US2685354A - Nailable structural member - Google Patents

Description

Aug. 3, 1954 cQLLlNs 2,685,354

NAILABLE STRUCTURAL MEMBER Filed Feb. 5, 1950 5 Shee'ts-Sheet 1 TAPPAN COLLINS ea 67 23 21 66 6| BY 22//--- 2 Y0) ATTORNE Aug. 3, 1954 T. COLLINS 2,685,354

NAILABLE STRUCTURAL MEMBER Filed Feb. 3, 1950 5 Sheets-Sheet 2 11 I I I ywz'w 42M INVENTOR TAPPAN COLL|NS ATTORNEY Aug. 3, 1954 T. COLLINS 5 Sheets-Sheet 3 INVENTOR. TAPPAN COLLINS ATTORNEY 1954 T. COLLINS 2,685,354

NAILABLE STRUCTURAL MEMBER Filed Feb. 3, 1950 5 Sheets-Sheet 4 183k Jug 203 2n I 208 2o|- I o 209 x HVVENTUR. TAPPAN COLLINS BY M/M ATTORNEY Aug. 3, 1954 T. COLLINS 2,685,354 NAILABLE STRUCTURAL MEMBER Filed Feb. 5, 1950 5 Sheets-Sheet 5 INVENTOR. TAPPAN COLL IN 5 Patented Aug. 3, 1954 NAILABLE STRUCTURAL MEMBER Tappan Collins, Gross signor to National ration of Delaware e Pointe Woods, Mich, as- Steel Corporation, a corpo- Application February 3, 1950, Serial No. 142,171

13 Claims.

The present invention relates to structural members and more particularly to nailable structural members formed of metal, such as steel sheet or strip, and adapted to receive and removably retain nails whereby boards or other collateral material may be attached to the structural members by means of nails and similar fastening elements.

It is an object of my invention to provide a nailable structural member that will securely retain nails and that will securely retain a nail subjected to a live load.

Another object of my invention is to provide an improved nailable structural member that will not be deformed by nails driven into the member.

Another object of my invention is to provide an improved nailable structural member formed of relatively thinner metal that is relatively stronger and more rigid than the nailable members heretofore provided.

Various types of metal nailable structural members have been proposed in the past. These nailable members have been intended to replace Woodenmembers and have been intended to receive and retain driven nails while permitting the removal of the nails when desirable. Only a few of the proposed types have been accepted for commercial use. The nailable members which have received commercial acceptance have, in general, been of the type in which a nail is driven into a tortuous or sinuous slot or groove defined by parallel spaced apart webs. These webs are provided with a single corrugation so that the nail is bent first in one direction and then back in the opposite direction through a single reverse curve. These structural members are designed to be used with a nail having a diameter substantially equal to the width of the slot. It has been considered by designers that the nail is held in place by friction and by resistance of the nail to straightening. While nailable members of this particular type have received fairly Wide acceptance for commercial use as beams, joists, columns, studs and the like, the members do have a number of drawbacks or deficiencies. One serious trouble encountered in using such a member is that while the nailable member may retain the nail against a constant withdrawal force applied in one direction, the nail is readily worked loose by a live load. For example, when the head of the nail is gripped and an attempt is made to pry the nail out of the groove by means of a suitable instrument, it may be found that it is quite difficult to withdraw the nail in this man- 2 ner, and it has been considered that the nailable member will satisfactorily retain nails during use. A difficulty arises when the head portion of the nail is subjected to a weaving, bending, lunging load-that is, a live load-for the nail is Walked out of engagement with the structural member. Each cycle of change in load application will pull the nail a short distance out of the nailing groove. Under nearly all conditions of commercial application, the nail is subjected to live load at least part of the time, and if the cycles are relatively rapid or if the live load is relatively great, the nail is quickly worked out of the nailing groove. Accordingly, the nailable members of the prior art have been characterized by relatively weak nail retaining qualities, especially when the nail is subjected to a live load.

Another difficulty encountered with nailable structural members is the tendency of the nails to deform the walls of the nail receiving and bending slot. If the walls are materially deformed or spread, the ability of the member to retain nails is either lost or greatly reduced. To overcome or reduce this tendency, it has been the practice quite frequently to make the member of relatively thicker metal. This in turn increases the problems involved in forming the nailable member and increases the cost of the member. This is particularly undesirable as the users of such members are often quite cost conscious, particularly where the structural member is being substituted for a wooden member. In many instances, the nailable member is made heavier than is necessary to support the loads applied to the member when in use so that the nail will not deform the member. In other words, the thickness of the metal in a structural member, such as a beam, is determined by the forces set up by the driven nail and not by theload carrying capacity required of the beam.

In accordance with the present invention, the nail receiving and bending means of the nailable, metal structural member is constructed and arranged in a novel manner so that the nail is securely held in place when subjected to a live load and not readily walked out of the nail receiving slot. It has been discovered that bending or corrugating the webs which define therebetween the nail holding slot so that the slot extends through two reverse curves greatly increases the retention of nails, particularly nails subjected to live loads. The addition of the second reverse curve increases the retention of nails more than the increase in the length of the nail receiving slot, if there is any increase in the length of the slot.

The reason why a nail receiving means which bends a nail through two reverse curves will retain a nail subjected to a live load while a nail receiving means which bends a nail through a single reverse will not retain a nail subjected to a live load is not accounted for by merely multiplying the properties of a single reverse curve by the factor, two. In addition, and as will be more fully hereinafter described, the addition of more reverse curves or corrugations does not correspondingly increase the resistance of the nail to withdrawal by a live load.

Further, it has been found that the structural member can be constructed of thinner metal without having the nail spread or deform the walls or webs defining the nail receiving slot, if the second reverse curve is made larger than the first so that the nail is bent more gradually. In other words, for each unit of longitudinal ad- Vance, the nail is bent through fewer degrees whensbeingndriven through;the second reverse curve than when being driven through the first reverse curve.

An unexpected advantageof the present inven tion has been in the discovery that the presence of, the second relatively larger revers curve enables the cross-sectional area to be proportioned so.- thatthe .nailable. structural. members, are now free ,or substantially free of any tendency to twist under loads tending to bend the members. Insofaras is known, the prior. art nailable structural members and particularly those which have re-. ceived commercial acceptance have been characterized bypoor structural stability. When these members have been used as beams, joists, columns, studs, or other frame members, it has been necessary to brace the members quite extensively to prevent .twistingor to use larger members or both.

These andnother objects and advantages will become apparent when considering the following description, taken with the accompaying drawings, in which:

Figure 1 is a cabinet view of a structural member embodying the principles of the present invention;

Figure 2 is a fragmentary view of the member of Figure 1 and showing a nail driven into the member;

Figure 3 is a fragmentary sectional view taken along line 3-3 of Figure 1;

Figure 4 is anend View of another structural memberuembodying the principles of the present invention;

Figure 5 is an endview of. another structural memberv embodying the principles of the present invention; and,

Figure 6 isan end view of a different structural member embodying the principles of the present invention.

Referring to the drawings and particularly to Figure 1 which is a cabinet view of a structural member embodying the principles of the present invention, the elongated member [9 is formed by bending and shaping a single piece of steel sheet or, strip.. The present invention is not concerned with the particular manner in which member 58 is formed although the member is preferably formed, by cold rolling steel strip. Metal other thansteel may be used. The member It includes a firstflange means H, a second flange mean 52 and a web means 13 connecting the flange means with the flange means i l and I2 extending along oppositesides, of the web means [3 so that the mcmberllilhas substantiallyan I-shape in crosssection. The flange means H includes a pair of coplanar, equal flange portions I5 and It. The flange portions are each made of two layers of metal with flange it having outer and inner layers i1 and I8 integrally joined along their outer edges and with flange It having outer and inner layers [9 and also integrally joined along their outer edges. Flange means 12 similarly includes a pair of coplanar, equal flange portions 2| and 22 with flange portion 2| having outer and inner layers 23 and 25 integrally joined together along their outer edges and with flange portion including outer and inner layers 25 and 26, also integrally joined together along their outer edges.

Adjacent each flange means H and i2, there is a nail receiving and bending means 28 and 29, respectively. The nail receiving means 28 includes a web or nail guiding portion SI and a parallel nail guiding portion 32 adapted to receive a driven .nailtherebetween. The web and .nail

guiding portions 3! and 32 are spaced apart andv define an elongated nail receiving slot or groove. 33 having a constant width throughout its length- .1 The nailreceiving means 29 also includes a web portion 33- and a parallel nail guiding portion.

