US2168925A - Joint in concrete slabs or pavements - Google Patents

Description

Aug. 8, 1939. L. 1. HEWES El AL JOINT IN CONCRETE SLABS OR PAVEMENTS Filed Feb. 25, 1937 [NI/ENTOPS I Ma 3. fwu

Patented Aug. 8, 1939 NITED STATES PATENT OFFICE .l'OINT 1N ooNoaErE SLABS on PAVEMENTS Laurence I. Hewes, San Francisco, and William Bertwell, San Mateo. Calif.

(Granted 'under the act of March 3, 1883, as amended, April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government, for governmental purposes without the payment to us of any royalty thereon.

This invention consists of a new and original form of joint between .adjacent sections of a rigid concrete pavement, or other concrete slab,

16 designed topermit contraction or shrinkage and also subsequent expansion and free warping orcurling of the slab or pavement, and for other purposes, and also at the same time designed to provide for load transfer or for such contact between the adjacent sections that superimposed loads near the joint are to a degree mutually supported by the adjacent sections. Such load support is provided by direct vertical support of one section by the other and by an induced distribution of flexural stresses from one section to the other through the interlocking action of the joint.

We are aware that various types of weakenedplane or dummy" joints or other joints are in use which provide a certain degree of mutual support for the superimposed loads by the two adjacent sections of the slab or pavement. Such joints, however, depend largely 'upon simple face interlock of aggregate in the joint sutures, upon keying or tongue-amd-groove action, upon a protruding part of one pavement or slab section of considerably less thickness than the entire section, upon metal bars placed perpendicular to the joint, upon a mechanical interlock of metal, 88 or upon combinations of these methods. This invention, however, employs substantially the entire depth of the slab or pavement in a positive mechanical interlock by the concrete surfaces of the joint in the transfer of load. This interlock is accomplished by the use of a multiple or sinuous warped or ruled surface or variations or approximations or combinations of such surfaces, so formed that each of the two adjacent pavement or slab sections. alternately supports the other and is supported by the other.

This new joint may be formed completely by a templet or pattern at the end of one section of the slab or pavement before placing the adja- 50 cent section, or in the case of continuously poured concrete it may be formed partly by small forming strips, templets, or pieces placed only at the top and bottom of the slab or pavement so that the remainder of the joint surfaces will be formed a as in weakenedmlane or dummy" joints by rupture under the action of stresses set up by temperature changes or by loads.

Figure 1 is an isometric view of the joint formed in a pavement.

Figures 2 and 3 are fragmentary sections 5 through the jointv at the planes 2,22,2 and 3,3-3,3, respectively.

In Figure 1 a straight forming piece I is the directrix at the top of the sinuous warped surface joint between the pavement sections A and 10 B and a waved forming piece 2 is the directrix at the bottom. The periodically curved or waved bottom forming piece 2 is comparatively thin, preferably of a hard material such as metal. The top forming piece. I may be a thin strip of any 16 suitable material, preferably thick enough to permit its later removal and the filling of the corresponding space with a bituminous or sealing material. The periodic waves or loops of the bottom forming piece 2 are preferably approximately 20 symmetrical about a vertical plane whose trace in the top surface of the slab coincides with that of the top forming piece I and whose trace in the bottom surface of the slab is marked 3. As the bottom forming piece 2 loops back and forth 2; through the vertical plane of symmetry any given individual loop of the curve results in a corresponding part of the warped or ruled surfaces which gives direct vertical support to the slab or pavement on one side of the joint only; but 30 the two adjoining loops result in warped or ruled surfaces giving support to the pavement section on the other side of the joint. Thus the joint surfaces are interlocking irregular surfaces of natural fracture, the trace of which in the plane 35 of the slab section is designated by the numeral 5. Thus, the joint is efiective in the transfer of vertical loads regardless of whether the load is on one side or on the other side of the joint. The joint also acts to transfer flexural stresses 0 in the direction of the joint, as, for example, when load 4 is applied on section A opposite the center of one of the loops 5 of the bottom forming piece 2 so that section A is not directly supported by the warped or ruled surface formed by the particular opposite loop 5. Then as the pavement section A on which load 4 is applied deflects under the load its bottom fibers are subjected to tension paraliel to the joint and so tend to elongate. As they elongate they bear against adto jacent surfaces of the pavement section B on the opposite side of the joint, thus forcing the fibers of that section into fiexural action also. In this manner the interlocked pavement with the load at t behaves structurally in the direction of the as,

joint to a large extent as if there were no joint.

The foregoing descriptions are merely illustrative and are not intended to define the limits of the invention. The forming templets or pieces may be bent into other curves than those illustrated, and may have differently shaped cross sections from that of a simple plate, such as a T or an angle, for example. In all such variations the essential actions are that each of two adjacent pavement or slab sections, A and B, alternately supports and is supported by the other and that these pavement or slab sections are so interlocked as to distribute flexural stresses from one side of the joint to the other. It is also obvious that this type of joint may be used with or without metal reinforcing bars passing across the joint, and with or without metal plates or other devices intended to exclude moisture or debris from the joint. Such additional parts, however, in no way affect the essential characteristics of the described joint.

Where a longitudinal joint intersects a transverse joint, the corresponding forming pieces in the top and bottom surfaces, respectively, should intersect preferably at angles of 90 degrees. This specific and preferred arrangement causes a vertical load on a corner of any one of the pavement sections to be partially transferred in turn to the corners of the three other pavement sections, so that all four corners aid in the support of the load.. It is, however, not necessary that the angles between intersecting for! :5 pieces be exactly 90 degrees, but only the general arrangement at the interact r shalt be approximately as iliustrated so that no interior corner of a pavement section is without support by an adjacent pavement section.

We claim:

1.. A concrete slab joint comprising a straight narrow strip of materiel-i in the top oi said. joint, another narrow strip or material in the bottom of said joint, said bottom strip being symmetn caIly sinuous about the vertical projection of said top strip, both of said strips being relatively narrow with respect to the slab thickness, the slab portion between said strips beinglfractured along natural lines.

2. In a concrete slab joint two spaced strips of material, one oi said strips being embedded in the top of the joint and being straight, the other strip being embedded in the bottom of the joint and being symmetrically sinuous about the vertical plane of the top strip, both of said strips being relatively narrow with respect to the slab thickness, the portion of the slab between said strips being naturally tractured, whereby the meeting ends of the joint contact each other along complementary interlocking warped surfaces,

LAURENCE I. HEWES. WILLIAM BERTWELL.

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