US3336708A - Shoring member for use as temporary support of concrete slabs - Google Patents

Description

SHORING MEMBER FOR USE AS TEMPORARY SUPRO 'HT OF CONCRETE SLABES 2 Sheets-Sheet 1 Filed Nov. 16, 1964 22, 1967 v R, D. RAMBELLE SHORING MEMBER FOR USE AS TEMPORARY SUPPORT OF CONCRETE SLABS 2 Sheets-Sheet .Fiied Nov.

United States Patent 3,336,708 SHORING MEMBER FOR USE AS TEMPORARY SUPPORT OF CONCRETE SLABS Robert D. Rambelle, Richmond Hill, N.Y. (1990 Chestnut St., Baldwin, N.Y. 11510) Filed Nov. 16, 1964, Ser. No. 411,502 9 Claims. (Cl. 52-309) The present invention relates to a horizontal shoring member for use in providing temporary support during the formation of concrete slabs and floors in multi-stor-ied structures, and, more particularly, this invention relates to a joist configuration of novel design and composition having numerous and significant advantages over shoring members heretofore utilized for this purpose.

Concrete used 'in large structural construction is a heavy, semi-liquid material, comprised of various proportions of sand, gravel, cement and water, and requires a firm base on which to be poured, so that it can set and harden. In the formation of concrete slabs and floors, horizontal shoring members (joists) are used to support a plywood or other type base upon which the concrete is poured. After the concrete has hardened, the shoring and plywood are then removed, as the concrete slab, which typically is reinforced with steel rods, has become self-supporting and capable of bearing substantial loads.

Conventional shoring members used for this purpose are in the form either of heavy wooden beams, cut to size, or adjustable girders of lightweight metal construction comprised of a telescoping box section and an I-beam section. In the latter type of shoring a built-in camber of adjustable curvature is usually provided so that when the girders are placed into position properly spaced and the concrete poured, the predetermined weight of the concrete bends the camber flat and results in a level floor.

However, there are serious and distinct disadvantages associated with each of the above types of shoring members which render them generally unsatisfactory for use in flat-slab high-rise construction. For example, conventional wooden shoring members have a low carrying capacity and a high deflection value in bending due to the low modulus of elasticity possessed by wood. As a consequence, it is necessary that the wooden members he vertically supported every four or five feet, thereby requiring a great number of supporting posts in the formation of a slab of even moderate size.

While wood possesses relatively high resistance to compression, this quality is not utilized in conventional concrete formwork since it is the carrying capacity of the horizontal shoring members, rather than that of the vertical supporting posts, which determines the location (and thus the number) of posts required. In many instances this limitation imposed by the use of wooden joist members results in the vertical supporting posts being loaded to only fifty percentof their working capacity. Furthermore, wooden formwork members deteriorate rapidly due to the combined efiects of environment and wear, and they therefore have but limited reuseability.

On the other hand, the adjustable metal shoring beams which have been recently developed and are now in widespread use in concrete construction, while being capable of a large number of reuses and having the advantage of combining lightness in weight with great bending strength, are not wholly satisfactory for a number of reasons.

First, the savings in material and labor cost obtained through the reduction of the number of pieces of form material required are more than offset by the labor cost of added erection and stripping operations, i.e., the adjustment of each girder member to its required length, locking and unlocking of the clamping devices which secures the two sections together, and telescoping of the Lbeam section into the box section during stripping. These timeconsuming recurring operations, which must be performed each time a concrete floor is poured, are expensive and render metal shoring beams of the telescopic type economically unfeasible for use in the high-rise, flat-slab structures which are being built today.

Secondly, there is no provision made in the conventional metal girder for securing, e.g., by nails, the plywood forms to the shoring beams. This deficiency makes the girder unsuitable as well as dangerous for application in high-rise structures where wind forces are of great magnitude and thus of considerable concern. Finally, the cost of fabricating and assembling the conventional adjustable metal girder, which is comprised of two separate telescopic sections as well as a clamping means, is quite high in view of the intricacy and number of different pieces involved.

In contradistinction, the shoring beam of the present invention retains all the important advantages of the adjustable metal girder (e.g., lightness in weight, high load-carrying capacity permitting the bridging of relatively long spans, great number of reuses) over the conventional wooden beam, without the attendant disadvantages and limitations.

