US2452462A - Concrete expansion joint - Google Patents

Description

Oct. 26, 1948.

\ Filed Sept. '7, 1944 CONCRETE EXPANSION JOINT J. N. HELTZEL 4 Sheets-Sheet l Oct. 26, 1948. J. N. Hx-:LTzEL CONCRETE EXPANSION JOINT Filed Sept. 7, 1944 4 Sheets-Sheet 2 9 Humm gime/wm Oct. 26, 1948. J, N, HELTZEL 2,452,462

CONGRETE EXPANSION JOINT 'iled Sep. 7, 1944 v 4 Sheets-Sheet 5 3mm l Oct. 26, 1948. J, N, HELTZEL I 2,452,462

' CONCRETE EXPANSION JOINT Filed Sept. '7, 1944 4 Sheets-Sheet 4 Patented ct. 26, i948 UNITED STATES PATENT Fries CONCRETE EXPANSION JOINT John N. Heltzel, Warren, hi Y Application September 7, 1944, Serial No. 553`,05'

2 Claims. 1

This invention relates to dowel means for concrete expansion joints, or contraction joints.

'I'he invention is more particularly concerned with improved dowel means for expansion joints as provided between concrete or similar slabs or sections of roadways, floors, airfield runways, Walls, and the like, for permitting relative horizontal movement of the slabs, while preventing the same from shifting laterally and vertically of their planes; and the Vpresent application is a continuation in part of my copending application Serial N-o. 313,128, Patent No. 2,358,328, led January 9, 1940,

Modern traffic conditions on highways and airfield runways have necessitated an increased use of load transfer members bridging joints, both longitudinal or transverse, between the opposed edges of adjacent concrete slabs. Experience has shown that the problem is not solved by the mere addition of load transfer dowels, such as commonly employed, for the shrinkage of plastic concrete when drying sets up a frictional drag on the embedded dowel bars, with the consequent breaking of the concrete at points remote from the joints between the slabs. It has been found, also, that where dowel bars alone are depended upon, there is an inevitable warping of the concrete slabs which tends to bend the dowel bars. This .bending prevents restoration of the slabs to their initial condition on the subgrade and in addition, there is a constant breaking away of concrete or falling off of the material at the faces of the concrete slabs in the areas surrounding and adjacent to the dowel bars.

The tendency of adjacent concrete slabs and the joints between the slabs to shift under changing atmospheric conditions as well as under the incessant loadsfpassing thereover has long been recognized, and the provision of efficient load transfer means at such joints has attracted the skill of engineers in many fields as well as steel and concrete contractors, and as a result many varieties of load transfer means in the form of dowels bridging concrete slab joint have been proposed and used.

In the use of such load transfer dowels, it is necessary of course that expansion and contrac- -tiori of the joint be permitted as a result of which,

the dowels must have relative movement to one of the slabs adjacent a joint in a direction axially of the dowels, and it is also essential that the dowels have relatively no movement transverse of their axes. i

It lhas been found that dowels in use with as to remain rigid therewith under all conditions of use, and that such united dowels be conf-ined to vaxial movement only relatively to another slab.

It has als-o been found that for maximum efliciency the load bearing members or dowel structures should be so constructed and arranged as to be balanced on opposite sides of the joint and that the dowel portions spanning the joint should have a maximum load bearing and transferring capacity vertically through the dowel.

It is a primary object of the invention, therefore, to provide dowel means for concrete expansion joints and the like which satisfy the above noted requirements in providing load transfer connections of maximum strength and eiciency.

An object of the present invention, therefore, is to provide improved means for producing joints in concrete roads and the like, utilizing dual dowel means in association with dual supporting shear plates, in which friction with respect to the surrounding concrete is reduced to a minimum by the novel bridging structure of balanced down and bearing members.

Another object is to provide, in such joints, means to eliminate `tension in the concrete itself and to confine such tension directly and uniformly to the dowel and shear plate means constituting the load transfer elements extending in balanced relation between the respective slabs.

