US1979642A - Beam - Google Patents

Description

Nov. 6, 1934. R. K. o. SAHLBERG I BEAM Filed April 24, 1933 3 Sheets-Sheet l INVENTOR /Z- /f. a. 04414,-

ATTORNEY NOV. 6, 1934- Q SAHLBERG 1,979,642

BEAM

FilecLApril 24, 1933 3 Sheets-Sheet 2 F E INVENTOR ATTORNEY NOV. 6, 1934. R K, O SAHLBERG 1,979,642

BEAM

Filed April 24, 1933 3 Sheets-Sheet 3 241 r I 23} f a INVENTOR ATTORNEY Patented Nov. 6, 1934 UNH'TEB STATES PATENT orrice 7 Claims.

The present case is a continuation in part of application of Rolf K. O. Sahlberg, filed May 5, 1932, Serial No. 609,368.

This invention relates to beams and partieularly to relatively light weight steel beams which are rolled or otherwise fabricated or built up of chord members and web members. More especially the invention relates to beams adapted to form a floor when spaced in accordance to load 10 and span and preferably with a suitable filler between them, entirely enclosing the beams, to constitute a relatively fire-proof and sound proof construction.

My improved beams are not limited for use with a filler which entirely covers them, but

may bev used in connection with slabs of concrete or other material forming the floor surface, with the beams exposed beneath the same, with or without a suspended ceiling below the beams.

The average stresses in a present steel beam of uniform cross section over the whole span are less than fifty per cent of the permissible stresses.

In consequence, the arrangement is highly oneconomical, since beams of unduly large size require to be used. By using the present steel beams for typical floor constructions, it is difficult to get a flat ceiling because of the relatively great height of the beams in vertical cross section. If a fiat ceiling is required the customary way is to use a hung ceiling supported below the beams, which means additional cost and increased height of the building due to greater thickness of the floors.

Furthermore, a construction using a hung ceiling it not fireproof nor sound-proof. With present floor constructions, where steel beams are used as load bearing members, a space for pipes and other conduits has to be provided and it has heretofore been the general practice to place these conduits in a layer of fill on top of the beams. Such a layer gives an additional thickness and weight to the floor construction with consequent increased height to the building.

These disadvantages are to a large extent overcome by my present invention where the beams are designed in such a manner that for full uniform load over the whole beam the steel is stressed up to the limit for practically every section of the beam.

By using beams designed in accordance with my invention the height of the beams can be substantially reduced as compared with present practice, and therefore, if a filler is used between the same and in which the beams are wholly imbedded (as is preferable but not necessary) the floor as a whole will be lighter and of less." thickness than can be secured with the use of fabricated beams of the present construction. As a result of the preferred arrangement a'flat ceiling may be obtained without any additional cost and the thickness of the floor construction may be reduced to a minimum.

In order that the invention may be better understood attention is directed to the accompanying drawings forming a part hereof and in which Figure 1 is a side elevation of one form of my improved beam illustrating a filler entirely enclosing the beam so as to form a floor of the type disclosed in the art, and also showing by broken lines an arrangement in which the main portion of the beam is cambered to a predetermined extent, for a purpose to be later explained.

Figure 2, an elevation of the parts shown at the left in Figure 1.

Figure 3, a section on the line 33 of Figure 1.

Figure 4 a longitudinal view partly in section of another form of beam showing the same supported in a building wall or partition.

Figure 5 a plan view of the arrangement shown in Figure 4 and indicated by arrow 5 on the latter figure.

Figure 6 an elevation of a portion of one of my improved beams of a different construction showing the same supported on a steel girder.

Figure 7, a sectional View on the line 77 of Figure 6.

Figure 8, a sectional view similar to Figure 7, showing a modified arrangement.

Figure 9, a side elevation of a portion of one of my improved beams of diiferent construction illustrating the floor surface as being formed of a concrete slab. v

Figure 10, a top view showing the arrangement of Figure 9 with the slab removed.

Figure 11, a side elevation of a portion of a difierent form of my improved beam.

Figure 12, a section on the line 12-12 of Figure 11.

Figure 13, a side elevation of a portion of a different form of my improved beam.

Figure 14, a section on the line 1414 of Figure 13.

Figure. 15, an elevation partly in section showing two of my improved beams supported by a single heavy longitudinal member and illustrating a preferred manner of tying the elastic reinforcing members together.

Figure 16, an elevation of the preferred form 0 locking plate for-tying together the adjacent ends of the longitudinal supporting members and showing two of such members in position.

