EP0372980A1

EP0372980A1 - Profiled steel sheet

Info

Publication number: EP0372980A1
Application number: EP89312803A
Authority: EP
Inventors: Mark Patrick
Original assignee: John Lysaght Australia Pty Ltd
Current assignee: John Lysaght Australia Pty Ltd
Priority date: 1988-12-09
Filing date: 1989-12-08
Publication date: 1990-06-13
Also published as: AU4553589A; AU627245B2; MY105154A

Abstract

A metal decking member of nestable configuration, having plural pans (14) and at least one intervening rib (12) with inclined sides, wherein the decking member has complementary integral flanges (16, 18), of substantially lesser height from the pans that said ribs, at opposite lateral edges of the decking member for forming lap joints with adjacent similar decking members, wherein at least one of the flanges (16, 18) further includes a longitudinally extending lip (20) which projects generally laterally of the flange and is thus disposed to be embraced by cementitious material overlying the decking member in a subsequent composite structural member such as a slab or beam incorporating the decking member, and to thereby enhance the composite strength of the structural member. The invention also includes composite structural members incorporating concrete slabs on steel decking.

Description

This invention relates to the provision of mechanical anchorage in composite steel and concrete structural members such as slabs and beams, and more particularly to steel or other metal decking members adapted to provide enhanced anchorage. The invention further extends to composite structural members incorporating concrete slabs on steel decking.
Composite steel and concrete structural members are normally formed in situ and typically comprise a concrete slab cast on underlying profiled steel sheet, commonly known as decking. The decking is usually an array of side-lapped members which are broadly panels and each of which typically has one or several longitudinally extending upstanding primary ribs and intermediate shallow stiffening ribs on intervening pans. The long side edges of the decking members have flanges which abut in the composite members and are thus generally known as lap-joint flanges. In some cases, the decking members are substantially channels in which the lap-joint flanges are the dominant features upstanding from the connecting pan.
It is known practice to anchor the slab and underlying decking together against excessive relative longitudinal movement by providing transversely projecting keying elements, usually at regular intervals over the whole length of the decking: these may be reinforcing rods welded to the rib tops (as, e.g., in Australian patent 223584 and French patent 1454164), tabs or perforations pressed from the ribs or pans of the sheet, multiple shallow-ribbed embossments stamped to project out of the ribs or pans, or end anchorage devices such as welded studs, flattened rib-ends, or rib-piercing rods.
The use of perforations to enhance composite strength is disclosed in Australian patent application 12358/88 to Monier Ltd which describes and illustrates decking members of the aforementioned channel type. The lap-joint flanges have overturned outwardly projecting edge lips which engage and overly similar lips on adjacent channels to define rectangular-section ribs. Extended skirt portions of one lip of each channel have elongate perforations which fill with concrete in the composite structure. Another known channel-type decking member has an outwardly projecting lip on one lap-joint flange and an inwardly projecting lip on the other: the outside lips overly inside lips on adjacent channels and may be fastened together in any suitable manner. A further example of a channel-type member is to be found in U.S. patent 2 284 923.
The most common mode of failure in composite steel and concrete structural members with decking is shear bond failure. Gravity loading of the slab between supports puts the lower portion of the slab into tension over all or part of a span, inducing cracking of the concrete. This cracking in turn leads to breakdown of the adhesion bond and a consequent transition from adhesion to a predominantly mechanical bond between the concrete and steel. Under dead weight loading, there is typically a dynamic transition at which sudden slip occurs between the concrete and the decking, with an accompanying sharp fall in the load carrying capacity of the slab. It would be desirable if this dynamic transition or brittle behavior could be avoided with a smoother, i.e., ductile, composite behaviour in which the components gradually slip with increased load but there is no sharp and sudden fall in load carrying capacity.