36. The portions 33.and 34 are spaced apart and define therebetween an elongated nailing groove 35.

Th flange means H and. the nail receiving means 23 constitute a T-shape as does the flange means i2 and the corresponding nail receiving means 29.. These two T-shapes are, joined by a flat web portion 33 which is integrally joined .along opposite edges to the web portions 3! and 33'. The web portions 3! and 33' constitute part of the nail receiving means as well as part of the web means joining the flanges and I2. As shown, axes sc-r and y-y are mutuallyperperidicular, coordinate axes of the cross-sectional area of the elongated member 16. These axes arelocated in a plane normal to the longitudinal axis 22 of the member. Axes -3: and y-y intersect at point 0. The web portion 315 is symmetrical about axis y-y as is flange I l andflange i2 According y, the cross-sectional area of the structural member, except for the cross-sectional area of. the two receiving and bending means 23 and 25!, is symmetrical about axis J"y'. The expression cross-sectional area means the area of metal measured in a plane normal to the longitudinal axis. Similarly, the cross-sectional area of the flanges H and I2 and web 36 is symmetrical about axis 93-52. Accordingly, point 0 is the 1 center of gravity for the cross-sectional area of the web 36 and flanges l l and i2, and these axes are gravity axes for this portion of the member.

Additionally, and for reasons more fully hereinafter pointed out, all values of y above axis a:a3 are positive, and all values of 4, below axis :r-sc are negative. All values of x to the right of axis g/y are positive, and all values of r to the left of axis y-y are negative as indicated on the drawings by the customary plus (-1-) and minus signs.

In each of the nail receiving means Hand 29, the parallel web and nail guiding portions are curved or corrugated through two reverse curves or two corrugations so that their axes curve in a particular novel manner for reasons more fully hereinafter set forth. Referring to the nail re ceiving means 28 and to Figures 1 and 2, the axis or center line 3101 the nail receiving slot 33 is midway between the opposed inner surfaces of the parallel pair of web and nail guiding portions 3|, 32. The nail guiding portion 32 is integrally joined to flange portion I 6, and at their juncture 38 the metal is curved about the center 39 which is to the right or one side of axis y-y. Similarly, the web portion 3! is integrally joined to the flange portion i5, and the metal at their juncture 4B is curved about center 4| which is on the left or opposite side of axis y-y. Points 39 and M are equally spaced from axis y-y and also from the coplanar flange portions l5 and l 6. The portions of metal 38 and id at the juncture of the nail guiding and web portions with flange portions IS and I5 define therebetween an entrance throat 42 and throat 42 is symmetrical about axis y-y Preferably, entrance throat or passage 42 has the outwardly diverging walls as shown so that the point of a nail will be guided into the nail receiving slot 33. The metal at d3, between flange portions l5 and it, is depressed and extends into throat 42 to form a nail guiding entering groove 44 extending longitudinally of the member between flange portions I5 and 16. The metal at the bottom c5 of groove 44 may be thinned to facilitate penetration of a nail point. The metal of both the web portion 3| and web portion 32 is curved about point 41 disposed on one side of axis yy so that axis 3? of the nail receiving slot, starting at point 48 where axis 31 coincides with and is tangent to axis y--y, curves to said one side of axis yy to point 5d, and the radius of curvature indicated by line 5| is relatively quite small. The radius of curvature 5| is equal to the horizontal distance of point 47 from axis y-y so that axis 3? is tangent to axis yy at point 48. The web and nail guiding portions 3!, 32 are next curved about point 52 disposed on the opposite side of axis yy so that axis 37 from point 50 curves away from axis y-y and then curves back toward axis y-y to point 53 through a radius of curvature indicated by line 56. Point 53 is the point at which a line drawn between centers 52 and 47 would intersect center line 3?. Thus, axis 3'! curves away from and to said one side of axis y-y and then back toward axis yy through a reverse curve. The web and nail guiding portions 3| and 32 are thereafter curved about center 55 disposed on said one side of axis yy. The axis 31 is curved from point 53 across axis yy to said opposite side of axis yy and then back toward and across axis y--y to point 5? through a radius of curvature indicated by line 58. Point 53 is the point at which a line drawn between centers 52 and 55 would intersect center line 3? and point 51 is the point at which a line drawn from center 55 to center 53 would intersect center line 3'1. Thus, that portion of axis 3? which extends from point 48 to a point between points 58 and 53 is curved or bent through a reverse curve and the remaining length of axis 3'? which extends to point 51 is curved through a second reverse curve. While the length of axis 3? which is curved about center 52 forms part of the first reverse curve and also part of the second reverse curve, the tortuous nail receiving slot 33 does contain two reverse curves, and the web portions 3! and nail guiding portion 32 each contains two corrugations with the corrugations of one portion parallel with the corresponding corrugations of the other portion. The radius of curvature M is equal to and may be longer than 5| but is shorter than 58 so that the first reverse curve is relatively sharper and the second or final reverse curve is relatively larger and more gradual.

The web portion 31 is curved about center 59 through an arc of relatively short radius so that the web portion it! joins the web portion 35. The nail guiding portion 32 is not curved around center 59 for the reason that the groove 33 at its inner end preferably should direct the point of the nail away from the web portion 36. If the inner edge portion of portion 32 were curved about center 59, then the point of a long nail would tend to curve into the web portion 36. With the arrangement shown, the point is directed away from the web 36. It will be noted that the inner surface of the web portion 3! curved about point 59 joins the inner surface of web portion 36 at a point that is tangent to a line parallel to axis g If axis 31 were extended as shown, the axis 3'! would intersect a horizontal line at a point 59' spaced from axis 11-11 a distance equal to one-half (the thickness of the metal plus the width of slot 33). Thus, the lower end of axis 37 is shifted to the right of the upper end of axis 37. This is done to bring the center of web portion 3! over to axis g/-y.

The web and nail guiding portions 33, 34 of the nail guiding means 29 are curved through two reverse curves and contain two corrugations so that the axis 66 of nailing groove 35 also is curved in a particular manner. The nail guiding portion 3t is integrally joined to flange portion 22 and at their juncture 6! the metal is curved about the center 82 which is to the right or on said one side of axis yy. Similarly, the web portion 33 is integrally joined to the flange portion 2!, and the metal at their juncture $3 is curved about point '54 which is on the left or on the said opposite side of axis yy. Centers 62 and 64 are equally, oppositely spaced from axis yy and are also equally spaced inwardly from the outer face of the coplanar flange portions 2i and 22. The portions of metal 6!, "3 define therebetween a nail entering throat 55 which is symmetrical about axis yg. Preferably, the nail entering throat 65 or passage has outwardly diverging walls so that the entering point of the nail will be guided into the nail receiving slot 35. The metal at 66 between the flange portions 2| and 22 and more particularly between the outer layers of flange metal 23 and 25 is depressed and extends into throat 65 to form a nail guiding entering groove 61 which extends longitudinally of the member between the flange portions 2i and 22. The metal at the bottom 68 of groove 61 is thinned out to facilitate penetration of a nail point. The metal of both the web portion 33 and the nail guiding portion at is curved about a center 10 disposed on said one side of axis yy so that axis 6t starting at point i! where axis G9 meets or coincides with axis y-y curves to said one side of axis y-y to a point 12 and the radius of curvature indicated by line it is relatively short. The radius of curvature i3 is equal to the distance of point Hi from axis y-y so that axis 68 is tangent to axis y y at point ii. The web and nail guiding portions 33 and 34 are next curved about a point "P5 disposed on said opposite side of axis y-y so that the axis 6d curves from point 12 back toward axis yy to point l6 79. =-;Thus,.,thatportionof axis 68 which extends and the remaining length of axis .653 which extends to point '59 is curved through a second reverse curve. As stated in connection with the first nailing means 28, the length of axis 6% which is curved about the center 75 forms part -of the first reverse curve and also partrof the second reversecurve. and the tortuous nail receiving slot 35.:does contain two reverse curves and the Web. portion 33 and nail guiding portion 34 each contains two corrugations with the corrugations of-.one:-portion parallel with the corresponding corrugations of the other portion. The radius of curvature ll is equal to the radius of curvature.

it but is shorter than the radius of curvature 88 so that the first reverse curve is relatively sharper and the second or final reverse curve is relatively larger or more gradual. The web portion 33 is curvedabout center 8| through an are having a relatively short radius of curvature which brings the web portion 33 into web portion 35. The nail holding portion 28 which extends from point 2 to 59' :and the nail bending and holding portion 29 which extends from a horizontal line drawn through point Hi to a horizontal line drawn through center 8! are symmetrical about axis I have discovered that the addition of the second corrugation or second reverse curve greatly increases the ability of the nailing member to retain a nail driven into the nail receiving slot, particularly when the nail is subjected to a live load. I also have discovered that having the second reverse curve larger than the first reverse curve produces certain important advan tages in addition to greatly increasing the ability of the nailing beam to retain a nail subjected to live load. While I do not want to be limited to any particular theories, it is believed that the addition of the second reverse curve greatly increases the ability of the member to retain a nail subjected to live load because of a difference in the manner in which the nail is gripped. This will be more readily understood by considering the difference between a nail holding means having a single corrugation and a double corrugation. Referring more particularly to Figure 2, assum ing that the nail receiving means 28 is constructed in the manner heretofore used by the priorart, particularly in the members which have received commercial acceptance, the nail receiving means 28 has been constructed as though it were severed at about the point 53. The addition of web and nail guiding portions below point 53. which additional portions are parallel to the axis, did not and will not materially,

alter the problem or prevent the nail from being walked out-of the groove by a live load. The nail which is driven into the nail receiving groove is substantially the same width as the nail receiving groove so that it engages the interior surfaces of the web and nail guiding portions throughout the reverse curve. Thus, the nail apparently is held in place both by frictional engagement with .thewalls of the tortuous nail receiving slot and,

ample, if a force is applied to the head of the nail in a direction parallel to the axis y-y tendingtopullthe nail out of the slot, a relatively large force will be required to remove the nail. While the nail may be removed when desirable by applying a sufficiently great force, the nail will .be. relatively securely held in place when subjected only to a static load.

