AU603051B2

AU603051B2 - Double top chord

Info

Publication number: AU603051B2
Application number: AU23544/84A
Authority: AU
Inventors: Ernest O Butts; Felix F Laurus
Original assignee: Hambro Structural Systems Ltd
Current assignee: Hambro International Structures Ltd
Priority date: 1983-01-17
Filing date: 1984-01-17
Publication date: 1990-11-08
Anticipated expiration: 2004-01-17
Also published as: KR910008086B1; HK79093A; JPH0561420B2; AU2354484A; ATE37413T1; DE3378068D1; EP0113972B1; CA1172463A; JPS59134262A; KR840007451A; EP0113972A1

Abstract

A steel joist for use in a composite steel and concrete construction consists of a web (17), a bottom chord (16) and a double top chord (18) construction consisting of two elongated substantially identical members (21) each of S or Z cross-section and being connected to or integral with the web (17). The members (21) are positioned in mirror relation tone another to provide symmetry about a vertical axis, and in use are embedded in a concrete slab, with the web (17) and bottom chord (16) not being embedded in the concrete.

Description

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FORM

FORM 10 SPRUSON FERGUSON COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: 603051 Class Int. Class @06

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0 0 00 S S S '354q-/t4, Complete Specification Lodged: Accepted: Published: Priority: Related Art: This documn'nt contains the amendments made under Section 49 and is correct for printing.

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6 Name of Applicant: HAMBRO STRUCTURAL SYSTEMS LIMITED Address of Applicant: 215 Colonnade Road, Ottawa, Ontario, Canada, K2E 7K3 Actual Inventor(s): FELIX F. LAURUS and ERNEST O. BUTTS Address for Service: Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: "DOUBLE TOP CHORD" The following statement is a full description of this invention, including the best method of performing it known to us JP/ALB/13U '~Ly -2- The present invention relates to improvements in steel joists and compsite steel and concrete construction systems. The present invention constitutes an improvement upon the applicant's prior invention patented in US patent No. 3,845,594 on November 5, 1974.

It is the object of the present invention to provide an improvement on the abovementioned patented invention.

There is disclosed herein a composite action steel and concrete floor system wherein a plurality of steel joists span horizontally and in spaced parallel relationship between spaced support members, each said steel joist including a top chord, a bottom chord and an intermediate web vertically extending between said top and bottom chords, composite action being achieved by complete embedment of each top chord in a poured concrete slab, shear connection between said top chord and said slab resulting from clamping action, and in which said joists are subject to construction loads during a non-composite stage of construction of said floor system due to their own weight, construction live loads and wet concrete, wherein each top chord of each joist comprises a pair of identical, longitudinally cant' uous, symmetrical, oppositely-positioned S shaped members extending fn a parallel relationship for the length of the respective joist, said S shaped members being in mirror relation to one another with the right-hand one appearing in cross section in a regular upright S form and the left hand one in reverse S form and being transversely spaced apart symmetrically relative to said web providing a joist having symmetry about a vertical axis passing through said web.

Accordingly, an improvement in lateral stiffness which greatly improves the strength of the composite structure during the construction stage permitting safer construction procedures particularly where long spans are involved is achievable. Thus, applicants are able to erect long span constructions in excess of the present limit of 13 meters and may extend these'spans to 20 or 25 meters without difficulty. By utilizing angles, channels or tubes for web member, it is possible to increase the radius of gryration of these sections over a solid round section and thus higher unit stresses may be tolerated in the web members and a saving in steel weight results in a more efficient joist construction.

4/ I I -3 A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 Is a perspective view from below of a composite construction utilizing joists of the present invention, Figs. 2A and 2B are vertical sections through joists constructed in accordance with the present invention illustrating alternative arrangements of the top chord members, Figs 3a, 3B, 3C ad 3D Illustrate features of joists in which the web Is a continous sheet, and Figs. 4A, 4B, 4C, 4D, 4E and 4F Illustrate further details of top chord to web connections, and joist fabrication techniques.

Fig. 5 Is a perspective of an in-fill framing system using joists the 00.. cross-section of which Is shown in Fig. 4E and Fig. 6 Is a section through a composite steel and concrete 5M construction In accordance witht another aspect of the present invention.