Figure 1'7 is an elevation of one of the locking plates showing one set or pair of elastic reinforcing members secured therein.

Figure 18 a sectional View illustrating a long beam centrally supported and showing the supporting members extending continuously on both sides of the central support.

Figure 19, a diagram showing the preferred form of one of the elastic reinforcing members and showing in dotted lines another arrangement thereof.

Figure 20, a diagram showing a different form of one of the elastic reinforcing members.

Figure 21, a diagram showing adifferent form of one of the elastic reinforcing members, and

Figures 22 to 27 respectively are diagrams which illustrate the principle of my improved beam as compared with simple beams.

In Figures 20 to 21 inclusive of the foregoing views corresponding parts are represented by the same characters and in Figures 22 to 2'7 inclusive corresponding parts are represented by other characters.

The beam shown in Figure 1 is formedwith an upper flange l, a lower flange 2, and a continuous integral web 3. This beam is shown as being supported at its ends by brackets 44 from heavy longitudinal beams 5. The cross beams are spaced apart a sufficient distance to carry the load, such spacing depending upon the size of the beams and the load to be carried. Between the cross beams is a filler 6 of suitable material.

With the arrangement of Figure 4, the cross beams comprise the top and bottom flanges 1 and 2 and the web 3. With this arrangement there are cut-out portions '7 in the web for the purpose of lightness. With this arrangement the beam is shown as being supported in a mass of concrete 8 poured in a sustaining wall 9. The mass 8 is preferably the usual non-porous concrete.

With the arrangement of Figures 6 and 8 the flanges 1 1' and 2 2 are separate from and welded or otherwise secured to the web 3. Here the web is not only formed with cutout portions '7 but with additional cut out portions 10 to further reduce the weight. With this arrangement the crossbeams are carried upon the upper flange of the longitudinal beams 5 instead of upon brackets as at Figure 1. 1 With the arrangement shown in Figures 9 and 10 the web is formed of lattice members 3 and is supported in a mass of concrete 8 poured in a sustaining wall 9 as in Figure 4. With this arrangement a floorslab 17 of suitable material rests upon and is carried by the beam. With the arrangement of Figures 11 and 12 the beam is channel shaped in crosssection, with .upper flanges 1' and 1', a bottom 2 corresponding with flange 2 of Figure 1 and webs 3-3, the latter being formed with cut-out portions as shown. Here the beam is shown as being supported by brackets 4 from the longitudinal beams 5 as in Figure 1.

The beam shown in Figures 13 and 14 is the same as that illustrated in Figures 11 and 12 except that the webs 3 are not perforated'and a different arrangement is adopted for forming the reinforcing member as will be hereinafter described.

With all arrangements of beams above indicated, I make use of one or more elastic reinforc-' ing members 11 designed for stresses governed by the load, the span and the geometrical form of such reinforcing member or members. I prefer to use the geometrical form shown in Figures 1, 4, 6, 9, 11, 13, 18 and 19, but other forms may be employed. The reinforcing member 11 may for example be of an angular form as in Figure 20 or of curved form as in Figure 21, or even reversed as shown in dotted lines Figure 19 so as to be stressed for compression.

With the arrangement of Figures 1, 2, and 3, the two reinforcing members 11 are supported at two pointseach comprising a pair of blocks 12 and 13 held together by bolts 14 passing through the flange 3. The upturned ends of the two reinforcing members extend parallel with upper flange 1, and are welded or otherwise secured thereto. The ends of said members are shown as being formed into downwardly extending hooks 15 which are embedded and anchored in the filler 6.

The importance of using large and strong hooks at the end of the reinforcing members and of anchoring them so as to resist longitudinal strains will be later pointed out when the p inciple 01' my improved beams is demonstrated mathematically.

With the arrangement of Figure 4, the two reinforcing members 11 are welded or otherwise secured to the lower flange 2 where said members are parallel with said flange and are welded or otherwise secured to the upper flange 1 where said members are parallel to said flange. These members are formed with hooks 15 extending downwards and embedded in the concrete mass 8.

The arrangement shown in Figures 6 and 7 differs from that of Figures 4 .and 5 in that the lower web 2 is bent upwardly and the beam is supported on the top of the heavy longitudinal beam 5 instead of by a bracket as in Figure 1. In Figure 7 the welding between the reinforcing members 11 and the lower flange 2 is between the surfaces 16- 16.

In Figure 8 the reinforcing members 11 are shown as heavy rods being mounted upon the beam by brackets corresponding substantially with the construction of Figure 3.

