US2864471A

US2864471A - Joist construction

Info

Publication number: US2864471A
Application number: US567223A
Authority: US
Inventors: John K Williams
Original assignee: Central Texas Iron Works Inc
Current assignee: Central Texas Iron Works Inc
Priority date: 1956-02-23
Filing date: 1956-02-23
Publication date: 1958-12-16
Anticipated expiration: 1975-12-16

Description

1958 J. K. WILLIAMS JOIST CONSTRUCTION R m8 WM u I W K N m 6 J 5 "3 9 1 3 2 b e F d e l 1 F ATTORNEYS rorsr coNsrnUcrroN l ohn K. Vliiiiams, Waco, Tern, assignor to Central Texas EronWorirs, Waco, Tex, a corporation of Texas Application February 23, 1956, Serial No. 567,223

1 tllaim. (Cl. 1S937) This invention relates to structural building units and more particularly to a metallic joist construction of the kind adapted for use as a horizontally disposed bearing member for supporting vertical loads such as would be imposed on floor joists or rafters of a building.

Joists of the general class to which this invention relates are well known in the art and customarily include top and bottom chord members interconnected by a zigzag web structure. In designing joists of this kind two important considerations are that the joist parts be constructed from material, e. g., angle iron, which possesses a relatively large inherent resistance to bending stresses and that the parts of the joist be so arranged as to eliminate or minimize the imposition of secondary stresses on the parts when the joist is subjected to load. The elimination or minimization of the imposition of secondary stresses on the joist parts may be accomplished by so arranging the several parts that the neutral axes of all intersecting parts meet at a substantially common point. In actual practice, however, the common point of intersection of the neutral axes of the intersecting parts is difiicult to achieve and particularly is this true with respect to the fabrication of joists from angle iron sections. The Steel loist Institute has recognized this difficulty as is evidenced by the establishing of a maximum permissible deviation of the intersecting neutral axes from a common point of intersection not to exceed three-fourths the cross sectional dimension of the largest intersecting member. Most manufacturers of angle web joists perforce must take advantage of at least a portion of the permissible deviation due to the mechanical difliculty which existed heretofore in producing joists in which the neutral axes of the intersecting members actually intersect at a substantially common point.

An object of the invention is to provide an improved joist construction of the kind referred to in which the neutral axes of intersecting chord and web parts intersect at a substantially common point.

Another object of the invention is to provide an improved joist construction which is symmetrical about a vertical plane through its longitudinal neutral axis so as to be equally resistant to the application of force from either side of the joist.

A further object of the invention is to provide an improved angle web joist construction having uniform lateral stability and being substantially free from secondary stresses when under load.

Other objects and advantages of the invention will be pointed out specifically or will become apparent from the following specification and appended claims, when considered in conjunction with the accompanying drawings, in which: V

Figure 1 is a side elevational view of ajoist constructed in accordance with the invention;

Figure 2 is a bottom plan view of the construction shown in Figure 1;

Figure 3 is a sectional view taken on the line 3-3 of Figure 1;

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Figure 4 is an enlarged, perspective view of a portion of the construction shown in Figure 1; and

Figure 5 is an enlarged fragmentary view, partly in elevation and partly in section, showing the relative positions of parts of the construction.

A joist constructed in accordance with the invention comprises a first or top chord member or structure 1 composed of a pair of similar, parallel companion angle iron elements 2 and 3, so positioned relatively to one another that the respective fianges 4 and 5 are horizontal and uppermost whereas the flanges 6 and 7 are vertical and adjacent to one another. A second or bottom chord member or structure 8 is composed of similar, spaced, parallel companion angle iron elements 9 and 10, but the latter elements are so positioned that the flanges 11, 12 lie in a vertical plane and the

horizontal flanges

13 and 14 are lowermost. A web structure generally indicated by the reference character 15 is connected to and between the elements of the chord members 1 and 8 so as to maintain the elements of each chord member and the two chord members in their respective spaced and parallel positions with a common central plane midway between the companion elements of each chord structure.

The web structure includes a plurality of serially adjacent, relatively short, right angular or. angle member components 16, each of which preferably is formed from the same stock that is used in the formation of the, chord elements 2, 3 and 9, 10. An advantage of using the same stock in the formation of the chord elements and the 1 web components is that short pieces of material left over from cutting the chord elements may be used for web components, thereby reducing theamount of scrap loss.

Each of the angle member components 16 comprises

flanges

17 and 18 extending an equal distance from the apex 19 of the V. The apex 19 of each component 16 may also be considered a longitudinal central edge extending parallel to and between the longitudinal outer edges of the

flanges

17 and 18. As is best shown in Figures 3 and 4, the longitudinal outer edges of the

flanges

17 and 18 of each component 16 are rigidly secured as by welding to the vertical flanges of the elements 2, 3 and 9, 10.