I believe that the forces retaining the nail in place when subjected to a live load are different than those retaining the nail in place when subjected to a static load. When a. nail is subjected to a live load, it is not only subjected to a force tending to pull the nail out of the groove but is subjected to forces tending to bend the head portion of the nail first in one direction and then in the opposite'direction. These cycles of load application upset or alter the nail holding characteristics of the beam. Before discussing this point, it is to be noted that if a forceis applied to the nail and the nail starts to move, the frictional force resisting movement of the nail is reduced. Ii e force necessary to overcome friction between two stationary parts is greater than the force required to maintain movement. The

starting friction is always greater than the moving friction. As a result, once the nail starts to move, friction alone can not stop movement of the nail.

Once the nail starts to move or moves a very short distance, the nail tends to straighten out so that it is no longer accurate to consider the nail as being engaged throughout its length. The nail in the prior art structures acts as though it were engaged only at two points along its length. When a live load is applied to the head portion of the nai1,-the head portion is bent back and forth and these points of engagement change.

the live load is relatively great the nail will be I quickly walked out of the slot.

In contradistinction, when a nail 85 is driven through a board 88 into slot 37 and bent through two reverse curves, the nail is held at a plurality of points of engagement along its double corrugated length. When a live load tends to shift board 85 back and forth and tends to bend the head portion 87 of the nail 85 back and forth,

at least two of these points of engagement are not shifted or changed. These points of engagement never completely let go of the nail, and the nail can not be walked out of the slot. Additional bends would be redundant.

Regardless of whether or not the foregoing theory is exactly correct, it is true that the addition of the second reverse bend or corrugation does greatly increase the ability of the member to retain nails, particularly when the nails are subjected to live load, and this ability to retain nails is much greater than would be expected from the additional friction established as a result of the additional length of nail engagement. It has been found that the second'reverse curve should be larger--that is, have a greater radius of curvature than the first reverse curve. With the radius 58 longer than radius 54, the nail is first bentv through a relativelysharp bend and The head portion of the nail is relatively easily bent work-hardened. The work-hardened nail is then bent through the larger more gradual reverse bend. The work-hardened nail has a greater resistance to being bent than the original nail, and, by having the second reverse curve larger, the force required to bend the nail, through one reverse curve is equal or more nearly equal to the force required to bend the nail through the other reverse curve. This results in two advantages. First, the structural member can be produced from thinner steel sheet or strip. Second, there is less tendency for the nail to spread apart the walls of the nail receiving slot. Where, as has happened in the past, the nail spreads the web and nail guiding portions, a length of the nail receiving means loses its ability to retain nails. This is true despite the fact that the walls of the nail receiving means are usually held together by suitable fastening means at spaced points, as will be hereinafter described. Thus, having the second reverse curve larger than the first reverse curve increases the ability of the member to retain securely a driven nail.

Referring more particularly to Figures 1 and 3, fastening means 90 are located at spaced intervals along the length of the nail bending and holding means 28. The fastening means 90 revents spreading apart of the web portion 3| and the nail guiding portion 32 and fastens these two portions together so that the flanges l5 and I6 and portions 3! and 32 are tied together whereby the flanges will equally support a load applied uniformly to the flanges. The exact spacing apart of the fastening means depends on a number of factors including the thickness or gauge of the metal. Any suitable type of fastening means may be used though the type of fastening means shown and hereinafter described is preferred, The fastening means 9!! is similar to that shown and described. in patent No. 2,457,148 to William J.

Hall et al. The lower nail holding means 29 also includes identical fastening means 9!] for holding the web and nail guiding portions 33 and 34 together in properly spaced. relationship.

The fastening means 92'! comprises a flattened portion 95 formed on the curved web portion 3! and a flat portion 92 formed on the curved nail guiding portion 32. The two flat portions st and 99 are bosses displaced laterally from their respective portions 3 I, 32 so that when the flat portions Hi, 82 are in abutting relationship, the web and nail guiding portions are spaced apart to provide the nailing groove therebetween. An opening 93 is formed in boss 91. An opening is formed in boss 92, and the metal 96 around this opening is formed into a tubular projection at which extends through and snugly fits opening 93. The outer end of the projection 9% is flanged or flared outwardly at 95 against the outer surface of the boss iii to securely hold together the web portion 3! and the nail guiding portion 32. The bosses 9! and 92 are in contact with each other, but throughout the length of the nail receiving means 28 the web and nail guiding portions 3 l, 32 are spaced apart except at the location of the fastening means. The fastening means SE located along the lower nail receiving means 29 is identical with the upper fastening means Gil and will not be described in detail.

The important discovery has been made that the introduction of the second, more gradual reverse curve to the tortuous nail bending groove enables the nailable structural member ill to be constructed so that the member when loaded will develop maximum strength and stiffness and will 10 not twist. In the following discussion, it will be assumed that the load is uniformly distributed over the area of the flanges and that the load is applied vertically-that is, in a direction parallel to axis y-y in Figure 1, unless otherwise stated.

The section properties of a structural member are always figured about coordinate axes. These coordinate axes are two axes which intersect each other at and which are located in a plane normal to the length or longitudinal axis of the beam. Coordinate axes are axes of the area of cross-section of the beam. Axes :r:r and y-y are coordinate axes for the section of the beam of Figure l intersecting at point 0.

For a structural member to develop maximum strength and stability, coordinate axes :rx and y-y should be gravity axes, should be principal axes and should be axes of the section outline. For axis .rx to be a gravity axis, the static moment about a:a: must equal zero, or expressed mathematically fydA=0. In other words, the area A, the area of the cross-section, would balance on a knife edge along axis x:z:. Similarly, for axis yy to be a gravity axis, the static moment about y-y must equal zero or fxdA=0. The area A would balance now on a knife edge along axis y-y.

The axes zcx and yy may be gravity axes without being principal axes and may be principal axes without being gravity axes. For axes ar-r or y-y to be principal axes, the product of inertia must equal zero or fatydA=0. By inspection of Figure 1 it can be seen that if axis ac-zc is a principal axis, it is the major axis or a minor axis, depending on whether the moment of inertia about axis .ra:, which may be expressed as .iy dA, is greater than or less than the moment of inertia about axis y-y expressed as fzc dA. If axis ar-ac is the major axis, then axis y-y is the minor axis and fy dA is greater than fx dA.

For members having an I-shape such as is shown in Figure 1 and which are used as beams, the greatest bending load is applied against the flanges, and it is important that the bending load be applied about the principal axis that is the major axis, for the beam is stiffer about the major axis. If the axis of bending is not a principal axis, some of the bending force or load will produce twist. It also is desirable in beams that the major axis be parallel to the outside faces of the flanges and midway between them so that axis IZ-.,'-'; is a major axis. In columns, it may be desirable to have the greatest stiffness about axis y-y so that axis y-y is the major axis. In a loaded beam, the area above the axis about which bending is applied is under compression, and the area below this axis is under tension. If this axis-aXis x-x-is not exactly midway between the outer faces of the flanges, then the flange farther from this axis will be overstressed before the full allowable stress is developed in the other nearer flange. The beam cannot be fully loaded. If the major axis about which the bending load is applied is not parallel to the outer faces of the flanges, then twist will develop.

In addition, the minor axis-axis y-ymust be normal to the outer faces of the flanges or the bending load will develop twist because the center of the load will not be directly above the center of gravity. The center of load is midway between the outer extremities of the flanges, and if the minor axis is a coordinate axis of the outline of the area, then the center of the load is located along a principal axis. If, as previously i to meet the foregoing-requirements. words, the beamcan be arranged so that coor- --plane of zero stress.

. about axis 11 described, the minor axis is a. gravity axis, .the center ofgravity is located along this axis and the beam will have structuralsymmetrythat is,

. there will be no tendency to twist under bending.

It has been discovered that the addition of the second reverse curve enables the nailin 'beam it] In other dinate axes :c-:r and yy are principal axes intersecting at the centroid O of the cross sectional area so that these axes are gravity axes. Additionally, the axis xa:' may be the major axis and the axis yy the minor axis. Axes r:c and y-y are. axes of the outline of the crosssectional areathat is, the major axis :r-ac is parallel to the outer faces of the flanges and midway therebetween and minor axis "gy is midway between the outer edges of-the upper and lower flanges. The polar. axis ez is located along the Accordingly, thebeam develops maximum strength and stability against twisting.

