Screed rail

This invention relates to screed rails of the leave-in-place type, intended in use to constitute the boundary between adjacent concrete floor slabs especially of large buildings such as warehouses where the floor is required to be essentially flat over a large area and capable of supporting loads exerted typically by racking with goods stored thereon, fork trucks and the like.

A conventional leave-in-place screed rail or formwork is supported by leg members which, in use, are placed on the ground so that the screed rail is in an upright position and adjusted in height relative to the feet such that the upper edge is horizontal and the upper edges of adjacent rails, whether in longitudinal alignment or defining a slab corner, are in the same plane. Concrete is then cast in the areas defined by the screed rails, up to the level of the upper edges, and allowed to cure. As curing takes place, the concrete shrinks in volume and, as a result, gaps are formed between adjacent slabs. It is thus desirable firstly for the screed rails to provide protection to the arriss or upper edge corners of the slabs, to prevent them from being fractured under load in use, and also for the screed rails to be formed in two parts, arranged initially with their front or outer faces together but adapted to separate and move apart as the concrete cures. It is also desirable for the screed rails to carry horizontal dowels or plates to provide load transfer between adjacent slabs or bays of the overall floor area.

The requirement for vertical adjustment of the screed rails implies that, in a face-to-face arrangement, the two parts must be held together, but this requirement conflicts with the need for the parts to be separable as the concrete cures. It is therefore conventional to use frangible connectors such as nylon bolts or nuts the threads of which will strip under tensile load, but the leg members require stronger connections which still causes a problem with separation of the rails.

It is an object of the present invention to provide a leave-in-place screed rail which overcomes the problem as set out above.

In one aspect, the present invention provides a screed rail comprising first and second elongate plate members arranged in face-to-face configuration, the first plate member being attached to leg members by height-adjustable lock means and the second plate member being attached to the first plate member by frangible joining means with the upper edges of the plate members in registration.

By “upper edges in registration” is meant that the upper edges of the plate members are parallel and in the same plane, substantially orthogonal to the plane of the plate members themselves whereby, in use and with the screed rails arranged vertically, the upper edges thereof will be in a common horizontal plane.

In screed rails according to the invention, the first plate member is attached to the leg members and by independent frangible connections to the second plate member, whereby the plate members can separate laterally as the concrete cures without the attachment of the leg members inhibiting movement of the second plate member relative to the first.

In a preferred arrangement, the second plate member is the same length as the first plate member but is shallower in depth, whereby the lower edge of the second plate member is disposed above the lock means which attach the leg members to the first plate member. In such an arrangement, the screed rail is cheaper to manufacture since it uses less material than a screed rail in which both plate members are of the same depth and there are no potential inhibitions to separation of the plate members as the concrete cures other than the frangible connections.

Preferably, height adjustment of the first plate member is provided by vertical slotted apertures through which the lock means pass, the second plate member being out of contact with the lock means. Vertical adjustment of the first plate member relative to the leg members, when laying the screed rail in place, thus effects vertical adjustment of the second plate through the frangible joining means, the lack of contact between the releasable lock means and the second plate member permitting the plate members to move apart as the concrete cures following breakage of the frangible joining means.

Preferably, the plates include means for accommodating laterally-disposed dowels or plates for providing load transfer between adjacent slabs; preferably, the dowels or plates are encased on one side of the screed rail with a sleeve member to allow the dowel or plate to move in the horizontal plane relative to the sleeve member and to the concrete of the floor slab in which it becomes buried as the edges of the floor slabs move apart on curing of the concrete, but to prevent relative vertical movement of the dowel or plate within the sleeve member. Preferably, the plates are in the form of diamonds or trapezoidal plates and the sleeves are adapted to accommodate sideways movement of the plates as well as horizontal movement orthogonal to the screed rail. The plates themselves may have essentially flat upper and lower surfaces or may be corrugated or otherwise configured to increase the strength thereof.

Conveniently, the means for securing together the first plate member and the leg members comprise bolts and wing nuts; the wing nuts may be tightened against a flange member attached to the foot members, vertical adjustment being accommodated by virtue of the slotted aperture in the first plate member. The frangible securing means may comprise bolts with nylon or other plastics lock nuts the threads of which will strip under shrinking forces as the concrete cures.

Preferably, the plate members are provided or formed with at least the upper edges being turned over to define a substantially horizontal (in use) planar upper face and a return or downwardly-extending lip, to add strength and rigidity to the plate members and, in use, to lock the members against the edge of the cured concrete slab. Preferably, the horizontal upper-facing surfaces are formed with apertures, which may extend partially to the vertical or main part of the member and/or to the lip, to allow release of entrapped air as concrete is poured and rises within the turned-over region. The lower edge of the first plate member is also preferably formed with a similar turned-over region comprising a flange or an upwardly-extending return lip to impart enhanced longitudinal stiffness to the plate member.

In an alternative embodiment, the plate members have a plain straight upper edge without a turned-over region. In this embodiment, the first plate member is preferably formed with at least one groove or channel formation extending from one face, preferably from that face against which the second plate member is attached, to add strength and rigidity to the first plate member. The second plate member is preferably formed, along its lower part, with a laterally-extending, preferably angled, skirt region for embedding in the concrete, preferably having an array of spaced-apart longitudinally-disposed apertures formed therein for additional keying with the concrete. The plate members may additionally be provided with laterally-extending studs or other connectors or formations on one or both sides to provide enhanced keying with and arriss protection of the concrete, especially for use in heavy-duty applications.

The first and second plate members may be joined together in a longitudinally offset relationship, to provide an end lap on one plate member for attachment to a corresponding lap on the other plate member when joining the members in end-to-end relationship.