US3427773A - Structure for increasing the loadcarrying capacity of a beam - Google Patents

Description

Sheet c. KANDALL INVENTOR: CHA/nfs KANU/:LL

STRUCTURE FOR INCREASING THE LOAD-CARRYING CAPACITY OF' A BEAM Feb. 18, 1969 Filed June 6, 19646 90A Rw ATTORNEY.

c. KANDALL 3,427,773 STRUCTURE FOR INCREASING THE LOAD-CARRYING CAPACITY OF A BEAM Feb. 18, 1969 Sheet Filed June 6, 1966 INVENTOR.'

CHARLES KANDALL ATTORNEY.

United States Patent O 3,427,773 STRUCTURE FOR INCREASING THE LOAD- CARRYING CAPACITY OF A BEAM Charles Kandall, 2383 Cornaga Ave., Far Rockaway, N.Y. --11691 Filed June 6, 1966, Ser. No. 555,490 U.S. Cl. 52-225 Int. Cl. E04c 3/10, 5/08 4 Claims ABSTRACT OF THE DISCLOSURE My present invention relates to an improved method of increasing the load-carrying capacity of structural members, such as beams and girders, and structures embodying this method; more particularly, this improvement relates to the modification of the load-carrying capacity of pre-existing structural members including beams or girders in place within existing structures and similar structural elements which have been designed on the basis of certain load-carrying characteristics but which require modification because of design changes, the desire to eliminate deflections and stress due to sustained loads and the like.

In structures such as buildings, bridges, elevated roadways and the like, girders and beams frequently are provided to support a load between spaced-apart locations spanned by these structural members and are designed to sustain the loads originally expected or predicted. Typical of such structures are 'beam and girder arrangements carrying a-iloor of concrete `or other structural material.

It frequently happens that the beams or girders must be altered so as to enable them to sustain loads greater than those for which they were originally designed, or to distribute the loads differently from the original system. The conventional method of effecting such increase in the load-carrying capacity involves an increase in the section modulus of the girder or beam by riveting, bolting or welding steel plates, angles and other structural shapes to the top and bottom flanges of the structural member. In cases in which the load is supported directly above the upper flange, such methods require the demolition, removal or lifting of the loading structure, while in some cases the existence of sufficient headroom permits attachment, albeit with considerable difficulty, of an appropriate structural shape to the bottom flange. Thus, it is frequently required to demolish a portion of an existing floor to apply the requisite structural shape or shapes to the upper flange. Furthermore, since the beam or girder is supporting the load it has Ibeen deformed and stressed thereby, and it is frequently necessary to jack the beams up at one or more locations to relieve them of the deadload stresses before the new steel shape is connected to the upper or lower flange. Any portions of the structure removed to afford access to the beam or girder must then rbe repaired at substantial cost.

The general object of my present invention, therefore, is to provide a method of and means for increasing the load-carrying capacity of a beam, girder or other loadbearing structural member without having to increase its section modulus and, therefore, without the need for affix- 3,427,773 Patented Feb. 18, 1969 ing structural shapes along the flanges of the structural member.

A further object of this invention is to provide a method of redistributing the loading of a girder or beam which `avoids the need for demolition and temporary removal of overlying structures and also any necessity for jacking the beam or girder to relieve dead-load stress.

A further object of this invention is to provide a method of eliminating the deflection and stresses in an existing beam, lwithout the necessity of vertical jacking.

I have found, in accordance with the :present invention, that the aforestated objects can be realized by tensioning an elongated flexible tension element (a tendon) of polygonal configuration and anchoring it -to a compression member, specially provided for this purpose, which is free and independent of the beam at the time of tensioning. The polygonal configuration is obtained by means of pins, brackets, stiffener plates or similar devices connected to the beam at locations intermediate the anchoring locations and capable of taking the vertical components of the tension. Thus, it s an important lfeature of this invention -that in the case of a generally horizontal beam adapted to support downward forces, including the dead weight of the Ibeam, the tendon or tension element is affixed thereto at a vertex of its polygon so as to produce an upward force by virtue of the tension applied to that element. In this manner the dead loads, which cause bending stresses in the girder, can be balanced in whole or in part by counter-forces imparted to the structural member by the elongated or longitudinally extending flexible tension element. As the dead loads are counteracted by the upward vertical components of the tensioning steel, new additional dead or live loa-ds may be :placed on the member without the necessity o-f increasing the section modulus. In accordance with an important feature of this invention, this relieving of the stresses of the structural member is effected without applying additional stress thereto by installing an independent compression member-longitudinally extending along the beam or girder and supported at the aforementioned force-transfer locations-t0l anchor the wires, strands, cables or other elements making up the tendon. The compression member is mounted `with freedom of longitudinal displacement relative to the beam or girder to prevent direct axial (i.e., compressive) stress from being transferred to the girder.

Thus, if a simply supported girder having a tension element stretched between force-transfer points at the extremities of the girder and at least one vertex at which the tension element bears upon the girder between these points, an upward force is generated at any such vertex to counteract the downward dead load or reduce the net downward loading of the girder at this point by any predetermined amount (as established by the tension upon the element and the angle of attack at the vertex). Downward forces are applied a-t the anchor points corresponding to the force-transfer locations mentioned earlier.