Heretofore, it has been impossible to develop a nailing beam having-tortuous nailing slots along opposite sides that would not tend to-twist when loaded. The prior art nailing beams of this type usually could not carry their maximum 1oadthat is, a load which stressed both flanges equally.

The manner in which addition of the second :reverse curve enables proportioning the beam so that it will provide maximum stability and can so-that-static moment about axis y2/ is zero and the expression fzcdA=O is satisfied. Similarly, axis a:a: is a gravity axis as the static moment the area of the web connecting the flanges as long as the connecting web is symmetrical about both axes.

-Now -assume that the first reverse curve of each nail receiving means is added to the flanges H and 'i2,- the'axis y-y is no longer an axis of gravity. The static moment aboutaxis yy is not zero andthe expression rdA=0 is no longer correct The first reverse curve of thenail-receiving means 28 comprises the curved portions of web portion SI and nail guiding portion 32 extending from point 48 to point 53. This first reverse curved portion of the nail receiving means ..will be hereinafter referredto as curved portion F-|.- The first reverse curved portion of thenail receiving means 29 consists of the curved portions of web portion 33 and of nail guiding portion 35 .extendingto point 16 and is hereinafter referred to as 1 2. The reversed curved portions F-[ and F-2. are symmetrical about axis :c:c but asymmetrical about axis 11-y. While the static moment about axis xx equals zero, the static moment about axis yy is no longer zero andaxis yy is not a gravity axis. Accordingly, axes. a::c and y-y can notbe principal axes intersecting at the centroid or center of gravity of the area of the beam, and the beam when loaded along the upper flanges will tend to twist. The principal axis for point 0 would xx is zero. and the expression fydA=0 issatisfled. This is true regardless of -tain the structural symmetry.

-be displaced and the principal minor axis for the area through the center of gravity would'be to the right so that if the flanges were equally loaded, the center of the load would be to the left of the minor axis. This is especially pronounced when thenail receiving means comprises walls spaced apart to provide a nail receiving slot. This spacing apart of the walls accentuates the unbalance or tendency of the beam to twist under load.

The areas of the second reverse curved portions 8-! and 8-2 are proportioned relative to the respective areas of F-l and F-2 so as to bring the area of the beam back into balance and so as to bring the static moment about axis yy back to zero whereby axes x-x and y-y are principal axes intersecting at the centroid of the crosssectional area of the beam. In this one piece beam, this can only be done if radius 58 is longer than radiusfld. If radius 58 equalled radius 54, then web portion 35 would be to the left of its position shown and would not be symmetrical about axis y-y.

. As the cross-sectional area of the member H1,

except for the nail receiving and bending portions, is symmetrical about axis yy, the member when used as a beam and uniformly loaded only along the upper flange will not tend to twist if the two nail receiving and bending means are arranged so. that these means together main- With the area, except for 28 and 253,- being symmetrical about axis yy, it is believed obvious that flange l5 must be equal to flange l 6 and flange 2! must be equal to flange 22 and that axis x:c is parallel to the outer surfacesof the flanges. Usually with structural members, and especially columns, some load is directed against the side of the member. This load will cause twist if the axis 91-02 is not midway between the flanges H and i2. Accordingly, the member preferably should 7 be structurally symmetrical about axis ac-m with axis .r-a: being midway between the outer surfaces of the flanges so as to reduce the bracing required.

As an illustration, the structural member of Figure 1 having the previously described characteristics can be produced by using, for example, 18 gauge steel and by having radii 5|, 5E, 13 and H each equal to .221 inch and by having radii 58 and 80 each equal to .540 inch. With this particular arrangement, the distance between center 59 and the inner surface of web portion 3! equals .186 inch with the width of slot 33 equal to .70 inch.

Referring more particularly to Figure 4 which a is an end view of a structural member embodying 7 equally outwardly from the coordinate axis yy.

Flanges I93 and 196 are coplanar and extend equally outwardly from axis yy. Adjacent the pair of flanges I02 and H15, there is a nail receiving and bending means 39. There is a similarnail receiving and bending means H0 adjacent flanges I 03 and. I06. The nail receiving and bending means I09 includes a web portion I II and a parallel, nail guiding or web portion II2 adapted to receive and bend a nail driven therebetween. The parallel web portions III and I I2 are spaced apart and define an elongated nail receiving slot or groove II I having a constant width throughout its length. The nail receiving and bending means I III includes a web portion IIB and a parallel, nail guiding or web portion II1 constructed and arranged to define therebetween an elongated tortuous nailing groove H8 at a constant width throughout its length. The web portions III and H1 are connected together by a flat web portion lie which is part of the web I01. The web portions H2 and IIS also are connected together by a fiat web portion I20 which is part of the channel web I06. The structural member of Figure 4 has substantially an I-shape. The flanges I02 and I05 together with the nail receiving and bending means I09 constitute a T-shape as do the flanges I03 and I06 taken with the nail receiving and bending means I I0. These two T-shapes extend along opposite sides of the member with the legs of the Ts being directed inwardly toward each other. The two T-shapes are joined by web means which in this structural member is made u of the web portions H9 and I20.

As shown, axes .r-a: and y-y are coordinate, mutually perpendicular axes of the cross-sectional area of the elongated structural member. These axes are located in a plane normal to the longitudinal axis of the member and intersect at point 0. As will become clear from the following description, all of the various structural members are arranged and proportioned in a certain manner relative to a pair of coordinate axes. There is a similarity of the various members to the coordinate axes of each member. To simplify this relationship, the coordinate axes for each structural member will be referred to as axes a:ar and yy. Each pair of coordinate axes intersect at a point, and this point of intersection is designated as point 0.

Referring to Figure 4, the flanges I02 and I05 are symmetrical about axis 11-4 as are flanges I03 and I06. The web portions H9 and I20 also are symmetrical about axis y-y. The cross-sectional area of the entire structural member except for the cross-sectional area of the two nail receiving and bending means I09 and I I is symmetrical about axis yy. The cross-sectional area of flanges I and I02 is symmetrical with the cross-sectional area of flanges I03 and I00 about axis x-x. The two flange portions H9 and I20 are also symmetrical about axis ac-x. Accordingly, the cross-sectional area of the sectional member, except for the cross-sectional area of the two nail receiving and bending means I09 and H0, is symmetrical about axis x--ac. Except for the nail receiving and bending means, the structural member is symmetrical about both axes so that axes .r-x and y'y are principal axes intersecting at the center of gravity for the crosssectional area of the beam if the area of the two nail receiving and bending means is excluded. As will be more fully hereinafter described, the two nail receiving and bending means are arranged so that the axes a:-:r and yy are principal axes intersecting at the center of gravity of the structural member.

It will be noted that despite the fact that the flanges and fiat web portions are symmetrical about both axes, the cross-sectional area of the structural member is asymmetrical about axis :c-a: and is asymmetrical about axis y-y. The two nail receiving and bending means and, therefore, the entire beam are anti-symmetrical. In other words, if that portion of the cross-sectional area below axis :c-.r: is rotated through about point 0, the boundaries of the area of the rotated portion will coincide with the boundaries of the area of the portion above axis :c--:c. This is of particular importance because as will be more fully hereinafter described, the two channel members I00 and IOI are identical. When they are arranged in back-to-back relationship, one of the members is turned upside down relative to the other. The corrugated web portion H6 is identical with the corrugated web portion II I, and the corrugated web portions H2 and III are identical.

In each of the nail receiving means I09 and I I0, the parallel web portions are curved or corrugated'through two reverse curves or two corrugations so that the axis of each nail receiving groove curves in a particular manner. At least a portion of the web portions defining each nail receiving means are curved to provide means for bending a nail driven therebetween. The longitudinal axis I 22 of the nail receiving and bending slot H4 is located midway between the opposed inner surfaces of the parallel web portions III and H2. The web portion III is integrally joined to the flange I05 and at their juncture the metal at I23 is curved about the center I24. Similarly, the web portion I I2 is integrally joined to the flange I 02, and at their juncture the metal I25 is curved about center I20. Centers I24 and I26 are equally and oppositely spaced from axis 11-11 and are located along a line I21 which is normal to axis y-y. The portions of curved metal I23 and I25 define therebetween an entrance throat I29, and this throat is symmetrical about axis y-y. Preferably, the throat has the diverging walls as shown, so that the point of a nail will be guided into the nail receiving slot II I. Starting at line I21, the metal of both web portions III and H2 is curved about the center I30 disposed on one side of, or to the left of, axis yy so that the axis I22, starting at point I3I where axis I22 coincides with and is tangent to axis y-y, curves to point I34. The radius of curvature indicated by line I35 is relatively quite small. Web portions III and H2 are next curved through an arc about center I36 disposed on the opposite or right hand side of axis y-y so that axis II2 curves from point I34 away from axis y-y and then back toward axis 11-11 to a point I 31. The radius of curvature about axis I35 is indicated by line I38. Point I34 is the point at which a line drawn between centers I30 and I 35 would intersect center line I22. The web and nail guiding portions III and H2 are next curved about center I 30 disposed on said one side or left side of axis yy. The axis I22 is curved from point I31 across axis y--y to said opposite or right hand side of axis y-y and then back toward axis yy to point MI through a relatively large radius of curvature indicated by line I 22. The point I31 is the point at which a line drawn from center I20 to center I36 intersects axis I22. The web portions H2 and III are finally curved about point I43 to join web portions HM and I01. The axis I22 is curved from point IQI about center I 43 to point I 44 which point is on axis 2, -1 and which point is located along a horizontal line drawn from center I 43. The radius of curvature of this final portion of axis I22 is :zrelatively small andis indicated by :line, I45. :tPoint- I43 is a point at'which a line drawn from center we to centerldii intersects'the-axis I22. Thus, that portion of axis I22 which extends from point I33 to point I31 is bent or curved through a single reverse curve, and the remaining length of axis I22 which extends from point I3? to point Idd is curved through a second relatively larger and more gradual reverse curve. It is essential that radius I42 be longer than radius I38.