With the arrangement of Figure 9 the reinforcing rods are welded or otherwise secured to the lower flange 2 as in Figures 4and 6, but here the hooks 15 are'shown as being reversed and are embedded in a concrete mass8. Integral with the concrete mass 8 is a slab 17 forming the floor. With this arrangement the welding of the reinforcingmernbers 11 is at the point where they cross over the upper flange.

With the arrangement of Figure 11 a single reinforcing member 11 is shown welded or otherwise secured to the bottom 2 of the channel shaped beam and welded at the top to the inside of the flanges 11'. Here the hook 15 extends downward and is embedded in a concrete flller as in Figure 1.

With the arrangements of Figures 13 and 14 the reinforcing member 11 is formed by sawing or cutting the bottom of the channel beam on the line 18. In this case the formation or" the reinforcing member will have to be effected before the webs 3 are bent into parallel relationship.

In cases where several spans of cross beams are to be used, it is desirable that the reinforcing members 11 of one span shall be rigidly connected or tied to the corresponding reinforcing members of an adjacent beam. This may be conveniently done by the arrangement shown in Figures 15, 16 and 17. Here the central supporting longitudinal beam 5 has a plate 19 bolted thereto and formed with mortised channels 20 for receiving the expanded ends of the reinforcing members 11. Wedges 21 are driven into the crotch in the end of the member 11 to lockthe same rigidly in place. 7 I

.Instead of this arrangement the construction of" Figure .18 may be employed where a long beam is used and where the reinforcing member or members 11 are continuous, being welded otherwise secured to the upper flange 1 immediately above the central supporting beam 5. A latticed beam is shown but obviously other constructions may be employed. 1

An ordinary beam supported at its ends on 1on-' gitudinal girders or load bearing walls, has, for a uniform load, a parabolic shaped moment curve as shown in Figure 26. The maximum moment in the center of the span is wL /8 where w is the load per linear foot and L is the span,

My improved beam acts in a different way.v

The beam rests upon twofixed supports such as the longitudinal beams 5-5 or supporting walls 9. These in Figure 22 are indicated at 13 and 14. The beam also rests upon two intermediate elastic supports, namely, at the points of attachment between the intermediate members 11 and the lower flange 2. These supports in Figure 22 are indicated by 15 and 16. In Figures 1, 4, 6, 9, 11, 13, 18 and 19 these elastic supports are indicated by e and Due to the action of these elastic supports the moment in the beam is negative over these supports. The maximum bending moment in the beam member (top chord, bottom chord and web) of my improved type is wL /64, where w is the load per linear foot and L is the distance between the outside fixed supports. By forming the reinforcing members 11 with heavy strong hooked ends as explained and embedding the same in a suitable filler the stresses in such mem bers will be transmitted to the filler. 1

During the erection of a floor construction with my improved beams as load bearing men bers, there is a time when the beam is called upon to carry a load before the filler is in place. In

order to bring the reinforcing members 11 into action during this interval, I prefer as above pointed out to weld or otherwise secure such members to the top flange of thebeam.

In my improved beam the shear stresses are greatly reduced due to the action of the reinforcing members or member 11. With an ordinary beam the maximum shear is equal to wL/2 where w is the load per linear foot and L is the span in feet between the end supports, see diagram Figure 2'7. With my improved beam the maximum shear is equal to wL/4 where w equals the load per linear foot and L the distance between points 13 and 14 in Figure 22. 1

Due to the small shear stresses which amount to about one-half of these in an ordinary beam,

a saving of material in the web can be obtained The beams embodying my invention may be manufactured in such a manner that the main portion of the beam, i. e., the top and bottom flanges with the connecting web, whether solid or open, is provided with a camber. This is to say, the beam is slightly curved as indicated by the broken lines 22-22 in Figure l, and when the beam is placed on the job. the apex of the curve will be upwards. The elastic reinforcing members on eithersi'de of the main beam should in this case be separate members connected by welding or otherwise to the'bottom flange of the beam at the points where these reinforcing members are bent upwards.

The reinforcing members also should be connected by means of welding or otherwise to the top flange of the beam at the ends of the same. The camber thus given to the main member of the beam can'be predetermined, so that when the beam is encased with the filler, the weight of this material plus the weight of the beam will cause a down deflection, whereby the curved beam will straighten out and become'horizontal. This arrangement will eliminate the necessity of posts for the form work during construction.

