US3316574A - Road expansion joint - Google Patents

Description

May 2, 1967 R. PARE ROAD EXPANSION JOINT 4 Sheets-Sheet 1 Filed July 28, 1965 INVENTOR ROBERT LEE PARE' May 2, 1967 Filed July 28, 1965 R. L. PARE ROAD EXPANSION JOINT 4 SheetsSheet 2 INVENTOR ROBERT LEE PARE ATTORNEYS y 2, 1967 R. L. FARE 3,316,574

ROAD EXPANSION JOINT Filed July 28, 1965 4 Sheets-Sheet 3 82 42 466-08658 94 F I G. 6

II III/11111111114 INVENTOR ROBERT LEE PARE ATTORN EYS y 2, 1967 R. L. PARE 3,316,574

ROAD EXPANSION JOINT Filed July 28, 1965 4 Sheets-Sheet 4 I H l' :64

V1! A 65 v tlllu. g lllll I////// United States Patent 3,316,574 ROAD EXPANSION JOINT Robert Lee Pare, 1890 Broad St., Crauston, R1. 02910 Filed July 28, 1965, Ser. No. 477,360 23 Claims. (Cl. 14-16) This is a continuation-in-part application of Ser. No. 275,980, filed Apr. 26, 1 963, and of Ser. No. 298,840, filed July 31,1963, both now abandoned.

This invention relates to a highway expansion joint and exhibits particular utility when used in connection with joints in roadways that are supported on piers, such as in bridges.

It is quite common in the first lay a concrete deck slab roadway and then phaltic concrete.

roadbuilding industry to as the foundation for the place on top of this slab a layer of'as- The slabs are generally of a length of the order of forty feet and are laid so that a space is left between adjacent slabs to accommodate the normal thermal and moisture caused expansion that takes place in concrete. Normal expansion for concrete is something on the order of approximately three-quarters of an inch per hundred feet, and it is, therefore, quite common to leave a space between the abutting ends of concrete slabs. A similar practice is adhered to when concrete is used as the vehicle surface itself wherein a small area is left between adjacent slabs which in the past have been generally filled with an asphaltic compound generally of the tar family. In the following description which will be principally directed to the use of concrete slabs as the foundation piece in bridge construction, it should be understood that alternate uses are available for the expansion joint disclosed herein and that the specific examples herein given and illustrated is not to be construed as limiting except within the scope of the appended claims.

In bridge construction it is quite common after the supporting piers have been erected to place beams across these supporting piers, which beams may either be steel I beams of pre-cast concrete beams. Directly on top of these supporting beams, on the upper flanges thereof, forms are erected which serve as the base for pouring a concrete slab. The concrete slabs are then poured onto these forms that have been erected and are poured to varying thicknesses and usually will be reinforced through the use of steel reinforcing rods as is quite common in the industry. It is common to form the concrete slabs in rather large single poured sections on the order of seventy feet in length and of varying widths depending upon the job, and it is therefore quite apparent that a considerable mass of concrete is poured in a single piece. Each of these slabs is spaced from each other longitudinally of the roadway to permit expansion between adjacent slabs. In the past it has been quite common to use metallic plates such as steel plates that overlap the joint between the concrete slabs. In any event, no matter which prior method is used, it permits a continuous road surface to be presented, and the gap successfully bridged between the slabs. The steel plates have several disadvantages, among which are their high cost, inability to seal out water, and the fact that they often become loose after a period of time and have to be removed from their foundation pieces and re-attached, since they are fastened to foundation members that are embedded in the concrete slabs. This is a time consuming and costly method of replacing worn out expansion joints, and it has long been the desire of the road-building industry to have a joint which is simple in construction and which could be more easily replaced in the field. It is, accordingly, a main object of this invention to provide a new form of expansion joint which may be preformed away from the job and readily installed.

Another object of the invention is to provide an elastomer expansion joint formed at least in part from material which has elastic properties and which will be resistant to surface wear by vehicle trafiic.

Another object of this invention is to provide an expansion joint that is watertight and will exclude moisture from penetration into or eliminate water passing through the joint.

Another object of the invention is to provide an expansion joint for a roadway which will be quiet for the travel of vehicles thereover.

With these and other objects in view, the invention consists of certain novel features of construction as will be more fully described and particularly pointed out in the appended claims.

In the drawings:

FIG. 1 is-a broken perspective view of a portion of a bridge using the invention. FIG. 2 is a sectional FIG. 1.

FIG. 3 is an enlarged sectional view taken through the expansion joint of FIG. 2.