As previously pointed out, the nail receiving and bending means I I is anti-symmetrical relative to the nail receiving and bending means I09.

' This in turn meansthat there are definite fixed relationships between the various portions of the nail receiving and bending means H9 and the corresponding portions of the nail receiving and bending means I09. The nail bending Web portion H6 is integrally joined to flange I63, and at their juncture I4? the metal is curved about center use which is to the right and on said opposite side of axis yy. Similarly, the web portion I I? is integrally joined to the flange I and the metal at their juncture I49 is curved about center I59 which is on the left or on said one side of axis yy. Centers Hi8 and I50 are equally oppositely spaced from axis y-y and are also equally spaced inwardly from the outer face of coplanar flanges I63-and I06. The metal at m and I49 define therebetween a nail entering and guiding throat IEI which is symmetrical about axis y--y; The metal of web portions H6 and HT, starting at line I52 which is a line drawn between centers I48 and I50, is curved about a center I53 disposed on the right side of axis y--y. The axis I54 of the nail receiving and bending slot H3 starting at point I55 curves toward the right and away from axis y-y to point I555, and the relatively small radius of curvature is indicated byline IE'EI. The centers I53 and I30 are equally oppositely spaced from axis y-y. The axis I54 of the nail receiving slot or groove is tangent to axis yy at point I55. The web portions IIii.and II! are next curved about a center i553 disposed on the left side of axis yy so that axis Its curves from point I58 away from and then back toward axis yy to point I60 through a radius of curvature indicated by line itI. The center I59 and the ,center I36 are equally and oppositely spaced from axis yy. The point 1% is that point at which a line drawn between centers I59 and I53 intersects axis I54. Thus, axis I54 curves from point I55 away from and to the right of axis y-y and then back toward axis y-y through a single reverse curve. The web portions III; and II! are next curved about center I62 disposed to the right of axis y'y. The axis IE4 is curved from point I80 across axis y-y to the left of axis y-y and then back toward axis yy to point I63 through a relatively long radius indicated by line IE4. The point I60 is the point at which a line drawn between centers I59 and I62 intersects axis I54. The last or final portion of the web portions IIG and Hi are curved about center I65 so that ax I54 curves from point I63 about center I55 to point I67 at which point the axis I 54 coincides with and is tangent to axis yy. The radius of curvature of this last or final portion of axis I54 is indicated by line I68. Thus, that portion of axis iBd which extends from point I55 to point I59 is bent or curved through a reverse curve, and the remaining length of axis Ifidwhich extends I frompoint I60 topoint I61 isbent through a :second reverse curve.

The radius of curvature :Ifi' is equal to the radius of curvature i 42 and is longer thanthe radius of curvature It I.

- The addition of the second corrugation or second reverse curve greatly increases the ability of the member to retain a nail driven into the I repeated at this time.

nail receiving slot, particularly when thenail is subjected to a live load. The nail is securely retained when subjected to live load for the reasons pointed out in connection with the structural member shown in figure 1 and will not be The second reverse curve is larger than the first reverse curve so that as the nail has been relatively sharply bent by-the first reversed curve portion, it is then more gradually bent by the second reverse curve portion. As the work-hardened nail is moregradually bent in t- 2 second reverse curved portion, the forces required to confine the nail beingbent .by either reverse curved portion are more nearly equal and the structural member may be made from relatively thinner metal.

The two channel-members It? and IilI may be vfastened together by any suitable means and may be fastened together at spaced points throughout their length by means of fastening elements substantially as shown and described in connection with the structural member of Figure 1.

With the structural member of Figure 4, like the structural member. of Figure l, the important d scovery has been made that the introduction or" the second more gradual reverse curve to the tortuous nail bending groove enables thevarious portions of the nailable structural member to be constructed and arranged so that the member will develop maximum strength and stiffness and will not tend to twist.

The axes -33 and y-y are coor inate axes of the area of cross-section of the structural member, and these axes inter- .sect at point .O. The addition of the second reverse curve that is relatively larger and more r .gradualthan the first reverse curve to, each of 1 the nail bending means I69 and II!) permits the willnot tend to twist.

..load will be concentrated along axis y-y. This load will produce twist if the axis g!y is not a gravity axis so that the center of gravity lies alonga point on the axis and will develop twist if axis y.-1 is not a principal axis that is midway between and normal to the two pairs or flanges I82, I and I83, I96. This last is merely another way of stating that axis c;x must be parallel to the outer surfaces of the flanges coordinate axes are always perpendicular to each other. If the structural member is to be used as a column I and if a load is uniformly applied against, the

side of the structural member, then this load or ,force will be centered on axis a:-a:. This load will tend to twist the column if axis 53-41: is not a principal gravity axis equally spaced from the outer surfaces of the flanges. Accordingly, it is preferable that the axis :r-:c beequally spaced from the outer surfaces of the flanges for, regardess of where the structural member is used in a building framework, some force will be applied to the side of the structural member. Accordingly, if axis arr-c: is not a principal gravity axis midway between the outer surfaces of the flanges, considerable bracing will be required. For axis .r-a: to be a gravity axis, the static moment about axis x-x must equal or expressed mathematically fycZA=0. In other words, the area A, the area of the cross-section, would balance on a knife edge along axis :c-x. Similarly, for axis y-y to be a gravity axis, the static moment about axis yy must equal 0 or fccdA=0. The area A would then balance on a knife edge along axis 11-11. For axes :c-m and y-y to be principal axes, the product of inertia must equal 0, or expressed mathematically, fasydA=0.

As previously described, it has been discovered that the presence of the second reverse curve enables the nailing beam shown in Figure 4 to meet the foregoing requirements. This can be done only because the second reverse curve, particularly that portion between points l3! and I, is larger than the first reverse curve, particularly that portion between point I34 and I31. In other words, the radius I42 must be longer than the radius I313. While nailable structural members of general I-shape and having reverse curves similar to the first reverse curves have been used heretofore, these structural members have not been stable and have tended to twist. The manner in which the addition of a second reverse curve enables proportioning the beam so that it will provide maximum stability may be more readily explained by first considering a structural member which does not have any nail bending and holding means. Assumin that the structural member of Figure 4 does not contain the nail holding and bending means IE9 and I Ill, it is believed clear from the foregoing description that the axes :c-zc and y-y would be principal axes intersecting at the center of gravity 0. If the first reverse curve is added to each nail receiving and bending means, the axis y'y will be a gravity axis but will not be a principal axis. This follows from the fact that the first reverse curve of the nail bendin means I 69 adds a larger negative (my) value than it does a positive (my) value. Obviously, the area of metal on the left of axis yy is greater than the area of metal on the right of axis y--y. The first reverse curve of the nail bending means III] which is antisymmetrical to the first reverse curve of the nail bending means I59 also adds a greater negative (my) value than positive (ary) value so that the product of inertia no longer equals 0 and the expression frcycZA=0 is no longer satisfied. In other words, the principal axes for the point 0 will be rotated anti-clockwise from the position shown in Figure 4 and the axis y-y will not be normal to the flanges. Thus, when a load is uniformly applied against the flanges I02 and let, the center of this load will not coincide with axis y-y and the load will tend to twist the beam. For the same reason, a load applied against either side of the beam will also tend to twist the beam. By the addition of the second reverse curve, it is possible to have the axes a:-:r and 1 -41 principal axes intersecting at the center of gravity. The area of the second reverse curve portion of webs III and H2 must add as much positive (03y) value as the first reverse curved portion of web portions IIS and II! adds negative (22y) value. The second reverse curved portion of the nail holding and bending means H9 must similarly balance the first reverse curved portion. of the nail holding and bending means I 09. To do this, the area of the second reverse curved portion must be larger than the area of the first reverse curved portion because the distance of the center of gravity of the second reverse curved portion from axis 03-90 is less than the distance of the center of gravity of the first reverse curved por tion from axis a:-:r. Therefore, to satisfy the expression frvydA=0, the second reverse curved portions must have a relatively greater area and be curved more gradually than the first reverse curved portion-s. In view of the foregoing, and remembering that the cross-sectional area of the structural-member is symmetrical about both axes except for the nail bending means m9 and H6, the nail bending means I09 and the nail bending means I I ii must be carefully arranged so that together they satisfy the three expressions fttda=0, fydA=0, and fzcydA=O, if axes .r-a: and y-y are to be principal axes intersecting at the center of gravity. If this is done, and with the axes .ra: and yy being principal gravity axes for the cross-sectional area except for the nail holding and bending means 99 and II 0, then the nail holding and bending means will not shift the principal gravity axes for the entire cross-sectional area, and these axes will be the principal gravity axes for the entire member whereby the member will have the greatest structural stability.

