SHEAR CONNECTOR FOR USE IN A CONCRETE AND STEEL STRUCTURE

FIELD OF THE INVENTION

The present invention relates to structural composite building elements such as decks, beams and columns. In particular, the invention relates to shear connectors and improved arrangements for confining concrete around shear connectors.

BACKGROUND TO THE INVENTION

Shear connectors are used in many types of structural composite members, for example composite floors, beams and columns, where a structural steel section is connected to the surrounding or adjacent concrete by the welded-stud shear connectors.

A particular shear connector is disclosed in International Patent Application No PCT/AU03/00288 (published as WO 03/076734). The problem addressed by the shear connector disclosed in the aforementioned PCT application is a similar problem to the problem addressed by the present application. The below background to the invention is substantially reproduced from the aforementioned PCT application.

Forming concrete composite structures in building construction involves assembling a structural framework with cross-connecting primary beams and secondary beams, and laying a ribbed decking across the supporting primary and secondary beams.

Reinforcing bars or mesh are then layed on top of the decking. Concrete is poured on top of the decking to complete the composite structure. In construction works the structural framework is usually made of steel. Figure 1 illustrates an example of a steel/concrete composite floor 5. When the concrete 70 hardens and reaches sufficient compressive strength, the decking 50 provides the main reinforcement for the concrete slab and the slab becomes the top flange of the composite beam.

Connectors in the form of shear connector studs 30 are often used to strengthen the connection between the steel framework 90 and concrete slab 70 as illustrated in Figure 1. The studs are fixed, generally by welding them, upright through the steel decking 50

or through a pre-punched hole in the decking, before the concrete is poured and are placed above the primary or secondary beams. Once the studs 30 are cast in concrete, they become an important part of the connection formed between the steel framework 90 and concrete slab 70.

Depending on the profile of the decking and the nature of the studs, the strength, ductility and efficiency of the shear connection formed between the concrete slab and framework can under ultimate load conditions lead to the common problem of rib punch-through failure.

Referring by way of example to steel/concrete composite structures, rib punch-through failure occurs when the studs are subjected to longitudinal shear forces between the concrete and steel framework. The weight of the structure and the load it supports have the effect of thrusting the concrete against one side of each stud creating concentrated stresses at the base of the stud and forming a break-away wedge in the concrete which, under the longitudinal shear force, is pushed into the ribs of the steel decking and away from the studs. This situation is illustrated in Figure 2A. Arrow 9 indicates the direction of shear force in the concrete 70 against the stud 30 fixed through decking 50 to steel beam 80. The break-away concrete wedge is denoted by 7. With the steel stud 30 no longer confined by concrete 70 around its base, it can be bent relatively easily under the effects of the shearing force. This mode of failure significantly reduces the shear strength of the welded studs, making their shear force/ slip behaviour possibly brittle and overall reducing the strength of the composite structure.

The likelihood of rib punch-through failure increases as the number of shear connectors per pan increases and/ or as the size of the connector increases.

Ductility is a desirable feature of shear connector studs and in some countries it is mandatory in their national design Standards that the behaviour of shear connector studs in composite structures be ductile. Ductility can be assessed according to the relationship between the shear force and slip, where the slip occurs longitudinally

between the concrete slab and steel beam. The slip is indicated in Figure 2A by dimension 31. The definition of a ductile shear connector stud in some national design standards is one having a characteristic slip capacity exceeding 6 mm. Noting that slip capacity in a solid slab increases with shank diameter, studs with certain dimensions are considered ductile. For example, some national design Standards accept a headed stud as being ductile if the stud has an overall length after welding of at least 4 times the shank diameter, and with a diameter of not less than 16 mm and not exceeding 22 mm.

Areas most prone to cracks and wedges forming in concrete slabs or structures are regions close to edges or voids. Examples of voids include profiled ribbing on steel decking creating notch-like voids in the concrete body, while hollow cores in pre-cast concrete panels also create voids. Of the open or closed type of steel decking ribs the more significant problems are associated with the open type ribs which are more responsible for creating notch-like voids in the concrete body.

