US2305979A

US2305979A - Compressible cap for dowel bars

Info

Publication number: US2305979A
Application number: US350846A
Authority: US
Inventors: Robert E Mitchell
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-08-03
Filing date: 1940-08-03
Publication date: 1942-12-22
Anticipated expiration: 1959-12-22

Description

Dec 22, 1942. R. E. I VIITGH ELL 5, 9

I COMPRESSIBLE. CAP FOR DOWEL BARS Filed Aug. 3, 1940 "Tiwmbm r ATTORNEYS Patentecl Dec. 22, 1942 UNITED STATES PATENT OFFICE COMPRESSIBLE CAP FOR DOWEL BARS Robert E. Mitchell, Seattle, Wash.

Application August 3, 1940, Serial No. 350,846

4 Claims. (01. 94-18) My present invention relates to the general art of concrete paving and more particularly to a compressible cap for dowel bars.

Where concrete pavement is made in slabs or panels it is necessary to join these-panels so as to assure that they will not become displaced and thus permit one to sink below the surface of the other, and thus cause an uneven road surface. The usual method of achieving this result is to place steel bars at frequent intervals which extend half in one slab and half in the abutting slab. It has been found, however, that due to temperature changes there is considerable movement of the slabs. Normally, to provide means for insuring a smooth road surface, the joint between the two slabs is filled with an expansion joint material, usually of felt or fibrous base that is impregnated with asphalt or some similar substance. Thus, when the pavement becomes heated, it will contract, and when the pavement shrinks away, the material will tend to shrink back into its normal position. This expansion joint, however, provides an excellent lubricant for the slab edges, and further makes more acute the necessity for the dowel bars. great shearing strain is sometimes placed on the dowel bars themselves, and it becomes necessary that the ends of the dowel bars not be restricted against movement, or at least, that one end of each dowel bar be free to move into the adjoining slab as expansion occurs.

My device consists essentially in providing a flexible rubber cap which is adapted to fit on the end of a small bar and to provide means for displacing sufiicient of the concrete as the same is being poured so that a cavity is formed at the end of the dowel bar which will permit its fullest expansion and contraction without injury to the edge of the concrete slab. This general object is achieved by having the rubber cap made generally in cross-section to the shape of the dowel bar and, by providing that it fit over the end of the dowel bar, a cavity of sufiicient size to permit the free movement of the dowel bar is assured.

Many devices have been provided for this purpose. Devices to accomplish this purpose have been made of metal or paper, but have proved to be difficult to handle, particularly in wet weather and the like, and are often subject to serious damage in handling. With my present flexible cap, being made of a readily yieldable rubber, the caps may be put in place at their point of manufacture, and then may be transported and delivered and used without danger of the caps be- With this working of the slabs,

coming damaged to the point of not serving their intended purpose.

The principal object of my present invention, therefore, is to provide a cavity-producing cap for dowel bars that is made from yieldable material.

A further object of my present invention is to provide a yieldable rubber cap for dowel bars that is so arranged interiorly as to accurately position the cap on the dowel bar.

A further object of my invention is to provide a flexible rubber cap for use on dowel bars that is so proportioned as to accurately provide a cavity of ample proportions to take care of any expansion to which the dowel bar may be subjected.

Other and more specific objects will be apparent from the following description taken in connection with the accompanying drawing, wherein Figure 1 is a perspective view of a rubber cap made after the teachings of my invention.

Figure 2 is a typical longitudinal section through the same.

Figure 3 is a sectional view similar to Figure 2, but showing a cap in its proper position on a dowel bar, which dowel has, in turn, been suitably treated for use.

Figures 4, 5 and 6 are cross-sectional views taken along similarly numbered lines of Figure 3.

Figure 7 is a perspective view showing one half of a modified form of a rubber cap with the cutaway portion indicated by dotted lines.

Figure 8 is a perspective view, showing a further modification of my dowel bar cap, the same being cut away so as to show one half of a cap which has been out along its center in section.

Figure 9 is a perspective view showing another cap made after my preferred arrangement and illustrating how it is adaptable to rectangular dowel bars.

Figure 10 is a perspective view showing the manner in which dowel bars are used, and illustrating the manner in which my caps are employed thereon.

Referring to the drawing, throughout which like reference characters indicate like parts, l2 designates generally the shell of my cap. This I prefer to make of rubber of such a temper that it will be resistant to distortion but, under pressure, can be distorted. It should be of sufiicient rigidity so that the concrete, which is normally poured to a depth of six inches at its extremes over it, will not displace the cap. 0n the other hand, it should be sufiiciently fiexible that it can be easily put on the end 01' a dowel bar. even though the end may not be cut accurate and true. The ability of the cap to accommodate a sheared-off dowel bar effects a very considerable saving over those devices which require that the dowel bars be machined on the ends, as is normally required when metal tubular caps are employed.

