FIELD OF THE DISCLOSURE

This disclosure relates to cold rolled steel joists and in particular unitary steel joist that are for use with a concrete floor.

BACKGROUND

Cold rolled steel joists are becoming more popular. Where cold rolled steel joist is a unitary steel joist heretofore they were designed to be used as bottom chord bearing joists. In general a unitary steel joist is not designed to be used as a top chord bearing type joist. Accordingly it would be advantage to provide a unitary steel joist assembly that can be used in a composite steel joist/concrete assembly, with increased end reaction load capacity capabilities. SUMMARY

The present disclosure relates to a steel joist assembly for use in association with a concrete slab and being adapted to form a composite steel joist including a steel joist and a pair of end connectors. The steel joist has a top portion with a generally planar top surface and a planar web generally orthogonal to the generally planar top surface. An end connector is attached at each end of the steel joist. Each end connector has a strut and a diagonal member. The strut has a generally planar bottom surface which is attached to a portion of the generally planar top surface of the steel joist and the diagonal member is attached at one end thereof to the strut and at the other end thereof to a portion of the planar web of the steel joist.

The end connector may further include a shoe attached to the distal end of the strut.

The strut may be a pair of generally L-shaped members arranged back to back, each having an upper lip extending outwardly. The pair of generally L- shaped members may each have a plurality of holes formed therein adapted to receive reinforcing bars.

The diagonal member may be a generally L- shaped member. The steel joist assembly may further include a steel deck attached to the generally planar top surface of the steel joist. The steel deck may have a dovetail pattern which provides a mechanical interlock with the concrete slab. The dovetail pattern may include a plurality of bottom portions, a plurality of top portions and a plurality of side portions connecting the top portions to the bottom portions wherein the side portions are sloped inwardly over the bottom portions.

The deck may be attached with a plurality of screws. The steel deck may be attached with a plurality of screws with multi-shear connectors attached thereto which extend upwardly. The screws may be spaced no greater than 10 inches centre to centre.

The steel joist may be a unitary steel joist.

The steel joist may have a generally vertical planar web; a generally horizontal bottom flange extending outwardly on each side of the planar web, the bottom flange having a double thickness; a generally horizontal top flange extending outwardly on each side of the planar web, the top flange having a double thickness; a bottom wing extending outwardly from one side of the planar web; a bottom planar web portion extending between the bottom flange and the bottom wing; a top wing extending outwardly from one side of the planar web; a top planar web portion extending between the top flange and the top wing; and whereby the planar web, the bottom flange, the top flange, the bottom wing, the bottom planar web portion, the top wing and the top planar web portion are made from a unitary piece of steel.A steel joist system for use in association with a concrete slab to form a composite steel joist system includes a plurality of steel joists and a deck attached to the plurality of steel joists.

A steel joist system for use in association with a concrete slab to form a composite steel joist system includes a plurality of steel joist assemblies each comprising: a steel joist having a top portion with a generally planar top surface and a planar web generally orthogonal to the generally planar top surface; a pair of end connectors, one attached at each of the steel joist; and a steel deck attached to the plurality of steel joists having a shear connection between the steel deck and the concrete slab.

The end connectors may have holes formed therein to receive reinforcing bars. The steel joist system may further include a plurality of reinforcing bars extending through the end connectors. At least some of the reinforcing bars may form a perimeter around a predetermined floor area. A wire mesh may be placed on top of the reinforcing bars.

A multi-shear connector includes a bottom portion, a back portion, a sloped portion and two side portions wherein the bottom portion rests on the deck, the back portion extends upwardly from the bottom portion, the side portions extend inwardly from the back portion and the sloped portion is sloped inwardly from the back portion whereby the side portions and sloped portions are shaped to receive a reinforcing bar.

