and applying to the cable a downward deflectiomatweach ofthese points. The points 35 :and 3! are on opposite sides of the upwardly deferred form of distributed crossesectional area of a load-sustaining:elementp.being a modified Tcross-section inverted; and

Figure.;8 .is anendelevation in cross-section showing. a:ircompositei'astructuregtfor; a stiffened load-sustaining. element;

...:fiected points iii. The point 39 and M are on opposite;:sides of the upwardly'defiected points Figurelshows a harness embodying the. inventionwinwhich the upper lengthwise tension elements of; the harness are not co-extensive with :the, load-sustaining element. This figure illus- ;;.trates the-use of an inverted-T cross-section, of

In thexdrawings, Figure .1 shows how thezprin-mri; ciples-ofz theinvention-may be applied forista-a bilizing2a suspensionbridge in .which the 'princiewhich Figurefl. is an example, which provides for localized stiffiness between the harness-connected ipoints. whose: movements. are restrained by the harness. '1; In Figure .2. the. load-sustaining. ele.-:

ment Ilil extends from the center span over the towers H2 and through the side spans to anchorages II4. It supports a platform II8 by hangers (not shown) which may be of usual style. The harness in Figure 2 comprises lengthwise harness elements 50 which are only in the center span and extend from a point 49 and an end-quarter-portion of the center span of element IIO to a harness-connected point 5| in the third-quarter-portion of the same span, counting from the same tower. Intervening between point 5| and the mid-point of the span there is a strut 54 between the harness element 50 and the principal load-sustaining element I I0 beneath it. The top of the strut 54 bends the harness element 52 upwardly, thereby providing a downward defiection of the load-sustaining element at the point 55 at the bottom of the strut. In the loadsustaining element I I 0, from points 59, BI in opposite directions from each harness-connected point 49, each of which applies upward deflection,

ties

58, 50 extend downwardly to the adjacent tower and each apply downward deflection to the load-sustaining element III].

The structure thus described with reference to Figure 2, even though having only one of the two pictured harness elements 50, is suflicient to apply to the load sustaining element I I0, a substantial stabilizing influence which, except under extreme conditions, is adequate to prevent the travel of undulation along the principal element, that is, to prevent travel from anon-harnessed portion of the principal element, through that portion of the span where the harness-restrained points are, to another portion ofthe principal element. Undulations arising in a non-harnessed part of the structure will be arrested in the harnessed part. Obviously the stability of the structure as a wholewould be improved by having two harness elements 50, with their associated elements as described, and as illustrated in Figure 2 in the center span.

I have demonstrated by experiments that the overall stability of a suspension bridge having side spans depends in large measure upon the stability of those side spans. In engineering discussions of the undulation of suspension bridges resulting from the impact of winds it has been recognized that the greatest disturbances are caused by quartering winds, without the reason being known, so tar as I am aware. I have discovered, and have demonstrated by experiments, that a force acting intermittently and having a component lengthwise of the bridge very readily sets up vibrations of the whole bridge in which the undulations extend the whole length of the bridge. In fact I have demonstrated that a light lengthwise force applied intermittently and rhythmically at the top of one tower only of a bridge of conventional type is sufiicient to set up violent undulations throughout the whole length of the principal load-sustaining elements if they are not adequately stabilized. The applying of the harness of this invention to these load-sustaining elements, and extending the harness through the side spans eliminates such undulations.

In Figure 2 an element of the harness is applied to the side spans by providing upward extensions II3 of the towers IIZ, above the level where the load-sustaining element III) is supported by those towers H2; and there is a tension element 10 of the harness running downwardly from the top of this extension to an anchorage IIB above the anchorage I I4 of the chain I ID. A tie I2 connected points 15 and TI.

nects a mid-portion of this element ID to the principal element lIll beneath it at a point 13 in that element. The downward bend in the tension element 10 at the tie I2 provides an upward deflection oi the principal element I In at the point I3. In the side span, in opposite directions from the point 13, there are harness-con- From the point I5 a tie I4 extends downwardly to a lower part of the tower II2. From the point 11, the tie I6 extends downwardly to an anchorage 5 which is substantially below the anchorage II4 of the element IIII. The ties I4, 16 provide downward deflections in the element I I0 on opposite sides of the upward deflection therein at the point 13.