The structural member of Figure 4 is substantially an I-shape and the structural member is so constructed and arranged that the axes x-a: and yy are principal gravity axes with the flanges I82 and I85 and I53 and N35 being symmetrical about the yy axis and with the axis .r-x parallel to the outer surfaces of these flanges. Where the structural member is to be used as a beam, it is usually desirable to have axis x--ac the major axis because the beam is usually uniformly loaded along the top flanges and the beam has the greatest stiffness about axis w x. Under certain conditions, it may be desirable to have the beam stiffer about axis yy than axis :v-.'n. This may be true if the structural member is used as a column, but under certain conditions also may be true when the structural member is used as a beam. Accordingly, the flanges and the connecting webs may be proportioned so that axis y-y is the major axis. Where the structural member is used as a beam that is uniformly loaded along the flanges I 62 and me, the load may be considered as a single force applied along axis yy. If this is the case, axis a:-:c must be parallel to the outer surfaces of the flanges but may be nearer one pair of flanges than the other pair without the load tending to twist the member. In practice, beams are nearly always subjected to some lateral force tending to bend the beam about axis y y. If axis a::r is not exactly midway between the outer surfaces of the flanges, then this lateral force can not be considered as a force directed along axis :cr and will tend to twist the beam. Thus, if axis a:a: is not exactly midway between the flanges, it is necessary to brace the member quite extensively when it is used in a building framework. Accordingly, it is preferable for the axis :1:-a: to be midway between the outer surfaces of the two pairs of coplanar flanges.

As has been previously pointed out, the struc tural member of Figure 4 is made up of two identical channel members Iilll and II, with one channel member being reversed relative to the other. With this arrangement, two identical 19- channels can be used to ..al:.e the member and the of tools for producing the two shapes is much less than it WOllid. be if the channel members not the same. It cost were ignored, the channel members its and Ill! could be made so that the nail bending portions instead of being anti-symmetrical would be symmetrical. It is to be noted that if this were the case, then the first reverse curve would be rotated about axis y-y through 130 so that the centers 55% and 35 would been the same side of the axis gy. This does not change the fact that the addition of the first reverse curves would change conditions so that axes ."c--x and g;-y would not be principal gravit r axes. The condition produced would be substantially the same as is produced in a structural member like that shown in ure 1 by the addition of the first reverse curves.

Referring more particularly to Figure which shows a structural member also embodying the principles of the present invention, this structural member is made up of a pair of channel members Ill and H2 fastened together in backto-back relationship. The channel member iii comprises a web ['33 having flanges I'M and H5 disposed along the opposite sides thereof. The channel member 172 also includes a pair of flanges I16 and IT! joined by a web 179. The axes :1:-;n and yy are coordinate mutually perpendicular axes for the cross-sectional area of the member and these axes intersect at point 0. Axes :c-m and y-y are located in a plane normal to the longitudinal axis of the structural memher. As will be more fully hereinafter described, the cross-sectional area of this structural member is symmetrical about axis 56-1: and aesymmetrical about axis y-y. The web H3 includes a flat portion 18! adjacent flange H5. Similarly, the channel web H9 includes flat portions E83 and I84. Flat portions I89 and I83 are parallel and spaced apart to define a relatively short straight nailing groove hi5 therebetween. The flat portions IE! and I84 are parallel and spaced apart to define a relatively short straight nailing groove or slot i8! therebetween. The metal at the juncture of web I13 and flange ill is curved about center 88. The metal at the juncture of web [89 and flange H6 is similarly curved about center 89 so that these two curved portions of metal define an entering throat 190. The throat His and the slot 186 are symmetrical about axis y-y as are the flanges I'M and H6. The metal at the juncture of web H3 and flange lit is curved about the center I91 and the metal at the juncture of web 79 and flange i1? is curved about the center I92. These two portions oi curved metal define a nail guiding and entering throat (9d, and throat E94 and the relatively short straight slot i8! are symmetrical about the axis y-y. The nail bending and holding means which extends from line I95 to 195 comprises the parallel curved web portions I97 and 98. It is believed obvious upon inspection that the crosssectional area of the structural member except for the crosssectional area of the nail bending means between lines I95 and HE is symmetrical about the axis y-y. This nail bending means is not symmetrical about axis y-y.

In the structural member of Figure 5, there is no flat web portion or portions joining the inner edges of the web portions which define the nail bending means. There is an overlapping of the nail bending means. The web portions 19? and 198 are parallel and define therebctween a tertuous nail receiving passage 20!} having an axis 20!. These Web portions are bent so that the axis 281, starting at point 283 which coincides with axis y-y, curves to the right about center 2%. The radius of curvature is indicated by line 285 and is relatively short. The axis 261 next curves from point 255 about center 26'. and curves away from axis yy and then back toward y-y to point 298. Thus, the nail bending groove 23% is curved through a first reverse curve and a nail driven into the nail receiving groove through the entering throat lQfl is curved first to the right and then back toward the left. The axis 261 is next curved from point 283 about center 269 to point Qiii. The radius of curvature about center 201 is indicated by line ?.H and is relatively short. The radius of curvature about center 299 is indicated by line 2i3 and is relatively long. From point 219, the axis as: curves about center 2l5 to point 2H5, and the radius of curvature is indicated by line 211. The radius of curvature 2i? and the radius of curvatur 2 H are equal and centers Edi and H5 are disposed on the left side of axis yy. From point tilt, the axis 201 is curved about center EH9 to point 229 which coincides with axis y-y. he portion of the nail bending groove 239 which extends from point 229 to 258 constitutes the first reverse curve for a nail driven into the nailing groove through the entering throat I9 3. The nailing groove extending from point 2 i s to point 2st constitutes the second reverse curve for both of the first reverse curves. If a nail is driven through the throat res, the nail is bent through a first reverse curve and then as the end of the nail travels through the nail bending groove and beyond the point 293, it is bent through a second reverse curve. Similarly, if a nail is driven through throat its into the nail bending slot 280, the nail is bent through a first reverse curve and then as it moves past point 2H3, it is bent through a second reverse curve. Thus, the por tion of the nail bending means between points 2 l9 and 288 constitutes part of the nail bending means adjacent flanges lid and iPB and also con stitutes part of the nail bending means adjacent flanges H5 and ill so that this portion or" the nail bending means serves a dual function. lfifhen a nail is driven into the nailable member through either throat, the point or leading end extends beyond axis ;r--a: so that the nail is bent through two reverse curves and is securely held in place when subjected to a live load as described in connection with Figure l.

The addition of the second reverse curve to the nail bending means enables making the structural member of Figure 5 structurally stable so that it will not tend to twist. This can only be done if radius H3 is longer than radius 2H. For the structural member to be stable when loaded only on the top, axis 11-11 must be principal gravity axis midway between the flange extremities, axis :r-x must be parallel to the outer surfaces of the two pairs of coplanar flanges and axis a2-x must be a principal gravity axis. Preferably, axis a:-:c is also midway between the outer surfaces of the two pairs of flanges so that point 0 is the center of gravity for the crosssectional area of the member and so that the member will be stable and not tend to twist when a uniform load is applied against the side of the member. omitting the nail bending means between lines I and H38, it is believed clear from inspection that the cross-sectional area is symmetrical about coordinate axis y-y and, there fore, axis yy is a principal axis and coordinate axis :r-:r is parallel to the flanges. Further, axis :v-:c is a principal gravity axis midway between the outer surfaces of the two pairs of flanges.

As described in connection with Figure 1, if the first reverse curve adjacent each pair of flanges is added, axis yy and axis a:-a: are no longer principal gravity axes and the member is not stable. Axes rx and 11-21 are no longer principal axes because they are not principal axes for the metal of the two reverse curved portions. The addition of the second, larger reverse curve counteracts the unbalance produced by the first reverse curve so that coordinate axes :c-a: and yy are again principal gravity axes. For this condition to be true, the first and second reverse curved portions must be so proportioned that axes rx and 11-11, are principal gravity axes for these curved portions when taken together. If axes :r-zv and yy are principal gravity axes for the curved portions, that is the nail bending means, then if axes :r-a: and y-y are principal gravity axes for the remainder of the cross-sec tional area, these axes are principal gravity axes for the member.