With reference to Fig. 1 of the attached drawings, therer is shown a composite steel and concrete floor system 10 consisting of a plurality of open web joists 11 connected together with roll or spanner bars 12, which serve to support form work 13, on which a concrete slab 14 is poured, which 0:'10 slab Includes reinforcing mesh 15. Each of the open web joists 11 consists of a bottom chord 16, which as shown in Fig. 1 may consists of a pair of righ angle members 16, a series of web members 17 and dual top chords 18.

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i: chords are provided with appropriate slots through which the roll or spanner bars may be inserted to support form work, the roll or spanner bars being either permanent roll bars intended to remain in the structure when complete, or may be removable roll bars as taught for example in applicant's prior U.S. Patent No. 3,945,168.

Referring to Fig. 2A there is shown in vertical section, an open web joist 11 having a pair of bottom angles 16, forming the bottom chord of the joist, a pair of top chord members 18, and a web which may be for example formed of hollow rectangular cross-section tubular members, or of channel members 17. As illustrated in Fig. 2A the two top chord members are welded together at 19 and to the web members 17 by welds 20. The welds 20 as illustrated may be spot or seam welds, and are positioned to provide the maximum strength, and to enable a welding electrode to be inserted inside the member 17, to make a satisfactory weld. Each top chord member 18 is formed of an identical cross-section profile shape having an upper S or Z portion 21 and a downwardly depending leg 22. As in applicant's prior patents, it is intended that the S or Z shaped portions 21 be embedded in the concrete slab of the composite construction, e* the S or Z shapes providing a superior shear connection :between the concrete slab and joists to provide a true composite action between the joists and the slab. It should be noted that the two top chord members are positioned in mirror image relationship to one another, thus providing a perfectly symmetrical configuration of joist about a vertical "Rj axis. The advantages of such symmetry are detailed hereinj: <~30 before.

ATJP/JMC/0076F i 4, i I IRI Fig. 2B illustrates a similar joist constructed in accordance with the present invention, also possessed of vertical symmetry, but in which the top chord members are arranged facing oppositely to the members in Fig. 2A. As before the top chord members are secured to the web 17 by suitable welds 20, and an additional filler plate 23 is secured between the top chord members 18, and serves to seal the space between the two top chord members to prevent the loss of concrete through the open web of the joist, during construction. The function of the two embodiments illustrated in Figs. 2A and 2B is virtually identical.

Fig. 2B also illustrates an optional form of top chord member 18, which may be provided with an optional lip 24, which is useful for increasing the compressive strength of the joist in the non-composite mode, that is before the •top chord has been embedded in concrete.

Fig. 3A illustrates in perspective an alternative form of joist in accordance with the invention in which the web and bottom chord are rolled from a single strip of steel. The web 37 of Fig. 3A is formed unitarily with the bottom chord 36, for example by the cold rolling of a suitable strip of sheet steel. As before, top chord members r 18 are connected to the web 37 by welding, and opening 38 in the top chord and the web may be formed either before or after welding by a suitable punching operation. It will be appreciated that if the slots 38 are formed before the top chord members 18 are welded to the web 37, it will be necessary to provide means for aligning the openings 38 which extend entirely through both top chord members and the web 37 Sprior to welding. This alignment may create problems in JP/JMC/0076F Cc~ cl I i fabrication in certain circumstances, and accordingly Fig. 3B illustrates an alternative to the structure illustrated in Fig. 3A in which the top chord members 39 are provided with only a very short downwardly depending leg 40 on the crosssectional shape which leg is, as before, welded to the web 37. In this case, the web may readily be punched for the openings 38 prior to affixing the top chord members 39, and there is no necessity to align openings in the top chord members with corresponding openings in the web.

Fig. 3C illustrates in exploded perspective an alternative form of joist construction in accordance with the invention. In Fig. 3C the joist is formed of a strip or plate 41 angles 42 as bottom chords and top chord members 43. The joist of Fig. 3C is fabricated by welding, and appropriate slots are formed in the top chord members 43 and aO in the web 41 prior to or after welding, with the necessary oc S-alignment being made so that the openings 44, 45 and 46 in the top chord members 43 and the web 41 would be e..

appropriately aligned prior to running the welds.

Fig. 3D illustrates an alternative form of bottom chord 47, which can be used in place of the angles 42 of Fig.

3C. In this case a cold rolled steel bottom chord shape as shown in Fig. 3D would be attached to the web 41 as by welding.