Figure 3 shows the center span only of a suspension bridge having a load-sustaining element 2 I It extending over and supported by towers 2I2 and carrying a platform 2I8 by hangers (not shown) which may be of usual type. This illustrates the simplicity with which the invention can be constructed, having in each end-half of the span only three harness-connected points, which in some cases will suffice.

There is an upper tension element 220 of'the harness which extends from a point 229 in the load-sustaining element 2I0, near one tower to another point 23I in that element near the other tower. There is a lower lengthwise harness element which extends from a point 223 in the loadsustaining element 2I0 across the mid-portion of the span to a point 221 in that element, each of these points 223, 221 being at distances in opposite directions from the center of the span. The

harness elements

220 and 222 are clamped together at the mid-portion of the span as by a clamp 226, which clamp should be sufficiently secure to prevent end-wise slip of these two elements relative to each other.

The point 223 is below a projection (dotted in Figure 3) of a straight index line extending from the point 23I to the clamp 226. Likewise the point 221 is below a projection of a straight index line extending from the point 229 through the clamp 226.

By this arrangement when a live-loading becomes incident on the principal element 2I0 near the point 223 there will be a resulting tendency to pull the clamp 226 downwardly, thereby relaxing that portion of the harness element 222 which extends to its connection 221 in the load sustaining element 2I0. Thereby that part of the dead load, imposed on that element 2H] at the region of the point 221, and carried, when the load-sustaining element 2| 0 is static, by the harness element 222 extending from that point to the clamp 226, is relieved by that live loading. The loading thus relieved is available to minimize the tendency to rise at the point 221 which is caused by the incidence of the live loading at the point 223. While the shift in loading may be not large it is in the direction which opposes rhythmic undulation of the element 2").

The structure shown in Figure 2 is operative without there being a clamp at the center of the span holding the harness elements 52 against lengthwise slip relative to each other; but optimum stabilization for a given weight of material is obtained by using such a clamp, as illustrated in Figures 1 and 3. If such a clamp is embodied in the structure of Figure 2 the locations of the points where the harness elements 50 are connected to the load-sustaining element I'll] within the mid-half-portion of the span should also preferably be below a straight index line, as de- 7 scribed 'with'reference to Figure-3, andas is seen in Figure -1.

In- Figure 3, in each end-half-portion of the span, between th points'229'and 223 at one endhalf, and between 221 and :23! at the other endhalf; there is a point 239, 2&9, from which a tie .238, .248, extends downward to a fastening on the adjacent tower, which as-shown in this Figure 3 is below the platform 218. One of these .ties 2'38 produces downward deflection of the load-sustaining element Zi-El at the point 239, andthat element is deflected upwardly at the harness-connected

points

229 and 223 by the

harnesselements

223 and 222 respectively. Likewise the other tie E l-8 produces downward deflection of the load-sustaining element 2H] at the point at are intermediate of the upward deflections of "that 'element produced by the harness at the'poin-

ts

227, 23!.

Figure 4 illustrates a new type of bridging structure that the invention makes possible by placing a compression member 382 between the endstof the principal load-sustaining element 3E9, at the tops of the send supports 3E2. These supports preferabiy are inclined inward of the spam as indicated. A number of hangers 3 !6 dependtrom the load-sustaining element 3H) to support the platform 398. The compression member is set with a bend upwardly at the points 3&3, one of which is in each end portion of the span, which provides an upward thrust at each bend 393. There are ties 353 i extending downwardly from the points 3% to the load-sustainiIlg elementiifl and providing upward deflections-of that element t-iil at the points 25%. Located between each point 335 and at the end con- .nectin points of the compression member 3532 to .the load-sustaining element 3H there is a point 367 in the loadsustaining element 3 l 6 from which the tie extends downwardly and outwardly to the lower end of its nearer support l2, which provides a downward deflection of the load sustaining element 388 .at the point Sill. In. the region of a quarter length of the span from each end there is a, strut 322 extending between and connected to the load-sustaining element 33b and the compression member 3&2. Thereare cross ties 332 extending each from the compression member 5382 .at the top of one of these struts 322 obliquely downward to a point 333., 5333 the load-sustaining element Slit at a substantial distance from and short of the bottom of the strut 322 which is toward the other end ,of the span, The tensions in each of these ties provides an upward deflection of the element are at its respective point 333. The same tension provides the downward load on the strut 322 at whoseltopit is connected, thus applying a downward deflection to the element 3w at the bot- .tomof that strut. Preferably the cross ties are clamped together by a clamp .336 where they crossat the middle of the span. There is a tie 3% extending downwardly from the clamp 3345 to a point 335 in the mid-portion of the principal load-sustaining element 3 i3. Tension in this tie-..pr.ovides upward deflection in that element at that point 335. There are also spacing struts by the hangers 3H6 without the heavierdead loadings and live loadings being transmitted from the platform to the compression member 302. Thereby the heavy inclined bracings which are an essential part of a truss as usually constructed are eliminated. This elimination of the need of transmitting heavy forces up to and back from a top chord not only dispenses with the long heavy inclined struts needed to transmit those forces but also saves the added weight required to stabilize the whole truss because of their great weight.

