US2916111A - Beam variable in length - Google Patents

Description

Dec. 8, 1959 PLEITGEN ET AL 2,916,111

BEAM VARIABLE IN LENGTH Original Filed Sept. 11. 1952 mm i x Uflitsd S e P m BEAM VARIABLE 1N LENGTH Max G. Pleitgen. and Ernst M. Klaus, Dusseldorf, Germany Original application September 11, 1952, Serial No.

309,019, now Patent No. 2,741,342,, dated April 10,

1956. Divided and this application February 21, 1956,

Serial No. 566,968

Claims priority, application Germany June 23, 1952 s Claims. 01. 189-37) The present invention relates to multi-part' beams, trusses or the like for use as support for forms in connection with the pouring of concrete to build straight ceilings and the like.

The present invention is a divisional application of our co-pending patent application, Serial No. 309,019, filed September 11,. 19 52, and now Patent No. 2,741,343.

It is a well known fact that when using a beam or truss for supporting a form to be filled with concrete, the beam will bend within certain limits due to the weight of the poured concrete. in; order" still to be able with such beams or trusses to obtain a straight ceiling or the like, a multipart beam has been developed in which the lower chords of adjacent beam sections are interconnected by a turnbuckle adapted to be adjusted so as to take up the undesired lengthening of the lower chord brought about by the load on said beam.

The adjustment of this type of beam, however, is relatively cumbersome, and is solely dependent on the judgment of and respective measurement by the workmen.

It is, therefore, an object of this invention to provide a multi-part beam for use in connection with the pouring of concrete straight ceilings and the like, which will overcome the above mentioned drawbacks.

It is another object of this invention to provide a beam or truss for the above mentioned purpose, which will make the employment of turnbuckles or other correcting means superfluous.

Still another object of this invention consists in the provision of a beam or truss which, when employed for the above mentioned purposes, will without correcting means produce a straight floor, ceiling or the like, even though the length of the beam or truss may vary.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

Fig. 1 is a side view of a single girder section forming a part of the beam or truss according to the invention.

Fig. 2 is a side view of an assembled arched beam or truss pulled out to a great span Width.

Fig. 3 illustrates a beam or truss of the type shown in Fig. 2 but adjusted for a small width.

Fig. 4 is a vertical section through Fig. 3 taken along the line IIIIII thereof.

The beam or truss according to the present invention is characterized primarily in that it is slightly arched and that corresponding cross-sections, i.e., cross-sections of the beam or truss which have the same distance from the supports for the ends of the beam or truss, have respectively the same curvature. This curvature is such that when the beam or truss is under the full load correspond ing to its respective length, it will bend through within elastic limits to such an extent that its upper supporting surface will for all practical purposes be horizontal. This will be the case for all lengths to which the beam or truss can be pulled out or be pushed together.

2,9 16,1 1 l Patented Dec. 8, 1959 'ice Referring now to the drawings in detail, the truss or beam illustrated therein consists of a plurality of girders 1, 2 movable relative to each other and arched upwardly in the direction of the longitudinal axis of said girders. The girders may be designed so that each girder has a plurality of different radii of curvature along the length of the girder as shown, for instance, in connection with the girder, 1 of Fig. 1, the different radii of curvature being respectively designated with the charcters R R R When making up a beam or truss from two girders of the type shown in Fig. 1, the radii of curvature of the two cooperating girders are respectively the same at those crosssections thereof which are equally spaced from the supporting. end surfaces.

However, if desired, each of two cooperating girders may have the same radius of curvature throughout its length as is shown in connection with the beam or truss 1, 2 of Figs. 2 and 3. The arch or curvature of the girder is selected in conformity with the respective actually occurring bend or deflection of the girders under load in such a manner that under the said lead, the girders will occupy a substantially horizontal position. V

More specifically, the truss shown in Figs. 2 and 3 is composed of two lattice girders 1, 2 each of which com prises an upper chord angle 3, a lower chord angle 4 and braces 5 welded to said angles 3 and 4. Each arched girder is, furthermore, provided with a flat rail or bar 6 likewise welded to the respective braces 5 and arranged in a manner described in detail in connection with our Patent No. 2,741,343, so as to allow the passage of connecting bolts between the rail 6 and the upper chord 3. It is, of course, understood that the chord angles are curved in conformity with a gauge prior to welding the angles and braces and rail 6 together. The upper portions of the girders are held together in any convenient manner, preferably by bolts 7 and nuts 8 as shown in Fig. 4, while the lower portions of the girders are held together by brackets 9, boltsv 10 and nuts 11 as likewise shown in Fig. 4. If desired, also any other means of holding the lower portions of the girders together may be employed.

