US2181005A - Dowel bar structure - Google Patents

Description

' NOV. 21, 1939. y C. HV WESTCOTT 2,181,005

DOWEL BAR STRUCTURE Original Filed May 20, 1935 fr Ig :Ill

fordlhsco" y ,LLS diie/"neg- Patented Nov. 2l, 1939 PATENT ori-Ica DOWEL BAB STRUCTURE v cnam-a n. Westcott. yom: Park, nl.,

mesne assignments, to Cal C. Robert S.` Bradshaw, Jr.,

ILouis, Mo.

Ol'illll 22,308. Divided application Msy'zo, 1935,

and this application Septemassignor, by Chambers .and as joint tenants, St.

berf14, 1939, Serial No. 294,916

20 Claims.

My present invention relates to highway construction and particularly to the buildingof con-A crete pavements, and more particularly to a device for transferring road loads from one con- 5 crete slab to the next adjoining slab, and is an improvement over what is known as the common dowel bar.

A This is a division of my prior and co-pending application, led May 20, 1935, Serial No. 22,308.

It is well recognized in volume due in a large sense to moisture content or temperature change, -and that as these volume changes tak` e place the concrete slabs,

under restraint, will rupture and establish natural joints or, preferably, mechanical joints are interposed at'predetermined intervals which permit of the unrestrained and unrestricted movement of the slabs.

When mechanical joints are employed, thus dividingjshe pavement into a plurality of relatively short slabs, and in order that the surface of the adjoining slabs may be maintained uniform and in substantially the same plane so as z5 to obtain a comparatively smooth and uninterrupted surface for the motoring public, it has been-customary for many'yearsl to dowel across from one slab to the next adjoining The common dowel has been universally accepted as the most practical means for this purpose, but the common dowel has many deficiencies. The common dowel,l economical due to its inherent shape, is lacking in bearing, and many methods have been employed in an attempt to extend the bearing of the dowel, for the purpose of distributingv the applied load both to the face of the slab and to points back within the slab. Most of these devices are prohibitively expensive to manufacture and install. They are very cumbersome {0&and create eld diiliculties and raise considerable uncertainty in engineers minds as to their flnal positioning within the slabs after the concrete has set. Y s

It is the province of the common dowel to ilrst 5 acquire a portionof the superimposed load, and

to carry it across the adjoining slabs, and then to distribute the load within object of this invention to; D -Erstreducethehigh at the edge of the slab Aby providing a greater area in contact with the concrete atthe edge oftheslab; and i Second, to` further reduce the high edge 5 stresses by virtueof '(01. si-is) in this art that concrete y Y pavements are continually undergoing a change.

radiating anchors which either absorb load or transmit-:and distribute the dowel loads to and within thefslaband thereby eliminate high stress areas in the slab that would otherwise exist.

A further object is to decrease the deflection of the short dowel during periods of load transmission by furnishing a definite structural support for the body of the dowel, which not only eliminates channeling within the slab, but by so doing, also decreases load transmission.

My object is to provide a shorter effective length of structural dowel member whereby the deflection of the dowel is materially reduced.

It is a further object to increase the load transmission capacity of the common dowel, as a dowel used for thepurpose of load transmission is required to withstand bending and shearing stresses, and I materially reduce these bending stresses in a dowel byl effectively. reducing the length of the dowel. I further increase the load transmission capacity of the dowel by virtue of its reductionv in length with its consequent increased capacity in bending. Due to this shorter length and consequent smaller deflection, the 'load transfer capacity of the dowel is consider- `ably increased, Naturally, the amount of this increase also depends upon thethickness of the slab and the modulus of the subgrade reaction.

It is a still further object of my invention to provide an air space at the end of the short deflection under periods of dowel so that the dowel may move freely within the slabs to accommodate the lateral movement` 'of Vthe adjoining slabs duringperiods of volume change. l Y

My present invention has these and other objects, all of which are explained in detail and may be more readily understood when read in 4conjunction with thel accompanying drawing (one sheet) which illustrates the preferred embodiment o! my invention, it being manifestv that changes and modlncations may be resorted to without departure from the spirit of the claims forming a part hereof. In the drawing: f

Fig. 1 is a perspective view of a commercial type of expansion joint showing my invention in its relative association therewith; the joint is shown in broken lines as forming no part of my invention; Y

- Fig. 2 is a vertical section through the same type, of expansion joint shown cast between the end faces of adjoining concrete slab sections, *one hall.l oi-the-unit is in section, the dowel and 'the opposite unit being shown in elevation;

Fig. 3 is a transverse section through the dowel and bearing taken on line 3-3 of Fig. 2;

Figs. 4, 5, 6 and 'l are illustrative of various cross-sections of conventional forms of dowel bars, which are considered applicable in carrying out my invention;

Fig. 8 is a sectional view, similar to Fig. 2, whereinjI have'shown a plurality of concentric fins cast integral with the dowel bearing; and

Fig, 9 is a section through Fig. 8 taken on line 9 9.