FIG. 4 is a partial sectional view of a modified form of the expansion joint.

FIG. 5 is a partial sectional view of a further modified form.

FIGS. 6, 7, 8, 9, 10, 11, 12, and 13 are all sectional views of further modified forms of the expansion joint according to this invention.

In accordance with this invention, an expansion joint is formed by extruding, molding or otherwise forming an elastomer section which will withstand downwardly directed forces due to vehicle loads and yet be elastic to thus accommodate relative movement of the slabs.

Referring now to FIG. 1 of the drawings, there is illustrated therein a bridge structure including a typical pier having a footing 12 with a number of columns 13, 14, and 15 supporting a top beam 16 spanning the lateral distance between the columns. A number of steel I beams such as 21, 22, suitably spaced, span the distance between the adjacent piers. Usually, the I beams 21 and 22 are free to slide on the lateral beam 16. The sliding movement is desired since the I beams 21 and 22 will expand and contract along their length and it is to permit this expansion that the sliding motion on the lateral beam 16 is permitted. Additionally, the inner ends of the I beams 21 and 22 are spaced from each other on the lateral beam 16 so that during this expansion and contraction, they will not abut each other. On the top of the I beams rest slaps of concrete 25 and 26 which form a roadbed.

Referring now to FIG. 2 for a more detailed illustra tion of the joint, the I beams 21 and 22 have welded to the bottom flanges thereof wear plates 28, 29 which in turn rest on domed feet 30 and 31 which are secured to the lateral beam 16. Perpendicularly secured to the webs of the beams 21 and 22 are channels 32 and 33 which serve to support the thickened end portions of the slabs 25 and 26. At the ends of slabs 25 and 26, pockets 34 and 35 are formed in the wearing surface and into these pockets and supported on the base slab 25 and 26 is fitted the expansion joint of this invention generally designated by the numeral 40.

Referring now to FIG. 3 of the drawings, an enlarged and detailed cross-sectional view of the expansion joint is shown. Here, the concrete slabs have cast therein, to form end pockets, a formed sheet of metal or pan 41 which is reversely bent in S form to provide end walls 42 and 43 with a bottom wall 44. The sheet metal piece 41 maybe formed in any convenient length and has affixed view taken on line 2 2 of at spaced locations on approximately one-foot centers to the wall 44 thereof concrete bolt anchors designated 45. These bolt anchors are of standard form and are provided with a threaded bore 46 therein to receive a threaded bolt. A similar sheet metal piece 41 is embedded in the concrete slab 26 which sheet metal bar bears like specific reference numerals with a prime. In some instances, the sheet metal piece is not used, in which event only bolt anchors need be provided.

Traversing the space across the two slabs 25 and 26 and received on the bottom walls 44, 44 of the bars 41 and 41' is the expansion joint 40. In one form, this expansion joint consists of end bars 50, 51 which have a thickness equal to the depth of the pocket formed in the illustrated example by the sheet members 41 and 41. The inner end walls of these bars 50 and 51 are each provided with discontinuous surfaces 52 and 53 which may take a variety of forms. Illustrated is a tongue and groove form, although a variety of shapes may well suffice, the main requirement being to provide as long a surface as is practicable to which there may be adhered an elastomeric section generally designated 54. For approximately two-thirds of the lateral dimension of this elastomeric section 54 there is provided a pair of portions as at 55 and 56 which are characterized as being portions having a number of voids therein that are so arranged to exhibit resistance to downward deformation in the direction of the arrows 57 but with considerable elasticity in the direction of the arrows 58. In some cases it may be unnecessary to provide such voids. One particular form of voids would be a plurality of elongated voids such as 59 at FIGURE 4.

Adjacent to these two sections is a central section 60 which is provided immediately adjacent the sections 55 and 56 with voids 61 and 62, the purpose of which is to create a transition zone into a central non-voided section andto preclude the formation of humps on the upper surface of the elastomer block as the slabs 25 and 26 move toward each other, as due, for example, to thermal expansion. Molded within this central section 60 is a reinforcing bar 63 which is of a dimension to span the open portion between the two concrete deck slabs 25 and 26 and to provide a stiffening factor and a resistance to a bending moment from a force applied in the direction of the arrows 57. The bar is preferably of metal. The end'bars 50 and 51 are provided with bores 65 and 66, respectively, which are countersunk bores, these bores being arranged on the same centers as the centers of the concrete anchors 45, 45'. In this fashion, the expansion joint 40 by the use of socket head bolts may be fastened to each of the deck slabs 25 and 26- by being bolted thereto through and into the anchors and in this fashion the expansion joint may be readily placed into the structure. Prefer-ably, the expansion joint is made of a width that will accommodate any variations in the forming of the concrete slabs 25 and 26 and any inaccuracies in the setting up of the sheet metal portions 41 and 41 so that, if necessary, a sealant composition may be poured into any voids formed between the end walls 42, 42' and the expansion joint 40, such as at 68, 69.

