IL24416A - Roadway structures - Google Patents

Description

ROADWAY STHOCmiRES This invention relates to overground roadway structures for automotive vehicles, adaptable for roads, bridges, overpasses, by-passes, overhead roadways, and the like.

The structure is far lighter in weight than other overground roadways for a given load carrying capacity.

Rapidity of erection is far greater, and—because of the relative infrequency of spacing of the ground supports and their comparatively 3-ight loads—erection in heavily built-up areas or in rough terrain is greatly simplified.

The invention is based on the use of highly pre- stressed longitudinal load-bearing members ( for example , cables) to support the wheel-bearing surfaces. The longitudinal load-bearing members are selected as to size and amount of pre-stress so that the roadway can remain substantially a straight line even when dynamically loaded, i.e., the mid-span sag is slight enough that vehicles riding on It undergo only minimum up-and-down motion when traversing the sections between supports. By such use of a high pre -tension, plus lengthwise "crowning" of the wheel bearing surfaces in going from support points to mid-span, it is possible to achieve very low overall weight requirements for the roadway tracks (plus their supports) while maintaining a substantially level riding surface.

All of the load-bearing portions of the structure can be , and preferably are, below axle level of the vehicles riding thereon.

The su or s ma e roadway, and whose function is primarily to transmit to the ground the vertical weight loads and the horizontal components of the dynamic loads. The latter are generally much smaller than the pre-tension loads. Means are provided to stabilize the channels as much as possible with respect to dimensional and angular changes under loads imposed by wind and by passing vehicles, so as. to provide riding characteristics within the vehicle which have minimum roll, pitch, yaw, jounce , and tilt.

In spanning rivers and the like, overhead supports' may be used.

The Invention is not limited as to material used nor the cross-sectional shape or structure of the horizontal, longitudinal tension-bearing members used to absorb most of the load. The material usually best suited from the standpoint of high modulus and low cost is steel. Use of steel in the form of cable (wire rope) will usually be preferred on the basis of convenience and speed of erection; however, the lower cost of other forms of steel may in many design situations favor. some form other than cable.

Any of the more commonly used techniques for absorbing the very high stresses can be used, such as imbedded anchorages. Generally, as few stress-bearing anchorages as feasible will be used—i.e. at turns, terminals, access and egress points—so that the ground supports will bear only the vertical weight loads plus relatively small horizontal components of the dynamic loads.

Figure 1 is a general view in perspective of a section of an overhead roadway on a city street; Figure 2 is a vertical section across such a roadway; Figure 3 is a detail showing the relation of a support and a preferred channel construction; Figure 4 is a cross-sectional detail on line 4-4 of Figure 1; Figure 5 is a perspective view of a 2-channel lane and associated ground support; Figures 6, 7 and 8 are comparative diagrammatic views in elevation which show the advantages of longitudinal crowning; Figure 9 shows the overhead roadway spanning a ravine; Figures 10, 11 and 12 are cross sections on the l es 10-10, 11-11 and 12-12 respectively, of Figure 6 showing the relation of a channel element and two load-bearing members at different distances from a ground support; Figures 11 and 12 each showing the relation of unloaded (full lines) and loaded (dot-dash lines) positions; Figures 13 to 17 are elevations of different designs of channel elements and associated load-bearing members-; Figures 18 and 19 are elevations of different designs of channel elements and a different type of load-bearing members., Figure 19 showing the relation of unloaded (full lines) and loaded (dot-dash lines) positions; -figu e 20 shows an L-shaped member and channel instead of two channels; Figure 21 shows a pair of L-shaped elements that Figure 22 shows graphs of the effect of the pre -tension versus mid-span sag; • Figure 23 is a graph showing the relation of the crown of the load-bearing members to the distance from a support; Figure 24 is an elevational view of a main anchorage at one terminal of a roadway, and the first ground support arch; and Figure 25 is a perspective view of an attachment assembl showing the connection of horizontal load-bearing tension members to the ground supports, and a means of adjusting tension to compensate for temperature changes.