A still further object is to provide a dual dowel assembly concrete slab in a joint installation fo-r transferring vertical load strain to the dowel means at the joint by the employment of cooperating dual shear plates associated with the concrete slabs and dowels..

A further object of the invention is the provision of dowel Ameans. for concrete expansion joints including a dowel and dowel shear plate and socket arranged for rigid connection with each slab adjacent a joint therebetween with pro-- vision for each dowel to telescopically engage within a socket in the expansion and contraction of the joint.

A still further object of the invention is the provision of a dowel unit for use in concrete expansion joints comprising a pair of shear plates, each having a dowel and dowel socket rigid therewith, each shear plate having an aperture for confining the dowel of the other shear plate to axial movement in expansion or contraction of the connected concrete slabs, and each shear plate 'having means rigid therewith for transmitting 3 joints including elements for cooperation at opposite sides of the joint and which elements are of like construction whereby manufacture and the setting up of the dow'el means is simplified to a notable extent. g y

A still. further object of the invention isy the provision of dowel means for concrete expansion joints wherein the joint is greatly strengthened and bal-anced at each side thereof.

With the above and other objects in view, which will become more fully apparent as the nature of the invention is better understood, the 'same con;- sists in the novel features of construction, corn-` bination and arrangement of parts as will be hereinafter more fully described, illustrated 4and claimed in the accoinpanyingdrawings.

In the drawings, wherein like characters of reference Vdenote corresponding parts in related views:

Figure l is a perspective view disclosing a pair of cooperating shear plates, `each provided with a dowel, the plates being in separated and alined relation with the doweis positioned for entry through an opening in an expansion joint strip thence into an` alin'ed socket in the opposed shear plate; 1

Fig. 2 i's a top. plan' view,y partially in section, of the; structure of Fig. l in assembled position;

Fig: 3 is a vertical longitudinal section, showing the structure of Fig. l operatively positioned adj acent the joint between a pair of concrete slabs;

Fig. 4v is a perspective view simil-ar to Fig. 1 showing modified forms. of; shear plates and dowels;

Fig, 5-is a perspective view showingA the separated elements of Fig. 4 in assembledY position;

Fig. 6` is a diagrammatic. View in side elevation showing the effectiveness of the structure of Figs. #i and 5 at the joint betweenl a pair of concrete siabs; i 1 i Fig. '7 is: also a diagrammatic view showing the WellI known jacleknilng of the concrete slab joints in the absence of effective load' transferring and reinforcingmeans; f

Fig. 8 is a sectional perspective View disclosing a further embodiment ofthe invention;

Fig. 9, is an enlarged transverse sectional view substantially in the plane of line 9 9, Fig. 8;

Fig. le() is a perspective View of a still further embodiment of the invention;

Fig. 1l is a 'horizontal sectional view on a reduced scale, as observed in. the plane of line I-I--IIeLFigt 10;

Fig. 1-2 isfa .perspective viewv of .a still further embodiment of thel invention;

Fig. 13 is a perspective view of a still further flrs't to Figs. 1 'to 3, wherein-is disclosed.' a dualA i doivel reinforcing and load transferring-structure for use at the joints` of concrete slabs and which structure` is symbolic of ail the modifications di's' closed', the structure, as shown includes a pair of cooperating unitary elements II) which are VIof i assaiez horizontal thickness extends through the aperture l2 in each plate Il at one side thereof and is rigidly secured to the plate as by welding, indicated at I4.

Each barwI3 Mincludes a relatively long end port-ion` I5` for projection into the body of the concrete slab remote from the shear plate and joint, as shown in Fig. 3, and an opposite end portion which constitutes the dowel portion I6.

The apertures I2 are of a transverse Width equal to double the thickness of the respective bars |13l such that when the elements IU are operatively positioned an aperture of the size of each dowel l5 will be provided in each plate I I adjacent the bar I3 which is rigidly secured thereto. The dowel portions I6 will thus lap each other when assembledy and slide into the respective apertures I2 upon moving'theshear plates I I into operative positions, as in Figs. 2 and3.