One widely-used type of steel decking is generally known as W-decking and features a trapezoidal rib configuration which permits nesting of the individual decking members for storage and transport. Each W-decking member typically has two or three pans separated by large ribs of trapezoidal cross-section. Such W-decking members are disclosed, e.g., in U.S. patent numbers 3812636 and 4453364. Because of the nestability requirement, the lap joint between adjacent W-decking members is a simple engagement between upstanding edge flanges on the respective members, for example a flat flange on one member, and an overturned flange on the other, providing a downwardly open groove. The groove and flat flange are usually fastened together in situ, for example by screwing, puddle welding, button punching or clinching.
It is an object of the invention to improve the design strength of composite concrete and steel or other metal structural members which incorporate nestable decking members of the W-decking type. The design strength may be enhanced by improved load carrying capacity, and/or by achieving more ductile rather than brittle behaviour during the transition to mechanical bonding.
It has been surprisingly found that the composite strength potential of nestable decking members of the W-decking type can be substantially enhanced by forming a laterally projecting lip on one of the flange components of the lap-joint, the lip being so positioned that it lies within concrete in a subsequently formed composite structural member. Such lips have been provided on channel decking members, as described above, but there has never been any suggestion that the lips per se enhanced the composite strength of the subsequently formed structural member. Conventional wisdom is that improvement in composite strength requires transversely projecting keying elements or perforations and indeed the purpose of the extended lips in Australian patent application 12358/88 is to provide a location for such perforations. It is thus unexpected that a laterally projecting lip without embellishment is capable per se of enhancing composite strength: as an adjunct to the lap-joint flanges of W-decking, the result is even more surprising since the lap-flanges are relatively much smaller perturbations from the decking pans than the large trapezoidal-section ribs.
The invention therefore provides a metal decking member of nestable configuration, having plural pans and at least one intervening rib with inclined sides. The decking member has complementary integral flanges, of substantially lesser height from the pans than the ribs, at opposite lateral edges of the decking member for forming lap joints with adjacent similar decking members. At least one of the flanges further includes a longitudinally extending lip which projects generally laterally of the flange and is thus disposed to be embraced by cementitious material overlying the decking member in a subsequent composite structural member incorporating the decking member, and to thereby enhance the composite strength of the structural member.
The invention further extends to a composite concrete structural member incorporating decking comprising one or more of the described decking members.
To facilitate assembly of a decking, the female formation may comprise an overturned flange with inclined sides defining a longitudinally extending groove to receive and thereby locate the other flange of an adjacent decking member, said lip portion being formed by an outturned integral extension of the overturned flange. This lip portion is preferably inclined laterally upwardly.
The lip portion advantageously has an angled secondary lip at its free edge. Embossment or apertures may be provided on the web or lip portion and/or the lip of the male formation, to even further enhance the composite strength of the joint in a composite member.
The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a fragmentary perspective view of a steel decking member according to the invention;
Figure 2 is an end view of the decking member shown in Figure 1, also depicting a second decking member to exhibit the nestable configuration of the decking members;
Figure 3 is an end view of a composite structural member including decking formed by lap-jointing three of the decking members of Figures 1 and 2;
Figures 4 and 5 are respective cross-sections of the complementary lap-joint flanges of two adjacent decking members according to Figures 1 and 2, shown before and after a button punched lap-joint is formed between the members;
Figures 6, 7 and 8 show alternative embodiments of lap joint flanges;
Figure 9 is a graph indicating typical lap joint resistances, as explained hereinafter, for conventional lap joints (A) and several different lap joints between decking members according to the invention;
Figure 10 is a graph of mid-span vertical deflection and curvature versus total applied load and bending moment for composite steel and concrete structural members respectively incorporating conventional W-decking and W-decking consisting of decking members according to the invention.