Referring more particularly to Figure 6 which illustrates another embodiment of the present invention, the nailable member shown in this figure is formed from a single piece of sheet metal. This nailable member includes a pair of coplanar flanges 2E5 and 256' and a second pair of coplanar flanges 2H and 2l8. The two pairs of flanges are joined by the parallel webs 2m and 220'. This member may be formed out of a single piece of sheet metal in any suitable manner and may be formed by cold rolling steel strip of sifltable width. The flange 215 comprises two layers 22! and 222 of metal while the flange 216 comprises two layers 223 and 224 of sheet metal. The flanges H5 and 2H5 are symmetrical about axis y-y and extend outwardly and equally in opposite directions from axis y-y. Flanges 2H and 218 are made up of a single thickness of sheet metal, and each flange terminates in an outer free edge 225 and 226, respectively. The flanges 2i? and 2| 5' are joined by the web H9, and, more particularly, web 2 i9 is integrally joined to the inner layer of metal 22 Similarly, the web 220 is integrally joined to the inner layer of metal 223 of flange 2M3. The two webs H5 and 22% are parallel and spaced apart to define a nail receiving and bending slot therebetween similar to the nail receiving and bending slot shown and described in connection with the nailable structural member of Figure 5. The nail bending means extends from line 229 to line 238. The web portions between these lines define the nail receiving passage or slot 2M having a longitudinal axis 232. The axis 232 is curved exactly the same as axis 23! of the nail receiving slot 238 in Figure 5 and, therefore, will not be described in detail.

It will be noted that the axes :c-a: and y-y are mutually perpendicular coordinate axes for the cross-sectional area of the member and that this area is neither symmetrical about either axis, nor is it anti-symmetrical. The cross-sectional area of the member, except for the cross-sectional area of the nail bending means, is symmetrical about axis 'Jy but asymmetrical about axis :c-x although both axes are principal gravity axes as will be described hereinafter. The metal 234 at the juncture between flange layer 22! and web 219' is curved as is the metal 235 at the juncture of web 220' with the inner layer 223 of flange 2E6. The metal at 235 and at 234 defines an entering throat 236 that is symmetrical about axis y-y. The upper layers of flange metal 222 and 224 where they join are preferably depressed to form a groove 23". which aids in guiding the point of a nail into the throat 236. The metal at the bottom of the groove may be thinned as shown to facilitate piercing of the metal by a nail point. The metal at 240 at the juncture of web 2H9 and flange 2 I1 is curved as is the metal at 24! at the juncture of web 220' and flange 226. The metal at 24!! and 24! defines an entering throat 242 which is symmetrical about y-y. The two flanges 2H and 218 extend outwardly in opposite directions from axis 1, -y, and these two flanges are symmetrical about axis 'J-il as are the two flanges 2l5' and 216'. The pair of flanges 2H and 218 are not symmetrical about axis 93-47 with the pair of flanges 2 l5 and 256. As more fully pointed out in connection with Figure 5, the nail bending means between lines 229 and 230 is curved in such a manner that axes yy and :r-r are principal gravity axes for the cross-sectional area of this portion of the nailing beam. With the flanges being symmetrical about axis y-y, axis 31-11 is a principal axis for the nailable member, but it does not necessarily follow that axis :v-m is a principal gravity axis for the nailable member. For axis xx to be a principal gravity axis, certain conditions must be met. First, the crosssectional area of the two flanges 2H and 2| 8 when multiplied by its average distance from the axis xar must be balanced or be equal to the area of the two flanges H5 and 2l6' multiplied by its average distance from axis .r-r. If this be true, then the static moment about axis x;r=0 and the expression fzcdA=0 is satisfied. With the flanges properly spaced from axis ac-x and of the correct relative size, then axis zr-ar is a gravity axis. As previously stated, for axis 33-1 and axis yy to be principal axes, the prod cut of inertia must equal 0 or fazydA=0t It will be noted that the area of flange 2!? is at a slightly greater distance from axis :c-x than is the area of flange 2E5. While the flange M5 is made up of two layers of metal and flange 2 I I is made up of a single layer of metal, the flange 2| 1' may not be quite twice the width of flange 215 as a result of this slight difference in distance from axis a:-a:. In addition, and in order to have a completely stable nailable structural member that will develop maximum strength, the outer surface of the two flanges 2H and H3 should be the same distance from axis xx as is the outer surface of flanges 2E5 and 2%. Accordingly, axes :1:--:c and y-y are principal axes for the nailable member of Figure 6. It is to be noted that for the reasons set forth in connection with the other nailable members, if axes zr-rc and y-y were not principal gravity axes for the nail bending means located between lines 229 and 239, then these axes would not be principal grav ity axes for the beam despite the fact that the flan es are arranged as described.

The structural member of Figure 6 is particularly intended where web stiffness is not too important. It will be noted that neither web 219' nor 22!! includes a flat web portion. If the entire web is corrugated or curved as shown, web stiffness is sacrificed. Web stiffness is particularly important for the deeper nailable members such as is shown in Figures 1 and 4.

In each of the structural members previously described in detail, axes -y and :r-sc are coordinate axes located in a plane normal to 23 the length of the elongated member. The crosssectional area of each of these members may be divided into two parts-the first part or portion being the area of the metal exclusive of the two nail bending means. This portion or" the area will hereinafter be referred to as area A. The second portion of the cross-sectional area is the area of the metal of the two nail bending means. This portion of the area will hereinafter be referred to as area B. Now considering more particularly area A, it is believed clear that the area A is symmetrical about axis y-y so that axis tr-y is a principal gravity axis for area A. In addition, if the area A is symmetrical about axis y-y, the two pairs of coplanar flange portions are located in planes normal to axis y--y or in other words, axis :r-r is parallel to the outer surfaces of the two pairs of coplanar flanges. It is also believed clear that axis :c-sc

is a principal gravity axis for area A.

In the nail bending means of some of the structural members, the parallel web portions which define the nail bending groove or slot are curved about three centers whereas in others these web portions are curved about four centers. In each of the nail bending means and starting at the outer end of the nail receiving slot, the axis of the slot curves from a point tangent to axis y-y away from and to one side of axis y-y through a first are about a center located on the one side of the axis y-y. The axis of the nail receiving slot then curves further away from axis 11-11 and then back toward but not to axis -y through a second are about a center located on the opposite side of axis y-y. The axis of the nail receiving slot then curves to and across axis y-y and then away from and thereafter back toward axis y-y through a third are about a center located on the one side of axis 111-11. The three radii just mentioned are so proportioned that the two nail bending means together are arranged such that axes .r-zr and y--y are principal gravity axes for the two nail bending means. These axes are not principal gravity axes for only one of the nail bending means. In fact, axis y'y is not a principal axis for one of the nail bending means but is only a principal axis for the two nail bending means.

Thus, for area B, the addition of the third relatively larger curve to each of the nail bending means enables the nail bending means to be arranged so that axes :zr-rc and y-y are principal gravity axes for the two nail bending means.

It is only by the addition of the second relatively larger reverse curve that it is possible to have axes :r-:c and 'J-g principal gravity axes for area B. In each of the structural members, if this relatively larger curve were eliminated, it would be impossible to arrange the nail bending means in such a manner that axes :c-a: and y-y would be principal gravity axes.

As axes r-a: and y-y are principal gravity axes for area B and area A, axes :r-at and y-y are principal gravity axes for the entire area.

Area A is symmetrical about axis y-y with axis x;-m parallel to the outer surfaces of the two pairs of coplanar flange portions and, thus, the structural member will have greatly increased stability and will not tend to twist when uniformly loaded along the outer surface of either pair of coplanar flange portions. In addition, the preferred form of each structural member is shown with axis x-zr midway between the outer surfaces of the two pairs of coplanar flange portions So that each one of the structural members also has lateral stability. A load uniformly applied against either side or the structural member will not cause twisting and lateral bracing can be greatly reduced or eliminated. As structural members which are used as beams in a framework are usually subjected to some lateral loads, it is preferable that the principal gravity axis a:-:r be midway between the outer surfaces of the two pairs of coplanar flange portions so that the beam will not have to be extensively braced.

The nailable structural member of Figure 5 is shown with parallel web portions interposed between the nail bending means and each pair of coplanar flange portions. These parallel web portions are symmetrical about axis 11-y and are symmetrical about axis ;c:r. Similar web poi-- tions may be added to the other structural members between the nail bending means and the corresponding flange portions.