A dowel socket or housing I1 must be provided in each concrete slab for slidably receiving each dowel I6 and such socket is preferably formed by mea-ns of a sheet of thin metal bent into rectangular form and one side having its opposed edges welded as at I8 to the top and bottom faces of the bar i3. As best shown at the extreme left of Fig. 1 the vertical web of the sheet metal housing -is of greater length then the top and bottom faces so as to be bent therebetween and-welded at 2d into engagement with the bar I3. These sockets or housings I'I are therefore closed except for the Vdowcl entrance I-Z in the shear plate whereby admission of concrete is avoided for free relative sliding of the dowels I6 during expansion or contraction of the concrete slabs S (Fig. 3).

The usual expansion joint sealing strip 22 is provided with a rectangular openingk 23 adjacent each plate and 'dowel structure for receiving the relatively slidable dcwels I6 as is clearly indicated in Figs. 2 and 3.

The rear end of the bar portions I5 extend well into the concrete vslabs S at Vopposite sides of the joint between two slabs and function to anchor the'dow-els and distribute the stresses therein and to transmit strains remote from the joint directly tothe .shear plates in the opposed faces of the slabs.

The 'dual dowel structure herein disclosed in -higlfily'efiicient for thispurpose and overcomes the ineffectiveness of dowel structures heretofore used or proposed. It is here to be particularly noted that while each dowel llli s freely movable in the socket I 'I of thecooperating dowel, said dowelsare rigdlyvsupported by its vrespective shear plate ll.

'The'dowels are positioned flatw-ise against each other or in laterally-contacting relation to mutufally support eachother when the slabs contract or expand. Under this condition the dowels will 'slide in opposing directions, -each dowel bearing 'on the-shear plate "of the other dowel, and the pair of dowels cooperating to dorm 'a double -truss spanning the j'oint at 'required intervals .bet-Ween the 'concrete slabs.

As disclosed, the pr'esent `structure provides a pair vof unitary rigid elements each embodying van 'anchoring portion, a shear plate, a dowel, 'and a vldowe'l receiving socket, and leach said element will be'rigidlyembedded in Ian vedge -or 'end face of a concrete slab as indicated in Fig. 3. rThus, thecoaction of both elements Yorunits, which may be identical, will result yinthe most efficient and rigidf'or'in of `doweli'ng,"and one iwhich will prevent jackikning of the :slab as indicated diagrammatically in Fig` 7, with ample #provision Ahowever 'f-for. t'h'e :free .longitudinal movement fof the dowels within the sockets and within the shear plates to permit the slabs to expand or to contract.

It is further to be noted that by the improved structure herein disclosed a balanced effect is provided on both slab ends of and adjacent a joint therebetween which is necessary for continued operation of a dowel as a supporting element and for the efficient action herein described. This is not found in other structures of this general character heretofore used or proposed.

Referring nowfto Figs. 4 and 5 wherein is illustrated a structure similar to that of Figs. 1, 2 and 3, the shear plates are provided with upper and lower flanges 25 and 26 for anchorage in the concrete slabs whereby holding the shear plates eiectively in position. Their upper anges 25 are preferably provided with openings 21 to permit concrete to iiowabout the structure and honeycombing of the plastic material. The openings 21 further functionlto more rmly unite the flanges with the concrete. The bar portions I5 in this embodiment are'provided with laterally deflected rear end portions 28 for the purpose of greater anchorage in the concrete body of a slab as well as stress-relieving.

AIn the embodiment of the invention the bar portions |59' are provided with openings 29 for receiving a wirefsupport 30. The support may comprise opposed portions 3| each having a linear subgrade engaging portion provided with an angle portion 32 to permit contraction and expansion of the slabs. The support is primarily adapted to maintain the structure above the sub-grade and when it is desired to elevate the structure to a higher position, the portions 3| are brought closer and when it is desired to lower the structure, the

portions 3| are spread apart. In this manner the assembly may be'` supported in a variable position above the sub-grade. Otherwise the structure is the same as that of Figs. 1 to 3 and functions in substantially the same cooperative manner.