In Figures 1 and 2, two-lane structures for traffic in both directions are shown. It is understood that there may be one or more lanes, though usually each lane is limited to one-way traffic. In Figures 1, 5 arid 9 the channels or tracks 5 and 5' are shown as continuous, although actually they are built up of many elements, for example, spaced, flat plates 6 perpendicular to the supporting pre-tensioned cables 7 and supported thereon at notches, as illustrated in Figures 10 to 21.

Overlaid on the plates 6 may be various gratings or other surfaces on which the wheels ride. Preferably one wheel- bearing track is wider than the other (Figure 2) so that vehicles with wheels spaced different distances can be carried over the same tracks. Each track may be a channel; or one channel may be used with one perfectly flat track or an L-shaped track, or both tracks may be L-shaped with the two u ri hts on either the inside or the The roadway may be a single wide track somewhat wider than the maximum wheel separation of the vehicles to be carried. The plates are preferably each about 1/16 to 1/4 inch thick, and in no case more than 1/2 inch thick, maintaining a space of 1 to 5 inches between each two plates by means not shown.

At each of the arches 9 is a stabilizing cross member 10 anchored to the arch by U-bolts 11. These members 10 serve both to prevent the channels from making rotational movements about their longitudinal axes and to minimize side sway of the entire structure. Attachment assemblies 13 (of the same or different widths) which support the cables 7 by attachment collars 14 are fastened to the cross members 10.

In Figure 1, the inner channel of each lane is shown as not directly affixed to a ground support 9. Therefore, it is rigidly affixed to the cross member 10 in order that the latter can absorb both the vertical and the horizontal components of the dynamic load imposed upon them.

The channel plates 6 are fastened to the cables, either directly or through supporting members. They are separated sufficiently to permit snow, rain and wind to pass between them freely. Figures 1, 4 and 5 show stabilizing bars between elements 6 of the two different channels, at quite frequent intervals (particularly near mid-span) in order to prevent the channels from making rotational movements about their longitudinal axes. Figure 5 shows cross-bracing cables 18 which prevent lateral swaying. The flat planar members 6 in Figure 3 - narrow enough that they cause tires to track down their center. Usually, only one channel would be of this construction, and the other channel of each pair is preferably much wider and flatter in order to accommodate a range of wheel separations. (See Figures 2 and 4.) Neither wheel-bearing surface need be channel shaped because only one inner and one outer guide is necessary to keep a vehicle on the track. Instead of forming the wheel-bearing surface from individual channel-shaped members a grating track may be used which is advantageously supported on bars 15 which are hung slightly below and at varying heights from cables 7.

Figures 10 to 12 show a single basic channel shape, with the individual flat planar members comprising the channel suitably modified according to their positions along the horizontal load-bearing member, particularly with reference to the height of attachment to the latter. Adjacent channel elements, 6 are attached to the cables 7 at slightly different heights relative to their wheel-bearing surfaces 20, though several of identical construction would be grouped, preceded and followed by groups of slightly different construction.

The element 6 of Figure 10 is used adjacent the arch support 9, the element 22 of Figure 12 is used mid-way between two supports and the element 23 of Figure 11 is used between the other two, as clearly indicated in Figure 6. In channel 6 of Figure 10 the cables 7 are at the tops of the sides, in channel 23 they are only a little above the load-bearing surface 20, and in channel 22 they are below the load-bear the reference lines through Figures 10-12 to compensate for the slight sag in the cables under static load.