In order that the essential principle underlying my improved beam may be more clearly understood, attention is particularly directed to the diagrams in Figures 22 to 27 inclusive. Referringfirst to Figure 22 it may be assumed that the fixed supports 20 and 21 for the reinforcing member are substituted for fixed supports 22 and 23 along the vertical lines through 15 and 16. In other words, the reinforcing member 12 instead of extending between the points 20-15162l now extends through points 22-151623.

The beam member in this case as will be obvious to those skilled in the art will be carried by two fixed supports 13 and 14 and by two elastic supports 15 and 16 where the elasticity in the latter supports is determined by the elongation caused by the tension in the reinforcing member 12 between the points 15 and 22 and the points 16 and 23. The reaction from the reinforcing member in the supports 22 and 23 is obviously vertical, the horizontal component being 0.

Now if it be assumed that the fixed supports 22.'and 23 are moved to points 24 and 25 along vertical lines through the fixed supports 13 and 14 a vertical reaction still remains in this case but in addition to that, a horizontal reaction is developed namelyH=R cos y, where R equals the tension in the reinforcing member 12' and 9 equals the angle indicating the slope of the member 12" in relation to the horizontal line. The condition of the beam member 11 is obviously unchanged in comparison with the first assumed case and consequently may still be considered as resting ontwo fixed supports 13 and 14 and two elastic supports 15 and 16.

As a third assumption consider the fixed supports 24 and 25 as being moved along vertical lines down to the points 20 and 21. Nothing in the system is changed by this assumption excepting the numerical value of the horizontal com ponents in the fixed supports 20 and 21 originating from the stresses in the reinforcing member 121 ..Conseque'ntly it is obvious that the beam member 11 is resting on the two fixed supports 13 and 14 and 'on the two intermediate elastic supports 15 and 16. It will of course be seen that this last assumption corresponds identically with the various constructions of my improved beam above referred to. I I

It is obvious from the foregoing discussion that my improved beam construction develops intermediate elastic supports. The moment diagram for that beam is determined by the formula 1I/I M1H h, where M1 is the bending moment ina simplesupported beam over the span l3--14; H is the stress in the reinforcing member 12 between points 15 and 16 and h is the distance from a line through the points 20 and 21 to the center of the reinforcing member 12.

The numerical value of the bending moment in a section through the elastic supports depends upon the ratio between the sectional area of the reinforcing member 12 and the stiffness (moment inertia) of the beam member 11. Such ratio can be so chosen as to give a negative bending moment in the points 15 and 16 equal to the positive bending moment in a section half way between those points. If the elastic supports 15 and 16 are placed in the quarter points of the span the maximum bending moment in the beam member 11 is as compared to for a simple supported beam.

Figure 23 shows a bending moment diagram and also the influence due to the reinforcing member 12. The value of the term H h is represented by the area abcda which is to be deducted from the moment diagram for a simple supported beam represented by the area enclosed by the parabola e and the line ad in order to get the moments in the, beam member 11 resting on intermediate supports.

Figure 24 gives the same moment diagram transferred to a horizontal base line in order to make the diagram directly comparable with the moment diagram for the simple supported beam shown in Figure 26.

Figure 25 gives a shear diagram for the beam member 11 in the reinforced beam. Here it will be noted that the maximum shear occurs at the elastic supports and its numerical value is half of the maximum shear for a simple supported beam as shown in the shear diagram of Figure 27.

In order to utilize the benefit of the reinforcing members it is essential to provide for the transmission of the stresses located in them to a member capable of resisting the horizontal component. A considerable part of the. total steel area in the bottom flange must becomprised of the reinforcing members. It is therefore obvious that with my improved reinforced beam the reinforcing members must be provided with large and strong hooks or other equivalent anchoring arrangement embedded in a material so strong that it can resist the surface pressure against the steel and that the strength of any lock between the reinforcing member (see Figures 15, 16, and 15) shall be equally great.

The reason for the necessity of a relatively large area in the reinforcing member is that the efiectiveness of the intermediate elastic support is to a great extent predicated upon the ratio.

between such area and the moment of inertia .of the beam section. If, for instance, the top and bottom chords together with their interlacing form a beam of a considerable moment 'of inertia and reinforcing rods of comparatively small cross section are employed then the effect of the reinforcing rods to produce intermediate supports becomes negligible and the beam will therefore act as a simple beam between its end supports. 1

Again referring to Figure 22' and assuming supports 22 and 23 it is clear that considerable stress is to be taken in the vertical part of the reinforcing member 12. The vertical reaction in points 15 and 16 if placed in the quarter points of the span is equal to V=0.455 w L, and consequently the tension in the members 15-22 and 1623 reaches the same amount. This formula indicates that nearly half the load over the span is taken in each of the intermediate supports, due to the continuity of the beam member 11. For the same load, over the span L the tension R. in the sloping part of the reinforcing member 12 increases with the decreasing numerical value of the angle-f, representing the slope from the horizontal line. On the assumption that the supports for the reinforcing member have been moved to the points 20 and 21, the tension R in the reinforcing member 12 is, within a close range, equal to R=0.455w L/sine f.