In an exemplary embodiment of the invention, the temporary joist member is in the form of a fixed-length beam formed of a suitable lightweight metal, such as aluminum, having an Lshaped bottom web portion and a thinwalled U-shaped upper portion. A- thin cross-member of polyvinylchloride, plastic resin, or other suitable semirigid material is inserted between the leg elements of the U near its top for increasing the structural rigidity of the beam and for providing a nailing surface for the plywood forms used in the fabrication of the concrete slabs. For further strengthening of the joist the hollow U-shaped portion of the beam may, in a modification of the invention, be filled with a rigid expanded polymer (i.e., cellular plastic) material, such as urethane foam or the like.

At the endpoints the bottom web portion of the beam is cut away for a substantial distance inwardly along the length of the beam. This design permits the beam to be supported on the vertical support posts by hearing flanges located at the upper half or U-shaped portion of the beam close to the center of gravity of the beam crosssection, thereby providing the beam with exceptional stability against tipping and other desirable structural characteristics as will hereinafter be described.

The length of the cut-away portions of the beam at the end bearing points is selected so as to provide an adequate range of span variations. Span adjustments between supports are easily made by lapping the bearing ends of the joist members in adjacent bays. The vertical edges of the web on the main body portion of the beam act as a stop and prevents the joist from being cantilevered too far beyond the bearing points, thereby providing a safe catwalk for workers at the edges of the slab formation which is free from the hazards of tipping or overturning due to mechanical instability.

In order to compensate for the deflection produced in the joist by the weight of the supported concrete slab, a pre-formed camber may be readily provided in a beam member of the present design by machining the upper edges of the thin leg element-s of the U-shaped upper portion into the desired cambered configuration. Since with this technique the beam as a whole need not be bent into a cambered configuration, the necessity for special rolling or stretch-forming equipment ordinarily required to produce such a camber in a metal girder is obviated.

By reason of its simplified unitary construction and its rapid adjustability within a relatively wide range of span lengths, the novel joist design of the present invention is exceedingly economical both in its manufacture and in its use. Particularly in the construction of multi-storied, high-rise buildings, wherein the dimensions of the floors and the location of their permanent supporting columns are generally invariant for a considerable number of floors, the utilization of the fixed-length shoring beams disclosed herein is especially attractive in view of the considerable time and expense saved in the erection of the temporary support forms for the concrete slabs.

It is therefore a principal objective of the present invention to provide a novel design for a horizontal shoring member, for use as a temporary support in the formation of concrete slabs, which is of unitary, lightweight and economical construction, has high load-carrying capabilities and inherent stability against tipping, and is readily adaptable to cover a relatively wide range of span lengths.

It is a further object of the present invention to provide a novel temporary support beam of lightweight metal for use in the formation of concrete slabs which may be readily provided with a cambered surface without cambering said beam as a whole.

It is another objective of the present invention to provide, in a temporary support beam of hollow, lightweight metal construction for use in the formation of concrete slabs, a thin insert of semi-rigid, nailable material for increasing the structural rigidity of the beam and for providing a means for securing slab forms to said beam.

It is still another objective of the present invention to provide a light temporary support beam of increased strength for use in the formation of concrete slabs which is comprised of a hollow shell of lightweight metal, a thin insert of semi-rigid material, and a core of rigid expanded polymer material.

The foregoing and other objectives, features, and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.

FIG. 1 is a side elevational view of an illustrative embodiment of a joist member constructed in accordance with the present invention. The initial camber of the joist has been slightly exaggerated to show it more clearly.

FIG. 2 is an enlarged vertical sectional view taken along the line 22 in FIG. 1.

FIG. 2A is an enlarged vertical sectional view of a modified embodiment of the joist member shown in FIGS. 1 and 2.

FIG. 3 is a detail view of a portion of FIG. 2 illus trating in a schematic form the force components produced upon the application of a vertical load to the joist member.

FIG. 4 is a perspective detail view showing the lapping and spacing arrangement of several of the joist members when in use and providing temporary support of a concrete slab during formation.

FIG. 5 is another perspective detail view, similar to FIG. 4, showing the lapping arrangement of the ends of adjacent beam members under maximum span conditions.

Referring now to FIGS. 1 and 2, there is shown an illustrative embodiment of a joist member, for use in providing temporary support in the formation of concrete slabs, constructed in accordance with the teachings of the present invention. The joist, designated generally by 10, is fabricated from a suitably strong and lightweight metal material, such as aluminum, extruded into a beam member having an I-shaped lower section 20 integral with a U-shaped upper section 30.