In FIGS. 4 and there are shown two alternate forms, half of the expansion joints 40 being illustrated wherein in each case the end bars 50 and 51 have been replaced by a different structure. In FIG. 4 the end structure of the expansion joint consists of the elastomeric material being carried out the full distance and having a reinforcing bar 70 at the edge thereof embedded therein. A number of countersunk holes 71 on centers equal to the centers of the concrete anchors 45, 45' are formed into the end of the body and with the use of the steel insert 70, sufficient strength and stiffness are imparted to the elastomeric material so that it resists to a great degree forces that would be exerted in the direction of the arrows 58 as shown in FIG. 3. In FIG. 5, a still further form that the invention may take has been illustrated wherein an upper and lower steel plate 73 and 74 have been fastened to the end portion of the expansion joint, and as with the embodiment of FIG. 3, a countersunk hole 75 has been formed through plates 73 and 74 at spaced locations equal to the center distance of the concrete inserts 45, 45 to receive the socket head bolts for fastening the expansion joint in place as discussed in connection with FIG. 3.

In FIGS. 6, 7 and 8 additional alternate forms are illustrated and, in each of these cases the more elastic section of the expansion joint is shown as removable. In FIG. 6, the removable sections are designated as and 81; in FIG. 7, the removable sections are designated as 82 and 83, and in FIG. 8, the removable sections are designated as 84 and '85. In each case, the sections are elastomeric and for securing them in position they are provided with grooves 86 to mate with tongues 87 in the removable section. These grooves are duplicated at each end of the section to mate with corresponding tongues. Splines 88 with enlarged edges 89 serve to hold this in place. In FIG. 6, openings or voids 90 are formed of such a shape that there is a greater void at the upper portion than at the lower portion so that a greater resistance in compression will be had in the lower portion of the removable section and below the central axis, thus causing a downward force as compression occurs due to expansion of slabs 25 and 26. With reference to the sections 82 and 83, these sections have voids 91, 92, and 93 with upper and lower walls 94, 95, 96, 97, 98 and 99 which cause them to deform by reason of the movement of the upper and lower walls inward as expansion occurs, in somewhat of an accordion fashion. The same is true of the sections 84 and 35 where the voids 100, 101, and 102 are somewhat similar and the upper and lower Walls 103 and 104 above and below the voids are somewhat similar and this section will operate similar to section 82 above described.

The more elastic part of the insert will be the section that receives the greatest working as expansion and contraction occurs, and, therefore, the part that will have the greatest wear; .so it is of advantage to have these sections removable so that they may be easily replaced.

A further alternate form is shown in FIGS. 9, 10, and 11 in which the use of the bolts 46 and anchors 45 may be omitted. Here, each of the roadbed slabs designated and 111 have their pockets formed by undercuts as in 112 and 113 and the expansion joint 115 has its edges beveled as in 116 and 117 and is put into positoin in the abutment 110 and 111 under compression. The angular relation between the end of the insert is such that pressure will exist at the upper edges 118 and 119 of this insert thus compressing the upper, outer surface which compression will tend to bulge the entire section downward in the direction of the arrow 120. This section may have a reinforcing bar 63 as above mentioned.

The expansion joints are so formed as to be more easily compressible above the horizontal centroid than below the horizontal centroid. The greater resistance of the lower portion together with the application of force at or above the horizontal centroid urges the central portion of the expansion joint downwardly and prevents upward movement of the central portion or buckling of the joint.

In some cases, the pockets may be fitted with a metal liner with the end portion 131 thereof extending inwardly toward the joint as in FIG. 10 and extending above the bottom portion 132. The expansion joint may take the form shown in FIG. 10 and is here designated as 135 and is provided with voids 136 and 137 on either side of the center and above the horizontal centroid of the elastomer block and with the reinforcing bar 63.