The structures illustrated involve the application of my invention to a roadway slab, and for purposes of description only, Ichoose to deiine my invention` as applied to this particular construction; however, I wish it understood that its adoption and use are equally applicable to any poured or pre-cast structure, whether it be a roadway slab or a retaining wall, daxnv or building structure, for, as a matter of fact, my invention is applicable to an almost unlimited number of structures.

For purposes of illustration, I have shown a conventional type of expansion joint comprising at the bottom and supporting a metallic seal 22 with a mastic cap 23, the seal is provided with lateral anchors 24-24 adapted -to be cast into adjoining slab sections A and B; and whereas I have shown and described such a joint, I wish it understoodthat any type of joint may be employed in connection with my invention, whether it be an expansion joint, contraction joint, or only a'construction joint or space.

My invention consists in spanning the space or gap provided bythe joint betwen slabs A and B with a relatively short dowel bar 25, positioned at substantially mid-depth of the slabs, parallel with the top surface thereof, and normal to the plane of the joint; and whereas I have shown the dowel 25 as thecommon rolled bar of circular cross-section, it willbe apparent to those skilledV in the art, that dowels of various cross-sections maybe employed without departing from the spirit of my invention. Figs. 4, 5, 6, and 7 are illustrations (as before described) of the most commonly used steel sections which I employ for this purpose.

The ends -of the dowel 25 are telescoped into a pair of counterpart `and relatively reversed rigid bearings or sleeves 26, each of which consists of a single unitary casting adapted to be imbedded in its respective slab, and each such sleeve or bearing comprises a cup-like portion which is reamed to provide a snug and tight sliding 't for the dowel and of a length suicient to provide an air chamber 21 of a depth substantially equivalent to one-half of the gap 'or space between the adjoining slabs. sealed with a well 28, whereas the inner faces 29 areA placed approximately flush with the face of their respective slab sections, so that the axis of the bore is substantially horizontal and at right angles to the slab end.

As shown at Figs. l and 2, a pair of radial arms or anchors 30-30 are cast integral with the wall 28 of the sleeve 26, the anchors 30 diverge therefrom and approach (but do not penetrate) the surface, top and bottom, of their respective slabs. Theouter ends of the anchors 30 are enlarged in cross-section to establish bulb-like portions or knobs 3l. Y

Lateral bearings or anchors such as ns 32 may also be provided to increase the bearing in the concrete; such ns, one on each side of eachunit The outer ends of the sleeves are or anchors 42 and 43 which are cast as an integral part of and encircle the bearing sleeve. The rings oranchors 43 are preferably positioned directly adjacent the open end of the sleeve and immediately adjacent the slab face, whereas the anchors 42 are spaced therefrom, and as shown, may be located directly adjacent the closed end of the sleeve. And laterally disposed anchors 44, similar in purpose and function to the anchors 32, may also be employed, preferably positioned intermediatefand connecting the encircling rings or anchors 42 and 43 as shown, whereby the unit pressure on the concrete surrounding the anchors, when the dowel is under load, will be lessI than that in the concrete which directly contacts the sleeve.

In the assembly of this dowel structure, the dowel 25 is rst passed through the joint with equal lengths protruding on each side thereof, a pair of sleeves 26 are next placed over the protruding ends of the dowel as shown, and then temporarily keyed in place wtih soft metal pins 35 driven through aligning holes in the sleeve and dowel. Thedowel structure just defined is assembled at spaced intervals throughout the length of the mechanical joint, and at the desired spacing to accommodate the estimated loads the pavement is to carry. The entire structure, in-

the load is' absorbed by the dowel structure and particularly the radial anchors 30, 32, 42 and 43, concentrated, and then transmitted to the sleeve and dowel and thence across the joint to a like unit on the opposite side or next adjacent slab,