In Figures 6, 7 and 8 exact size relationships between horizontal and vertical dimensions have not been observed. The wheel 26 is large relative to the horizontal dimension between supports 9, and it is supposed that the weight of the vehicle load is centered at the center of the wheel. The distance between the supports 9- is inordinately short, the scale of the vertical dimension being many times that of the horizontal dimension. The dotted lines 27 and 27' are parallel horizontal reference lines through, respectively , the wheel-bearing surface 20 (Figures 10-12) of the channels and the horizontal tension member 29 at consecutive ground support points. The line 28 represents the wheel- bearing surface, and line 29 represents the cables or other load-bearing members. As the wheel 26 moves from above one support 9 toward the next support, the wheel-bearing surface 28, whose longitudinal crowning causes it to rise well above reference line 27 between the supports when not loaded, tends to flatten out under load, and this is progressive as the wheel advances. At the same time the cable sags more and more until the wheel passes the mid-span point, after which it sags progressively less. As clearly illustrated in Figures 6 to 8 the longitudinal crown is calculated to be substantially equal to (or only slightly more than) the sag, thus offsetting the sag. Thus under dynamic loads, the cable sag at mid-span is substantially below reference line 27, whereas the wheel-bearing surface yCFi s.' 6 to 8)J significantly from reference line 27' However, in order to keep cable sizes as small as possible and/or spacing between supports as great as possible, it may be desirable from an economic standpoint for wheel-bearing surface 28 to be depressed 27 as much below reference line as is permissible by riding qualities within the vehicle. Generally the maximum depression of 28 below 27 will be less than 4 inches for spaces up to 100 feet. For very long spans, substantially greater sag would be tolerable. If the distance between supports is 100 feet, the crown of the unloaded load-bearing surface and the sag of the loaded cables may together be of the order of one or two feet. For longer spans, the sag can be correspondingly greater.

The crown is formed by attaching the cables at different heights on the sides of the channels with respect to the wheel-bearing surface, as discussed in connection with Figures 10-12.

Figures 13 to 19 illustrate different channel configurations. In Figure 13, the road-bearing surface 30 is flatter than surface 20.

In Figure 14, the outer retaining member 32 of the channel is taller than the inner retaining member 33. The latter is positioned under the vehicle, and its maximum height is limited to five to seven inches by the necessity of avoiding the lowermost structures on the undersides of cars traversing the roadway .

Three cables are used to support the channel 34 of Figure 15, the central cable 35 being of larger size. located out from under the vehicle.

The channel 37 of Figure 17 has the channel wider just below the point of attachment to the cables, to aini-ize tire sidewall contact with channel walls and to prevent tendencies of tires to "ride" out of the channels.

In each of the types of channels shown in Figures 13 to 17, consecutive groups of channel-forming members will be used in which the load-bearing cables support the channel-forraing rnernbers at different heights from the wheel-bearing surface, similar to the method employed in Figures 10-12, Figures 18 and 19 show channels 40 and 41 associated with bar stock 42 of rectangular cross section used as the load-bearing members rather than cables. In Figure 19, the position of an unloaded channel 41 located away from the ground support is shown in full lines and its position under load is shown in dot-dash lines. Tubing, rods, I-beams angles, channels, and other comnon forms of a long, high-strength metal stock may be used in place of bar stock.

Figure 20 shows an L-shaped element 45 used with a channel 46, instead of two channels. The channel 46 keeps the wheels on one side of the vehicle in line so there is no need for even one wall on the L-shaped element. It might be perfectly flat.

Figure 21 shows two L-shaped elements 47 and 48 with the wall of each on the inside. It might equally well be located on the outside. Means will be provided for attaching cables to each of these modifications, shown in Figures 13 and 21 at IMPORTANCE OF HIGH PRE-TENSION.

To show how an acceptably low sag and an economically feasible size can be achieved with this invention, comparisons are made in Table 1 between the following structural arrangements of a single lane, 2-channel roadway, each channel being supported by two cables, the distance between cable supports being 100 feet: CASE 1: Highly pre-tensioned cable, pre-tensioned to approximately 30 per cent of its ultimate tensile strength (including static load), and having, the smallest diameter consistent with an acceptable safety factor, a mid-span deflection (sag) which is within the range which can be tolerated from a ride-comfort standpoint, and a practical degree of separation between ground supports.

CASE 2: Same size cables and separation between ground supports as in Case 1, but with the pre -tension (including static load) of only 7 per cent of ultimate strength. This situation produces an unacceptably large sag from a ride-comfort standpoint.

CASS 3:' Larger cables than Cases 1 and 2, same spacing between supports, cables pre-tensioned to same percentage of ultimate strength as in Case 2 (7 per cent), and with cable size selected to give about the same mid-span sag as Case 1. This situation gives a more nearly acceptable ride, but is economically far less attractive than Case 1.