In some cases, the bar 63 may be omitted as shown in FIG. 11 where the expansion joint designated as 140 will be formed with elongated voids 141 on one side, and equivalent voids 142 on the other side of the center with additional voids 143 and 144, located above the centroid of the elastomer block, on either side of the center of the insert block. The pocket liner 145 will have a bottom wall 146 supporting the insert block 140 with an end wall 147 inclined inwardly and with a lip 148 extending over the upper surface at the end of the insert.

Referring now to FIGURE 12 of the drawings, the numerals 25 and 26 again represent adjacent concrete roadbed slabs. Also, internally threaded concrete anchors 45 and 45' are embedded in the roadbed slabs and carry, respectively, bolts 65 and 66. The numeral 150 denotes an elastomer joint which includes an elastomer block 151 having a plurality of voids 152, 154, 156 and 158 therein, the void configuration in the right and left portions of the block being symmetrical. It will be observed that the total void volume above the horizontal centroid of block 151 is greater than the void volume below the centroid. The numeral 160 denotes a stiffening member, as in the form of a metal bar, embedded in the elastomer block and spanning the gap between the roadbed slabs 25 and 26. Angle members 162 and 164 are held down by anchors 45 and 45 at spaced intervals along the length of the join-t and their upstanding sides abut the sides of block 151. In some installations, the angle sides may be bonded to the elastomer block. An undercut 159 is provided at the bottom sides of the block, leaving a gap between the lower edges of the block and each angle member.

After the joint has been assembled as shown in FIG- URE 12, a road surface material such as asphalt is poured on top of the slabs 25 and 26 up to the top of block 151, contacting the block at overhanging lip portions 163. In operation, as slabs 25 and 26 move towards each other, as by virtue of thermally induced expansion, block 151 deforms, a portion of the deformation going into the gaps adjacent the undercuts 159 and the remainder received by the various voids. During slab movement, the upper horizontal portion of the block is more easily deformed than the lower horizontal portion, thus inhibiting the formation of a bulge in the top surface of the block. This is due to the greater void volume in the upper portion. It is further due to the presence of the stiffening member 166 which spans the slab gap, the member being positioned in the lower portion of the block and undergoing substantially no horizontal strain during deformation of block 151. The provision of undercut portions 159 further assists this action, the application of compressive forces by angle members 162 and 164- being confined to the upper and middle horizontal portions of the block.

In FIGURE 13 of the drawings, a further modification is illustrated. Many of the elements are identical to those of the embodiment of FIGURE 12. and the joint 170 thus exhibits the same general form. An elastomer block 171 is positioned between angle members 162 and 164 and contains a plurality of voids 172 located on one (right) half only of the block. As in the embodiment of FIG- URE 12, the void volume above the horizontal mid-portion of the block is greater than the volume of the voids which are below the horizontal mid-portion. The stiffening member which spans the slab gap is denoted by 174 and its left end abuts left angle member 162. Its right end abuts a portion of block 171 spaced from right angle member 164. Only the right part of block 171 is cut away at 159.

During operation of the joint of FIGURE 13, thermally induced contraction of the roadbed slabs 25 and 26 narrows the gap therebetween, thus causing deformation of the elastomer block. The deformation is taken up by voids 172. Stiftener member 174, here in the form of a metal plate, is positioned below the horizontal centroid of block 171. With movement of the roadbed slab ends towards each other, the upper portion of block 171 is more easily deformed than the lower portion, inhibiting the formation of a bulge on the top surface of the block. The stiffener member 174 may be, as in the other embodiments, completely encased in the elastomer.

By the arrangement present in all of the embodiments,

the upper portion of the insert is more easily contracted than the bottom portion so that movement of the slabs towards each other, as would occur in warm weather, urges the elastomer block downwardly. This action reduces to a minimum the tendency of the elastomeric block to buck upwardly and thereby cause humps in the road surface. The foregoing description of the abutment slabs 25 and 26 moving toward one another, as due to expansion, applies fully as well to the contraction of these slabs. The action of this contraction is to open the gap between these slabs stretching the expansion joint generally described in FIGURE 2 by numeral 40. As the stretching of the elastomer causes no buckling forces to be induced, no special description of the action of the various adaptations and modifications of the joint to provide for expansive movements of the joint is necessary.

While the foregoing description is directed to a highway structure such as bridges, it is possible to utilize the teachings of this invention in joints in building structures. This structure has application in any instance Where it is important to provide an expansion joint that is watertight and will provide continuity across a gap whose width is subject to variance.