Fig. 4A illustrates a form of top chord member provided with a longitudinal rib 51 on the vertical leg 52 of the top chord section, which rib 51 would assist in electric resistance welding of the top chord member 50 to an Sappropriate web structure.

3 Fig. 4B illustrates an alternative form of top chord )ic_ d LiiC 111 member 53 provided with a plurality of slots 54 in the sloping face of the top chord section to enhance the shear connection between the top chord and the concrete slab by permitting concrete to fill the slots 54 when the slab is being poured.

The top chord member 53 is also provided with a right angle flange 55 which may be used to support appropriate formwork, as an alternative, or ancillary to the use of conventional spanner or roll bars.

Figs. 4C and 4D are perspective views illustrating the use of channel shapes as web members 60, which web members may be positioned centrally of the joist as in Fig.

4D, wherein the channel member 60 is positioned between the vertical legs 61 and 62 of the open web joist. In Fig. 4D where heavier construction loads are to be encountered, the vertical legs 61 and 62 of the top chord members are positioned tightly together, and channel web members 60 are positioned on either side of the vertical legs 61 and 62.

Similarly, bottom chord members 63 shown in Fig. 4D as angle members may be positioned between the web members A further and highly desirable fabrication practice is to use channels for all compression members of the truss or open web joist, which are positioned inside or between the top chord members, and to use angles for tension members, which are positioned outside the top chord flanges, Figs. 4E and 4F illustrate two additional fabrication techniques. In Fig. 4E two identically shaped members 70 and 71 are welded back-to-back to provide a complete joist. Each member 70 and 71 is one half of the completed joist, the joint between the two members coinciding with the vertical T /JMC/0076F V 1 8 axis of the completed joist. In Fig. 4F a first member 72 includes an S or Z shaped top chord 73, a bottom chord portion 74, and a web 75. A second top chord portion 76 is welded to the web 75 to form the completed double top chord joist.

The fabrication technique illustrated in Fig. 4E provides a particularly advantageous technique in practicing the present invention.

The symmetrical sections may be rolled, welded and punched to provide an economical and versatile joist for use in composite construction.

When fabricated as a shallow depth joist an efficient in-fill technique for steel beam stuctures is obtained. If a deeper joist is formed, an efficient regular span joist is obtained.

^Referring to Fig. 5, there is shown a portion of a building floor system, including steel beams 80 and 81 supporting a pair of double top chord joist 82 and 83. Spanner boards 84 and 85 as taught in prior U.S.

"i .5 Patent No. 3,845,594 connect the joists 82 and 83 and would support suitable sheeting (not shown) on which a concrete deck slab may be poured.

Thus a smooth concrete slab may be poured.

In Fig. 6 a pair of steel beams 90 and 91 support ledger angles 92 and 93 on which a joist 94 is shown, embedded in and supporting a concrete slab 95. By the use of the ledger angles 92 and 93, a thickened slab may ~be obtained compared to the slab of Fig. 5, which may for example be used for an in-floor electrical distribution system (not shown).

Thus summarizing, the present application discloses an improved composite steel and concrete floor system utilizing a novel form of joist having a pair of symmetrically opposed top chord members connected to a suitable web which in turn is connected to a suitable bottom chord structure. The applicant's top chord now consists of two S shaped members which may be identical to those taught in applicant's prior patent with the exception that the downward vertical leg is modified In that it may be lengthened to provide the required additional welding surface for web connections. The lip In the present top chord construction may be either deleted or rolled in the opposite direction If necessary so as to interfere with web members which are placed between or outside the top chord elements.

In an alternative, some web members may be located between the top chord elements and some outside the top chord elements. This option has definite advantages so far as welded connections are concerned in order to more easily align the web and chord member,-.

SN/f 51 -9- The top chord member of the present invention is stronger than the prior top chord since the joist is symmetrical about its vertical axis. The downstanding legs of the top chord elements may of course be extended to increase welding surface area as required.

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The web system of the present invention may be constructed of individual members which can be any shape conventionally used for such members. Commonly angles, flats, channels and rectangular sections may be used, although round rod pieces or serpentine web could also be used if required for any particular application. The bottom chord of the joist may be of any conventional shape although generally a pair of angles is the most commonly encountered configuration.