Further features will be described or will become apparent in the course of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will now be described by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of an embodiment of the steel joist assembly with a portion of the deck removed;

Fig. 2 is a cross sectional view of an embodiment of the steel joist assembly including multi-shear connectors and reinforcing bars;

Fig. 3 is a cross sectional view of an alternate embodiment of the steel joist assembly;

Fig. 4 is a cross sectional view of the steel joist assembly similar to those views shown in figures 2 and 3 but taken perpendicular to those views;

Fig. 5 is a perspective view of a multi-shear connector;

Fig. 6 is an enlarged cross sectional view of an embodiment of the steel joist assembly showing multi-shear connector and a reinforcing bar located therein;

Fig. 7 is an enlarged cross sectional view of an embodiment of the steel joist assembly similar to that shown in figure 6 but without the reinforcing bar;

Fig. 8 is an enlarged cross sectional view similar to that shown in figure 7 but showing an alternate deck having a dovetail cross section; Fig. 9 is an enlarged cross sectional view similar to that shown in figure 8 but showing the deck screwed to the supporting steel joist;

Fig. 10 is an enlarged view of screw connection of embodiment shown in figure 9;

Fig. 1 1 is a perspective view of an embodiment of the steel joist system;

Fig. 12 is a cross sectional view of the strut used in the end connector; and

Fig. 13 is a cross sectional view of the diagonal member used in the end connector.

DETAILED DESCRIPTION

Referring to figures 1 to 4, the steel joist assembly is shown generally at 10. Steel joist assembly 10 includes a steel joist 12 and a pair of end connectors 14. The end connectors 14 could work with any steel joist having a generally planar top surface and a planar web generally orthogonal to the bottom surface. The end connectors 14 may be used with any I beam shaped joists, alternatively they could be used with C-shaped joists. Accordingly this system is not applicable to open webbed steel joists. In an embodiment shown herein steel joists 12 are unitary steel joist as described in US application 1 2/942,714, publication number US

201 1 /0162319 A1 , filed November 9, 2010 and entitled Unitary Steel Joist and having the same inventors as shown herein. Steel joist 12 has a top flange 16, bottom flange 1 8 and a planar web 20 therebetween. The top flange 16 has a generally planar top surface.

The planar web 20 is a generally vertical. A generally horizontal bottom flange 1 8 extends outwardly on each side of the planar web 20. The bottom flange 18 has a double thickness. The generally horizontal top flange 16 extends outwardly on each side of the planar web 20. The top flange 16 has a double thickness. A bottom wing extends outwardly from one side of the planar web. A bottom planar web portion extends between the bottom flange and the bottom wing. A top wing extends outwardly from one side of the planar web. A top planar web portion extends between the top flange and the top wing; and the planar web, the bottom flange, the top flange, the bottom wing, the bottom planar web portion, the top wing and the top planar web portion are made from a unitary piece of steel.

End connector 14 includes a strut 24 and a diagonal member 26. The strut 24 has a generally planar bottom surface which is attached to a portion of the generally planar top surface 22 of the steel joist 12. The diagonal member 26 is attached at one end thereof to the strut 24 and at the other end thereof to a portion of the planar web 20 of the steel joist 12.

In an embodiment shown herein the strut 24 is a pair of generally L- shaped members 28 arranged back to back and each having an upper lip 30 extending outwardly, across sectional view of which is shown in figure 1 2. The diagonal member 26 is a generally C- shaped member as shown in figure 13. The strut 24 has a plurality of holes 32 (shown in figure 1 ) formed therein adapted to receive reinforcing bars 34.

The End connector 14 may further include a shoe 36 attached to the distal end of the strut 24. In an embodiment shown herein the shoe 36 is an L- shaped member.

The steel joist assembly may include a steel deck attached to the generally planar top surface of the steel joist. In an embodiment the steel deck 38 is a corrugated steel deck having generally a trapezoidal shape.

The steel deck is held in place with a plurality of screws 40. In the embodiment shown therein multi-shear connectors 42 are connected to the screws 40 and extend upwardly over the deck 38. Referring to Figure 5, the multi-shear connectors 42 have a bottom portion 44, a back portion 46, a sloped portion 48 and two side portions 50. The bottom portion 44 has a pair of holes 52 formed therein. Bottom portion 44 rests on the deck 38 and are held in place by screws 40 that fit through the holes 52. The back portion 46 extends upwardly from the bottom portion 44. The side portions 50 extend inwardly from the back portion 46 and the sloped portion 48 is sloped inwardly from the back portion 46. The side portions 50 and sloped portions 48 are shaped to receive a reinforcing bar 34.