I claim:

1. An elongated elastomeric block for a roadbed expansion joint, said block being of generally rectangular cross section, an elongated plate of rectangular cross section and having a width greater than its thickness and embedded in said block, horizontally disposed top and bottom surfaces of said block generally parallel to each other, said embedded plate being positioned nearer the bottom surface than the top surface of said block, and width of said plate being less than the width of said block, said plate having its widthwise surfaces generally parallel to the top and bottom surfaces of said elastomeric block, the edges of said plate being in contact, at all surface portions thereof, with said block.

2. The elastomeric block of claim 1 wherein said block is provided with voids therein, said voids being positioned widthwise generally laterally of said elongated plate.

3. The elastomeric block of claim 1 wherein said block is provided with voids, the volume of said voids which arein the upper half of said block being greater than the volume of said voids which are in the lower half of said block.

4. The elastomeric block of claim 2 wherein the vertically disposed longitudinally running edges of said block are provided with means to fasten the elastomeric block to an external structure.

5. The elastomeric block of claim 4 wherein said fastening means comprises a pair of elongated and apertured plates having a portion of said elastomeric block sandwiched therebetween.

6. The elastomeric block of claim 4 wherein said fastening means comprises an apertured plate secured to said elastomeric block in abutting relation, said plate being of substantially the same thickness as that of said block.

7. The elastomeric block of claim 4 wherein said fastening means comprises an apertured and elongated plate embedded in said block.

8. An expansion joint in a roadbed comprising two spaced roadbeds slabs having separated adjacent transverse edges thereby defining a gap therebetween, an elongated elastomeric block generally rectangular in cross section, said block having top and bottom surfaces generally horizontal and parallel to each other, bottom surface portions of said block being supported on said spaced roadbed slabs, said block having an elongated bar whose longitudinal axis is generally parallel with the longitudinal axis of said gap, said bar being positioned in said block, the bar being of a width which is greater than the width of said gap, said bar overlying said gap and spanning it.

9. The joint of claim 8 wherein said block is provided with voids therein, said voids positioned laterally of said roadbed gap.

10. The joint of claim 8 wherein said bar is positioned in said block nearer to the bottom surface of said block than to the top surface of said block.

11. The joint of claim 8 wherein said block is provided with voids therein, said voids positioned laterally of said roadbed gap and wherein said bar is positioned in said block nearer to the bottom surface of said block than to the top surface of said block.

12. The joint of claim 11 including abutment means for maintaining said elastomeric block on said roadbed slabs, whereby movement of said roadbed slabs towards each other causes compression of said elastomeric block.

13. An expansion joint in a roadbed, comprising two spaced roadbed sections, said sections being voided forming pockets adjacent their nearest edges, said pockets ex tending to the said nearest edges, said pockets each including generally vertical end walls spaced from each other along the longitudinal axis of said spaced sections, an elongated and generally rectangular in cross-section elastomeric block positioned within the space defined by said pockets, said block having a plurality of voids therein, said voids positioned laterally of said roadbed gap.

14. The joint of claim 13 wherein the generally vertical end walls of the pockets formed in the slabs are canted inwardly towards each other and abut the upper longitudinally running edge portions of said elastomeric block, to thereby define a space between the lower longitudinally running edge portions of the block and the lower portions of the said end walls of the pockets.

15. The joint of claim 13 including a liner on the surfaces of said slab pockets.

16. The joint of claim 13 wherein the upper portions of the longitudinally running sides of the block are abutted by the upper portions of the longitudinally running sides of the slab pockets, and a space exists between the lower portions of the longitudinally running sides of the block and the lower portions of the longitudinally running sides of the slab pockets.

17. The joint of claim 13 including means to anchor said block within said pockets, whereby movement of said roadbed sections towards each other causes compression of said elastomeric block.

18. An elastomeric block assembly for a roadbed expansion joint, said assembly including first and second blocks, said first block being of generally rectangular cross-section, an elongated plate of rectangular cross-section and having a width greater than its thickness and being embedded in said first block, horizontally disposed top and bottom surfaces of said first block being generally parallel to each other, said embedded plate in said first block positioned nearer the bottom surface than the top surface, the width of said plate being less than the width of said first block, said plate having its Widthwise surfaces generally parallel to the top and bottom surfaces of said first elastomeric block, said second block being elongated and generally rectangular in cross-section and having top and bottom surfaces generally parallel to each other, said second block fastened at one of its longitudinally running edges to one longitudinally running edge of said first mentioned block, said second block having a plurality of voids therein, the top surfaces of said first and second blocks being substantially coplanar.

