CA1106127A

CA1106127A - Stringer

Info

Publication number: CA1106127A
Application number: CA331,327A
Authority: CA
Inventors: Ronald J. Johnston
Original assignee: Aluma Systems Canada Inc
Current assignee: Aluma Systems Canada Inc
Priority date: 1979-07-06
Filing date: 1979-07-06
Publication date: 1981-08-04
Also published as: BR7907414A; NO793246L; GB2054691A; JPS5612451A; ES486410A1; DK426479A; IT1120613B; DE7929834U1; DE2942566A1; FR2461071B1; AU522430B2; IT7950624A0; FR2461071A1; SE7908294L; AU5227179A; JPS6016545B2

Abstract

ABSTRACT OF THE DISCLOSURE

A beam, suitable for use as a joist or stringer in heavy concrete forming applications, is disclosed. The beam has an upper top hat section, web portion and a base portion with a bolt slot and slightly concave base flanges;
and includes downwardly extending flanges at the outer extremities of the top hat flanges and upwardly extending flanges at the outer extremities of the base flanges.
The underside of the top hat flanges and the upper side of the base flanges, at their outer ends, are curved, so as to accommodate identical clamps for securing the beam to other structures, as required.

Description

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FIELD OF THE INVENTION:
This invention relates to an improved extruded aluminum beam having very high strength and stiffness to weight ratios, and being particularly intended for use as a stringer in concrete forming applications.
' B~CKGROUND OF THE INVENTION:
Concrete forming structures have been provided for shoring and providing the formwork for placement of concrete, horizontally such as in apartment floors and the like, and vertically as in walls or tunnel liners, and the like.
Generally, the horizontal shoring comprises a plurality of secondary joists which may be supported by primary supports such as trusses or stringers which are supported by vertical shoring members. In vertical shoring, a plurality of joists or wales may be provided, which are in turn supported by strongbacks or the like. The secondary shoring members may be securely fastened to the primary supporting members, especially in instances where the shoring or concrete forming structure is to be "flown" from a first working position to a second and subsequent working position.
In many instances, the concrete forming structures are formed of extruded aluminum members, either totally or at least in respect of the secondary and primary shoring members which are directly in contact with the plywood sheathing which forms the actual face against which the concrete is placed. Several specific structures have been taught, for instance, in Canadian Patents 941,138 and 990,481 dated February 5, 1974 and June 8, 1976, respectively, each issued to Peter J. Avery and assigned to ~, ~'6~Z7 a common assignee of the present invention. Those patents are particularly related to concrete forming structures which are for use in horizontal shoring situations, and have proven particularly useful for the placement of concrete in the great majority of cases where highrise residential apartment or condominium buildings, certain kinds of office buildings, and the like are being constructed.
Likewise, for use in vertical forming,Canadian Patent 1,037,234 issued August 29, 1978, in the name of the present inventor, and also assigned to a common assignee herewith, shows a very successful wall forming~
system.
One common element to all of those systems, apart from the fact that they are all formed substantially completely of extruded aluminum members, is the beam which is particularly described in the aforesaid Avery Patents. That beam has exhibited both strength and stiffness; i.e., it is strong in that it is capable of withstanding applied buckling and bending forces, and it is stiff in that it does not deflect more than an allowable limit under given loading conditions.
There are, however, certain conditions when it is desirable to place heavier concrete loads than normal, such as in parking garages or large scale projects, and the like. In such instances, it is very often desirable to provide shoring which carries the load of the concrete to vertical shores, which ; may not necessarily be trusses as the job situation may require specific shoring placement on a one time only basis. In such circumstances, very often the shoring is provided by scaffold frames, and may include intermediate posts. In those cases, while the secondary joists being used may be the Avery beams f mentioned above, it may happen that there is an inadequacy in the strength of~such beams for use as stringers -- i.e., primary supporting members which are, themselves, supported by the vertical shoring beneath them. In such cases, in the past, it has been normal to provide stringers of timber or steel, which are of necessity very heavy. For example, a 12 inch x 12 inch spruce wood stringer has a weight of 30 pounds per foot (44.65 kilograms per meter) dry weight. Such weight makes the physical handling of the stringer and the placing of it in its working position, difficult, with a cost in labour and time.
Reference is also made to Burrell Canadian Patent 1,045,348, issued January 2, 1979, which teaches a lightweight aluminum joist having approximately equal widths across its top and bottom flanges, and where the side walls of the top hat channel increase in thickness from bottom to top. In this manner, the inner surfaces of the channel converge upwardly, while the outer surfaces of the channel walls are parallel. Stub flanges are provided which are parallel to the outer surfaces of the channel side walls, so as to protect the edges of the Elanges during frequent re-use of the joist.
The principal purpose of the Burrell joist, however, is to provide the channel shape described above, so as to accommodate wooden inserts which are not perfectly rectangular, and have rounded corners.
One purpose of this invention, is, therefore, to provide an extruded aluminum stringer which not only exhibits ~reatly improved strength and stiffness characteristics, but does so with very little increased weight, so that a stringer according to this invention may be handled at the job site by one man.