Once the cable or other tendon has been tensioned against the compression member between the vertices at its bearing points upon the girder, the compression member may be fixedly secured to the beam since it will not thereafter impart any compressive stresses to the beam, except temporarily under live load.

The term beam as herein used is intended to er1- compass all rolled sections, built-up girders or composite girder-type construction elements, and trusses whether made from metal or from other elastic materials, although steel beams and girders are primarily contemplated. With a truss structure, it will be evident that the members spanning the upper end lower chords are the equivalent of the beamweb for the purposes of the present invention. These structural shapes can be put into place within an existing structure, as indicated earlier,

and indeed the present invention has its greatest applicability in situations in which the girder is under stress and its load-carrying capabilities must be modified to balance additional stresses or compensate for heavier types of load than originally contemplated. In addition, the invention pertains to structural members which may be encased in concrete subsequent to application of the tension element and compression member and to encased structural members to which the tension element can be attached along a ank thereof.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a side-elevational view of a beam forming part of a structure whose load-carrying capacity is to be increased in accordance with the principles of the invention;

FIG. 2 is an enlarged sectional view of an end portion of the bracing assembly of FIG.1;

FIGS. 3 and 4 are cross-sectional views taken on the lines III-III and IV-IV, respectively, of FIG. 1;

FIG. 5 is a side-elevational View similar to FIG. l, showing another embodiment;

FIG. 6 is a cross-sectional view taken on the line VI- VI of FIG. 5;

FIGS. 7, 8 and 9 are further views similar to FIG. 1 illustrating still other modifications; and

FIG. 10 is a diagram illustrating the principles of the present invention in greater detail.

On referring first to FIG. 10, which illustrates an I- bea-m having upper and lower flanges, it will be seen that the structural member is supported at S and S adjacent its extremities. If a load L is applied to this beam, both the dead weight of the beam (represented by an arrow W) and the load L will bear downwardly and the downward forces will be transmitted to the supports S and S. If, in accordance with the principles of this invention, it is desired to balance all or part of the load applied to the beam in the region of the load L, a flexible tendon is stretched between force-transmitting points P' and P", preferably located directly above the supports S' and S for the direct transmission to these supports of the downward component of the force sustained by the tension element T as represented by arrows F and F". At its vertex V the tension element is anchored to the beam by means described in detail hereinafter and represented by a pin P. Since the tendon T is under high tension, an upward force component represented by arrow F will be applied to the beam to counteract the downward forces thereon. The axial compression components C' and C of the tension wire are taken up by a compression member M specially provided for this purpose, which is free and independent of the beam, and are thus not transferred to the beam 1. The tension upon the tendon T is represented by the arrows T and T. The member M is slidable parallel to itself and is merely held against the beam to prevent buckling. To transmit the downward forces F and F" to the support S' and S, I provide stitfeners to constitute force-transmitting members as described in detail hereinafter. These stifeners may be formed by the existing stiffeners of conventional beams or plates or angles specially provided for this purpose and such stiffening members can be reinforced in the regions through which the tension element T passes.

From FIGS. l-4, it will be evident that the steel beam 1 rests upon a pair of longitudinally spaced supports 11 and 12 and carries a dead load represented by a concrete slab 10. The structure, of course, may also include additional beams, not shown, extending parallel to the beam 1.

The ybeam y1 is shown to lhave the usual `I-proiile with a lweb 13, an upper llange I14 and a lower flange 115. The flanges are spanned on one or both sides of the web 13 by stitfener plates 16 ithrough which the `compression member can pass or upon which it may be mounted so that its ends are closer to ,said supports than to the midpoint of said member. The compression member 3, in this case, is a downwardly open angle, as best seen in FIGS. 2 and 3 and is connected with the ends of a tension cable or other tendon 2 by nuts and beveled washers 4 and 4 or other means conventionally used as anchors. Thus, when the cable 2 is tensioned, axial compression forces are applied longitudinally to the compression member 3. Such compression is not transferred to the beam 1 since the compression member 3 is freely movable longitudinally of the beam and only negligible friction forces are transmitted in longitudinal direction therebetween. The tension element 2 and, of course, the compression member Iaixed thereto are supported by brackets 5, or stiteners, similar to or identical with the stiffener plates 16 spanning the llanges; the brackets 5 receive -tihe bar with freedom of relative sliding motion. Other brackets 6 with downwardly open recesses engage the tendon 2 from above and serve to transmit the upward component of the forces of the cable to the beam 1 at the vertices of a polygon corresponding ito intermediate p-oints between the bar-supporting frests r16 and Athe anchor means represented generally at 4. The brackets 6 represent any suitable means for transmitting the upward Kforce to the structural member. 1As can 'be seen from fFIG. 4, cross beams 7 interengaging with beam 1 may be provided with brackets `7' and apertured to guide the compression member 3 and the tension element 2.