For the structure of the principal load-sustaining element, a cable is preferable, if the span is long, because in a long span the size required, .for carrying the total tension load only, is sufiicient to provide a satisfactory localized stiffness of the load-sustaining element between the spaced-apart harness-restrained points. In shorter spans the size of cable required merely for carrying the tension load may be not sufficientto produce the desired stifiness between the spaced-apart harness-restrained points. In such shorter spans it is desirable to provide a distribution of material which produces the required resistance to bonding with a minimum of weight of material.

If the load-sustaining element is a bar of T- cross section, used with the stem of the T upward as indicated in section in Figure '7 and in side elevation in Figures 2, 3 and 4 (where the vertical extent of the bar relative to its length is exaggerated), the required stiffness between the harness restrained points is obtained, from the stem of that T, with the use of much less material than if the element were of the usual I-beam cross-section. Figures 5 and 6 being a side and an end elevation of an I-beam illustrate one reason for this. The dotted line 350 represents the neutral axis at the mid-height which, in engineering calculations as to stiffness, is supposed to remain at that position. This results because the total loading of a beam i assumed to be at right angles to its axis. However in an I-beam used to fulfill a two-fold function, as an element sustaining-load by pull at its ends and as a beam, the tension load due to the pull becomes added to the lower flange of the I, and the neutral axis moves upward as the ratio of the total load carried by tension increases relative to the load carried by compression in the upper flange of the I, i. e. the effective beamdepth diminishes as the ratio of the tension load to the compression load increases. This is indicated graphically by the upper broken line 352 in Figures 5 and 6. In extreme cases the bending resistance is only that of a flat bar represented by the upper flange. But in contrast to this, by the invention, material that might be in the upper flange of the I-beam is redistributed into the vertical stem of the inverted T. Therefore a given amount of material distributed as in Figure '7 is advantageously distributed in the load-sustaining element to combine with the stabilizing harness to approach an optimum of stability with a minimum weight of material in a load-sustaining element as in Figures 2, 3 and 4. In such a combination the principal element is restrained against large indulatory movements at spaced-apart points with which the harness is connected, so that no large tension load can ever be imposed upon the upper end of the stem of the T, which is normally under compression; and the resistance of such a principal element to localized bending between the harness-connected the desired points is suficient to provide for whatever stiffness is required for avoiding localized undulations in the platform which is supported by the hangers between those points. The static location of the principal element, at least in those sections which are between the harness-restrained points, should be such that substantial compression stress exists in the upper part of the cross-sectional area of such an element, i. e., its curvature before assembly should be less than the curvature is when it is in assembled position; thereby the curvature in the assembled position will be less than parabolic for that section of the element which is between harness-restrained points.

This structure possesses many practical advantages over the usual truss alone, or a suspension bridge having its load sustaining element stabilized by stiifeninggirders. It results in great savings in cost, as well as improved stability in spans which are much shorter than have hitherto been considered practicable for bridges of suspension type, because of the cost of required stiffening girders.

The essential characteristic here is that the lower tension carrying area of the principal element shall be much greater than the upper area which carries compression.