TABLE 1 CASE 2 CASE 3 CASE 1 ■·. Conditions Larger cables, Cable pre-ten- similar to Case % pre-ten- sioned to 1, except only sioned to 3C of tensile 1 pre- give same sag strength tension as Case 1 Dlam. of cable, inches (l) 1.5 1.5 .3.5 Cable weight/ oot,, lbs. 4.7 4.7 25.5 Total weight/foot/ cable, lbs. (2) . 10.7 10.7 31.5 id^-span sag* under static load only, inches (3) 2.0 8.3 4.5 Mid-span sa * with dynamic load of 1500 lbs. , inches ( ) 6.8 23 8.7 Notes: (1) All calculations based on use of galvanized bridge strand, having ultimate tensile strength of ca. 200,000 psi . (2) Channel assumed to weigh 12 lbs. per foot of channel length, equivalent to 6.0 lbs. per foot of cable length. (3) Calculated from: y = mid-span sag (feet) = ws21 where 8t w = weight per foot of cable plus channel; s - span, feet (= 100 feet); t = static loaded horizontal tension in cable, lbs. (82,000 lbs. for Case 1; 19,300 lbs. for Case 2; 77,300 lbs. for Case 3). (4) Calculated from y - Gs *· ws2 , where G = weight of 4t 8t concentrated load, lbs. (= 1500) and the other letters have the same meaning as in note 3. t for Case 1 = 95,000 lbs. under dynamic load; for Case 2, 31,000 lbs., and for Case 3, 105,000 lbs.

"Sag is for cable only, not for the wheel-bearing surface of the channel; the latter will ordinarily be "croivned" in the lengthwise direction, as dealt with in detail below.

It is clear from a comparison of th figures in Table 1 that pre-te sioning of the minimum size cable consistent with safety, as in Case 1, gives an acceptably small sag from a approximately equivalent to Case 1 in cost (i.e., same cable size), there is far too much sag under load for satisfactory ride qualities; and (b) in Case 3» which has a more nearly acceptable degree of sag, there is approximately 5-l/2 times as much cable required as in Case 1, making th economics very unfavorable for the use of heavy cables at low percentage pre-tension loads.

As an indication of the economies possible with the instant invention, a 2-lane roadway based on the construction of Case 1, weighing 45 to 50 lbs. per lineal foot, would weigh of the order of 2 per cent or less of a conventional 24-foot wide 2-lane concrete-and steel overhead roadway of similar weight and traffic capacity. Further, erection would require only a minute fraction of the time required for conventional construction.

Other considerations being equal, it will almost always be preferable, to select the size of cable which, when pre-tensioned and dynamically loaded to the maximum mid-span sag (under load) that permits an acceptable riding quality in the vehicle. Generally, in order to accomplish this, the horizontal pre -tension load (including the static load imposed by the weight of the channels) will preferably be large in comparison to the additional load imposed by passing vehicles, and in comparison to side loads imposed by high winds. To illustrate these points further, Figure 22 shows a graph of mid-span sag under combined and dynamic load versus pre-tension load (as a per cent of ultimate tensile strength), showing a family of curves for several sag of the tension member itself rather than the net sag experienced by the wheels of a passing vehicle, which latter can be as much as 8 to 12 inches less than the former as a result of lengthwise crowning applied to the wheel-bearing surface of the channel. (The beneficial effects on economics and ride qualities are recounted more fully in the next section.) As in Table 1, all calculations are based on the use of galvanized bridge strand of approximately 200,000 lbs. per square inch tensile strength, with each cable supporting a design dynamic load of 1500 lbs. and being supported at 100-foot intervals by ground supports . The area within the dotted oval in which the pre-tension load is 15 to 35 per cent of the ultimate tensile strength, and on occasion may be as much as 40 per cent, is believed to represent the region wherein optimum compromises between costs (of which cable will be a major portion) and acceptable ride qualities will generally lie. Values significantly higher than 30 per cent are generally not permissible because of the necessity of maintaining safety factors of three or more, and values less than 15 per cent require excessively large cable sizes and/or degrees of sag. The figures for Table 1 and Figure 22 are based on a selected condition of loading and vehicle density (spacing) which may differ considerably in an actual installation from that shown. For example, designing to accommodate a number of vehicles per 100-foot span may be incorporated in some cases for safety purposes, although it will usually be preferable to provide means (warning devices, - It is evident from the foregoing that, in order to combine acceptable ride qualities with acceptably low costs, pre-tensioning to a degree sufficient to limit the sag of the horizontal tension member under its dynamic load to much lower values than are commonly used is essential. Generally, the sag under dynamic load will be less than 1 per cent of the span, and--in order to fall within the objectives of this invention—invariably less than 1.5 or 2 per cent.