In order to determine the ratio between the 1 area of member 12 and the area at the bottom chord of the beam member 11 it may be assumed that the height is equal to 1/35 of the span L and that 15 and 16 are located in the quarter points of the span. Under these assumptions the angle i=6 40 and sine f=0.116. Consequently R=0.455w L/0.116 or R=3.92w L.

The cross section area of the steel being in direct proportion to the stress, the ratio between the area of the reinforcing member 12 and the bottom chord of the beam member 11 is consequently 3.92/0.55=7.15. By choosing different values for the moment of inertia of the beam member, for the height of the beam member, for the location of the points 15 and 16 and choosing materials of different elastic properties for the reinforcing member this ratio can be varied within wide limits. The above ratio may be considered an upper limit and the ratio for a lower limit can be brought down to about 1.

By making a comparison between the two diagrams 24 and 25 representing bending moments and shear occurring in my reinforced beams, with diagrams Figures 26 and 27 representing bending moments and shear in a simple supported beam the obvious difference in the two types is clear.

With the above assumptions, my reinforced beam develops a maximum bending moment in the beam member 11 of only one-eighth of the maximum bending moment in a simple supported W0 beam and the maximum shear is half of the same for the simple supported beam, occurring not at the fixed ends support but over the elastic support.

Having now described my invention, what I claim is new thereinand desire to secure by Letters Patent is as follows:

1. An improved beam supported at its ends and comprising compression and tension members and an intermediate web for resisting vertical bending moments, and a reinforcing member 00- operating therewith and anchored at its ends to the compression member with suilicient rigidity and being of suflicient tensile strength as to give support to the beam between its ends, said beam being initially camberedor curved whereby when in place with its associated permanent load the beam will become horizontal.

I 2; An improved beam supported at its ends and comprising compression and tension members and an intermediate web for resisting vertical 14G bending moments, a reinforcing member cooperating therewith and having a heavy hooked end and a concrete mass for anchoring said hooked end, the tensile strength of said reinforcing memher and the rigidity of its anchorage being sufficient to give support to the beam between its an intermediate web for resisting vertical bend- 15o;

ing moments, a reinforcing member having a heavy hooked end and a filler of concrete entirely surrounding said beam and reinforcing member including said hooked end, the tensile strength of said reinforcing member and the rigidity of its anchorage being sufficient to give support to the beam between its ends.

4. In a floor construction the combination with a vertical support and two cross beams supported thereby and in line with each other, a mortised plate carried by said support and in line with said beams, a reinforcing member for each cross beam each being anchored at one end to the compression member of each beam and being secured within said mortised plate at the other end, the anchorage of said reinforcing members and their connection with said plate being sufficiently rigid and the tensile strength of said reinforcing members being sufficiently great to give elastic support to each of said beams between the ends.

5. In a floor construction the combination with a vertical support and two cross beams supported thereby and in line with each other, a mortised plate carried by said support in line with said beams, the reinforcing member for each cross beam being anchored at one end to the compression member thereof and being expanded in said mortised plate by a wedge, the anchorage of said reinforcing members and their connection with said plate being sufficiently rigid and the tensile strength thereof being sufliciently great to give elastic support to each of said beams between their ends.

6. An improved beam supported at its ends, comprising compression and tension members and an intermediate web for resisting vertical bending moments and an associated reinforcing member cooperating therewith and adapted to be anchored at its ends in the compression zone of the beam with sufiicient rigidity and being of sumcient strength when so anchored as to give elastic support to the beam between its ends, said compression zone including the compression member of the beam.

7. An improved beam supported at its ends comprising compression and tension members and an intermediate web for resisting vertical bending moments, a slab carried by and bonded to said compression member and an associated reinforcing member cooperating with the beam and anchored at its ends in said slab within the compression zone of the beam with suflicient rigidity and being of sufiicient strength as to give elastic support to the beam between its ends, said compression zone consisting of the compression member and said slab.

ROLF K. 0. SAHLBERG.

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