In connecting the web components 16 to the respective chord members 2 and 8, the individual components are positioned at angles to the vertical and are so arranged longitudinally of the chord members as to present from the side a substantially zigzag appearance. The web components 16 are so arranged between the elements of the respective chord members that the apex 19 of each component faces in the same direction, i..e., towards theleft as viewed in Figure 1, and, as is best shown in Figure 2, the apex of each of the web components is located on the longitudinal center line of the joist. The

positioning of each of the web components so that its apex or longitudinal central edgeis along the longitudinal center line of the joist, that is the central plane com- 7 mon to the two chord structures 1 and 8, results in a number of advantages, one of which is that the elements forming the top and bottom chord members are given maximum lateral spacing, thereby assuring maximumlateral stability of the completed joist. An advantage of the maximum spacing of the chord elements is the provision of adequate space between the elements-of the component 16 so that it faces in the same direction permits the converging contiguous ends of adjacent web components 16 to be nested. That is, one end of a component may be received within the channel formed by the

flanges

17 and 18 of the adjacent component, and the opposite end of this latter, component may be received within the channel of the next adjacent component, and so on. It is preferred that the nested ends of the web components be secured only to the adjacent flanges of the associated chord elements as distinguished from being secured both to the adjacent chord elements and to each other, so as to provide a drainage opening as at 20 (Figure 4) whereby to avoid the creation of pockets in which pools of paint or the like may collect when the joist is dipped in or sprayed with a protective coating.

Ioists of the general class to which the invention relates usually are supported at their ends by the upper chord member, necessitating the provision of means to minimize bending strains in the upper chord member.

In the disclosed embodiment of the invention the means for minimizing bending strains in the upper chord member comprises a tension member 21 at each end of the joist. Each of the members 21 preferably is composed of a strip of metal having a width equal to the lateral distance the respective chord elements 2, 3 and 9, 10 are spaced apart by the web components 16, so as to enable the member 21 to occupy the space between the respective chord elements. Each of the members 21 is bent adjacent to its lower end 22 so as to lie beneath the lower end of the associated outer web component 16 in the plane of the

flanges

13 and 14, and these lower end portions 22 are welded or otherwise rigidly secured to the vertical flanges 11 and 12 of the lower chord elements 9 and 10 respectively.

Each of the tension members 21 is bent substantially at right angles as at 23 to form a downwardly projecting end portion 24 which extends below the top chord member 1 and is welded or otherwise secured to a support plate 25, which is itself rigidly secured as by welding to an intermediate point 26 of the member 21. The members 21 are rigidly secured, preferably by welding, to the flanges 6 and 7 of the respective chord elements 2 and 3 adjacent to the bends 23. When the joist is in its normal upright position, the plates lie in a horizontal plane which is substantially coincident with the horizontal neutral axis of the joist. To facilitate the installation of the joist the plates 25 may be apertured as at 27 for the reception of studs (not shown) connected to the supporting structure.

The construction of the joist is such that its longitudinal center line coincides with the line of the apices 19 of the web components 16. Thus, the joist is symmetrical about its longitudinal axis and the longitudinal neutral axis of each of the chord members 1 and 8 will lie in the same vertical plane as the longitudinal axis of the joist. Since the joist is symmetrical about its longitudinal axis, it will be capable of resisting equally well the application of forces from either side.

Referring now to Figure 5, the longitudinal neutral axis of the chord member 1 is represented by the line A and the longitudinal neutral axis of the chord member 8 is represented by the line B. Each of the web components 16 has a longitudinal neutral axis, represented in the drawing by the line C, and this neutral axis also will lie in the same vertical plane as the axes A and B. Thus, when the parts are assembled in the disclosed manner, the arrangement will be such that the neutral axes C of each two converging mutually adjacent web components 16 will intersect each other and the neutral axis A or B of the adjacent chord member 1 or 8 at a substantially common point D. As a result of this construction, the imposition of load on the joist will not subject the parts to secondary stresses tending to cause relative movement of the chord members and the web component. Preferably, the web components 16 project across the neutral axes A and B of the chord structures 1 and 8, as shown in Figure 5. A joist constructed in accordance with the invention, therefore, may be expected to possess greater inherent strength than one constructed of similar materials, but in the conventional manner. This expectation has been confirmed by the testing of a joist manufactured in accordance with the disclosure. The test showed that the joist carried 2.62 times its recom mended capacity, thereby assuring a more than adequate factor of safety.

The disclosed embodiment is representative of a preferred form of the invention, but it is intended that the disclosure be illustrative rather than definitive of the invention. The invention is defined in the appended claim.

I claim:

A joist construction comprising a first chord structure including two similar horizontally spaced parallel companion elements, each of the same angle member stock; a second chord structure including two similar horizontally spaced parallel companion elements, each of the same angle member stock as the said first chord structure elements; and a web structure connecting said chord structures in spaced parallel relation with a common central vertical plane midway between the elements of each chord structure, said web structure comprising a plurality of angle member components of the same stock as said chord structure elements and each having two longitudinal outer edges and a longitudinal central edge and having its opposite ends interposed between and contacting mutually opposed faces of the companion elements of said first and second chord structures respectively establishing and maintaining the horizontal spacing of the companion elements of each chord structure, the longitudinal outer edges of said components being united to said chord structure elements on the said mutually opposed faces of said chord structure elements and connecting the companion elements of each of said chord structures in spaced parallel relation, the central edges of said components being disposed substantially in said common central plane, the neutral longitudinal axes of each two web components having mutually adjacent ends intersecting each other substantially on the neutral axis of the contiguous chord structure, all of a plurality of serially adjacent web components being positioned with their longitudinal central edges facing in the same direction longitudinally of the joist construction, and contiguous ends of adjacent web components being nested with each other between the mutually opposed faces of said chord structure elements between which said web component contiguous ends extend.

References Cited in the file of this patent UNITED STATES PATENTS Austria Oct. 10, 1953