CHANNELS AND OTHER ¾EEL-BEARING SURFACES The channels. r other wheel-bearing surfaces in or on which the tires -ride- may be continuous solid surface; a perforated or slotted surface; grating; or a series of closely spaced planar members transverse to the channel axis, shaped in cross section to accommodate the wheels and to engage the tensioned longitudinal load-bearing members. The' last-named construction will be preferred in .r.any situations, because of lo-w weight and minimum lateral wind re sistance .

EFFECT 0? CROWNING- • By proper design of the amount of crowning of the wheel-bearing surface in the lengthwise direction as 'a function of distance from support points—that is, so as to. be-approxim tely equal to the amount of cable sag at the point in question —a substantially level- ride can be achieved even though the tension member sags appreciably. When not loaded with a passing vehicle, the bottom of the channel is appreciably above a straight line between channel bottoms - surface 28 between the supports 9 is appreciably above the surface at the supports when unloaded, but more nearly approaches a horizontal line when under dynamic load, as in Figures 7 and 8. Figure 23 is a graph of the amount of longitudinal crowning^, (which is preferably non-linear as shown) as a function of the distance from a support point. As shown, it takes a relatively sharp rise (raising the wheel-bearing surface relative to the cables or other tension members) just before and after each support point- Use of longitudinal crowning markedly lowers .overall costs. For overground roadways of appreciable length, it will be preferable in most cases to space the ground supports as far apart as practical, where separation will usually be arrived at by balancing ride qualities against the costs of heavier cable necessary to maintain a mid-span sag below some pre-selected maximum. Generally speaking, this maximum will be determined by the vertical dimension of the walls of the channel, the inner of which may be shorter than the outer as illustrated in Figures 14 and 16; or the inner legs may be omitted entirely as by transposing ■ the L-shaped members illustrated in Figure 21 to avoid all such difficulty. The top-most and lower-most points of the inner leg (where an inner leg is used) would normally represent the limits within which attachment of the channel to the tension members would be made. If this range were, say, 10 inches, the latter figure would fix the maximum utilizable crown which could be applied. Since a moderate amount of vertical' movement of the wheels—perhaps of the order of two tolerable from a ride standpoint, this amount can be added to the crown to obtain the total permissible sag of the tension member. Applying this total of, say, 12 inches to Case 1 of Table 1 calculated earlier, that of two l-l/2-inch cables supporting each channel, and cable pre- tensioned by 82,000 lbs. and carrying a design static load of 10.7 lbs. per foot (including cables) and a coving load of 1500 lbs., it can be shown by calculation from the formula in footnote 4 of Table 1 that the support points can be as far apart as 150 feet by use of 10 inches of crown plus two inches of vertical movement of the vehicle's wheels; whereas if no crown were used, a maximum spacing of only 33 feet would be. necessary to keep the vertical bounce within two inches.

In designing roadways of considerable length which must accommodate a range of vehicle weights, it will usually be preferable to use an amount of crown which gives a virtually level ride for the most common weight of vehicle. Vehicles heavier than this average weight will experience a jounce (in proportion to the amount by which they exceed the design load) caused by the bottoms of their wheels at mid-span dipping below the imaginary straight line between channel bottoms at consecutive support points, whereas vehicles lighter than the design load will experience a bounce caused by their wheels rising above this imaginary line at mid-span.

An additional advantage of high pre -tension on the channel-supporting members is that auxiliary means for absorbing side loads caused by high cross winds will, in most cases, be unnecessary. It can be shown- by calculation that vertical deflection imposed by the moving loads, even with minimum side bracing.