The I-beam section comprises a web portion 22, a lower flange portion 24, and upper flange portion 26 which forms the base of the U-shaped upper section 30. The U-shaped section 30 in turn is comprised of a pair of channels 32, each having a web portion 33, a lower flange portion 26:: formed out of the flange 26, and a reinforcing shoulder flange 34 located on the outside and near the top of the channel and running the length of the beam. Juxtaposed opposite each of these reinforcing flanges 34 and on the inside of the channel 32 is a dovetailed channel 36, having lips 36a and 36b, for receiving a mating shoulder 42 of a recessed insert strip 40 comprised of a semi-rigid material, such as polyvinylchloride or other suitable plastic resin. At either end of the beam 10 the web 22 and bottom flange 24 of the lower I-beam portion 20 of the extrusion are cut away for a substantial distance to leave only the projecting upper portion of the joist as end supports 38.

The upper chord of the joist 10 which is formed into a composite box-member, comprised of the base 26, channels 32, and the semi-rigid insert strip 40, provides excellent resistance to buckling stresses caused by lateraltorsional forces exerted on the beam during loading conditions. The connection between the polyvinylchloride (PVC) insert 40 and the thin sidewall channels 32 of the aluminum beam is designed such that compressive stresses which are normal to the cross-sectional plane of the joist, and produced by longitudinal bending under load, are taken up only by the channel 32 of the joist. On the other hand, compressive and tensile stresses which are perpendicular to the center line of the joist, and caused by the application of lateral forces to the flanges 34 or the upper protrusions 39 of the channel portions 32 of the joist, are taken up by the PVC insert 40 which thus performs a bracing function.

The PVC insert is incapable of transmitting any substantial bending stress due to vertical loading of the aluminum channel members, although the dovetailed joint configuration 36 suggests a moment connection. The semirigid plastic insert, when subjected to the application of a direct vertical load, would deform considerably, thus causing undesirable lateral forces to be exerted on the thin channel members. It is for this reason that the insert 40 is preferably recessed, so that any vertical load is applied directly to the primary structural component, i.e., the channels 32, of the joist. The PVC insert can thus be considered as a secondary structural component or bracing member, providing continuous lateral support to the reinforcing flanges 34 of the aluminum channels 32.

To further explain the important structural function provided by the PVC insert, consider the conditions which prevail when a vertical load is applied onto the upper protrusion 39 of one of the aluminum channels 32. As

represented in the schematic diagram of FIG. 3, the shear center of the channel is horizontally displaced at a distance from the point of application of the vertical load P. This eccentricity produces a clockwise moment which is resisted by a counterclockwise moment, A-a=B-a, where A and B are the resisting forces in the insert 40 and the aluminum horizontal bearing member 26, respectively.

The presence of the force A induces tensile stresses in the plastic insert. However, the centroid of the channel 32 is likewise displaced horizontally from the application point of load P, at a distance 2. This latter eccentricity produces compressive stresses in the plastic insert which are only partially offset by the tensile stresses caused by the shear eccentricity. However, the bending stresses which are concurrently produced upon the application of a vertical load to the joist tend to exert transverse forces on the upper lug portion 39 of the channels 32, causing them to move outward towards the neutral axis. This tendency of the sidewall channels 32 to rotate outward, which is maximized at the midspan of the joist, is counteracted by the semi-rigid plastic insert 40, producing tensile stresses in the insert which are, however, neutralized to a considerable extent by the compressive stresses induced in the insert in response to the centroid eccentricity. The channels 32 are thus effectively braced against lateral movement due to shear or bending by the rigid lateral load transmission connection provided by the plastic insert member 40.

The above stress analysis was confirmed by the results of loading tests conducted by Columbia University on joist members constructed in accordance with the illustrative embodiment of the present invention which is described herein. With the joist members supported at their very ends, failure due to the combined effects of bending and shear stresses occurred at the point where there is an abrupt change in cross-section as the bearing ends 38 merge into the body of the joist. In failure the entire U-shaped upper chord 30 of the joist buckled, thus indicating that the upper shoulder flanges 34 were effectively braced by the PVC plastic insert 40 against localized buckling of these flanges prior to the attainment of the point of ultimate compressive stress.

