US2318214A - Form for casting concrete floor beams - Google Patents

Description

. y 1943- B. F. FRIBERG FORM FOR CASTING CONCRETE FLOOR BEAMS Filed July 3, 19:59

FIGJ.

IN(VEN TOR BEN I F. FRIBERG ATTORNEY Patented May 4, 1943 FORM FOR CASTING CONCRETE FLOOR BEAMS Bengt F. Friberg, St. Louis, Mo., assignor to Laclede Steel Company, St. Louis, Mo., a corporation of Missouri Application July 3, 1939, Serial No. 282,619

3 Claims.

It has in the past been customary to construct floors consisting of light structural steel truss members over relatively long spans up to twentyfour times the depth of the trusses, covered on top by thin concrete slabs. These thin concrete slabs are not in themselves strong enough to distribute concentrated loads over a number of joists. At the same time the spans of the steel members are usually long enough that these steel members are subject to relatively great deflections under load. The structural combination, therefore, as used heretofore results in a flexible floor of small resistance to concentrated loads.

Steel struts have been applied between adjacent steel trusses as a system of cross bridging to increase the rigidity of the floor. These struts have not been connected rigidly enough to the truss members to fulfill their intended purpose, nor has it been possible to so apply the transverse struts that local bending in the steel truss chords has been avoided. Particularly is this the case in trusses of Warren type.

Concrete beams running transversely of the steel truss members have sometimes been used for this purpose, but the arrangements of these concrete members have then not made it possible to locate the concrete transverse members where they could serve efiectively as a part of the structural floor.

One object of my invention is to construct a composite steel truss and concrete floor structure which includes concrete reenforcing means in the form of transverse concrete bridging enclosing top chord panel points of the trusses so that the maximum strength may be imparted to the structure as a whole.

A further object of my invention is to provide improved forming means by the use of which the structure may be conveniently and economically produced; to insure that the steel truss members are adequately braced during construction; and to so arrange the supporting forms that the concrete may be deposited without waste, filling the voids immediately below the truss top chords.

In the accompanying drawing which illustrates a portion of a structure embodying one form of my invention, Figure 1 is a sectional view taken in the direction of the length of the joist; Figure 2 is a section taken on the line 22 of Figure 1; Figure 3 is a perspective view of a telescoping bridging form unit; Figure 4 is a top plan view; Figure 5 is a view similar to Figure 1, but showing the structure after the concrete has been poured and the supporting forms removed; and

Figure 6 is a perspective view of a portion of the completed structure. 1

In the construction illustrated the joists are each composed of a top chord formed of two angle irons 6, a bottom chord formed of two angle irons 1 and a web formed of a rod 8 bent in zigzag form and Welded between the angle irons of the chords to produce inclined web bars.

The bends of the web form the upper panel points 9 through which stress is transferred from the web bars to the top chord of the joists.

Each unit of the bridging form consists of two trough-shaped forms ll each comprising a pair of upper flanges iii, a pair of inclined side Walls and a bottom l2, The inner ends of these parts overlap to provide a unit the length of which may be adjusted by telescoping the parts, one form being slightly narrower than the other. The outer ends of the forms are beveled as shown at l3 (Figures 2 and 3). This beveling of the forms allows the lower part to project beyond the upper part to form an enclosed space below panel points 9 and yet permit the web bars 8 to pass between the forms.

To support thebridging form, I provide a pair of angle bars M which are positioned against the lower edges of the vertical legs of the angle irons 6 and against the web bars 8. Any suitable means may be employed to secure the angle irons in position, such as wire loops l5 which maybe secured by twisting together the ends IS. The flanges ID of the bridging form reston the horizontal legs of the angle bars l4. These flanges H! are extended beyond the angle bars to serve as support for form boards I! of varying lengths. In placing the bridging forms in position, they are overlapped as far as permitted by contact of their beveled ends l3 with the web bars 8 forming a continuous and closed trough. Variations in the inclination of the web bars will vary the amount of the overlap, but this as well as the variation in spacing between joists will be accommodated by the adjustment secured by telescoping of the two bridging forms.

The distance between the two angle bars l4 varies with the inclinationof the web bars 8. The bridging forms are, therefore, formed wide enough to spring between the angle bars to permit the concrete bridging beam to occupy the full space underneath the panel point. The form boards ll hold the bridging forms in place until concrete is deposited in the forms.

After the bridging forms and form boards are placed in position, concrete is placed to form a slab l8 and the integral bridging beam I9. Both splices are staggered. The ends ol' continu parts may be provided with reenforcing, such as wire mesh 20 in the top slab and bar 2! in the bridging beam.