19. The elastomeric assembly of claim 18 including a third elastomeric block generally rectangular in crosssection, said third block having top and bottom surfaces generally parallel to each other, said third block fastened at one of its longitudinally running edges thereof to the remaining longitudinally running edge of said first mentioned block, the top surfaces of said first, second and third blocks being substantially coplanar.

20. An expansion joint in a roadbed comprising two roadbed sections spaced from each other to thereby define a gap therebetween, an elongated elastomeric block of generally rectangular cross-section having its longitudinal running edges supported on said sections, said block having top and bottom generally parallel surfaces, abutment means maintaining said block on said sections, the bottom of said parallel surfaces being that surfaces of said block portions which are supported by said slabs, said block exhibiting a greater resistance to deformation forces generally parallel to said surfaces and generally longitudinal with respect to said roadbed sections in the lower half of said block than in the upper half of said block, whereby upon a longitudinal movement of said roadbed sections towards each other, upward buckling centrally of said elastomeric block is inhibited, a stiffening element, said stiffening element being positioned in said block, said stiffening element positioned below the mid portion of said block and being of lesser width than the width of said block, said stiffening element spanning and overlying said gap between said roadbed sections.

21. The joint of claim 20 wherein said elastomeric block has a plurality of voids therein, the volume of voids in the upper portion of said block being greater than the volume of voids in the lower portion.

22. The joint of claim 21 wherein said abutment means comprises angle members secured to said roadbed sections.

23. An expansion joint in a roadbed comprising two roadbed sections spaced from each other to thereby define a gap therebetween, an elongated elastomeric block of generally rectangular cross-section having its longitudinal running edges supported on said sections, said block having top and bottom generally parallel surfaces, abutment means maintaining said block on said sections, the bottom of said parallel surfaces being that surface of said block portions which are supported by said slabs, said block exhibiting a greater resistance to deformation forces generally parallel to said surfaces and generally longitudinal with respect to said roadbed sections in the lower half of said block than in the upper half of said block, whereby upon a longitudinal movement of said roadbed sections towards each other, upward buckling centrally of said elastomeric block is inhibited, a stiffening element, said stiffening element being positioned in said block, said stiffening element positioned below the mid portion of said block and being of lesser width than the width of said block, s'aid stiffening element spanning and overlying said gap between said roadbed sections, said block being provided with the plurality of voids therein, the greater part of the volume thereof being on one side of said gap between said roadbed sections, said stiffening element having one portion thereof abutting said abutment means.

References Cited by the Examiner FOREIGN PATENTS 896,034 5/1962 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

N. C. BYERS, Assistant Examiner.

Claims (1)

1. 20. AN EXPANSION JOINT IN A ROADBED COMPRISING TWO ROADBED SECTIONS SPACED FROM EACH OTHER TO THEREBY DEFINE A GAP THEREBETWEEN, AN ELONGATED ELASTOMERIC BLOCK OF GENERALLY RECTANGULAR CROSS-SECTION HAVING ITS LONGITUDINAL RUNNING EDGES SUPPORTED ON SAID SECTIONS, SAID BLOCK HAVING TOP AND BOTTOM GENERALLY PARALLEL SURFACES, ABUTMENT MEANS MAINTAINING SAID BLOCK ON SAID SECTIONS, THE BOTTOM OF SAID PARALLEL SURFACES BEING THAT SURFACES OF SAID BLOCK PORTIONS WHICH ARE SUPPORTED BY SAID SLABS, SAID BLOCK EXHIBITING A GREATER RESISTANCE TO DEFORMATION FORCES GENERALLY PARALLEL TO SAID SURFACES AND GENERALLY LONGITUDINAL WITH RESPECT TO SAID ROADBED SECTIONS IN THE LOWER HALF OF SAID BLOCK THAN IN THE UPPER HALF OF SAID BLOCK, WHEREBY UPON A LONGITUDINAL MOVEMENT OF SAID ROADBED SECTIONS TOWARDS EACH OTHER, UPWARD BUCKLING CENTRALLY OF SAID ELASTOMERIC BLOCK IS INHIBITED, A STIFFENING ELEMENT, SAID STIFFENING ELEMENT BEING POSITIONED IN SAID BLOCK, SAID STIFFENING ELEMENT POSITIONED BELOW THE MID PORTION OF SAID BLOCK AND BEING OF LESSER WIDTH THAN THE WIDTH OF SAID BLOCK, SAID STIFFENING ELEMENT SPANNING AND OVERLYING SAID GAP BETWEEN SAID ROADBED SECTIONS.

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