A further ob~ect of this invention is to provide a stringer which may be substituted for use as a joist, either ; in very heavy concrete placement work, or in any event as a replacement or substitute for the ordinary extruded aluminum ~oists such as those used in the Avery and Johnston Patents aforementioned.
All of the above objects and characteristics are accomplished by the provision of an extruded aluminum beam having an upper, inverted top hat portion, a centrally located web portion and a base portion in which there is a centrally disposed channel suitable for receiving a head of a bolt. The stringer of the present invention, being a beam, is extruded aluminum having constant cross-section throughout its length, ~ -ana ln particular has a pair of downwardly extending flanges which are formed at the outer ends of each of the top hat flanges, and a pair of upwardly extending flanges which are farmed at the outer ends of each of the outwardly extending base flanges.
The heights of all of the downwardly and upwardly extending flanges are substantially equal to each other. The minimum 20 thickness of each of the outwardly extending flanges of the upper portion -- the top hat flanges -- is greater than the minimum thickness of each of the base flanges; and the thickness of each of the inwardly extending flanges which go to define the bolt slot in the base portion, are greater than the minimum thickness of each of the outwardly extending base flanges.
In a preferred embodiment, the lower surfaces of each of the outwardly extending flanges of the upper portion -- the top hat flanges -- are curved, while the upper, load supporting surfaces are substantially planar. Likewise, 30 the upper surfaces of the outwardly extending flanges of the lX7 base portion are curved at their outer extremities with substantially the same radius of curvature as that of the outer extremities of the lower surfaces of the top hat flanges, so that identical clamps may be used to secure the beam to other structures, as required.
BRIEF DESCRIPTION OF THE DRAWINGS:
The present invention is described in greater detail hereafter, in association with the accompanying drawings, in which:
Figure 1 is a perspective view of a stringer, according to the present invention, showing the principal characteristics and features thereof;
Figure 2 is an end view of a stringer according to the present invention having a wooden joist secured in f the upper portion thereof; and, Figure 3 is a perspective view showing the stringer in association with other construction elements in a typical instance of use of the stringer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Referring first to Figures 1 and 2, there is shown a stringer 10 in accordance with this invention, which stringer 10 is formed of extruded aluminum, and subject only to the . usual conditions of extrusion and fabrication, exhibits a constant cross-section throughout its length. The stringer (beam) has an upper portion 12, a web portion 14 and a base portion 16.
The upper portion 12 has a generally U-shaped channel 18, with a bottom wall 20 and side walls 22, and a pair of : flanges 24 which extend laterally outwardly, one from the 30 upper end of each of the side walls 22.
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;lZ7 The web portion 14 is substantially centrally located beneath the upper portion 12 and over the base portion 16, and has a web 26 which is of substantially constant thickness throughout its height, except at its transitions 28 and 30 to the upper portion 12 and base portion 16, respectively.
The base portion has a centrally disposed channel 32 which is suitable for receiving the head of a bolt, and it is evident that the channel 32 is substantially smaller both in width and height than the channel 18. The channel 32 is particularly defined by a pair of short flanges 34 which extend laterally inwardly one from each of the lower ends of the side walls 36 of the channel 32. A pair of base flanges 38, extends laterally outwardly, one from each lower end of the channel side walls 36. The overall width of the base flanges 38 is greater than the overall width of the upper flanges 24; that is, the base flanges 38 extend to a greater extent than the upper flanges 24. The undersurfaces of the base flanges 38 are, overall from side to side, slightly concave. Thus, with the beam at rest andctherwise unstressed, the short flanges 34 which serve to define the bolt head channel 32 are higher than the outer edges of the lower surfaces of the base flanges 38.
As noted above, the principal requirements of the stringer are that it should exhibit both strength and stiffness ; -- as discussed above -- and that such characteristics be considerably higher on a per weight basis than, for instance, wood or steel stringers.
These additional characteristics are particularly exhibited by a stringer according to the present invention, which in addition to the above description, possesses the following:

1~61Z7 At the outer ends of each of the outwardly extending flanges 24 of the upper portion 12 of the stringer, there is formed a downwardly extending flange (return) 40. Likewise, at the outer ends of each of the base flanges 38, there is formed an upwardly extending flange (return) 42. The heights of all of the downwardly and upwardly extending flanges 40 and 42 are substantially equal to each other.
The outwardly extending upper flanges 24 have substantially planar upper surfaces, which function as load receiving surfaces in the normal use of the stringer. The lower surfaces of the flanges 24 may be planar, or in the preferred embodiment, they are curved as at 44. In any event, the minimum thickness of the flanges 24 is greater than the minimum thickness of either of the base flanges 38.
Likewise, the thickness of the flanges 34 which define the bolt slot 32 are greater than the minimum thickness of each of the base flanges 38.
It has been noted that the base flanges 38 have a minimum thickness; and in the preferred embodiment of the stringer according to the present invention, the outer extremities - of the upper surfaces of the base flanges 38 are stepped at 46, so that the outer portions 48 are curved with the same radius of curvature as the outer extremities of the curved portion 44 of the flanges 24. In this manner, the downwardly extending flanges 40 and upwardly extending flanges 42, or return, may accommodate identical clamps, as discussed hereafter.
In certain instances, particularly when it is intended to utilize the stringer as a joist, or when it may be otherwise appropriate so as to secure another member to the stringer by driveable fastening means driven into a wooden joist member ~1~6~Z~

or the like, a wooden insert 54 -- nominally 1.5 inches x 1.5 inches (31 mm x 31 mm~ may be forced downwardly into the channel 18. So as to assist the securement of the insert, particularly so as to resist upward movement thereof, teeth 50 may be formed on the inner surface of the side walls 22 of the upper channel 18, or on either of those surfaces. Driveable ~ -means such as screws 52 may also be driven into the wooden insert 54, and those fasteners 52 may be started from a starter groove or indent 56 formed in the outer surface of the walls 22 or either of them.
The consequences of the above features and characteristics of a stringer according to the present invention are physically manifested in a beam having a standard overall height (nominal) of 7.5 inches (190 mm), an overall width at the base of 5.0 inches (127 mm), and an overall width across the upper flanges of 3.875 inches (98.4 mm). That stringer has a moment of resistance which is substantially equivalent to that of a 12 inch x 12 inch spruce wood member, which weighs 30 lb/ft. (44.65 kg/m), dry weight, while weighing only 5.2 lb/ft. (7.7 kg/m) complete with a 1.5 inch x 1.5 inch wood insert.

Compared with a standard "ALUMA BEAM" -- a beam substantially as described in the Avery Patents noted above --the moment of inertia about the horizontal axis (IXX) is 34.06 in4 (1417 cm4) compared to 16.445 in4 (685 cm4); and a moment of inertia about the vertical axis (Iyy) of 4.72 in4 (196 cm4) compared to 2.528 in4 (105 cm4).
An "ALIJMA BEAM", as particularly taught in the aforesaid Avery Patents, has a weight of 4.0 lb/ft. (6.0 kg/m);
30 and has an overall height (nominal) of 6.5 inches (165 mm), an lZ7 overall width at the base of 5.0 inches (127 mm) and an overall ; width across the upper flanges of 3.2 inches (80 mm). Thus, quite surprisingly for a weight increase of approximately only 30%, there is a much higher IXX and Iyy~ giving the following comparative figures as to strength and stiffness from which it will be seen that the stringer of the present invention has both strength and stiffness increases of approximately 100% for the stated 30~ increase in weight.
; TABLE I
Comparison of ALUMA BEAM to subject Stringer (on basis of ALUMA BEAM characteristics) BEAM STRINGER
~. _ Weight per Unit Length1.0 1.3 (includlng wood insert) Deflection Resistance 1.0 2.0 . ._ . .
Moment of Resistance 1.0 1.85 . ' .. .... . ' .... _ .