If for any reason it is desired to form the beam with sharply defined angles where it joins the floor slab, the form boards H are brought up to the face of the form I i, as shown at the left hand side of Figure 1, and the ends are beveled at H to form a continuation of said side. For convenience of illustration the beams in Figures 5 and 6 are shown as so formed. Usually, however, the

boards terminate short of the wall of the form II as shown at the right hand side of Figure 1. While this will result in a projection at the base of the beam, it is not objectionable when the beam is hidden by the ceiling of the room below.

In construction the steel trusses l are first applied between supports (not shown). The angle bars M are then applied transversely of the joists at some panel point 9 near the center of the span,

at least. The length of the angle bars it is snfiicient to span several joist spacings, and these an gle bars M are so arranged that their abutting angle bars it do not need to fit closely against the other, as the strength of the bridging forms H and their telescoping arrangement is such that they will bridge without difiiculty across gaps between successive angle bars Id. The angle bars M are wired securely, for instance, by means of wire loops l5 to the steel trusses. In this manner the panel points of neighboring trusses are all aligned, and in addition, the wire ties and the angle bars M hold the trusses correctly spaced and braced sideways during cons-t no on. Upon completion of the floor, the wires ii: e cut, the angle bars l5 dropped from their position to the lower chord of the joist and may be withdrawn, and the form boards ll removed. The tapered sides ll of the bridging forms permit easy removal of the bridging forms, and in addition insure that concrete completely fills the space inside these forms.

In the completed floor, the concrete bridging beam I9 ties all steel trusses transversely together; 'A concentrated load on any one joist is transferred partially to the supports for the trusses and partially through the bridging beam ill to several neighboring trusses on each side. As by necessity this transfer takes place at the panel points of the steel trusses, the structural strength of the floor is not impaired by local bending in the top chord 6, the web bars 8, or the bottom chord l. In this manner it is possible by means of bridging beam 19 to transfer the complete load from one truss to the adjoining trusses.

The bridging beam I5 is considerably deeper than the concrete top slab l8 and, therefore, exhibits great strength under vertical loads. Con-- centrat-ed loads of sufiicient magnitude to break the top slab l8 and be resisted only by one of the steel trusses will, through the bridging beam it, be spread over a number of trusses, resulting in a stronger and less flexing floor.

In the illustrated application, the bridging beam 19 has been shown extending down only a part of the distance between the truss top and bottom chords 6 and 1, giving a convenient space for plumbing, wiring, ducts, and so forth, above the bottom chord which may be enclosed on the underside by a plastered flat Ceiling. It would, however, be possible without deviating from the invention to extend the bridging beam completely down to the truss bottom chord, dividing completely the inside vertical space of the floor.

While the top slab and concrete bridging may be formed at the same time as above described, my invention is also applicable where the top slab .or a portion of it consists of pro-cast members [8, such as concrete or gypsum planks or panels (see Figure 6). In such construction the pouredin-place bridging beam should be interlocked with the abutting pre-cast members in order to be practically integral therewith. This may be accomplished by means of tongue and groove 22 or dowel pins 23. The bridging beam will as before extend under the steel truss panel points 9 and the upper flanges ll] of the bridging forms will serve to form a varying space between the edges of the pro-cast members and the bridging beam.

Having fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. Forming means for concrete beams in a steel truss and concrete floor structure, which means comprises a bridging form composed of a plurality of units extending between the trusses, each unit being formed of telescoping troughshaped members and having beveled ends, the beveled ends of adjacent units overlapping to form a continuous trough and also to provide lateral truss passages, and means for supporting the bridging form in transverse relation to the floor trusses.

2. Forming means for transverse concrete beams in a steel truss and concrete iloor structure, which means comprises a bridging form composed of a plurality of units, each unit made up of telescoping trough-shaped members, the ends of adjacent units overlapping at the bottom of the form to provide a continuous trough but spaced apart at the top of the form to permit the passage of a portion 01": a floor truss, and means for movably securing the bridging form in position.

3. Forming means for transverse concrete beams in a steel truss and concrete floor structure, which means comprises a bridging form composed of a plurality of units, each unit made up of telescoping trough-shaped members provided at their upper edges with horizontal flanges, said upper edges of adjacent units being spaced apart to provide lateral truss passages, a pair of supporting bars projecting through a roof truss and engaging at each end with one of the flanges, the bottoms of the units projecting beyond the flanges and overlapping to form a continuous trough, and means for securing the form units to the supporting bars in transverse relation to the fioor trusses.

BENGT F. FRIBERG.

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