The above problems are not exclusive to concrete composite beams but are also found in structures where a component is attached to a concrete body through bolts or fasteners embedded in the concrete body. The connected structure may be a pole, beam, leg of a larger structure, or the like. Figure 2B illustrates such a situation where two bolts B cast in a concrete slab C connect a structural component SC to the concrete slab through a plate P to which the bolts are connected with nuts N. With the upper shear force travelling in the direction of Arrow 9, a cracked wedge 7 is likely to form at the free edge FE of the concrete slab. The free edge has a similar effect on the casting-bolts as the voids in the composite beam examples given above, that is, the free edge is a point of weakness in the concrete where a crack may form. If a connecting bolt is located close to the free edge illustrated in Figure 2B, a wedge of concrete breaking off at the free edge could weaken or dislodge concrete around the embedded bolt and weaken the bolt's hold in the concrete. The resulting problem is equivalent to rib punch-through failure in composite beams.

It is an object of the invention to provide a shear connector component that facilitates the maintenance of the integrity and strength of composite concrete structures.

SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a shear connector component for use in a composite concrete and steel structure, the component including a coiled wire having a coil axis, the coiled wire including: a first terminal annular portion defining an aperture having a first internal diameter; a second terminal annular portion defining an aperture having a second internal diameter; and an intermediate portion shaped, at least in part, as a spiral helix, the intermediate portion having a first portion and a second portion, the first portion diverging from the first terminal annular portion in an inwards direction along the coil axis and the second portion diverging from the second terminal annular portion in an inwards direction along the coil axis.

Preferably the first portion has a first pitch and the second portion has a second pitch, wherein the first pitch is larger than the second pitch.

The larger pitch of the first section facilitates the ingress of concrete including aggregate into the coiled wire while the smaller pitch of the second section provides a greater total wire cross-section and therefore a higher tensile capacity of the coiled wire through a plane coincident with the coil axis.

Preferably the second internal diameter is larger than the first internal diameter.

Preferably the intermediate portion includes a helical portion.

According to a second aspect of the invention, there is provided a shear connector component for use in a composite concrete and steel structure, the component including

a coiled wire defining a coil axis, the coiled wire having: a first terminal annular portion defining an aperture having a first internal diameter; a first spiral helix portion having a distal end and a proximal end, the distal end extending from the first terminal annular portion; a second spiral helix portion having a distal end and a proximal end, the proximal end of the second spiral helix portion extending from the proximal end of the first spiral helix portion; and a second terminal annular portion defining an aperture having a second internal diameter, the second terminal annular portion extending from the distal end of the second spiral helix portion.

Preferably the second internal diameter is larger than the first internal diameter.

Preferably the first spiral helix portion includes a first section having a first pitch and the second spiral helix portion has a second section having a second pitch, the first pitch larger than the second pitch, whereby concrete including aggregate more readily passes through the first section than through the second section.

According to a third aspect of the invention, there is provided a shear connector component for use in a composite concrete and steel structure, the component including a coiled wire defining a coil axis, the coiled wire having: a first terminal annular portion defining an aperture having a first internal diameter; a first spiral helix portion having a distal end and a proximal end, the distal end extending from the first terminal annular portion; a helical centre portion having first and second ends, the first end extending from the proximal end of the first spiral helix portion; a second spiral helix portion having a distal end and a proximal end, the proximal end of the second spiral helix portion extending from the second end of the helical centre

portion; and a second terminal annular portion defining an aperture having a second internal diameter, the second terminal annular portion extending from the distal end of the second spiral helix portion.

Preferably the second internal diameter is larger than the first internal diameter.

Preferably the helical centre portion includes a first section extending from its first end having a first pitch and a second section extending from its second end having a second pitch, the first pitch larger than the second pitch, whereby concrete including aggregate more readily passes through the first section than through the second section.

According to a fourth aspect of the invention, there is provided a steel structure provided for a composite concrete and steel deck, the structure including: a structural steel member; a stud having a head and a base, the stud base welded to the structural steel member; and a coiled wire having a coil axis, the coiled wire disposed around the stud and retained in place by retention means, wherein the retention means retains the coiled wire around the stud during a concrete pour.

Preferably the retention means is integral to the stud and the coiled wire, the retention means comprising: a first terminal annular portion of the coiled wire defining an aperture; an outer peripheral surface of the stud head, the surface and the aperture mutually sized and shaped to resist movement of the first terminal annular portion over the head during the concrete pour.