The plastic insert also serves as a means for securing wooden slab forms to the joist. Nails driven through the relatively thin insert strip 40 can freely penetrate beyond theplastic into the intervening hollow area or core 35 without damage to the aluminum base member 26 and without deformation of the nails, thereby permitting their ready removal during stripping operations. The recessing of the insert strip 40 slightly below the bearing lugs 39 prevents damage to the plastic during erection and stripping of the slab supports, and enables repair of damage due to nail perforations to be easily made through the lamination of thin strips or patches of plastic material atop the insert, thereby obviating the necessity of replacing the entire insert.

In use, as illustrated in FIG. 4, the joist member is supported near either end by lateral wooden support beams or stringers 11 mounted atop vertical posts or shores 12. The length of the bearing ends 38 of the joist is selected so as to provide an adequate range of span variations. As shown, span adjustments between support beams 11 are made by lapping the bearing ends 38 of the joist members 10 in adjacent bays. The vertical edges of the web portion 22 of the I-beam section 20 of the joist act as a stop to prevent the joist from being cantilevered too far beyond the bearing points which would cause hazardous conditions of instability for workers, The plywood forms 50 for the formation of the concrete slabs 55 are laid down on top of the rows of lapped joists 10 and aflixed to the joists by nails 58 driven through the plastic insert strip 40, as previously explained.

If desired, or if particular job situations so require, the joist 10 can be secured to the Wooden support members 11, as indicated in FIG. 4, by driving nails 60 into these members in such a manner that the nailheads rest on the laterally extending protrusions 26a of the base portion 26 of the joist end 38. This is particularly recommended when the ends 38 of the joist members 10 are arranged between support beams 11 under maximumspan conditions, as illustrated in FIG. 5.

At its end projections 38 the joist is supported on the wide bearing flange 26 located at the base of the upper section 30 of the joist. Since this bearing surface is located close to the center of gravity of the joist crosssection, exceptional stability against overturning is achieved. Furthermore, as illustrated schematically in FIG. 3, the ends 26a of the bearing flange 26 are preferably designed to protrude a substantial distance g beyond the line of application of the vertical load P to the side wall channels 32 of the beam, thus generating a moment of magnitude P'g which resists tipping of the beam. Although the depth of the joist member 10 is substantially reduced at its end supports 38, such a configuration is feasible from a design standpoint as the bending moment produced at these supports due to loading of the beam is only a small fraction of the maximum moment which exists at the center of the span where the joist possesses its full depth.

Another feature of the novel joist construction of the present invention is illustrated in FIG. 1 which illustrates the nature of the camber a which can be readily provided in the joist by machining, and without cambering the joist as a whole. It will be joist is formed by extrusion,

.the beam will be of uniform cross-section throughout its length; in particular, the bearing lugs 39, protruding above the reinforcing flanges 34 on the channels 32 of the'U-shaped section 30 of the joist (see FIG. 2), will initially be of uniform height throughout the length of the beam. However, after the extrusion is formed, these protrusions 39 may be cut down, in accordance with any conventional machining process, so that the height is gradually reduced, proceeding from mid-span to the ends 38 of the joist. Thus, under a predetermined load of concrete slabbing, the cambered joist will exhibit a bending deflection of an amount a, thus affording a shoring support for the load lying in an approximately level plane.

FIG. 2A illustrates an important modification of the joist embodiment of the present invention wherein the hollow portion or core 35 of the composite box-member (formed in the upper section of the joist by the base 26, channels 32 and the plastic insert strip 40) is strengthened, without materially increasing its weight, by filling it with a rigid expanded polymer or cellular plastic material 35', such as urethane foam or the like, This modification in the joist construction may be readily eifected by injecting the foam chemicals into the hollow core portion 35 while it is temporarily closed at the ends of the joist with gaskets.

A suitable foam plastic material, such as urethane foam, having good adhesion and cohesion properties, will bond the dissimilar aluminum shell and plastic insert portions of the joist into a rigid and strong composite structure possessing excellent resistance to compressive and torsional forces. Thus the utilization of this foam material 35 as a bonding and reinforcing agent in the core portion 35 of the beam will premit a substantial reduction to be made in the thickness of the web 33 of the channels 32 and base member 26, as they will be laterally braced throughout the entire inner surface of the section 30. In addition, the plastic insert 40 will become a rigid, integral part of the upper U-shaped section 30 of the joist, and will therefore materially relieve the compressive stresses set up in the flanges 34 of the channels 32 under loading conditions.

