US3168815A

US3168815A - Arched mine gallery support and beam therefor

Info

Publication number: US3168815A
Application number: US834250A
Authority: US
Inventors: Blenkle Erwin; Seiz Rudolf
Original assignee: Bochumer Eisenhuette Heintzmann GmbH and Co KG
Current assignee: Bochumer Eisenhuette Heintzmann GmbH and Co KG
Priority date: 1958-08-16
Filing date: 1959-08-17
Publication date: 1965-02-09
Anticipated expiration: 1982-02-09
Also published as: AT220111B; GB925353A

Description

Feb. 9, 1965 E. BLENKLE ETAL 3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR 5 Sheets-Sheet 1 Filed Aug. 17, 1959 INVENTORS w ee/ml W su Ms W,

Fig. 2

Feb. 9, 1965 BLENKLE ETAL 3,168,315

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5 Sheets-Sheet 2 Feb. 9, 1965 Filed Aug. 17. 1959 E. BLENKLE ETAL 3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR 5 Sheets-Sheet 5 INVENTOR$ H 4 QM Mi '4, M W S ML am Feb. 9, 1965 E. BLENKLE ETAL 3,163,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5 Sheets-Sheet 4 x INVENTOR'S Wi 2w,

1965 E. BLENKLE ETAL 3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5 Sheets-Sheet 5 a INVENTOR5 w W21 Fig. 6 W M WKWM United States Patent 3,168,815 ARCHED MENE GALLERY SUPPORT AND BEAM THEREFGR Erwin Elenkie and Rudolf Seiz, Bochum, Germany, assignors, by mesne assignments, to Bochumer Eisenhutte Heintzmann & C0., Bochum, Germany Filed Aug. 17, 1959, Ser. No. 834,250 r Claims priority, application Austria, Aug. 16, 1953, A 5,735/58 Claims. (Cl. 61-45) For the supports of mine galleries, use is frequently made of trough-shaped support sections in a form after the style of a structural iron, which are connected together to form annular or arch-shaped support frames. With this type of support known as a sliding arch support the mutually congruent sections are placed with their ends co-directionally one inside the other and in the region of the overlap are clamped in such manner that when a determined rock pressure is exceeded they can slide axially in relation to one another, so that the support acquires the desired resilience.

These trough sections usually have a trapezoidal crosssection such that the webs disposed at a distance from one another and diverging towards the flanges are connected by a base part. The webs may be bounded either by substantially plane or curved surfaces so that they enclose between them an aperture angle which is either substantially constant or which decreases towards the flanges. This aperture angle is preferably between about 15 to 45. The base part connecting the spaced apart webs is in most cases of substantially plane construction. However, trough sections are also known which have a base part which is curved concavely towards the flanges and which merges, still with curvature, into the section webs. The shape and dimensions of the flanges, webs and base parts and hence the material distribution over the section cross-section are in most cases so selected that the moments of resistance in the two major axes are approximately equal or at least close to one another in such manner that they do not differ from one another by more than about 50%.

In the known trough-shaped mine support sections the section webs are connected by the section base at their lower edge remote from the section flanges. This section base usually has a wall thickness which is larger than the section webs, since on the bending of the sections and on the longitudinal displacement of the sections under the action of the rock pressure, for example, it is exposed to considerable bending and torsional stresses. The accumulation of material resulting from the reinforced construction of the section base must be equalized by a correspondingly intensive accumulation of material in the region of the section flanges and the upper part of the webs, in order to keep the mass centre approximately at half the section height and to maintain the largest possible moment of resistance in the X-axis. An accumulation of material of this kind in the region of the section flanges has the disadvantage, however, that on the bending of the sections relatively large opening-up forces occur which are a function of the masses disposed in the region of the edge zone, so that the webs have to be made relatively thick and can be given only a relatively slight inclination.

A trough section is also known, which has a curved section base which is dimensioned to be particularly thick and which to reduce the masses disposed in this region is provided with lateral recesses which enclose between them a thick middle rib. Since the recesses are disposed in the region of the transition of the section base to the section on the bending of the sections under the action of the rock pressure and their relative displacement particularly ddhbfii Patented Feb. 9, 1%65 intensive stresses occur, they can be given only limited dimensions, so that in order to obtain a uniform mass distribution the section flanges have to be given a thick construction. Such an accumulation of material in the region of the section flanges, in conjunction with the considerable angle of inclination of the section webs, however, results in considerable openingup forces on the bending of the sections, so that the webs also have to be made very strong.

In comparison with these previously known troughshaped mine support sections, according to the invention an improvement is achieved by disposing the section base at a distance which preferably exceeds its thickness but which is dimensioned to be less than half the section height, above the lower longitudinal edge of the section webs which is remote from the flanges. In these circumstances, it has proved particularly advantageous to make the distance of the section base from the lower web edge approximately equal to onethird to one-sixth of the section height.