Figure 8 shows a composite structure of this type for .a principal element in which tensioncarrying capacity is afforded by flat steel bars 3'50 in the form of ribbons beneath the flange 364 of a modified T 352 at the top of whose stem there is a larger rounded section 365. This has special utility for spans of intermediate length, longer than those for which the integral crosssection of element shown in Figure 7 would be suitable, and shorter than those spans in which the size of cables required for sustaining only the tension loads would be too small to produce localized stiffness between the harness-restrained points. In constructing such spans these ribbons may individually be drawn over the towers, and a stiffening bar 362 placed on top of a pile of such ribbons as indicated in Figure 8, all being later bound together as may be desired.

In structures stabilized according to the invention the magnitudes of the deflections at the harness-restrained points may ordinarily be small, and their upward or downward displace- ,ments from the true parabolic location of the In fact,

stabilization appears to reside more in the oppositeness of the displacements than in the equality of such displacements from the true parabolic position of the element when that element is static. Throughout this description the upward and downward deflections of the load- 10 deflected points, particularly in the end-quarterportions of the span, should be such that the normal traflic loading on the bridge will not cause further deflection. That is, if the tensions in ties which produce the downward deflections apply a static load about equal to the expected live loading, then the bridge will be exceedingly stable for that traflic; and these ties will not produce a continuous excessive stressing of the load-sustaining element because the static loading by such ties disappears when the expected live loading becomes incident, relaxing the ties. Deflections caused bytrafiic loadings heavier than normal, beyond the measure to which the particular installation is adapted, as when a heavier-than-normal truck passes over a highway bridge, may pass the limits at which optimum stability is attained without harm to either the load sustaining elements or the harness elements.

As to the upward deflections, it is observed that a degree of stabilization appears when the upper tension elements of the harness become taut enough to initiate upward deflections. The stability increases with increased stress in these harness elements, up to a magnitude which provides an upward force which is well below the downward force described as preferable for downwardly deflected points of the principal element. Increasing the stress beyond that up to the full magnitude of the said forces supplied to the downwardly deflected points makes no apparent change in the stabilizing characteristics.

It will be understood that the tension elements of the harness and the ties herein described each may have any suitable means for adjusting its tension, as, e. g., a turnbuckle, representations of such adjusting means being omitted from the drawing in the interest of clarity, being well known in the art. Also the Various described deflections of the principal load-sustaining element at the harness-connected points are omitted from the drawing, these being so small relative to the general curvature that their graphical representation in the figures of this drawing would distort the visual appearance from the true aspect of the load-sustaining element more than does the showing of that element undeflected from its parabolic position.

The harness-connected points in the load-sus: taining element need not be at uniform distances apart along that element, indeed some dissimilarity in distance is advantageous because it aids in preventing the development of nodes at uniform distances apart along the element. For example, in Figure 1 the points 29 and 4| are closer together than the points M and 23. The

points

23 and 25 are closer together than the points 25, 2 5 on opposite sides of the center of the span, and. also closer together than the points 23 and 4| in the opposite direction from the point 23. The distance between the points 23 and 4| may be relatively greater than is shown in the drawing as compared with the adjacent points 25 and 29.

Bridge engineers recognize that a suspension bridge may be suitably stable for traflic and may nevertheless be susceptible to large undulations, caused by winds. The problem of preventing such undulations is the subject of extensive research, but so far as I am aware no satisfactory solution for the stabilization of existing bridges has yet beenfound. The stabilizing harness of the present invention provides a simple and inexpensive method for stabilizing such bridges.

11- a'ga-in-st wind disturbances. The restraints prov'id'ed by this harness are s'uchthat thema-Ximum impactby a single gust of wind is unable to initiate a general travel of an undulation along the principal load-sustaining element and bridge. In consequence the larger undulations which are detrimental and even maybecorne destructive cannot be built up. The effectiveness of the general restraint which the harness imposes on the bridge structure appears to stem from the simple fact that no localized displacement resulting from intermittent loadings can be transmitted toward the remote parts of the load sustaining element without being diminished, retarded and arrested.

I claim as my invention:

1.. Means for controlling undulatory movements of a load-sustaining principal element which is anchored. at its ends and hangs with sag to sustain dead load at many points between supports by tension stress existing at least in the lower portion of said element and which stress is transmitted as a tension force'to the end anchorages, said principal element being subject to intermittent liv'e loadings which tend toproduce undulations of that element, said means comprising, in combination, a stabilizing harness having harness ele'inents which'a-re connected to that principal element from abovethe principal ele ment and from below the principal element at points which are spaced apart along the princi pal element, each said harness connection being the controlling restraint at its particular point of the principal element; and that principal element, when it is static, being thereby at one said point deflected upward and at an adjacent said point deflected downward; there being a plurality of said harness-connected points in each end-halfportion of said principal element between said supports, and there being at least one said upward and one said'downwarddeflection of the principal element at adjacent harness-connected points in each end-half-portion of the span between said supports.