The outer surface and the interior of the cap must, of necessity, conform in section to the section of the dowel bar it is to be used with. It should, however, be sufliciently larger than the dowel bar so'that there will be ample space for the rubber of the cap to flow or distort as the dowel bar under expansion tends to fill the chamber in the end of the cap.

In Figure 7 I have shown a modified form of cap where an adit chamber portion 32 is provided for the reception of the dowel bar and the entire cap is molded from a porous or sponge rubber so that when expansion of the dowel bar occurs the rubber mass in the head of the cap, as 34, may be compressed sufficiently to give adequate clearance for the dowel bar.

In order that my cap may be used to best advantage I have illustrated in Figure the manner in which they are normally employed. In Figure 10 I have illustrated two abutting concrete slabs 36 and 31. Into slab 31 projects one end of each of the dowel bars 38. The portion of the dowel bar extending into slab 31 is anchored therein by a bond that will be secured with the concrete. This bond will hold the dowel fixedly in that slab. The portion of the dowel bar in slab 36, exclusive of that portion covered by the rubber cap, is treated with some form of coating material or paint 40 which will serve both as a lubricant and to prevent the bonding of the cement to the dowel bar. Normally I provide that this painting or dipping of the bar extend partly into slab 31 after the showing in the drawing, so that the dowel bar will be held only for a sufiicient length to assure a gripping at one end, but not enough so that the difference in the coefiicient of expansion between the dowel bar and the concrete will cause the margin of the slab 31 to check or crack.

It is very essential that the cap be placed on the dowel bar in such a manner that adequate space is provided within the cap for the subsequent movement of the dowel bar. To assure this, even when the placing of the cap is entrusted to unskilled workmen, definite means are provided to form a section of wall, up against which the dowel bar can be placed and thus ade quate clearance is provided. The preferred arrangement is in providing a chamber having a plurality of webs l4 which, preferably, may intersect as is indicated in Figure 4 at 15. A further modified arrangement is to provide a substantially annular ring as part of the body of the cap, as is indicated in Figure 8 at l6. A further modification is illustrated in Figure 9, in which one or more webs l8 are employed, together with abutments as and 2|. This form is particularly adaptable to the dowel bars of rectangular cross-section.

Attention is directed to a desirable proportion of the two chambers of my cap. The adit chamber as 22, or 24 or 26, as shown in Figures 2, 8 and 9, is preferably less in size than the webbed interior or displacement chamber shown in the same figures at 28, 29 and 30 respectively. This arrangement is desirable in order that an interior diameter be provided for the reception of the dowel bar on expansion that will provide also sufficient space for the rubber of the cap which may be displaced into that space due to the slight movement of the cap under the end thrust of the dowel bar when expansion occurs.

It will be apparent that with the device installed as illustrated, it is believed, that when,

expansion or contraction occurs thedowel bar will be moved by its seat against the slab 31 and will be free to move within slab 36, inasmuch as it is not bonded in it. When extreme expansion occurs the dowel bar will be driven into the flexible rubber cap and into the cavity that the cap has formed in the concrete during the concrete pouring and setting operation.

The foregoing description and the accompanying drawing are believed to clearly disclose a preferred embodiment of my invention, but it will be understood that this disclosure is merely illustrative and that such changes in the invention may be made as are fairly within the scope and spirit of the following claims.

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

1. A cap for use in connection with dowel pins that are positioned between expansible members, said cap comprising a resilient elongated body having a cup to receive and accommodate a dowel end, and an inner flange medially located in said cup and adapted to space the closed end of the body a distance from an inserted dowel end greater than the thickness of the walls of the body.

2. A cap for use in connection with dowel pins that are positioned between expansible members, said cap comprising a resilient elongated body having a cup to receive and accommodate a dowel end, and a web in the inner portion of the cup adapted to space the closed end of the body a distance from an inserted dowel end greater than the thickness of the walls of the body.

3. A cap for use in connection with dowel pins that are positioned between expansible members, said cap comprising an elongated hollow body of resilient material having a single closed end, a member spaced from the inner bottom of said hollow body in the path of a dowel end inserted therein to space the same from said bottom, said member comprising a resilient Web integral with the body.

4. A cap for use in connection with dowel pins that are positioned between expansible members, said 'cap comprising an elongated hollow body of resilient material having a single closed end, a member spaced from the inner bottom of said hollow body in the path of a dowel end inserted therein to space the same from said bottom, said member comprising a cross-shaped resilient web integral with the body.

ROBERT E. MITCHELL.