In consequence of the fact that in the set of troughshaped mine support sections proposed according to the invention the section webs are connected by the section base, not at their lower end as in the known. sections, but in a middle region disposed preferably below half the web height, the mass centre or centre of gravity is shifted towards the flanges, that is to say in the upward direction. In consequence of this shift of the centre of gravity, the section flanges may be given a considerably lighter construction in comparison with the known forms of section. This reduction of masses in the region of the flanges has the advantage that the opening-up forces occurring on bending and on the relative displacement of the sections is considerably reduced. A particular advantage of the invention, however, is that as a result of the raising of the section base the distance from the section flanges and hence the ettective lever arm of the opening-up forces are considerably reduced, so that the bending stresses occurring in the section webs on the bending of the sections are reduced by a considerable degree in comparison with the previously known forms of sections. Thus, for example, given otherwise identical section construction, by reducing the section flanges and disposing the section base at a distance corresponding approximately to one-quarter to one-fifth of the section height above the lower web edges it is possible to reduce by 60 to the bending stresses occurring on bending in the section webs. The consequence of this is that given the same resistance of the sections to opening up, the section webs can be made considerably thinner, or that given equally thick construction of the webs the sections have a many times higher resistance to opening up. Since the magnitude of the opening-up forces occurring on bending is dependent, not only on the masses, but also on the strength properties in the region of the edge zones and on the aperture angle of the section webs, it is immediately possible to give the section webs a greater inclination or to temper the sections to a considerably higher degree than was possible with the forms of sections known heretofore. In consequence of the fact that the section webs and the section flanges can be made considerably thinner than hitherto owing to the more favourable mass distribution and the lower bending stresses occurring during bending, it is further possible to use steels of a lower grade for the rolling of the sections, that is to say, steels having less resistance to ageing (for example rimmed steels), since with such small wall thicknesses the cooling of the rolled sections proceeds so rapidly that there is no fear of any impermissible ageing phenomena.

In addition to a considerably greater cross-sectional stability, the trough section proposed according to the invention also has a better torsional stiffness, this being of r Z3 considerable importance in consequence of the frequently varying stresses of the sections by therock pressure, these stresses constantly chan ing their nature.

The reduced distance between the section base and the mass centre further has the consequence that a reinforcement of the section base has only a minor effect on the mass distribution so that the section base can immediately be made of a thickness such as is required for the purposes of the forces transmitted to the section base at any given time.

In every case, however, it is advisable to adapt the distance between the section base and the lower longitudinal edges of the section webs and the shape and dimensions of the flanges, webs and base part to one another in such manner that the mass centre is disposed approximately at half the section height. The construction of the flanges,

ebs and base part in the individual case, may, of course, differ greatly so that the guiding principle of the invention can be embodied in numerous forms of construction.

As a rule it is advantageous for the section webs to have beneath the section base a wall thickness which on the average is considerably greater than above the section base. This not only enables the section base to be disposed at a particularly great distance above the lower longitudinal edge of tie ection webs, while retaining a favourable mass distribution, but another advantage obtained is great cross-sectional stability of the Web parts disposed beneath the section base, so that on the bending of the sections under the action of the rock pressure no impermissible deformations of these web parts disposed beneath the section base need be feared.

In these cir cumstances the wall thickness of the part of the webs disposed beneath the section base advantageously increases towards the base preferably conically, so that in the transitional region subjected to the greatest stresses between the webs and the section base the greatest cross secion is available. The mutually facing wall surfaces of the web parts disposed beneath the section base are advantageously inclined to one another at a downwardly open small angle of, for example, about 6 to With such an aperture angle the lower web parts can also be rolled without difficulty, and in addition, even in the event of a' considerable distance between the section base and the lower web edge, the web cross-section does not become excessively large in the region of the transition to the section base. The part of the section webs disposed above the section base ma on the other hand, as a role be given a wall thickness which on the average is considerably less than the section base.

In one advantageous embodiment, the shape and dimensions of the section flanges, section webs and section bases are adapted to one another in such manner that the overlapping scction ends touch one another only between the lower web edges of the inner section and the section base of the outer section. This gives the possibility of concentrating on a small region the frictional forces transmitted on the relative displacement of the sections, while in particular the parts lying above the section base are kept quite free of frictional stresses occurring on the relative displacement, and can be given correspondingly small wall thicknesses. This arrangement of the sections further has the advantage that during rolling inevitable production tolerances have no effect in practice on the magnitude of the contact surfaces between the sections, so that in contrast to the friction-closure hitherto usually employed practically constant friction conditions are obtained in all cases over a relatively large part of the section. The concentration of the friction on such small contact surfaces further affords the advantage that given appropriate tightening of the clamping connections it is immediately possible to obtain a surface pressure which lies considerably above the permissible surface pressure and with which particularly favourable friction conditions are obtained. With such high surface pressures, as tests have shown, no seizure occurs at the contact surfaces sliding one upon the other, but a certain material displacemcnt occurs in the region of the contact surfaces, and this has the result that independently of the magnitude of the clamping force applied at any given time a substantially constant frictional resistance is obtained between the sections.