The decking member 10 illustrated in Figures 1 and 2 is formed by roll-forming steel sheet of suitable composition and gauge. The member is so-called "W-decking", having three large ribs 12 of generally trapezoidal cross-section and intervening pans 14. For ease of explanation, decking member 10 will hereinafter be referred to as a decking panel, although the presence of large ribs 12 renders this term appropriate only in a very broad sense.
Marginal partial- pan portions 14a, 14b terminate respectively at complementary male and female edge flanges 16, 18 at opposite lateral edges of the panel for forming lap joints with adjacent similar panels. Edge flanges 16, 18 are of substantially lesser height from pans 14 than ribs 12. The decking panel is of nestable configuration for optimum space efficiency during storage and transport: this is highlighted in Figure 2 by the indication of a second identical overlying panel 10a. Each pan 14 and the flat top 12a of each rib 12 has a central shallow strengthening ribs 15a, 15b and the inclined sides of ribs 12 have asymmetrical ribs 15c on which the overlying nested panel rests. The trapezoidal ribs also have conventional embossments 25 arranged along each larger flat face.
Referring in particular to Figure 4, male edge flange 16 is a simple flat flange which, for enhanced nestability is upturned at slightly less than 90^o to the plane of the panel pans 14. Female edge flange 18 comprises an upturned first web portion 19 inclined to the plane of the panel at an angle slightly less than 90^o, (again, for ease of nestability) and an overturned second web portion 21 which with the other web portion defines a longitudinally extending groove 30 to receive male flange 16 of an adjacent panel (Figure 5). In situ, this lap joint is secured by clinching or any other suitable known technique. Earlier however in the assembly of the decking, groove 30 receives and locates flange 16, thereby holding the two decking members together during assembly and prior to fastening.
Flange web portion 21 terminates in a longitudinally extending lip 20 which projects laterally outwardly, preferably (but not necessarily) being inclined upwardly at about 10 to 60^o, most preferably and as illustrated about 30^o to the plane of pans 14.
A composite structural member 8 (Figure 3) may be formed by applying cementitious material 9 in a mass atop a decking which consists of several successively lap-jointed panels 10. In this composite member, lips 20 are embraced by the cementitious material, typically concrete, and are found to thereby substantially enhance the composite strength of the structural member. This enhancement is further illustrated below.
Conventional W-decking might have ribs at least about 2 inches (50 mm) high and about 4 to 6 inches wide at the top; in a typical commercial decking, they are about 3 inches (about 76 mm) high. The male flange 16 conveniently projects at least 0.8 (20 mm), preferably less than 2 inches (50 mm) from the pan to adequately accommodate standard embossments clear of the pan. The lip 20 may be between 0.4 and 2 inches (10 to 50 mm), for example about 0.8 to 1.0 inch (20 to 25 mm) wide. The angle of inclination of lip 20 may be between 20^o and 60^o to the pan, for example about 30^o, and it will be appreciated from a value given above, that the lips 20 are of width usually less than, preferably substantially less than, half that of ribs 12.
Additional mechanical anchorage can be obtained by the optional enhancements shown in Figure 6. An angled, e.g. returned or depending, secondary lip 24 may be formed at the free edge of the lip 20, and embossments 26 of suitable type may be pressed at intervals in male flange 16 and female web portion 19, and/or (but not shown) in projecting lip 20. Instead of or in addition to embossments 26 any other suitable anchorage elements may be provided.
Figures 7 and 8 depict alternative lap-joint flange configurations in which both edge formations are simple flat flanges 16′, 18′, and the lip 20′ projects integrally from the outer free edge of one of these flanges. Again, as depicted in Figure 8, a secondary lip 24′ and embossments 26′ may be provided for further enhancement of composite strength. Although a lip 20′ parallel to the pans 14′ is satisfactory, it is thought that an inclined lip as in the embodiment of Figures 1 and 2 is preferable because there is less likelihood of voids remaining under the lip after the cementitious material poured onto the decking has set.
A test was devised for determining a measure of the improvement in composite performance achieved with lap joints between panels according to the invention. A set of simple composite structural segments was formed by setting concrete about a lap-joint formed between respective pairs of W-decking panels of cross-section similar to that depicted in Figure 2. It was known that the main ribs in the W-decking employed offered effectively no resistance to longitudinally slip at zero normal force across the steel/concrete interface. One segment incorporated panels of conventional construction, while the others contained panels of various configurations according to the invention.
Each composite segment was tested by compressing the supported segment under a vertical load V through a roller bearing which acts directly as a normal force across the steel/concrete interface, and applying an increasing horizontal load P aligned with the direction of the main trapezoidal ribs and joints, which acts directly as a shear force causing slip along the steel/concrete interface, until slip occurred and the horizontal load, to maintain the slip, stabilized. The horizontal and vertical loads were plotted, and the test repeated for successively higher and lower vertical loads. The best fit straight line curve thereby obtained is of the form:
P = R + µV (1)
It will be appreciated that µ is the decking/concrete coefficient of friction, while the constant R is the intercept on the P axis and represents the horizontal load required to overcome the mechanical anchorage: i.e. the "lap joint longitudinal slip resistance".
Figure 9 shows typical experimental curves according to equation (1) for four composite segments as follows:-
CURVE/LAP JOINT TYPE A - Conventional joint
B - Simple joint between flanges of the form shown in Figure 7, including lip 20′
C - Joint as shown in Figure 7, plus the secondary lip 24′ of Figure 8
D - Joint as shown in Figure 8.
It will be seen that the provision of the projecting lip 20′ produced an approximately 5 to 6-fold increase in lap joint longitudinal slip resistance R, with further significant improvements wrought by the secondary depending lip 24′ and the embossments 26′. Results similar to Curves B and D would be expected for decking with lap joints of the kinds depicted in Figures 4 and 6 respectively.
Figure 10 is a graph of mid-span vertical deflection and curvature versus total applied load and bending moment for respective composite steel and concrete structural members incorporating conventional W-decking (curve E) and W-decking consisting of 3-rib decking members according to the invention of the type D above (curve F). The aforementioned dynamic transition is clearly seen at E₁ for the conventional composite member. Shear bond failure is also evidenced by the failure of curve E to reach the theoretical moment-curvature curve assuming no slip (Curve G). In contrast, curve F shows no corresponding discontinuity and exhibits good ductile behaviour - a smooth gradual slip as the adhesion breaks down over a portion of the slab and mechanical bonding comes to predominate. Flexural failure is evident, as the curve in due course reaches the theoretical curve G. A much higher load carrying capacity, in excess of 100% higher, is evident in Figure 10 for the composite member having decking members according to the invention. It has been found that a relative increase of the order of 200% can be obtained by optimum choice of gauge thickness, steel grade, rib spacing, span, and other parameters. For example, the specimens employed to obtain the results of Figure 10 had a short span - about two metres - between supports: the precise span involved would affect precise results.