where the concentrated load is dissipated through the sleeve and the radial anchors and distributed into the slab structure. As the load crosses the joint and onto the next adjacent slab, the reverse of the above action starts 'at a maximum and diminishes as the load passes on. The short dowel remains at all times at or near the neutrai-axis of the slabs, whereas the radial anchors remain within the tension and compression areas intersecting the shear planes and reinforcing the edge of the slab. This actionof the dowel structure absorbs and' so distributes the load, that if failure does occur, it will take place place outside ofthe field embraced by the dowel bar structure, as the dowel in its bearing effectively transmits the full strength of one slab to the other without interruption; in fact, the employment of, this structure insures the highway against joint failures, as the slab, here, is stronger at the joint than at any other point, as the anchors 30, 32, 42 and 43 all increase the bearing value of the sleeve 26 in the concrete and assist in the distribution` of load to such an extent as to prevent channeling of the concrete structure.

Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. 'A load transfer device for bridging a gap between the adjacent end faces of two substantially horizontally aligned concrete slabs, comprising two counterpart and relatively reversed rigid major members each consisting of a single unitary casting having its integrated parts adapted to be imbedded in its respective slab, each major member comprising a cup-Alike sleeve portion opening at the end face of the slab in which that member is imbedded and adapted to have the axis of its bore horizontal and at right angles to said slab end and substantially within thez neutral plane of the slab, integral anchors ex' tending outwardly from the outer wall of the cup-like sleeve portion of each major member and into the body of the slab within which it is adapted to be imbedded, and a dowel-like bridging member adapted to seat and have bearing in the bore of the cup-likebsleeve portion of one major member and adapted to project beyond the end face of its respective slab and tobridge the gap intervening between the adjacent end faces of the adjoining slabs and to extendinto and slidablyv engage the bore of the cup-like sleeve portion of the other associated major member.

2. A load transfer device as per claim 1 in.

which the anchors, `which are in integral part of each major member, diverge away from the open end of the sleeve'portion of each major member and are symmetrical with respect to a horizontal. plane at right angles to the slab end for transmitting the imposed loads between the dowel-like member and the slab.

3. A load transfer device as per claim 1 in which the anchors, which are an integral part of each major member, diverge away from the open end of the sleeve portion of each major member and have their axes in a common vertical plane with the axis of the dowel-like member, and further have their free end portions formed for interlocking with the material of the slab in which that member is adapted to be imbedded to prevent a movement of that member toward the adjacent end face of the slab.

4. A load transfer device as per claim 1 wherein the anchors which are integra-l with the cuplike sleeve portion of each major member diverge away from the open Yend of the sleeve portion both upwardly and outwardly and downwardly and outwardly therefrom and into the body of the slab to transmit the imposed loads away from the slab face.

5. A load transfer device as per claim/1 which includes laterally disposed anchors extending outwardly from the sleeve portions in a substantially horizontal plane for transmitting pressure directly to the material of the slab, whereby the unit. pressure on the concrete around the sleeve and the anchors is less than that on the concrete which would directly contact the sleeve of the major member if the anchors were omitted.

6. A load transfer device as per claim 1 including an enlarged ring portion integral with and encircling the sleeve at a point adjacent the open end thereof and immediately adjacent the slab face for transmitting pressure 'directly to the material of the slab.

'7. A load transfer device as per claim 1 which includes a plurality of concentric fins integral with and encircling the sleeve at spaced intervals for transmitting pressurev directly to the material of the slab in which they are imbedded.

8. A load transfer device as per claim 1 wherein the integral sleeve portion of each major member is adapted to slidably house an end portion of the dowel' member, and wherein each sleeve portion has its bore of sumcient len th to afford an air space at each end of the ssembled dowel to permit relative movement betwee the dowel and its enclosing sleeves.

9. A load transfer device as per claim 1 whereinthe enclosed length of the dowel-like bridging member is less than the length of the bore of the cup-like sleeve portion to thereby establish an air space at one end of the dowel.

10. A load transfer device as per claim 1 in which'the dowel-like member has a close sliding t in the bore of the sleeve portion of the major member with a tolerance in clearance which limits the deflection of the dowel in its bearing when under load to within the bending limits of the concrete.

11. A load transfer device as per claim 1, wherein the dowel-like member has a snug sliding fit in the bore of the sleeve portion of the major member and wherein the clearance between the dowel and its bearing is less than three one-thousandths of an inch.

l2. A load transfer device as per claim 1 wherein the bearing of the enclosed dowel within the bore of vthe sleeve portion is greater in length than the diameter of the dowel.

13. A load transfer device as per claim. 1 in which the bore sectionof each. cup-like sleeve portion is of greater height than Width and wherein the greater section modulusof the dowel l opposes the bending moment and shear produced by the loading forces.