2. Means asin claim 1 for controlling undulatory movements, in which the harness-connected points include a series of three of such points in each said end-half portion of the said principal element, in each ofwhich said series the deflection at the intermediate point is opposite in direction from the deflections at the other two of. the three said points of the series.

3; Means as in claim 1 for controlling undulatory movements, in which the harness-connected points include a series of three of such points in at. least one end-quartereportion of said span, in which said series the deflection at the intermediate point is upward and the: deflections at the other two of the threesaid points of the series are downward; and, in the third quarter-portion of that span,-there is a said upward deflection and a said downward deflection which are at adjacent harness-connected points.

4. Means asin claim 1 for controlling undulatory movements, in which the said harness-connected points include a series of three of such points in each end-duarter-portion of the said principal element between said supports, in each of which said series of points the deflection at the intermediate point is upward and the deflections at the other We of the three points in 'that'series are downward.

5. Means "for controlling undulatory' 'movemerits or a load sustainingprincipal element which is anchored at its ends and hangs with sag tosustain dead load at many points between supports by tension stress existing at least in the lower portion of said element and which stress is transmitted as a tension force to the endanchorages, said principal element being subject to intermittent live loadings which tend to produce undulations of that element, said means comprising, incombination, a stabilizing harness'having. an upper harness element extending lengthwise or said span above said principal element and connected to that principal element within each end-quarter portion of the span; and another harness element which is located between the said upper harness element and the principal element, having its ends connected to the principal element at junction points which are within the middle-half-portion of the span, the midportion of this other harness element being clamped to the upper harness element so as to prevent lengthwise sliprelative to that upper element; and, in each end-portion of the span, at least one tying element connected to the principal element at a location which is spaced apart from the connection of said upper element in that end-portion of the span; these tyingv elements being each inclined downwardly, and being fast to the nearer end support, and'providing a downward deflection of the principal element; the harness elements: which are connected from above providing upward deflections of the principal elementg-"thesaiddeflections being provided when the principal element is static.

6. Means-as in claim 5, for controlling undulatory movements; in which the-said junction points are each below a projected straight'index line extending from a connection of the upper harness element to the principal element in an end'-quar ter portion of the span through the location where the said upper and other harness elements are clamped together:

'7. Means as in claim 5, for controlling undulatory movements in which there is a strut located intermediate of each said junction point and the clamp, between the principal element and the said other harness element, bending upwardly that other harness element and providing a downward deflection of the principalelement atsthe lower end or each said strut.

8. Means as in claim 5 for controlling. undulatory', movements, in which thesaid junction points are each below a projected straight index line extending from a connection of the upperharness element to the principal element in an endqua-rter portion of the span throughthe location where the said upper and other harness elements are clamped together; and there being a strut located intermediate of each junction point and the clamp, between the principal element and the said other harness element, bending upwardly that other harness-element and. providing adownward deflection of the principal element at the lower end of'each said strut.

9. Means as in claim 5 for controlling undulatory movements, in which, in each end portion of the span a connection of asaid tying element from below intervenes between the connections of a said upper element and a said other element to the principal element from above.

10. Meansas in claim 5' for controlling undulatory movements, in'which there are two said tying elements connected to the principa'lelement from r 13 below, in each end portion of the span, between which two the said connection of the upper harness element to the principal element intervenes.

11. Means as in claim 1 for controlling undulatory movements, in a structure in which the said supports are towers over which the said principal load-sustaining element extends through sidespans to the said anchorages; in which the harness elements comprise an upper element extending also between and over those towers and through side-spans to anchorages, this harness element being above the principal element between the towers and throughout at least a portion of each side span; there being in each quarter-portion of the span between the towers a tie connection of said harness element to the principal element, thereby providing said upward deflections of the principal element; and there being a tie connection of the harness element to the principal element at a mid-location in each sidespan, providing there an upward deflection of the principal element.