Preferably the aperture defined by the first terminal annular portion has a first internal diameter, and wherein a second terminal annular portion of the coiled wire defines an aperture having a second internal diameter, the second internal diameter larger than the first internal diameter.

Preferably the coiled wire is held in place during the concrete pour, at least to some extent, by a compressive force produced in the coiled wire by elastic compression of the coiled wire, the compressive force acting between the head and the structural member.

Preferably the coiled wire includes: a first terminal annular portion defining an aperture having a first internal diameter; a coiled joining portion having a first end and a second end, the first end extending from the first terminal annular portion; and a second terminal annular portion defining an aperture having a second internal diameter, the second terminal annular portion extending from the second end of the coiled joining portion.

Preferably the coiled joining portion includes an intermediate portion shaped, at least in part, as a spiral helix, the intermediate portion having a first portion and a second portion, the first portion diverging from the first terminal annular portion in an inwards direction along the coil axis and the second portion diverging from the second terminal annular portion in an inwards direction along the coil axis.

Preferably the first portion has a first pitch and the second portion has a second pitch, wherein the first pitch is larger than the second pitch.

Preferably the second internal diameter is larger than the first internal diameter.

According to a fifth aspect of the invention, there is provided a composite concrete and steel structure including:

a structural steel member; a stud having a head and a base, the stud base welded to the structural steel member; a coiled wire having a coil axis, the coiled wire disposed around the stud and retained in place by retention means; and a concrete body, the concrete body disposed around and within the coiled wire, wherein the retention means retains the coiled wire around the stud during a concrete pour.

Preferably the retention means is integral to the stud and the coiled wire, the retention means comprising: a first terminal annular portion of the coiled wire defining an aperture; an outer peripheral surface of the stud head, the surface and the aperture mutually sized and shaped to resist movement of the first terminal annular portion over the head during the concrete pour.

Preferably the aperture defined by the first terminal annular portion has a first internal diameter, and wherein a second terminal annular portion of the coiled wire defines an aperture having a second internal diameter, the second internal diameter larger than the first internal diameter.

Preferably the coiled wire is held in place during the concrete pour, at least to some extent, by a compressive force produced in the coiled wire by elastic compression of the coiled wire, the compressive force acting between the head and the structural member.

Preferably the coiled wire includes: a first terminal annular portion defining an aperture having a first internal diameter; a coiled joining portion having a first end and a second end, the first end extending from the first terminal annular portion; and a second terminal annular portion defining an aperture having a second internal

diameter, the second terminal annular portion extending from the second end of the coiled joining portion.

Preferably the coiled joining portion includes an intermediate portion shaped, at least in part, as a spiral helix, the intermediate portion having a first portion and a second portion, the first portion diverging from the first terminal annular portion in an inwards direction along the coil axis and the second portion diverging from the second terminal annular portion in an inwards direction along the coil axis.

Preferably the first portion has a first pitch and the second portion has a second pitch, wherein the first pitch is larger than the second pitch.

Preferably the second internal diameter is larger than the first internal diameter.

Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative, and are not meant to be restrictive of the scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the invention is illustrated in the accompanying representations in which:

Figure 1 illustrates a conventional composite floor deck in a cut away perspective view.

Figures 2a and 2b are cross-sectional views showing problems associated with prior art composite decks and concrete foundations incorporating shear connectors. Figures 3, 4, 5 and 6 are perspective, top, side and bottom views respectively of a shear connector component accordingly to the invention.

Figure 7 is an enlarged side view of the shear connector component of Figures 3, 4, 5 and

6.

Figure 8 is a view of a shear connector component according to the invention with a stud fitted through it.

Figure 9 is a perspective view of a shear connector component according to the invention with a stud fitted through it, the stud welded to a structural steel member. Figures 10, 11, 12 and 13 are perspective views of the shear connector component shown in Figures 8 and 9 being progressively assembled over a stud. Figures 14a and 14b are diagrammatic cross-sectional views of the shear connector component installed within a composite deck before and after concrete has been poured respectively.

Figures 15, 16, 17 and 18 are perspective, top, side and bottom views respectively of an alternative shear connector component according to the invention. Figure 19 is an enlarged side view of the shear connector component of Figures 15, 16, 17 and 18.