In the arrangement of Figs. 2 and 3, the radius of curvature R of the upper chord of the girders is the same for all sections of the girders and is preferably selected somewhat greater than 500 feet inasmuch as-.with the present customary trusses having a sufficiently high resistant moment, the actual deflection is very small. When the same curvature is selected for the upper and lower chords throughout the length of the girders, the upper and lower chords will respectively register with each other, even when the truss is changed from a short span shown in Fig. 3 with a curvature height 0 to a wider span according to Fig. 2 with a curvature height of d. It may be added that the curvature heights as shown in the drawings are considerably exaggerated in order more clearly to show the curvature. Furthermore, these changes in the span will bring about only minor deviations relative to the horizontal plane while the truss is under load. When employing a truss which comprises two lattice girders with upper chord angle 2.36 x 1.18 x 0.36 inches, with lower chord angle 1.18 x 1.18 x 0.197 inches, and braces in form of round bars having a diameter of 0.472 inches, while the height of the truss is 9.444 inches and a change in the span between 10.322 feet and 17.384 feet is assumed, the minor deviations relative to the horizontal plane are between plus 0.0394 and minus 0.1377 inch. These minor deviations are absolutely negligible from a practical standpoint.

The above described construction has the advantage that the actual occurring deflection of the assembled truss under load, which deflection is well within elastic limits, will stop at the horizontal so that no turnbuckles, intermediate supports or the like will be required, provided, of course, that the shop made curvature of the truss was in conformity With the information calculated on the respective deflection of the truss under load.

With a beam or truss according to the invention, the arch or the deviation of the uppermost surface point of the beam from the horizontal plane passing through the ends of the beam increases automatically in conformity with the length to which the beam is being pulled out and vice versa. This increase or decrease automatically takes care of the increased or decreased deflection when dealing with a greater span and a shorter span respectively so that, when the beam is under the respective load, it will again bend through or deflect until the upper beam surface is for'all practical purposes horizontal.

If desired, the respective contacting surfaces of the rails, the upper and/or lower chord elements may be knurled, grooved, corrugated or the like as shown in our Patent No. 2,741,343 so that, when pressing these elements together, the elevations of one contacting surface will enter the depression of the other contacting surface so that the contacting surfaces will actually interlock. This will definitely exclude any relative accidental movement'between said surfaces and will considerably reduce the heretofore necessary overlap of the girders so that said lap need be only one-third as large as heretofore. The deflection, as experience has shown, will naturally beless in view of the complete immovability of the respective chord angles.

While the girders illustrated in the drawings and described in the specification are lattice girders, it is, of course, understood that the invention is by no means limited to such girders, but is also applicable to other type girders such as box girders, plate girders and the like.

It is also to be understood that the present invention is, by no means, limited to the particular constructions shown in the drawings but also comprises many modifications within the scope of the appended claims.

What we claim is:

1. A girder for use in connection with trusses, beams and the like, said girder having means providing for longitudinally adjustable, substantially face to face engagement with at least one other substantially similar girder, for increasing or reducing the total span of said engaged girders, said first named girder, when not under load, having a slight gradual upward arch along a continuous line of curvature selected in conformity with the normal load to be carried thereby and corresponding to its deflection under said load, the upper surface of said girder, when assembled and under normal load, extending in a substantially horizontal plane, said first named girder being provided with means for locking Said girder in engaged position with said other girder.

2. A girder for use in connection with trusses, beams and the like, said girder having means providing for longitudinally adjustable, substantially face to face engagement with at least one other substantially similar girder, for increasing or reducing the total span of said engaged girders, said first named girder, when not under load, having a slight gradual upward arch with different sections thereof having different radii of curvature, the total curvature of aid arch being selected in conformity with the normal load to be carried thereby and corresponding to its deflection under said load, the upper surface of said girder, when assembled and under normal load, extending in a substantially horizontal plane, and means for locking said girder when in engaged position with said other girder.

3. In combination: a first girder, a second girder arranged for cooperation with said first girder, said girders being arranged in longitudinally adjustable, substantially face to face engagement with each other for increasing or reducing the total span of said engaged girders, each of said girders when not under load having a slight gradual upward arch along a continous line of curvature selected in conformity with the normal load to be carried thereby and corresponding to its deflection under said load, the upper surfaces of said girders, when assembled and under normal load, extending in a substantially horizontal common plane, and means for locking said girders when engaged in their respective relative positions.

References Cited in the file of this patent UNITED STATES PATENTS 1,853,645 Stambaugh et al Apr. 12, 1932 2,167,413 Bartlett July 25, 1939 2,386,161 Hawes Oct. 2, 1945 2,612,848 Sowden Oct. 7, 1952 2,626,688 Lagaard Jan. 27, 1953 2,687,193 Hinze Aug. 24, 1954 2,692,034 TidWell Oct. 19, 1954 2,793,720 Hawes May 28, 1957

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