12. Means as in claim 1 for controlling undulatory movements, in a structure in which the said supports are towers over which the said principal load-sustaining element extends through side-spans to the said anchorages; in which the harness elements comprise an upper element extending also between and over those towers and through side-spans to anchorages, this harness element being above the principal element between the towers and throughout at least a portion of each side span; there being in each endquarter-portion of the span between the towers a tie connection of said harness element to the principal element, thereby providing said upward deflections of the principal element; and there being a tie connection of the harness element to the principal element at a mid-location in each side-span, providing there an upward deflection of the principal element; said upper harness element crossing the said principal element in each side-span at a substantial distance from the anchorages, and there being connecting means at that crossing; the anchorages of said harness element being substantially below the respective anchorages of said principal elements, thereby providing downward deflection of the principal element at said connecting means at the crossing.

13. Means as in claim 1 for controlling undulatory movements, in a structure in which the said supports are towers over which the said principal load-sustaining element extends through side-spans to the said anchorages; in which the harness elements comprise an upper element extending also between and over those towers and through side-spans to anchorages, this harness element being above the principal element between the towers and throughout at least a portion of each side span; there being in each end-quarter-portion of the span between the towers a tie connection of said harness element to the principal element, thereby providing said upward deflections of the principal element; and there being a tie connection of the harness element to the principal element at a mid-location in each side-span, providing there an upward deflection of the principal element; there being also within each side-span ties connected to the principal element, extending downwardly obliquely to the tower, providing downward defleclatory movements, in a structure in which the said supports are towers over which the said prin cipal load-sustaining element extends through side-spans to the said anchorages; in which the harness elements comprise an upper element extending also between and over those towers and through side-spans to anchorages, this harness element being above the principal element between the towers and throughout at least a portion of each side span; there being in each endquarter-portion of the span between the towers a tie connection of said harness element to the principal element, thereby providing said upward deflections of the principal element; and there being a tie connection of the harness element to the principal element at a mid-location in each side-span, providing there an upward deflection of the principal element; said upper harness element crossing the said principal element in each side-span at a substantial distance from the anehorages, and there being connecting means at that crossing; the anchorages of said harness element being substantially below the respective anchorages of said principal elements, thereby providing downward deflection of the principal element at said connecting means at the crossing; there being in each side span a tie connected to the principal element, extending downwardly obliquely to the tower, providing a downward de flection of the principal element at a point which intervenes between said tie connection and the tower.

15. Means as in claim 1 for stabilizing undulatory movements in a structure in which the said supports are strut members whose top portions are joined by a compression member which is arched at a point in each end-quarter-portion of the span; there being means connecting each said arched point to the principal load-sustaining element beneath it and thereby providing a said upward deflection of that principal element.

16. Means, as in claim 1 for stabilizing undulatory movements in a structure in which the said supports are strut members whose top portions are joined by a compression member which is arched at a point in each end-quarter-portion of the span; there being means connecting each said arched point to the principal load-sustaining element beneath it and thereby providing a said upward deflection of that principal element; there being at least two struts between the said compression member and the said principal loadsustaining element; each of these struts being located at the vicinity of the lengthwise middle of one end-half-portion of said span; and there being ties crossing each other between said struts, each of these ties extending from the compression member at the upper end of a said strut to a junction point which is in the principal load-sustaining element and is spaced apart from the bottom of the other said strut and provides a said upward deflection of the principal load-sustaining element at its said junction point.

1'7. Means as in claim 1 for stabilizing undulatory movements in a structure in which the said supports are strut members whose top portions are joined by a compression member which is arched at a point in each end-quarter-portion of the span; there being means connecting each said arched point to the principal load-sustaining element beneath it and thereby providing a said upward deflection of that principal element, there being at least two struts between the said compression member and the said principal load-sustaining element; each of these struts being lo- '7 1 'sion'member at theupper;endeoLaLSaid strut to azi junction po'intrwhich isjmtheprincipalllnad-sus tainingzelement andiszspacedtaparat from-the bot tom "ofthe otherzsaid strntzandmrovidesmaid up element atxits saidzjunctiont point; saidxc'rossedz: ities'being held :together at ;their.-c,crcssing, and 1th'erexbeing" aetieuextending; from saidsicrossin 9;:

