Static structures (e.g. – buildings) – With lifting or handling means for primary component or... – Construction or component having means to engage hand or...
Patent
1995-12-12
1998-11-03
Safavi, Michael
Static structures (e.g., buildings)
With lifting or handling means for primary component or...
Construction or component having means to engage hand or...
521252, B66F 1902
Patent
active
058292071
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to reinforcing precast or cast-in-place concrete elements and is particularly concerned with arrangements to facilitate the use of lifting anchors which are partially embedded in the concrete and have a projecting portion to which a lifting device is able to be engaged.
BACKGROUND ART
A particularly important area of application is where the lifting anchor is placed in the edge of an end or side of a thin concrete panel and where the panel is to be lifted in a direction normal to the axis of the anchor with a shear load applied to the anchor. A common application of this type exists in the construction of tilt-up buildings. In this type of construction thin wall panels are cast horizontally at ground level and raised into the vertical position by tilting the horizontal panel about one (lower) edge by lifting with anchors set in the opposite (upper) edge until it is in the vertical position. Then it is lifted into its final position to form a wall element.
The invention is not, however, limited to tilt-up operations and can be used in any application where an anchor is set either in an edge, or close to an edge, and where a force is to be applied in a direction towards the edge. Here there is a risk of failure of the concrete in the region of the edge as a result of the shear forces generated by the application of the force to the anchor. In such applications there is only a small distance between the anchor axis and the surface of the concrete panel in the direction of the applied force. Therefore there is often an insufficient volume of concrete to resist the applied load without failure.
Lifting anchors now in widespread use comprise a bar which at one end has a hole through which is threaded a reinforcement member. Alternatively, the one end of the bar has an enlarged foot. The reinforcement member or foot provides an anchorage to the concrete inside the panel. The other end of the bar provides a connection to the lifting device. Such anchors are commonly forged from steel. The means of connection can either be an enlarged head or a hole. Such lifting anchors and the systems by which they are lifted are described in U.S. Pat. Nos. 3,499,676 (1970), 3,883,170 (1975) and 4,173,367 (1979) amongst others.
It is desirable to ensure that the head of the anchor to which the lifting device is attached does not project from the concrete surface and a recess in the concrete is formed around the anchor for that purpose. The recess is commonly formed using a recess former which typically comprises a solid hemisphere which has a hole in the pole of the hemisphere into which the anchor head is placed and retained with a rubber grommet. The base of the hemisphere is attached to the interior of the mould wall. Such attachment is typically achieved by a number of holes passing through the hemisphere and back through which are passed bolts or nails. These enable the recess former to be directly nailed or bolted onto the face of the mould. In some applications the recess former is bolted onto the form or, in the case of steel moulds, a steel former can be directly welded to the form.
Another type of recess former in common use comprises two quarter-spherical parts inter-connected by a hinge (as disclosed in U.S. Pat. No. 4,296,909) or otherwise fastened together. These types of recess formers are moulded from steel, rubber or plastics and have internal structures designed to tightly retain the head of the anchor when the recess is closed about the shaft of the anchor. This provides positive support for the assembly fixed to the mould wall. This type of recess is commonly bolted to the mould wall using a centrally locating bolt passing into the flat portion of the recess former.
Another type of recess former comprises a steel hemisphere which is bored with a central tapered hole thereby forming a tapered ring element into which are fitted two or more identical, externally tapered, collets with an internal form designed to accept the head of the lifting anchor. Provision is made to draw the
REFERENCES:
patent: 4000591 (1977-01-01), Courtois
patent: 4014151 (1977-03-01), Erhart
patent: 4087947 (1978-05-01), Turner
patent: 4386486 (1983-06-01), Holt et al.
patent: 4726562 (1988-02-01), Courtois et al.
patent: 4947613 (1990-08-01), Fricker
Mackay Sim Rodney
Metham Barry James
Alan H. Reid Pty Ltd.
Safavi Michael
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