Shear dowel assembly

Abstract

This invention relates to a shear dowel assembly for distributing loads between adjacent concrete slabs, separated by a joint. The shear dowel assembly includes a dowel sheath having a front face and a rear face. The rear face of the dowel sheath is imbedded within the first concrete slab, whereas the front face is left substantially flush with the side of said first concrete slab. The front face also has a portion defining an opening therein. There is also provided a shear dowel adapted to be inserted into the opening in the dowel sheath, with a first end of the shear dowel abutting the rear face of the dowel sheath, and a second end of the shear dowel extending out from the opening in the dowel sheath, whereby the shear dowel may be embedded within a second adjacent concrete slab to be poured. The shear dowel has a width of constant cross section, and is preferably trapezoidal (or in the shape of a trapezium) in plan view. The shear dowel assembly allows for increased differential movement of the adjacent concrete slabs, as the joint gap between the concrete slabs increases, whilst retaining the load carrying capacity of the shear dowel at all times.

Description

FIELD[0001]This invention relates to an improved shear dowel assembly, for use in relation to construction using concrete. The invention may be particularly suitable for use in distributing loads between adjacent concrete slabs, separated by a joint, and especially during the curing, shrinking and / or thermal expansion of the adjacent concrete slabs.BACKGROUND[0002]A majority of the floors in industrial buildings at ground level are constructed in concrete. The use of concrete introduces a widespread problem in the performance of these floors, since concrete is a material that shrinks slightly during the curing process.[0003]Concrete shrinkage is typically about 8 one thousandths of an inch in a one foot length, which, in a section of concrete 100 feet long, will give total shrinkage of about 0.8 inches[0004]The shrinkage in the concrete requires designers and constructors to install joints or breaks in the concrete, to establish locations at which the concrete shrinkage can be taken...

AI Technical Summary

Benefits of technology

[0031]the arrangement and construction being such that the shear dowel assembly allows for increased differential movement of the adjacent concrete slabs, as the joint gap between the concrete slabs increases.

[0055]It may be seen that the arrangement and construction of the shear dowel assembly allows for increased differential movement of the adjacent concrete slabs as the joint gap between the adjacent concrete slabs increases, and furthermore the load carrying capacity of the shear dowel is maintained due to it being of a constant cross section.

[0056]That is, as the joint gap develops its width, the shear dowel is pulled out of the dowel sheath, and the further the shear dowel is pulled out, the further the distance between the side edges of the shear dowel and the tapered sides of the dowel sheath, thus allowing for increased differential movement of the adjacent concrete slabs as the joint gap increases.

[0057]This is a major advantage as compared to the presently available diamond dowel assemblies because the load carrying capacity of the diamond dowel rapidly decreases as the diamond-shaped dowels are pulled out from the sheaths during significant movement across the joint gap. Namely, diamond dowels tend to lose their load carrying capacity when the joint gap exceeds approximately ⅜th of an inch. This is because the tapered nature of the diamond dowel means that the width of the dowel that remains in the sheath reduces as the joint gap increases. The reduced width rapidly reduces the load carrying capacity of the dowel as the joint width increases, and hence the dowels become ineffective as significant movement across the joint gap develops.

[0062]Preferably, the positioning means may adapted to break off if differential movement occurs between the adjacent concrete slabs, thus allowing for the differential movement of the shear dowel.

Problems solved by technology

The use of concrete introduces a widespread problem in the performance of these floors, since concrete is a material that shrinks slightly during the curing process.

If joints are not included in floors on a planned basis, then random and unsightly cracking will take place.

The need for joints creates a problem for designers because the design for the thickness of the concrete assumes that the concrete is continuous, and any location at which the concrete terminates becomes a location of reduced strength in the floor.

The design of shear dowels is a complex process, since several design factors must be considered, and the governing factors may change depending on how wide the concrete joint becomes.

Traditionally, round steel bars were used, however, these have a disadvantage in practical use.

Round dowels restrain this movement since they are tightly encased in concrete, and this restraint can contribute to cracking in the concrete, which is undesirable.

However, use of these steel dowel bars only allowed for very small amounts of differential movement of adjacent concrete slabs, and so their use is limited.

This occurs over a relatively short length of steel, so, if the dowel bar is also narrow, then a low effective contact area results, and stresses become high, which may govern the dowel capacity.

That is, as concrete shrinkage opens the joint and pulls the steel plate out of the triangular sleeve, a gap develops between the steel plates and the edges of the triangular sleeves.

However, the use of diamond dowels has its limitations, as they are only efficient where joint widths remain relatively narrow, that is, up to a maximum joint width of about ⅜ inch, or possibly a little more.

However, with many common design methods for concrete floors, the widths to which joints will develop cannot be accurately determined.

Diamond shaped dowels cannot provide effective load transfer when relatively wide joint widths develop (above about ⅜th of an inch), such as in those situations as described above.

The reduced width rapidly reduces the load carrying capacity of the dowel as the joint width increases, and hence the dowels become ineffective as relatively wide joint widths develop.

Such designs must allow a sufficient gap (between the sides of the steel plate and the sleeve) for all the expected differential movement of the sections of concrete at the joint, since this gap cannot increase with increased differential movement.

However, the amount of differential movement that occurs between two slabs of concrete generally increases in proportion to the increasing gap at the joint in the concrete.

Hence, these constant-width plate dowels have similar limitations as the diamond dowels.

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