In Fig. 6 is diagrammatically illustrated the structure of Figs'.` 4 and 5 in operative association with a concrete slab joint, but it is, however, to be understood that the dual dowel structures of the other embodiments of the invention will provide substantially the same eiiiciency. The slabs S as indicated are maintained in alinement when the improved plate and dowel structure are inoorporated in the joint due to the long strain transmitting bar portions |55, the dual truss dowels, and thebalanced support at each side of the joint.

When, however, ordinary structures of a dowel and socket embedded in the opposed end of the slabs is utilized at the joint, as heretofore proposed, insufiicient support and balanced relation is provided so that the slabs S will jack-knife as indicated in Fig. 7 and thereafter prevent operation of the parts as a supporting bridge.

A further embodiment of the invention is illustrated in Figs. 8 and 9 which show the same general organization as previously described. The shear plates ||b are provided with upper and lower right angular flanges 35 and 36 respectively, and the upper flanges 35 are each provided with an aperture 31. In this embodiment the usual expansion joint strip 22 is supported or held with its openings 23 in registration with the aperture l2 by a removable cap strip 38 which is of inverted U-shape. This cap strip as shown is provided with prongs 39 in registry with the apertures 31 and for entering same as indicated. This also temporarily prevents separation of the shearV plates from the strip 22 after setting up of the parts. v l

- In this embodiment the bar portions |5b are provided with downwardly projectingsupports 4|) for engagement with the sub-grade. l Such supports are of a length to support the joint strip 22 on the sub-grade, or if desired in a suspended position. The cap strip 38 is removed prior to the final nishing of' the concrete slabs. A wire spring member 4| may extend between the supports 40 to aid in holding the shear plates against the joint strip. However, when the cap strip 38 is used, such spring member may be omitted. The bar portions I5b may further be provided with upwardly diverted anchorage portions 42 for better uniting the bars with the concrete slabs. l

' A further embodiment of the invention is illustrated in Figs. 10 and 11, whereinthe shear plates ||c are each provided with a pair of adjacent horizontally spaced vertically elongated apertures 44 and 45, and the bars providing the dowels |6 are each formed into a U-shaped concrete anchorage portion 46. One leg of each U-shaped portion 46 is extended to'provide the dowel `which extends forwardly through the aperture 44, and the other leg terminates at the rearside of the shear plate laterally of but adjacent the aperture 45. These legs' of the U-shape'd flat bar portions 46 are secured to the shear plates as by welding at the point of contact therewith as at 41 and 48. Cover plates 49 and 50 may be secured as by welding or otherwise to the upper and lower edges of the U-shaped bar portions 46 so as to formfenclosed pockets, as indicated at the left in Fig. 10, thereby providing unobstructed dowel receiving sockets |1.

4l *A further embodiment of the invention is illustrated in Fig. 12 which, as in all embodiments, comprises shear plates |d each having rigidly secured thereto in horizontally spaced relation a dowel |6and a dowel socket I1". 'Each shear plate of this embodiment is provided with an integral laterally and inwardly directed iiange which seats on the sub-grade and which is returned upon itself in the form of a second superposed flange 53. A relatively flxedbase is thus provided which extends up into the concrete slab with which the plate is associated. The shear plates are provided with anchoring and strain transmitting members 54 which extend upwardly in continuation of the'dowels Hifi.'` The upper edges of the shear plates are provided with flanges 55 which are ribbed as at 56 for stiffening the ilange and providing better anchorage in the concrete slabs. The shear plates may further be provided with reinforcing and anchoring ribs 51 between the flanges.

A further embodiment of the invention is illustrated in Fig. 13 which is substantially of the form of Figs. 1 to 3 but wherein the bars are of I-beam form or construction. In this embodiment, the shear plates ||e are each provided with a relatively large centrally disposed rectangular aperture 59 through which extends an I-beam shaped bar 6D welded to the plate at the margin of the aperture as at 6|. The width of the apertures providesv for sliding contact between` adjacent anges of the bars in movement of the dowels ||ib through the apertures and into the sockets I1. These shear plates ||e are shown provided with upper and lower flanges 62 and 63, each ofwhich is further provided with an angularly disposed anchoring tongue 64. The anges 62 and 63 are

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