1. Field of the Invention
This invention relates to the field of expansion joints for substantially abutting slabs or panels wherein the joint is to be covered by a facing or covering material. In particular, the invention concerns an expansion joint between abutting decks in a building, to be covered with a facing material such as carpeting, tile or the like. In addition to accommodating expansion and contraction of a gap between the panels at the joint, the invention accommodates displacement of the panels from a coplanar relationship, for example due to unequal settling of the supports for the panels. The invention also applies to expansion joints in walls, ceilings, etc., wherein a facing material is to be placed smoothly over a varying gap between abutting panels which may be displaced from a nominally coplanar relationship.
2. Prior Art
An expansion joint in a floor, wall, ceiling or other structure joins two members defining substantially coplanar surfaces on at least one side, the two members generally abutting along a line but defining a gap between them. The width of the gap and the coplanar relationship of the two members vary over time. The width of the gap can change, for example, as a function of temperature and load variations on the means supporting the two members. Such variations may be periodic or may proceed slowly over a long time. For example, the two members can be displaced from a coplanar relationship if the supports for one of them settles more than the supports for the other. Although the span of displacement is typically small, the forces behind the displacement are substantial. To avoid cracking and similar structural failure of a rigid element of a structure or the means supporting the element, an expansion joint divides the element in two and allows the two parts to move relative to one another in a flexible manner over a limited span.
Known expansion joints have a number of objectives relating to maintaining a connection between the two relatively movable members notwithstanding the gap, and/or maintaining a smooth surface over the gap, for example for bearing traffic, and sealing between the two members. It is possible for a panel at an expansion joint to move relative to the other panel in a direction in its plane or perpendicular to its plane. Displacement in the plane either varies the gap width or simply causes the panels to be displaced longitudinally along the gap. Displacement perpendicular to the plane can result in a change in elevation as the panels remain parallel, or the panels can become rotated. It is usually desirable that the joint not define a discontinuity in the surface defined by the abutting slabs, panels or the like. In a floor expansion joint for example, a discontinuity on an upper surface is a tripping hazard.
Where a joint on a floor, wall, ceiling or the like is to be covered for example by carpeting, wall coverings, etc., a discontinuity may form in the covering material that is a bigger problem than the displacement of the panels at the joint This problem is not resolved even if the panels at the expansion joint remain coplanar or at least the facing edges of the panels remain parallel. Although an expansion joint structure may be arranged to hold the facing edges of the panels to maintain a smooth upper surface for the joined members, a discontinuity occurs in the covering material which passes over the joint. The discontinuity of course varies with the gap between the abutting members.
If one attempts to merely cover over an expansion joint between two panels, problems arise from the need to maintain an even upper surface and thereby avoid a tripping hazard. For example, it is possible to attach a flat strip of metal or other stock to cover the gap in an expansion joint. The strip is attached to one of the panels and allowed to extend across the gap to lap over the other panel by an amount greater than a span of variation in the width of the gap. To avoid raised edges, settable floor compound can be applied adjacent the strip and feathered (made progressively thinner) proceeding away from the strip to form a very gradual hump up to the level of the thickness of the strip, which lays on top of both panels in the area of the joint, but is attached only to one. Such feathered floor compound is effective to avoid a tripping hazard on the side of the joint where the strip is attached to one of the panels. On the other side, however, expansion causes a gap to open between the extreme edge of the strip and the edge of the flooring compound. Contraction of the joint exerts a pressure between the strip and the flooring compound tending to break away the flooring compound or causing the strip to bow upwardly. If the panels vary in height, the strip may be raised above the surface of the lower panel (if attached to the higher panel) or bent upwardly (if attached to the lower panel). In any of these cases, this technique is not effective to obtain a smooth upper surface without a tripping hazard in at least some of the conditions of the expansion and/or contraction of the gap.
A covering bridging over the gap further complicates the issue. The abutting members of an expansion joint are generally relatively movable laterally toward and away from the gap, but also may be movable longitudinally along the gap. Both forms of relative movement present the possibility of a bulge, ripple or similar discontinuity in any covering material. Assuming that it is possible to provide an expansion joint with variable length connecting structures that maintain a smooth upper surface, such structures still do not solve problems associated with covering layers, particularly of flexible material, applied over the gap. A carpet applied over a gap, for example, will bulge when the gap closes and will stretch or pull away from its moorings when the gap opens, even if the expansion joint applied to the floor is fully effective to maintain a smooth upper surface of the joined members. When the joined members are relatively displaced in height, the same displacement occurs in the covering material. There is a need to resolve the problems associated with expansion joints where the joint is to be covered, particularly where the members at the joint can vary in height.