Figures 20a and 20b are diagrammatic cross-sectional views of the alternative shear connector component installed within a composite deck before and after concrete has been poured respectively.

Referring to Figures 3 to 6, a shear connector component 10 for use in a composite concrete and steel structure, according to a first aspect of the invention, is shown. The component 10 includes a coiled wire 20 defining a coil axis 21. Turning to Figure 7, an enlarged view of Figure 5, it can be seen that the coiled wire 20 has a first terminal annular portion 22 (in this case, an upper terminal annular portion 22) and at its other end, a second terminal annular portion 28, (in this case, a lower terminal annular portion 28). The first and second annular portions define apertures. These apertures are sized to allow the connector 10 to be installed over a stud connector as is shown progressively in Figures 10 through to 13.

Again referring to figure 7, it can be seen that the coiled wire 20 also has a first spiral helix portion 23 having a distal end and a proximal end, a distal end extending from the first (upper) terminal annular portion 22. The coiled wire 20 also has a second (lower) spiral helix portion 27 connected to the second terminal annular portion 28. Joining the first and second spiral helix portions 23 and 27 is a helical centre portion 25.

The helical centre portion 25 includes a first section 24 having a first pitch and a second section 26 having a second pitch, The first pitch is larger than the second pitch. The large pitch of the first section 24 allows concrete including aggregate to readily pass into the void within the coil 20. The smaller pitch of the second section 26 provides a greater total wire cross-section and therefore a higher tensile capacity of the coiled wire through a plane coincident with the coil axis 21.

The attributes and performance of the shear connector component 10 is more readily understood in its application to a stud 30 welded to a structural steel member as is illustrated by Figures 9 to 14a and 14b. Referring to Figure 9, a body 50A to which the stud 30 is connected is shown. The body 5OA is, in this case, a structural steel beam underneath a galvanised structural steel deck. The stud 30 may be fired through the galvanised structural steel decking placed beforehand on top of the steelwork to act as formwork. The shear connector component 10, can be placed down over the head 32 of the stud 30 and will spring back under the head 32 holding itself in position in compression. This is progressively illustrated in Figures 10 through to 13. Figure 14b shows the resultant composite floor including the concrete 70 around and within the coil 20.

Referring now to Figures 7, 8 and 9, the first terminal annular portion 22 of the coil 20 is sized to fit snugly over a tapered stud head 32, but is sized to catch when the coiled wire 20 is released as is shown in Figure 13. The second terminal annular portion 28 defines a larger aperture man the aperture of the first terminal annular portion, the larger aperture facilitating easy fitment over the stud head 32. The snug fit or interference fit provided at one end of the coil 20 and the clearance fit provided at the other end, make it difficult for the component to be installed upside down.

Again referring to Figures 7, 8 and 9, in practice, the geometry of standard welded studs is selected as is specified in Australian/New Zealand Standard (AS/ NZS) 1554.2:2003, Structural Steel Welding, Part 2: Stud Welding (Steel Studs to Steel). The standard nominal shank diameters are 12.7, 15.9, 19.0 and 22.2 mm, with corresponding nominal

head diameters of 25.4, 31.7, 31.7 and 34.9 mm, and minimum head thickness of 7.1, 7.1, 9.5 and 9.5 mm, respectively. The practical minimum overall height of the studs is normally between three and four stud diameters after welding (noting that the studs burn down about 5 mm when resistance welded to the steelwork), depending on the application.

The heads of welded studs are forged onto the ends of drawn pieces of bar cut to length. The sides of the heads are slightly tapered, being slightly smaller in diameter at the top of the head than at the base of the head near the stud shank As explained above, advantage is taken of this important feature (to facilitate installation and subsequently retention of the coil) by the embodiment of the invention shown in Figures 10 to 12.

Referring again to Figure 7, it can be seen that the coiled component 10 is shaped such that it is suitable for use in a hand-operated dispensing cartridge that allows workmen to install the component while standing above or adjacent to the stud.

Once fitted on a stud the component cannot be knocked or pulled off without special effort or use of a special tool.

The first terminal annular portion 22 of the coil wire 20 defines an aperture. The outer peripheral surface of stud head 32 and the aforementioned aperture are mutually sized and shaped to resist movement of the first terminal annular portion 22 over the head 32 during a concrete pour.