In order to minimize tendencies for the channels to undergo incipient rolling about their long axes --ca us irg the wheels to ride on the low side and producing unpleasant ride sensations in the vehicle --rigid cross menbers, such as members 15, are attached transversely to both channels at intervals of from 2 to 25 per cent of the span length. Spacing between the channels is smaller near mid-span, as shown in Figure 1. As shown in Figure 4, such stabilizing cross members maintain the tensioned cables in fixed vertical relationship to each other, counteracting tendencies of either channel to undergo rotational movements about its long axis.

To minimize up-and-down vibration, connections between intermediate points along the horizontal load-bearing tension members to the ground below, to cables below and parallelling the load-bearing cables, to spring-suspended weights, or diagonally to the bases of the ground supports, may be desirable. Some change in the curvature of crowning (in the longitudinal direction) of the wheel-bearing surfaces --Figures 6, 7, 8 and 23--would be made in many instances in order to preserve as level a ride as possible.

Although, due to its ease of erection, cable (wire rope) will often be the preferred material for carrying the high pretension stresses, its high per pound cost relative to other forms of steel--such as rods, bars, angles, T's, I-beams, etc. --may in certain situations make one of the latter forms the longitudinal s rength-bearing meaber instead of cable.

For certain installations in heavily populated areas where minimum interference of ground-support structures with roadways, buildings, etc. already present could have an important bearing on decisions on whether the elevated structure of the instant invention would be adopted in preference to some alternative method of increasing traffic .handling capacity, it will prove expeditious to carry the lanes directly over the lanes of roads on the ground, and to use ground supports offering little or no obstruction to existing roadways. Figure 1 is a perspective of two lanes of overhead roadway, positioned over the two outer lanes of a four-lane nain thoroughfare in- a commercial section of a city.

METHOD OF ERECTION. " In sost overground roadways of appreciable length involving a nursber of ground supports, cost considerations will favor designing the supports to absorb only the vertica (weight) loads (&£d the horizontal component of the moving loads, and not the "iuch heavier horizontal pre-tensicn loads which latter will ordinarily be borne by heavy anchorages or piles at turns or terminals. An important requisite for attaining the cost savings resulting froir, not having the ground supports bear any significant part of the pre-tension load is a method of erection wherein the latter loads are not in-parted to the ground supports to any significant degree at any tir.e during erectirm, as well as not during use. A preferred method for achieving use of relatively the pre-tension load to each entire length of the tension □err.bers, previously positioned in place, prior to their being attached to the ground support structures. Thus, the additional stretch imposed by the static load is made before the tension member is rigidly affixed to the ground support, and there is no net horizontal force borne by the latter as a result of the pre-stre ssing operation.

Since individual tension members may be thousands of feet, or even miles, in length between points where the high pre-tension loads are borne to the ground--espe cially 3f sections each representing a reel of cable are end-linked together--there may be situations where many dozens of ground supports are attached (after tensioning) to a single length of horizontal tension member. However, vertical support would preferably be supplied by the ground supports during the* tensioning operation.

Alternatively, or in supplementation of the foregoing method, the pre-tension load can be applied o.re or less simultaneously to each section between ground supports, so that the net horizontal force on the latter remains at small levels (relative to full pre-tension force) while 'tension. is being increased to the designed pre-tension level.

Use of either of the two foregoing methods will allow use of ground supports whose horizontal load-bearing capacities are relatively low and which are correspondingly low. in cost and simple to erect. Figure 24, for example, shows schematically, the relative size of a terminal ground-anchorage 50 which must absorb the very heavy pre-tension comprising a channel in Case 1 of Table 1, and the much smaller anchorage 51 at each end of an arch of a ground supOort 52, which latter are required to absorb only the Increment horizontal load of ca. 26,000 lbs. (= 2 x (95,000-82,000) per pair of cables imposed when the dynamic load of I5OO lbs./cable passes. Thus, the anchorages for the ground supports are preferably sized to absorb less than 20 per cent of the horizontal load borne by the terminal cable anchorages. The pre-tension can be adjusted by turnbuckle 54·· In order to simplify construction in the region near the ground anchorage 50, vehicles are preferably carried over the imbedment point 59 and the turnbuckle 54-on a rigid, non-tensioned transition section 60, suitably cha.nneled at attachment point 61 for vehicles to ride into the wheel-bearing -channels 62 with minimum bounce. The bracing members 57 are under compression to make the change in angle more gradual in going over the first ground support.