The terms and expressions which have been employed here are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A horizontal joist member, for use in providing temporary support in the formation of concrete slabs, comprising,

(a) a longitudinally-extending beam member of lightweight metal construction with a cross-section generally in the form of an I-shaped lower section having a lower flange, a central web, and an upper flange integral with the base of a U-shaped upper section having thin vertical walls, and

(b) a thin strip of nailable, semi-rigid plastic resin material extending substantially along the length of said beam member, said strip being fitted as a lateral bracing cross-member extending between and secured to the vertical walls of said U-shaped section, and slightly recessed beneath the longitudinal terminal edges thereof, so that :any vertically-applied load carried by said horizontal joist member is borne solely on the projecting longitudinal terminal edges of said vertical walls.

2. A horizontal joist member according to claim 1, wherein said thin vertical walls of said U-shaped section are shaped so as to be higher toward the center of said beam than toward the longitudinal ends thereof, thereby to produce a camber in the uppermost surface of said beam without cambering said beam as a whole.

3. A horizontal joist member according to claim 1,

I wherein the web and lower flange portions of said I-shaped section are cut away at either end of said beam for a substantial distance inwardly, leaving the U-shaped upper section of the beam as a projecting end support with its base portion acting as a bearing surface for said beam.

4. A horizontal joist member according to claim 3, wherein the base of said U-shaped section is substantially narrower than the upper flange of said I-shaped section into which it is merged, whereby a vertical load applied to the walls of said U-shapcd section falls well within the width of said upper flange and produces a substantial counter-moment on the bearing surface at the end supports of said beam which resists tipping.

5. A horizontal joist member according to claim 3 wherein the center of gravity of said beam cross-section is located close to said bearing surface at the end supports of said beam, whereby the beam is provided with high stability against overturning.

6. A horizontal joist member according to claim 1 wherein a reinforcing shoulder flange extending substantially the length of said beam member is formed on the outside surface of each of the vertical walls of said U-shaped section and immediately opposite said recessed plastic strip for reinforcement of said walls at the point of their juncture with said bracing cross-member.

7. A horizontal joist member according to claim 1 wherein a dovetailed channel is formed on the inside surface of each of the vertical walls of said U-shaped section for receiving and engaging a mating shoulder flange carried on said plastic strip.

8. A horizontal joist member according to claim 1 wherein said plastic strip is comprised of polyvinylchloride material.

9. A horizontal support member according to claim 1, in which the cavity defined by said U-shaped section and said plastic resin strip is filled with a core of rigid expanded polymer material.

References Cited UNITED STATES PATENTS 1,725,439 8/ 1929 Carns 52729 1,815,447 7/ 1931 Richardson 52221 2,284,898 6/ 1942 Hartman 52696 X 2,448,109 8/ 1948 Michael 52--376 X 2,888,113 5/1959 Schwartz et a1 5228 2,898,758 8/1959 Henrickson 52710 3,226,891 1/1966 Heirich 52-263 X FOREIGN PATENTS 1,188,509 3/1959 France. 1,291,661 3/1962 France. 1,336,522 7/1963 France.

2,550 7/ 1874 Great Britain.

FRANK L. ABBOTT, Primary Examiner.

A. C. PERHAM, Assistant Examiner.

Claims (1)

1. A HORIZONTAL JOIST MEMBER, FOR USE IN PROVIDING TEMPORARY SUPPORT IN THE FORMATION OF CONCRETE SLABS, COMPRISING, (A) A LONGITUDINALLY-EXTENDING BEAM MEMBER OF LIGHTWEIGHT METAL CONSTRUCTION WITH A CROSS-SECTION GENERALLY IN THE FORM OF AN I-SHAPED LOWER SECTION HAVING A LOWER FLANGE, A CENTRAL WEB, AND AN UPPER FLANGE INTEGRAL WITH THE BASE OF A U-SHAPED UPPER SECTION HAVING THIN VERTICAL WALLS, AND (B) A THIN STRIP OF NAILABLE, SEMI-RIGID PLASTIC RESIN MATERIAL EXTENDING SUBSTANTIALLY ALONG THE LENGTH OF SAID BEAM MEMBER, SAID STRIP BEING FITTED AS A LATERAL BRACING CROSS-MEMBER EXTENDING BETWEEN AND SECURED TO THE VERTICAL WALLS OF SAID U-SHAPED SECTION,

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