In order to compens-ate for any weakening of the cross beams 7 or the stiffener -16 by the apertures requi-red for the passage of elements 2 1an-d 3, the lregion surrounding these apertures may be lreinforced with plates, Iangles or Ithe like. From FIG. 4 ilt can be seen that the compression member 3 may be mounted along and youtwardly of Ithe connection angles y8 whereas bracket members 5 serve for lthis purpose in the arrangement of FIIG. 3.

,The points of engagement between the cable 2 and the beam 1 'lie along a polygonal line which can substantially coincide 'with the moment line of the supported structure under dead load so that, as a consequence of the provision of the tensioning element 2, the load may be substantially uniformly distributed over the girder even though a nonuniform stress distribution was originally present. Naturally, each of the other beams of the structure, extending parallel to the beam 1, may be strengthened in like manner with Ithe corresponding bracing assemblies 2, 3 preferably Edisposed symmetrically on, Ifor example, confronting sides of adjacent beams. In cases where cross beams do not exist, bracing assemblies may be mounted symmetrically on opposite sides of the web 13 of a single beam.

Conventional means (e.g., hydraulic cylindrical arrangements) may be used for tensioning the cable 2 and anchoring the terminals to the compression member 3 to retain the cable under sufficient tension to keep the beam 1 substantially horizontal or even slightly cambered upwardly, under dead load, without subjecting this beam to any longitudinal compression. The compression member 3 may remain free of the beamr after tensioning or may be connected by welding to the points at which it is supported; such attachment does not alter the fact that the axial stress is taken up by the compression member.

FIGS. 5 and 6 show a generally similar arrangement wherein the beam 1 has been replaced by a built-up girder 1a with cover plates 18 and 19 included in its upper and lower anges. Stiffeners 8a carry brackets 5a, 6a through which the compression member 3a and the tension cable 2a pass. The compression member 3a is here shown to have an H-profile. It will be apparent that, in this arrangement also, the force-transmitting support plates for the assembly 2a, 3a and the means for attaching the tension element 2a to the beam at the vertices of the polygon can be formed at least in part by transverse beam or brackets as shown in FIGS. 1 and 4 or that elements 2a, 3a may pass directly through the stifeners, without requiring angles or the like to be mounted thereon as shown in the left-hand side of FIG. 6.

In FIG. 7 I have shown a conventional continuous beam 1b resting on an intermediate support 20` in addition to the two end supports 11, 12. The tension cable 2b again extends substantially along the moment line in a polygonal coniguration and bears upon the compression member 3b only at its extremities while being anchored at intermediate locations (corresponding to vertices of the polygon) to the |beam. IIn the system of FIG. 8, the beam 1c overhangs the supports 11 and 12 while the cable polygons likewise extend beyond these supports. In contradistinction to the preceding embodiments the compression member 3c extends underneath the associated tension cable 2c in this arrangement.

FIG. 9, nally, illustrates the possibility of subdividing a bracing assembly according to my invention into a plurality of tension elements 2d, 2d', 2d with respective compression members 3d, 3d', 3d, all carried on the web of the beam 1d; the smaller tension cables 2d', 2d" are of triangular conguration with their apices overlying the supports 11, 12 and lying close to the extremities of the main cable 2d. The longitudinal slidability and mounting of the compression members and the means whereby the cables are anchored to the beam are essentially the same as those described with reference to the previous embodiments. While nuts have been illustrated for convenience, other clamping devices conventionally used to anchor the terminals of cables can be employed.

The invention described and illustrated hereinabove is considered to admit of many modifications and variations which will be readily apparent to those skilled in the art and are intended to be included within the spirit and scope of the appended claims.

I claim:

1. A structure comprising a substantially horizontal beam resting on at least two horizontally spaced supports; a compression-resistant elongated member extending alongside said beam and having ends at locations closer to said supports than to the midpoint of said member; laterally extending means on said lbeam forming rests for the ends of said member while leaving said ends free to move longitudinally with reference to said rests; a exible elongated tension element anchored under stress to the ends of said member and extending downwardly from said ends; and laterally extending bracing means rigid with said beam bearing downwardly upon at least'one intermediate point of said tension element whereby the latter exerts an upward thrust upon said lbeam at said intermediate point without subjecting said beam to longitudinal compression.

2. A structure as defined in claim 1, further comprising retaining means for holding said member against said beam to prevent buckling of said member.

3. A structure as defined in claim 2 wherein said beam has a web, an upper flange and a lower flan-ge, said element and member extending along said web between said anges.

4. A structure as dened in claim 3 wherein said element is connected with said web at a plurality of intermediate locations Iby laterally projecting formations disposed substantially along the moment line of the structure.

References Cited UNITED STATES PATENTS 1,598,693 9/1926 Sereif 52-694 2,510,958 6/1950 COff 52-225 2,786,349 3/1957 Coil 52-723 2,822,068 2/ 1958 Hendrix 52-226 3,010,257 11/1961 Naillon 52-225 3,140,764 7/ 1964 Checkin 52-645 3,269,069 8/ 1966 Carlson 52-227 FRANK L. ABBOTT, Primary Examiner.

JAMES L. RIDGILL, JR., Assistant Examiner;

U.S. Cl. X.R.

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