:to: the principal .loadrsustaining:elementsb eneath latory movements; .furtherwharacterized: :in that 1 the. principal rload-sustainingaielement has a crss,-

h sectional areawhichiis;distributedmertically toresist downwardlben-dingeand isfdistributedhori- 1 zontallyltoaprovide'iri itsdower partsazztensionvw '3 carrying area;whichrisf'greater than that area of :its upper part. which:carriesacompression and in eachiof which .saidseries ;the:@fiectiom; at the? rintermediatepointnis vopposite irr-fdirection fromn V the deflectionsiat theothentwo'iofrthejthree points of .therseries.

a :whichis anchored atiits endsand hangswith sag J :tosustain deadrload:at many-pointsbetween supports" bylitension stressexistinget; leastizin the rlowerzportion of said-element andi'which stress is transmitted as a tension force-to the end anchor-w;

ages, said-principalelement being subject to intermittent tlive loads .whichztendto i-produce'unducated; at the iricinityr aofi 'oneiend-halfeportioniofeaidrspan: anct there be ing ties crossing each otherebetween ssaidsstruts z and anothervaharnesselement'whi'chvis located be- .of that element there.

aseriesxof threevof'suchipointswin eachrsaid endtherdengthwiselmiddle of; '1

16 ment and iconnectedtto that; principal celement within each end' quanteneportion of :thetyspan;

each. of thesel ties extending: fromxzthe'z comprestween; the saidvupper harness element and the aprincipalt =element,:rhaving-:its ends connected to the principal element at junction points which are ithin'zthe middle-half-vportion:.of-:the span, the l ,mid-portion of thisotherharnessfielement being i: c1amped::to the-upperelementg and; tying elementsy-of-the harness, in each-end-halfeportion ;'1Of,vthe spanyh'aving one of ti'IBSEwCOHHGGtSdtO the principal element at :a:location-in that -element which intervenes between-the connections -of the the crossing,:providingz:a said iipwarkzlzdieflection said upperandisaid otherharness elements from pl-5-.abov e;, each said tyingelement beingwinclined 18. .Means. as .:inclaim: llifOI controllingi undue: downwardly andheing'fast-to the saidsupport whichris-neamr t-oit; each eaid-tie-providing, at sangen'd'portion-ofthe spam-:a downward deflection,intervening between said connections of up- 20 :perand other harness: elements: to :theprincipal I element; those zlastjsa-id connections providing upward deflections of the principal element; the saiddefiectionsof the principal element being pro- ,vided' when that element isstaticv :20. -Means as'in'claim 19 for' controlling: undu- -;1at.ory; movements;further-characterized in that there is a strut 'locatedtintermediate :of each said junction point; andthemclamp; between, the principal: elementand the ':said; othertharness'element, bending upward that others-, harness :element and providing a-c'downward deflection of the principal element at the lower end of eachsaid strut.

' :MZMERL R'.@LFARD.

ward deflection of :the; principal leadesustaining-v that the said'harnesseconneoted :pointsiinclude a -f 1 half-portion: of thesaid:prinoipa1;;e1ement, inf"? said- '19.'.Means 'efortcontroliingi.:I1ndu1atorycm0ve1 ments of a load-sustaining principal:aelement.1 r;

a :REFEBENCES .CE'EED The-dollowihg references are-0f record-in the ufile of this patent:

elationsof that element, said means comprising;Q N b 3"; N 111; t

in combination; BI' i Tplincip l elev-;4-17,054;r:-Little Eecpili), 1889 ment inrwhich thecross sectional areais dis- 424,154 Wi1di1'1 et al.. *Mar:i25; 1890 tributed vertically to resist: downwardebending "510,064 2:1: Eddy Decgifi; 1893 :and is distributed-ihorizontally ito.-provide. =in the .-t.6'16,53.6 Hitson. 1- Dec: 2-7; 1898 lower part ofsaidelementatflnsion carrying area 1,481,019 ,r .ViLuebbert Jan-..il='5, 1924 V which is greater than thatarea ofits'upper part l, Y which carries compressionpa stabilizing :harness FOREIGN "PATENTS having 7 an" upper: harnessmelement eextendingi-mmNumber i :1, Country Date lengthwise of said span-.- aboveisaidr principal ele-