The cover or fillet plate used to fill the top of the joist between the top chord members may be made of very light 20 gauge material and its purpose is simply to prevent concrete from spilling through between the top chord elements. The uppermost portion of the individually web members is positioned so that it does not protrude above this cover plate. It would be logical to make the cover plate of light gauge steel and simply tack weld it into place. It would be considered a non-structural element and thus not included in the design calculations for the joist. Alternatively, however, a heavier cover plate could be utilized and welded into position to provide a more positive lateral connection 3 between the top chord elements than that which would normally /JMC/0076F P/JMC/0076F -H4 11 occur as a result of the top chord to web member welded connections. This heavier cover plate might then be included in the design calculations for the load bearing strength of the joist.

In general, the advantage of the applicant's improved joist structure is a great increase in lateral stability as result of the double top chord elements which are connceted together by either web connections or a heavier gauge filler plate. The Increased lateral stability or rigidity reduces the slendereness ratio of the top chord element and provides additional compression capacity during the non-composite structural stage of construction. Furthermore, the addition of a second top chord element provides increase cross-section area further enhancing the compression capacity of the joist. Thirdly the configuration now allows individual web members to be utilized more readily and provides for a more efficient web 4.

system which Is lighter in weight especially in the longer spands of feet and over, enabling the double top chord joist of the present application to be utilized in spans of 60 feet or more.

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Claims

1. A composite action steel and concrete floor system wherein a plurality of steel joists span horizontally and in spaced parallel relationship between spaced support members, each said steel joist including a top chord, a bottom chord and an intermediate web vertically extending between said top and bottom chords, composite action being achieved by complete embedment of each top chord in a poured concrete slab, shear connection between said top chord and said slab resulting from clamping action, and in which said joists are subject to construction loads during a non-composite stage of construction of said floor system due to their own weight, construction live loads and wet concrete, wherein each top chord of each joist comprises a pair of identical, longitudinally continuous, symmetrical, oppositely-positioned S shaped members extending in a parallel relationship for the length of the respective joist, said S shaped members being in mirror relation to one another S: with the rlght-hand one appearing in cross section in a regular upright S 0 00 form and the left hand one in reverse S form and being transversely spaced apart symmetrically relative to said web providing a joist having symmetry about a vertical axis passing through said web. @000 A structure as claimed in claim 1i, wherein each of said S shaped members has a downwardly depending leg and is connected to said web by welding said leg and said web together.

3. A structure as claimed in claim 2, said legs of said top chord members being provided with a plurality of longitudinally spaced openings therein for receiving the ends of spanner bars for holding said joist in said spaced parallel relationships.

4. A structure as claimed in claim 1 wherein said web c'mprises a flat cold rolled steel sheet or plate. A structure as claimed in claim 1 wherein said bottom chord comprises a pair of angle members connected to said web by welding.

6. A structure as claimed in claim 1 wherein said bottom chord is integral with and rolled from single piece of steel together with said web.

7. A structure in accordance with claim 1 wherein openings are provided in said web to receive said spanner bars to support concrete form work during erection of said composite steel and cosicrete structure. L ~ir r -I

8. A structure as claimed in claim 1 wherein said joist is formed of two identical cross-section members joined at said vertical axis, said web being of double thickness, the axis of symmetry passing through the centre of said web.

9. A structure as claimed in claim 1 wherein said joists are supported by steel beams and together with said slab form in an in-fill panel. A structure as claimed in claim 1 wherein said beams are provided with ledgers fixed to the webs thereof whereby a thickened slab is obtained.

11. A structure as claimed in claim 1 wherein each said joist is formed of two identically-shaped joist members joined back-to-back, each joist member containing one-half of the said top chord, web and bottom m* chord and constructed of rolled sections of sheet steel.

12. A structure as in claim 1 wherein each S shaped member has top .e •C and bottom flanges and an intermediate member connecting opposite ends of said top and bottom flange-s, the resulting free ends of said top and bottom flanges being pointed in opposite directions for allowing said concrete to flow between and totally fill the space between said S shaped members of each joist when said slab is poured.

13. A structure as claimed in claim 1 including a supplementary means including discrete apertures in said S shaped members along their length for enhancing the shear connection between each of said top chords and said slab.

14. A composite action steel and concrete floor system substantially as hereinbefore described with reference to the accompanying drawings. o DATED this TENTH day of AUGUST 1990 Hambro Structural Systems Limited Patent Attorneys for the Applicant SPRUSON FERGUSON 1/25221