In known expansion joint structures, connection flanges forming the opposite sides of the joint across the gap are rigidly fixed to the edges of the two members to be joined across the gap, and flexible or length-variable elements of the joint bridge across these rigidly-fixed flanges. The flanges are arranged flush with the surfaces of the two members, typically on the upper surface and also on the surface facing the gap. This requires that a space be formed in the two members for receiving the joint flanges such that the joint flanges are flush with the top surface and the end faces of the joined members U.S. Pat. No. 3,372,521--Thom discloses a floor joint cover assembly wherein bolts are embedded in both members of a floor joint formed of cast slabs, and the upper edges of the members at the end faces adjacent the joint are contoured to a shape complementary with the joint flanges. The structure must be installed when the slabs are not yet hardened, such that the bolts can be embedded and the complementary shape formed. It is possible in a joint of this type to mill out the area of the slabs to be occupied by the joint flanges after the slabs are set, or to devise molding frames of a shape complementary with the joint flanges, such that the necessary shape is obtained when poured slabs set. However, both these alternatives are complex and expensive. Moreover, the resulting joints do not resolve the problems of flexible coverings such as carpets.
U.S. Pat. No. 3,390,501--Driggers (see FIG. 2) discloses a joint having a structure that protrudes upwardly from the joint in the area of the gap, by an amount equal to the height of finish material such as plasterboard, which finish material abuts the protruding portions of the joint at both sides. This is an alternative to a joint similar to that of Thom, wherein anchoring structures must be embedded in a wet or green slab. The joint may be useful where the facing material (e.g., plasterboard) on the slab on either side of the joint is rigidly connected to the slab, and in view of the rigid structures of the slab and facing material, the composite structure is similar to that of Thom in that the joint resides flush in a complementary contour formed at the facing edges of the two rigid composite joined members. Notwithstanding these aspects, the Driggers joint defines a surface discontinuity and a resulting tripping hazard if the joint is used for floors.
One method of minimizing problems with gapping at an expansion joint is to provide a cover panel that floats between the end faces of the joined members, and means for centering the floating cover panel. An example is disclosed in U.S. Pat. No. 3,745,726--Thom. This means for dealing with the gap effectively reduces the extent of gap by splitting the gap in half, i.e., producing a smaller gap at each side of the floating panel rather than one full width gap. Nevertheless, gap problems remain.
Other joint structures having joint flanges embedded in the material of the slabs or the like are shown in U.S. Pat. Nos. 4,774,795--Braun; 4,784,516--Cox; and, 4,833,851--Ohmatsu. In general, the joints have flanges rigidly attached to the joined slab members, which flanges define a nip area between them over at least a portion of their extension, that encloses a flexible material. If the gap opens or closes, either a bulge will be raised in the flexible material or a gap will open at an edge. Therefore, these joints lack a continuous smooth coverage across the surface of the joint. If the joints are covered by a finish material (rather than simply provided with a finish material reaching just to the respective edges), the finish material will bulge or stretch even if the joint remains smooth.
U.S. Pat. No. 4,111,582--Tippett discloses a flexible material in a nip that is covered over by a continuous covering layer. Assuming that the flexible material is precisely dimensioned and has the necessary range of expansion without bulging, the joint does not arrange for expansion and contraction movements in the covering material. Instead, the slab members are arranged to move relative to the covering material and the covering material is fixed in place by undisclosed means.
There has been a need to simplify expansion joints while ensuring that the joint maintains a smooth upper surface. The complex expansion joints of the foregoing patents are quite expensive in terms of materials. As a result of the need for embedding the joint flanges in the edges of the joined members, such expansion joints are even more expensive to install. The present invention employs a joint apparatus forming a hinge-like two part channel for receiving a covering material in a central area, and having raised flanges or wings that extend over covering material adjacent the joint. A base part of the two part channel attaches rigidly on the surface of one of the two panels, with a raised flange or wing extending over adjacent covering material on its side of the joint. Means defining a hinge axis at the bottom of the two part channel are disposed between the panels in the gap. A free part of the two part channel is hingeably coupled to the base part at the means defining the hinge axis and has a raised flange or wing that extends over the covering material on the opposite side of the joint.
The joint apparatus is easily and inexpensively surface mounted. The joint apparatus overlaps the surface covering material by a fixed amount on the attached-side slab or the like, and overlaps by a variable amount on the opposite side, thereby accommodating expansion and contraction. The base part is mounted on the panel expected to remain relatively higher in the event the panels vary in elevation due to settling or the like. Such settling is accommodated by hinging of the base part and free part at the hinge axis.
In the central area of the joint apparatus (i.e., in the channel), the joint apparatus receives a strip of facing material such as a strip of the same covering material which borders the joint, tending to better conceal the joint by providing a relatively uninterrupted extension of facing material across the joint. The joint is effective, accommodates flexible facing material with minimal discontinuity, at a fraction of the cost of other expansion joints in either materials or installation.