14. A load transfer device as per claim -1 which includes two latch elements respectively housed by the sleeve portions of the major members, each of which latch elements latchingly engages the dowel member.

15. A load transfer device as per claim 1 which includes locking members engaged with said dowel-like members to prevent the relative rotation of said dowel members with respect to the cup-like sleeve portion ofthe major mem' bers.

16. A load transfer device as per claim 1 whichincludes locking members engaged with said cup-like sleeve portions of said major members to prevent the separation of the assembled device.

17. A load transfer device for bridging a I'gap between the adjacent end faces of two substantially horizontally aligned concrete slabs, comprising a relatively rigid major member consisting of a unitary casting having its integrated parts adapted to be imbedded in one ofthe two slabs, said member comprising a cup-like sleeve portion opening at the end face of the slab in which that member is imbedded and adapted to have the axis of its vbore horizontal and at right angles to said slab end and substantially within the neutral plane of the slab, integral anchors y extending outwardly from the outer wall of the cup-like sleeve portion of said member and adapted to enter into the body of the slab within which it is adapted tobe imbedded, a dowel-like bridging member adapted to seat within and slidably engage the bore of the cup-like sleeve portion of said major member and adapted to pro,- ject beyond the end face of its respective slab and to bridge the gap intervening between the adja- Y cent end faces of the adjoining slabs and enter and engage the opposite or opposed slab.

18. A load transfer device for bridging a gap 75 .tially horizontally aligned concrete slabs, com-.

between the adjacent end faces of two substanprising two counterpart and relatively reversed rigid major members each consisting of a single unitary casting having its integrated parts adapted to be imbedded in its respective slab, each major member comprising a cup-like sleeve portion opening at the end face of the slab in which that member is imbedded and adapted to have the axis of its bore horizontal and-at right angles to said slab end and substantially within the neutral plane of the slab, integral anchors extending outwardly from the outer wall of the cuplike sleeve portion of eachl major member and into the body ofthe slab within which it is adapted to be imbedded, a dowel-like bridging member adapted to lseat and have bearing in the bore of the cup-like sleeve portion of one major member and adapted to/ project beyond the end face of its respective slab and to bridge the gap intervening between the adjacent end faces of the adjoining slabsand to extend into and slidably engage I the bore of the cup-like sleeve portion of the other associated major member, and said anchors having their axes in a common'horizontal plane with the axis of the dowel-like bridging member.

19. A load transfer device for `bridging a gap between the adjacent end faces of two substantially horizontally aligned concreteslabs, comprising two counterpart and relatively reversed rigid major members each consisting of a single unitary casting having its integrated parts adapted to be imbedded in its respective slab, each major member comprising a cup-like sleeve portion opening at the.' end face of the slab in which that member is imbedded and adapted to have the axis of its bore horizontal and at right angles to said slab end-` and substantially within the neutral plane of the slab, integral anchors extending outwardly from the outer wall of'the cup-like sleeve portion of each major member and into the body of the slab within which it is adapted to be imbedded, said anchors comprising a plurality of spaced apart tins substantiallyconcentric. integral with and encircling the sleeve portion, and -a dowel-like bridging member adapted to seat and have bearing in the bore of the cup-like sleeve portion of one major member and adapted to project beyond the end face of its respective slab and to bridge the ga'p intervening between the adjacent end faces of thel adjoining slabs and to extend into and slidably engage the bore of the cup-like sleeve portion of the other .associated major member.

20. A load transfer device for bridging a gap between the adjacent end faces of two substantially horizontally aligned concrete slabs, comprising two counterpart and relatively re- Aversed rigid major members each consisting of a single unitary casting having its integrated parts adapted to be imbedded in its respective slab, each major member comprising a cup-like sleeve, portion opening at theend face of the lslab extending outwardly from the outer wall of the in which that member is imbedded and adapted v cup-like sleeve portion `of each major member and into the body of the slab within which it is adapted to be imbedded, a dowel-like bridging member adapted to seat and have bearing in the bore of the cup-like sleeve portion of one major member and adapted to projectbeyond the end face of its respective slab and to bridge the gap intervening between the adjacent end faces of the adjoining slabs and to extend into and slidably engage the bore of'the cup-like sleeve portion of the other associated major member, and each of said anchors being disposed in a vertical plane transverse to the horizontal axis of the dowel-like bridging member.

CLIFFORD H., WESTCOTI.

Images