I claim:

1. An elongated nailable structural member comprising a first pair of flange portions having coplanar outer surfaces, a second pair of flange portions having coplanar outer surfaces, the flange portions of each pair of flange portions being perpendicular to and oppositely disposed with respect to one axis of a pair of mutually perpendicular intersecting axes and the first and second pair of flange portions being parallel to and oppositely disposed with respect to the other axis of the pair of axes, a nail receiving slot defining means joined to each pair of flange portions for receiving and bending a driven nail, web

means joining the nail receiving slot defining means, the portions of the flange portions and the nail receiving slot defining means at the juncture of the nail receiving slot defining means and the respective pair of flange portions defining a nail entry throat symmetrical about the one axis, each slot defining means including a pair of nail guiding portions, the nail guiding portions of each slot defining means being spaced apart to define therebetween an elongated nail receiving slot extending inwardly from the entry throat, the nail guiding portions being curved so that the center line of the slot starting at a point tangent to the one axis extends inwardly and curvilinearly first to one side of and away from the one axis through a first are and then farther away from and then toward the one axis through a second arc and thereafter across and away from and then back toward the one axis through a third are having a longer radius than the second arc whereby a nail driven through an entry throat and into the respective nail-receiving slot is bent through two reverse curves of progressively greater radius by the curved nail guiding portions of the slot defining means, the axes being principal gravity axes for the area of cross-section of the nailable member exclusive of the curved nail guiding portions of the slot defining means, the relative proportionrnent of the cross-sectional areas of the curved nail guiding portions of the slot defining means establishing the relations J:cdA=il, f'JdA O and fzcydA=0 in which 3 corresponds to the one axis, x corresponds to the other axis and A corresponds to the cross-sectional area of the nailable member, whereby the axes are principal gravity axes for the nailable member.

2. A nailable structural member as defined in claim 1 in which the second axis is midway between the outer surfaces of the first, and second pair of flange portions.

3. "A nailable structural member as defined in claim 1 in which the second axis is midway between the outer surfaces of the first and second pair of flange portions and is the major axis of the area of cross-section of the structural member. e 4. An elongated nailable structural member formed from a single piece of sheet metal comprising a first pair of flange portions having coplanar outer surfaces, a second pair of fiange portions having coplanar outer surfaces, the flange portions of each pair of flange portions being perpendicular to and oppositely disposed with respect to one axis of one pair of mutually perpendioular intersecting axes and the first and second pair of flange portions being parallel to and oppositely disposed with respect to the other axis of the pair of axes, each flange portion including an outer and an inner layer of sheet metal with the outer and inner layers integrally joined at their outer lateral edges, a nail receiving slot defining means adjacent each pair of flange portions for receiving and bending a driven nail, each slot defining means including a web portion joined to the inner layer of one flange portion of the corresponding pair of flange portions and a nail guiding portion joined to the inner layer of the other fiange portion of the same pair of flange portions, the portions of the inner layers of the flange portions and the web and nai1 guiding portions at the juncture of the web portion and the nail guiding portion with the inner layers of the respective pair of flange portions defining a nail entry throat symmetrical about the one axis, the outer layers of each pair of fiange portions being integrally joined and overlying their respective nail entry throat, the web portion and the nail guiding portion of each slot defining means being spaced apart to define therebetween an elongated nail receiving slot extending inwardly from the entry throat, each nail guiding portion terminating in a free edge, a fiat web portion symmetrical about the one axis connecting the web portions of the slot defining means, the web portion and the nail guiding portion of each slot defining means including curved portions so that the centerline of the slot starting at a point tangent to the one axis extends inwardly and curvilinearly first to one side of and away from the one axis through a first arc and then farther away from and then towards the one axis through a second arc and thereafter across and away from and back towards the one axis through a third are of relatively longer radius than the radius of the second arc whereby a nail driven through an entry throat and into the respective nail receiving slot is bent through two reverse curves by the curved portions of the slot defining means, the axes being principal gravity axes for the area of cross-section of the nailable member exclusive of the curved portions of the slot defining means, the relative proportionment of the cross-sectional area of the curved portions of the slot defining means establishing the relations 'edA=0, fydA= and facycZA=0 in which y corresponds to the one axis, :1: corresponds to the other axis and A corresponds to the cross-sectional area of the nailable member, whereby the axes are principal gravity axe-s for the nailable member.

5. A nailable structural member as defined in claim 4 in which the second axis is midway between the outer surfaces of the first and second pair of flange portions.

6. A nailable structural member as defined in claim 4 in which the second axis is midway be- 26 tween the outer surfaces of the first and second pair of flange portions and in which the second axis is the major axis of the area of cross-section of the member.

'7. An elongated nailable structural member comprising a pair of channel members each including a web portion, the channel members being connected in back-to-back relation with the web portions in spaced relationship, a first pair of flange portions having coplanar outer surfaces extending laterally in opposite directions and joined to corresponding ends of the web portions, a second pair of flange portions having coplanar outer surfaces extending laterally in opposite directions and joined to the other ends of the web portions, the flange portions of each pair of flange portions being perpendicular to and oppositely disposed with respect to the one axis or a pair of mutually perpendicular intersecting axes and the first and second pair of flange portions being parallel to and oppositely disposed with respect to the other axis of the pair of axes, the plane of the web portions being parallel to and equally spaced from the one axis and being perpendicular to the second axis, the portions of the flange portions and the web portions at the juncture of the web portions of the channel members with the respective pair of flange portions defining a nail entry throat symmetrical about the one axis, a nail receiving slot defining means adjacent each pair of flange portions for receiving and bending a driven nail, each slot defining means including curved nail guiding portions being spaced apart to define therebetween an elongated nail receiving slot extending inwardly from the respective entry throat, the curved nail guiding portions of each slot defining means being curved so that the center line of the slot starting at a point tangent to the one axis extends inwardly and curvilinearly first to one side of and away from the one axis through a first'arc and then farther away from and then toward the one axis through a second arc and thereafter across and away from and then back toward the one axis through a third are of relatively long radius with respect to the radius of the second arc and finally back to a point tangent to the one axis whereby a nail driven through an entry throat and into th respective nail receiving slot is bent through two reverse curves by the curved portions of the slot defining means, the axes being principal gravity axes for the area of cross-section of the nailable member exclusive of the curved portions of the slot defining means, the relative proportionment of the cross-sectional area of the curved portions of the slot defining means establishing the relations jrdAzO, f' dAzO and fmydAzo in which y corresponds to the one axis, as corresponds to the other axis and A corresponds to the cross-sectional area of the nailable member, whereby the axes are principal gravity axes for the nailable member.

8. A nailable structural member as defined in claim '7 in which the second axis is the major axis of the area of cross-section of the member.

9. An elongated nailable structural member comprising a first pair of flange portions having coplanar outer surfaces, a second pair of flange portions having coplanar outer surfaces, the flange portions of each pair of flange portions being perpendicular to and oppositely disposed with respect to on axis of a pair of mutually perpendicular intersecting axes and the first and second pair of flange portions being parallel to,

27 and oppositely disposed with respect to the other axis of a pair of axes, first web means extending from one flange portion of the first pair of flange portions to one flange portion of the second pair of flange portions, second web means extending from the other flange portion of the first pair of flange portions to the other flange portion of the second pair of flange portions, the portions of the flange portions and the web means at the juncture of the first and second web means with the flange portions of each pair of flange portions defining a nail entry throat symmetrical about the one axis, the web means being spaced apart to define therebetween an elongated nail receiving slot extending inwardly from each entry throat, the web means including nail guiding portions curved so that the center line of the slot starting at a point tangent to the one axis extends inwardly and curvilinearly first to one side of and away from the one axis through a first arc and then farther away from and then toward the other axis through a second arc and thereafter across and away from the one axis to the second axis through a third are of relatively longer radius than the radius of the second arc with the center of the third are being located at a point on the second axis displaced from the one axis, the centerline of the slot then extending curvilinearly from the second axis toward the one axis through a fourth are about said center and then farther away from and then back toward the one axis through a fifth are having a radius less than the radius of the fourth arc and then tangentially to a second point on the one axis through a sixth arc whereby a nail driven through either entry throat into the nail receiving slot is bent through two reverse curves by the nail guiding portions of the web means, the axes being principal gravity axes for the area of crosssection of the nailable members exclusive of the curved nail guiding portions, the relative proportionment of the cross-sectional area of the curvednail guiding portions establishing the relations fydAzfi, fzcdAzo and fxydAzo in which y corresponds to the one axis, 3: corresponds to the other axis and A corresponds to the cross-sectional area of the nailable member, whereby the axes are principal gravity axes for the nailable member.

10. A nailable structural member as defined in claim 9 in which the second axis is midway between the outer surfaces of the first and second pair of flange portions.

11. A nailable structural member as defined in claim 9 in which the second axis is the major axis of the area of cross-section of the member.

12. A structural member as defined in claim 9 in which the flange portions of the first pair of flange portions are similar to the flange portions of the second pair of flange portions.

13. A structural member as defined in claim 9 in which the flange portions of the first pair of flange portions include an outer layer of sheet metal and in inner layer of sheet metal integrally joined along their outer edges, in which the flange portions of the second pair of flange portions each terminate in a free edge, and in a which the first and second pair of flange portions are symmetrical about the one axis.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,900,541 Buelow et al. Mar. '7, 1933 2,457,147 Hall Dec. 28, 1948 2,457,148 Hall et al. Dec. 28, 1948

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