Claims

1. A metal decking member of nestable configuration, having plural pans (14) and at least one intervening rib (12) with inclined sides, wherein the decking member has complementary integral flanges (16, 18), of substantially lesser height from the pans that said ribs, at opposite lateral edges of the decking member for forming lap joints with adjacent similar decking members, characterised in that at least one of said flanges (16, 18) further includes a longitudinally extending lip (20) which projects generally laterally of the flange and is thus disposed to be embraced by cementitious material overlying the decking member in a subsequent composite structural member incorporating the decking member, and to thereby enhance the composite strength of the structural member.

2. A decking member according to claim 1 further characterised in that said one flange comprises an overturned flange (18) defining a longitudinally extending groove (30) to receive the other flange (16) of an adjacent decking member, said lip (20) being formed by an outturned integral extension of the overturned flange.

3. A decking member according to claim 1 or 2 further characterised in that said flanges (16, 18) are upstanding from said pans (14) and said lip (20) is inclined laterally upwardly.

4. A decking member according to claim 1, 2 or 3 further characterised in that said lip (20) has an angled secondary lip (24) at its free edge.

5. A decking member according to any preceding claim further characterised by embossment (26) on or apertures in said flanges (16, 18) and/or said lip (20) to further enhance the composite strength of the lap joint in a composite structural member.

6. A decking member according to any preceding claim further characterised in that the decking member is a steel decking member.

7. A decking member according to any preceding claim further characterised in that each panel rib (12) is of generally trapezoidal cross-section.

8. A steel decking member for use with cementitious material in a composite structural member, said decking member being ribbed and of generally planar rectangular shape with a pair of longitudinal free edges having integral lap-joint flanges (16, 18), at least one generally trapezoidal rib (12) of substantially greater height than said flanges extending in a longitudinal direction between the free edges, characterised in that at least one of said flanges has an integral longitudinally extending laterally projecting lip (20), said lip being less than one half the width of the rib (12), said decking member being nestable with a second, identical decking member, said lip enhancing the composite strength of a composite structural member formed by attaching a plurality of said decking members together in an edge-to-edge array and applying a layer of unset cementitious material to at least one surface of the attached decking members and about said lips thereof, and permitting the cementitious material to set.

9. A decking member according to claim 8 further characterised in that said one flange comprises an overturned flange defining a longitudinally extending groove (30) to receive the other flange (16) of an adjacent decking member, said lip (20) being formed by an outturned integral extension of the overturned flange.

10. A decking member according to claim 8 or 9 further characterised in that said flanges (16, 18) are upstanding from said decking member (14) and said lip (20) is inclined laterally upwardly.

11. A decking member according to claim 8, 9 or 10 further characterised in that said lip has an angled secondary lip (24) at its free edge.

12. A composite structural member comprising a plurality of generally planar ribbed steel decking members (10) each having at least one generally trapezoidal integral rib (12) which extends in a longitudinal direction of each decking member intermediate said longitudinal side edges thereof, the plurality of decking members (10) being joined together at said longitudinal edges thereof in an edge-to-edge array to define a generally planar area larger than two of said decking members, characterised in that each said decking member (10) has a longitudinally extending integral lip (20) on one of respective flanges (16, 18) at said longitudinal side edges thereof, said lip (20) being less than one half the width of a said trapezoidal rib (12), said decking members (10) being nestable together when unattached prior to assembly of said composite structural member, and a layer of cementitious material on at least one surface of said planar area and about the lips (20) of the decking members, said lips (20) of the decking members enhancing the composite strength of the composite structural member.

13. Composite structural member of claim 12, further characterised in that the (16, 18) flanges of each said decking members (10) have respective longitudinal free edges, said lip (20) defining a generally planar surface which terminates at a said longitudinal free edge.