As a means of increasing safety factors without having to resort to unduly heavy tension members, terminal anchor-' ages, and ground supports, a means for distributing unexpected concentrated loads developing in one- span (due to several vehicles being bunched, for example) might be provided wherein linkages between the cable saddles and their associated ground supports will transmit only part of the unbalanced load caused by the vehicles to the two adjacent supports, and part of the unbalance will also be transmitted to the neighboring ground supports in either direction.

COMPENSATING FOR CHANGES IN PRE-TENSION CAUSED BY TEMPERATURE CHANGES. ; Seasonal and diurnal temperature ■■ variations result in expansions and contractions of the horizontal load-bearing members, which, if not compensated or, Kay—in certain design configurations—cause the pre -tension in the load- bearing members to exceed some desired maximum or drop below a desired minimus, with resultant fluctuations in the deflection under dynamic load. Por example, in Case 1 of Table 1, a change of -40° F. to 4-110° P.. would cause jz 0.2 inches difference in mid-span sag when dynamically loaded at 1700 lbs./cable, and 4.0 £ 0.2 inches when dynamically loaded at 1100 lbs./cable. Since the secure attachment of a single long length of load-bearing member to many ground supports along its length will ordinarily render it ' impractical to adjust pre-tension in the load- . bearing member by turnbuckles or other take-up devices at the terminals (which devices, however, are used to impart the initial pre-tension during erection) , a preferred 'alternative is to provide means for tension adjustment at the points of attachment to the ground .support. One such arrangement is shown in Figure 25, where vertically adjustable U-bolts 63, impinging on rigid rounded load distributors 67 exerting a strong downward force on the horizontal load-bearing members 64 impart a slight kink in the latter (shown greatly exaggerated in the figure), the vertical dimension or depth of which can be altered slightly by tightening or loosening nuts 65. Although not shown, means for bridging the kinked segment at the tension members pipes, or other rigid structure would traverse the notch between bearing points 66, so that the channel-forming mem ers (not shown) would be attached along a horizontal line as if no kink were present. method for compensating for tension changes in cables that s y be preferred in most installations where the number of ground supports per length of cable is relatively few would be the -employment of hydraulic jacks at the terminals. These can be accurately tensioned with calibrated jacks and pressure gauges, though their use would require loosening of the cable attachments to the ground supports during tension adjustment, followed by re-tightening. Λ3 a means of offsetting adverse psychological effects that might be experienced by passengers traversing overground roadways which interpose so little solid structure between the vehicle and the ground, roadbed screens giving the appearance of a solid structure under the entire vehicle may be attached to the underside of the channels so as to cover the open space between them. For example, a roadbed screen made of 3-inch wide strips- formed into a 6-foot wide grill having a basic rectangle of 3" x 12" would weigh only 1.2 lbs. per lineal foot of lane.

The elevated roadway of this invention has already built into it the most important prerequisites necessary in a roadway for an automatic transportati n system, namely, the capability of eliminating frequent intersections, by virtue of going over or under .crossing roadways at low cost; and the

Claims (1)

1. A roadway a of at s the to bearing members being at differen heights relative to the surfaces of the said points of being higher In relation the the at the supports than at away the and being lowest at substantially the midpoint between the ground the maximum crown at being substantially to two cent of the distance between said roadway of clai 1 in which the members are under full static load to between and forty per cent of their ultimate The roadway of either claim or claim 2 wherein the members are in the form of The roadway of eithe claim 1 o claim 2 wherein the members are substantially The roadway of either claim 1 or claim 2 wherein one member is in the form of a channel and the other member may be either a track an The roadway either claim 1 or claim 2 wherein the roadway is a singl wide track somewha wide than the wheel separation o th Vehicles to be carried An overhead or overground substantially as described herein and illustrated in Figures and of the accompanying ants insufficientOCRQuality