Referring to figure 1 1 there is shown a steel joist system that includes a plurality of steel joist assemblies and a steel deck 38. The deck is attached to the plurality of steel joist assemblies with a plurality of screws 40. The screws may have a plurality of multi-shear connectors 42 attached thereto. In an embodiment the steel joist system includes a plurality of reinforcing bars. The reinforcing bars 34 are positioned through the holes 32 in the struts 24. The reinforcing bars 34 may be spliced to create a continuous perimeter around a predetermined shape, the shape may be the entire floor area, a room or other predetermined shape. A plurality of reinforcing bars 34 extend through the multi-shear connectors 42. Wire mesh 54 is placed on top of the reinforcing bars. Bridging members 56 and cross bracing members 58 may also be used between adjacent steel joists 12. Concrete is then poured onto the deck to create a composite steel joist system having a concrete slab 60.

An alternate deck 62 is shown in figures 8 to 10. Deck 62 has a dovetail pattern, wherein the deck has a plurality of upper portions 66 and a plurality of lower portions 68. The upper portions 66 and lower portions 68 are connected with a plurality of side portions 70 which are sloped inwardly over the bottom portions such that the upper portion partially extends over the lower portion. The dovetail provides a mechanical interlock with the concrete slab 60. Deck 62 increases the resistance to horizontal shear between the supporting steel joist 1 2 and the concrete slab. As shown in figure 8, the combination of the multi-shear connectors 42, shoe 36 and the deck 60 creates a composite joist with three shear resisting elements; this provides the improved floor strength in a relatively simple manner. Figures 9 and 1 0 show an alternate method of connecting the deck 62 to the supporting steel joist 12. In this embodiment only screws 40 are used to secure the deck to the supporting steel joist. The deck 62 is attached to each joist 12 with a plurality of screws 40. The screws 40 typically number 10 screws and are spaced no greater than 10 inches centre to centre. In this configuration the shear capacity of the supporting structure is increased. It has been observed that the shear capacity can be increased by as much as 100 percent.

The deck 62 provides a superior mechanical interlock with the concrete 60 over the deck 38. The weight of the deck systems shown herein are substantially less than with precast concrete and it has been observed that they can be as much as 50 percent less than precast concrete. The prior art decks 38 or 62 were typically merely laid in place and were fastened to the supporting structure with screws or nails to accommodate gravity and diaphragm loads. These prior art steel decks were composite steel decks which could be used to increase shear resistance along the length of the metal decking such that the span of the deck between its supporting members was increased. In contrast the decks systems described herein are designed for their shear capacity along the length of the supporting member. The dovetail deck and cured concrete composite assembly, when sufficiently fastened to its supporting member, becomes the top chord of the (joist) supporting member. Therefore, with the composition of: the dovetail steel deck, cured concrete, the supporting member, and appropriately spaced fasteners; this may increase the strength of the supporting member by as much as 100%. This significantly increases the spanning capability of the supporting member.

In one embodiment the unitary steel joists 12 are cambered for dead load deflection.

There are a number of advantages that are realized by the composite steel joist system shown herein. For example end connectors 14 that sit flush with the supporting member 64, as shown in figures 2 and 3, so that the support connection is within the confines of the concrete slab thickness. The composite system described herein shows a method to transfer diaphragm loads from the concrete floor slab 60 to the perimeter beam in a concentric manner without the need for over-pour, this may be referred to as a passive concentric tie-beam.

The multi-shear connectors 42 can function alone without reinforcing bar and provide shear bond capacity between the steel joist 12 and the concrete slab 60. Alternatively the multi-shear connectors may be used in conjunction with reinforcing bar 34 which is "a high chair" for reinforcing mesh 54 and allows for the installation of a reinforcing bar 34 to reinforce the concrete slab 60. In addition the strut provides for a coordinated method of locating a short reinforcing bar at the joist end support to increase shear capacity at the joists most vulnerable location and provides a method to transfer loads from the joist end to the perimeter beam.

Generally speaking, the systems described herein are directed to a steel joist assembly and a steel joist system. As required, specific embodiments are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the disclosure may be embodied in many various and alternative forms. The Figures are not to scale and some features may be exaggerated or minimized to show details of particular elements while related elements may have been eliminated to prevent obscuring novel aspects. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure. For purposes of teaching and not limitation, the illustrated embodiments are directed to a steel joist assembly and a steel joist system.

As used herein, the terms "comprises" and "comprising" are to construed as being inclusive and opened rather than exclusive. Specifically, when used in this specification including the claims, the terms "comprises" and

"comprising" and variations thereof mean that the specified features, steps or components are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.