}~ Referring now to Figure 3, a typical use of the stringer according to the ~present invention, together with a standard "ALUMA BEAM" as aforestated, is shown. The stringer 10 may be supported from beneath by other shoring apparatus, such as highstrength scaffold, shoring posts or the like, and generally is supported in a U-head 58 which is associated with the vertical shoring 74. The stringer may be inserted into "standard"U-heads of the sort normally found on construction sites, either upsidedown in the case of 4 inch, or right side up for the wider 8 inch U-head. Otherwise, the stringer may be clamped to a plate instead of standing in a U-head, by a clamp such as clamp 62 mentioned hereafter.

_ g _ ~1~61Z7 A plurality of beams 60 are supported by the stringer 10, and similar stringers spaced therefrom along the length of the beams 60. The beams 60 may be secured to the stringer 10 using clamps 62 which are designed and adapted to be secured to the under side of the beam by inserting a bolt head in bolt slot 66 thereof and turning a nut 64 on the bolt. The clamping portion 68 of the clamp 62 overlies the return or downwardly extending flange 40, for secure attachment of the beam 60 to the stringer 10 if they are to be moved as a unit. Either pairs of clamps 62 may be used, on both sides of the stringer 10, or the clamps on consecutive beams may be on alternate sides of the stringer, with only one clamp per beam per stringer being used.
In the typical arrangement illustrated in Figure 3, -~ sheathing 70 is secured to the beams 60 by driveable fastening means passing downwards through the sheathing 70 into a wooden insert 72 placed and secured in the upper top hat portions of each of the beams 60.
B~ use of the stringer 10 such as in the manner illustrated in Figure 3, it is not necessary to insert web blocks between the upwardly extending walls of the U-head 58 and the web 26 of the stringer.
A stringer has been described which exhibits considerably greater strength and stiffness per unit of weight when compared with prior art beams, and is dimensionally such that the stringer can be used as a substitute for a standard extruded aluminum beam in concrete forming structures, without an excessive increase of weight. The advantages ascribed to the stringer of the present invention have been demonstrated, and the features and characteristics of the stringer have been . . .

described. Other features and uses of the stringer will become evident to those skilled in the art, and specific characteristics of the stringer may, of course, be altered or amended without departing from the spirit and scope of the appended claims.

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Claims

1. An extruded aluminum beam of constant cross-section throughout its length, having an upper portion, a web portion and a base portion; where the upper portion comprises a generally U-shaped channel having a bottom wall and side walls, and a pair of flanges extends laterally outwardly, one each from the upper end of each of the sidewalls;
the web portion is substantially centrally located beneath said upper portion and over said base portion, and is of substantially constant thickness except at its transition to the upper and base portions;
the base portion has a centrally disposed channel suitable for receiving the head of a bolt, said channel being of substantially smaller width and height than the channel of the upper portion; a pair of short flanges extends laterally inwardly one each from the lower end of each of the channel side walls of said base portion; and a pair of flanges extends laterally outwardly, one each from the lower end of each of the channel side walls of said base portion, to a greater overall extent than the pair of flanges which extends laterally outwardly from the upper ends of the channel side walls of said upper portion; the lower surfaces of said flanges of said base portion being,overall, slightly concave from side to side;
said beam being characterized in that:
a pair of downwardly extending flanges is formed at the outer ends of each of the outwardly extending flanges of the upper portion, and a pair of upwardly extending flanges is formed at the outer ends of each of the outwardly extending flanges of the base portion;
the heights of all of said downwardly and upwardly extending flanges are substantially equal to each other;
the minimum thickness of each of the outwardly extending flanges of the upper portion is greater than the minimum thickness of each of the outwardly extending flanges of the base portion; and the thickness of each of the short, inwardly extending flanges of the base portion is greater than the minimum thickness of each of the outwardly extending flanges thereof.

2. The beam of Claim 1 where a plurality of inwardly and downwardly extending teeth are formed in a portion of at least one of the side walls of the channel of the upper portion of said beam.

3. The beam of Claim 1 where the lower surfaces of each of said pair of outwardly extending flanges of said upper portion are curved, and the upper surfaces thereof are substantially planar.

4. The beam of Claim 3 where the upper surfaces of the outwardly extending flanges of the base portion are curved at their outer extremeties with substantially the same radius of curvature as that of the outer extremeties of the lower surfaces of the outwardly extending flanges of the upper portion.