Now referring to Figures 7 and 14, the helical centre portion 25 of the component 10 near the base of the stud 30 has an outside diameter of about 80 mm which is to encapsulate an annulus of concrete around the stud, noting that the nominal maximum aggregate size of concrete is normally 20 mm and may pass into this annulus.

The height of the second (lower) section 26 of the helical centre portion 25 of the component 10 with the 80 mm outside diameter should normally be between about 25

and 50 percent of the overall height of the welded stud shear connector 30. Its height may also depend on the height of the steel ribs of structural steel decking 50 and 60 through which the studs 30 are welded or placed, in which case it might be between 30 and 60 percent of the overall height of the steel ribs.

The steel intensity of the second (lower) portion 26 of the helical centre portion 25 of the component 10 with the 80 mm outside diameter is dictated by hoop tensile forces it must support (see below), and should be such that the tensile capacity of the wire through a vertical section of the loops equals about 400 to 2000 N/ mm of height depending on the diameter of the welded stud and other factors. This steel intensity or more precisely tensile capacity per unit height can be achieved by suitably adjusting the pitch, diameter and tensile strength of the wire. In particular, the steel intensity can be achieved by reducing the pitch in the second section 26 of the helical centre portion 25 as illustrated in Figure 7. It is desirable to leave the pitch large in the first section 24 of the helical centre portion 25, that is the upper region nearer the head 32 of the stud 30, to allow all of the concrete constituents (possibly including the largest pieces of aggregate) to readily pass through it into the annulus of concrete around the base of the stud.

The terminal portions 19 and 18 of the coiled wire 20 are formed such that: (i) they anchor the wire in the lower and upper regions of the composite slab which will have to support hoop tension when the concrete annulus dilates under pressure produced when the surrounded shear connector deforms under load; (ii) the second (lower) terminal end 19 locates at the base of the stud and has an internal diameter that easily passes over the head 32 of the stud; and (iii) the first (upper) terminal end 18 locates at the head 32 of the stud 30 and fits snugly over the head of the stud, but when the component is released catches on the underneath of the head 32 and cannot come off.

With the above described configuration of the terminal portions, it is difficult to put the coil 20 on the stud 30 upside down.

It can be seen clearly from Figure 7 that the second spiral helix portion 27 is conically shaped. This conical shape allows the coil axis 21 to be placed closer to projections on the base of a decking sheet than would otherwise be the case. This is illustrated in Figure 14a where the second (lower) spiral helix portion 27 of the coil 20 sits over a lap joint 55 formed between decking panels 50 and 60. In practice, the height of the spiral helix portion 27 should be between 5 and 20 mm depending on the application. For instance _/ small lap joints such as those illustrated in Figure 14a in the pans of steel decking through which welded studs 30 have been fired, will be about 15 mm high, so by making the lower spiral helix portion 27 about 15 to 20 mm high, in this case, would allow the component 10 to be fitted onto a stud 30 located close to the lap joint 55. (Studs are welded with temporary ceramic ferrules at their base, the diameter of the ferrules typically being slightly greater in diameter than the stud head. This limits how close a stud can be welded to such a lap joint). It is not necessary to have to orientate the component 10 in any particular way with respect to the projection _/ as it is simply clipped over the projection.

Referring to Figures 14a and 14b, it can be seen that the coiled wire 20 disposed around the stud 30 is centralized around the stud 30 by the relatively small diameters of the apertures of the first and second terminal annular portions.

Referring again to Figure 14a, it can be seen that once the coil 20 has been fitted it cannot easily be pushed significantly off center or be dislodged. The coil 20 is under compression since the overall free length of the coil 20 is longer than the clear gap between the underside of the stud head 32 and the top of the pan of the decking panel 50 through which the stud is welded, normally by 10 to 20 mm.

More generally, further embodiments of the invention include a steel structure provided for a composite concrete and steel deck as shown in figures 14a and 20a. The structure of those figures includes a coiled wire 20, the coiled wire disposed around the stud 30 and retained in place by retention means. The retention means retains the coiled wire around the stud during a concrete pour. For the coiled wire 20 and stud 30 illustrated the

retention means is integral to the stud and the coiled wire. In other embodiments separate retention means may be employed. Furthermore the coiled wire 20 is centralized around the stud 30 by the relatively small diameters of the apertures of the first and second terminal annular portions. With other embodiments of the invention (not shown) other means of centralizing may be provided.

Advantageously, the first (upper) terminal annular portion 22 of the coil 20 has tapered loops to squeeze tightly over the tapered head 32 of the stud 30. Furthermore, the top loop of the upper terminal annular portion 22 is too tight to fit over the stad head 32 if an attempt is made to install the coil 20 upside down.

At the other end of the coil 20 is the second (lower) terminal annular portion 28. This portion has an internal diameter several millimeters larger than the head 32 to facilitate easy installation over the stud.

In an alternative embodiment of the invention, an improved shear connector is provided as is illustrated in Figures 15, 16, 17, 18, 19, 20a and 20b. Referring to Figure 19, it can be seen that with this embodiment of the invention the first and second terminal annular portions 22 and 28 are the same as those of the first described embodiment of the invention. An intermediate portion 25' shaped, at least in part, as a spiral helix is provided. Intermediate portion 25' has a first portion 24' and a second portion 26'. The first portion 24' diverges from the first terminal annular portion 22 in an inwards direction along the coil axis 21 and the second portion 26' diverges from the second terminal annular portion 28 in an inwards direction along the coil axis 21.

Referring to Figure 20b, the conical shape allows the coil axis 21 to be placed closer to projections (such as lap joint 55) that would otherwise be the case.

The first (upper) portion 24' has a pitch that is larger than the pitch of the second (lower) portion 26'. The larger pitch of the first portion 24' facilitates the ingress of concrete including aggregate into the coiled wire while the smaller pitch of the second (lower)

portion 26' provides a greater total wire cross-section and therefore a higher tensile capacity of the coiled wire through a plane coincident with the coil axis. In this way and in a number of other respects, this embodiment of the invention performs in a similar way to the first described embodiment of the invention as described above. The alternative embodiment of the invention as illustrated in figures 15, 16, 17, 18, 19, 20a and 20 can however offer improved performance over the first described embodiment of the invention.

With the first described embodiment of the invention, illustrated in Figures 3, 4, 5, 6 and 7, a premature pull-off failure of the concrete can occur which allows the concrete slab to completely separate from the steel beam before the shear studs are deformed and loaded sufficiently. This is a result of the more generally cylindrical shape of the coil (in particular the helical portion 25 illustrated in Figure 7) which can provide limited resistance to uplift forces that develop with slip once rib punch-through has been initiated, leaving the cylindrical wire-encapsulated concrete around the stud without sufficient tying-down strength. The likelihood of this occurring increases by reducing the pitch of the wire coils, and increasing the depth of the second (lower) portion relative to the first (upper) portion.

Studs in shear in a composite slab may need to develop up to 20 or 30 percent of their ultimate shear capacity in tension. The stud illustrated in Figure 14a is less likely to achieve this with the coil 20 of the first described embodiment of the invention than it would be if the coil 20 of the alternative embodiment of the invention shown in Figure 19 was used. With the coil of the first described embodiment of the invention, shown in Figure 14a, the wire of the coil where it is closely spaced in the lower portion forms a weakened surface through the surrounding concrete even before force is applied to the shear connection. This is less of a potential problem where the coil 20 in Figure 14a is replaced by the coil 20 of the alternative embodiment of the invention shown in Figure 19.

With the alternative embodiment of the invention illustrated in Figures 15, 16, 17, 18 and 19, concrete 70 is trapped between the top of the flange 82 of the steel beam 80 and the lower tapered region 26' of the coil 20. As a result, pull-out of the stud 30 is resisted by a whole cone of concrete that extends over the entire height of the stud - in much the same way as it would be without the coil 20 present. The size of the cone can be increased by increasing the maximum diameter of the coils. It can be advantageous to limit the minimum pitch of the coils in the lower helical portion 26 of Figure 7 to allow some aggregate interlock to develop over this cylindrical portion. It is beneficial in any case to keep a gap of at least 2-3 mm between adjacent wires in the coil (once in the compressed state fitted to a stud) to allow mortar at least to ooze through the spiral, releasing any trapped air and improving pull-off resistance.

While the present invention has been described in terms of preferred embodiments, in order to facilitate better understanding of the invention it should be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.