A number of exemplified embodiments of the invention are illustrated in the drawing, in which:

FIGURE 1 is an elevation of a gallery support frame,

FIGURE 2 is a section on the line IIII on a larger scale,

FIGURE 3 is a cross-section through the trough sec tions disposed co-directionally one inside the other, as shown in FIGURE 2, on a larger scale,

FIGURE 4 is another embodiment of trough sections, likewise in cross-section,

FIGURE 5 is a cross-section through a third embodiment of trough-sections disposed co-directionally one inside the other, 7

FIGURE 6 is a fourth embodiment, likewise in crosssection.

In the arch-shaped gallery support shown in FIGURE 1, the side segments 1 consisting of trough sections are resiliently clamped by clamping connections 3 to the roof segment 2 of arch-shapedconstruction. The roof segment 2 is fitted by its ends co-directionally into the end parts of the side segments 1, while the clamping means 3 are disposed in the region of the overlap of the sections 1, 2. The clamping connections 3 are provided in known manner with coupling projections which engage over the ends of the roof segment 2-, in such manner that V on a relative displacement of the support segments 1, 2 under the action of the rock pressure the clamping connections 3 are driven by the ends of the roof segment 2.

As will be apparent from FIGURES 2 to 5, the outer section I and the inner section 2 have a congruent crosssection, so that the sections can be placed one inside the other in any desired manner or roof and side segments can be made from the same section bars.

All the exemplified embodiments illustrated in the drawing show trough sections having a substantially trapezoidal cross-section. In the drawings, the section flanges. are denoted by reference 5, the section webs by 6 and the section base by 7. In all cases, the section base 7 is disposed above the lower longitudinal edge 8 of the section webs 6 at a distance g which exceeds its wall thickness b by a considerable amount. In the exemplified embodiments illustrated in the drawing, the distance a corresponds approximately to one-fourth to'one-fifth of the section height h. The section webs 6 are divided by the section base 7 approximately in the ratio of 1:3 into an u per part do and a lower part 6b. The parts 6b of the Webs disposed beneath the section base 7 have a wall thickness which onthe average is considerably greater than the web parts 6a disposed above the section base 7. The average wall thickness of the upper parts 64 of the section webs is in addition considerably less than the thicke ness b of the section base 7.

While the lower longitudinal edge 8 of the section webs 6 is of rounded construction, the wall thickness of the web parts 6b increases conically towards the section base 7. The average wall thickness of the section parts 6b corresponds in these circumstances to approximately the thickness 12 of the section base 7. The mutually facing wall surfaces of the web parts 6b are inclined to one another at a downwardly open small angle a, which in the different exemplified embodiments illustrated in the drawing lies between about 6 and 10.

The outer surfaces of the section webs 6 diverging towards the section flanges 5, in the embodiments shown in FIGURES 3 and 5, are formed by outwardly convex surfaces, whichare curved according to a large radius of curvature and which are adjoined by the outwardly projecting section flanges 5. In the embodiments shown in FIGURES 3 and 5 the section flanges 5 have a height 0 stresses.

which exceeds by a considerable amount the thickness 12 of the section base 7. The inner walls of the parts 6a of the section webs disposed above the section base 7 are likewise bounded by outwardly convexly curved surfaces having a large radius of curvature, so that the web parts 6a have a slightly curved cross-section tapering conically towards the flanges 5. The aperture angle 5 enclosed by the mutually facing wall surfaces of the upper web parts 6a decreases from about 28 to 22 from the section base 7 towards the flanges 5.

In the exemplified embodiment shown in FIGURE 4, the outer surfaces of the webs 6, which surfaces are remote from one another, are formed each by two plane surfaces inclined to one another by small angle. In similar manner the mutually facing insides of the upper web parts 6a are bounded by in each case two plane surfaces inclined to one another by a small angle. In consequence, in the exemplified embodiment shown in FIG- URE 4 as well, the aperture angle 8 enclosedby the inner walls of the upper web parts 6a is smaller in the region of the section flanges 5 than just above the section base 7. Similarly, the wall thickness of the upper web parts 6a decreases from the section base '7 towards the flanges 5. The height of the section flanges in the embodiment shown in FIGURE 4 is smaller than the thickness b of the section base 7. On the other hand, they have a considerably greater width d in comparison with their height.

In the embodiment shown in FIGURE 5, the section base '7 has a downwardly projecting rib-shaped reinforcement 9 disposed between the section webs 6. The ribshaped reinforcement 9 is disposed symmetrically to the Y-axis of the section and has a wall thickness which increases conically towards the section base and which corresponds approximately to the wall thickness of the lower web parts 612. The lower longitudinal edge of the rib 9 provided on the section base 7 is of rounded construction and is disposed in the same plane as the lower longitudinal edges of the section webs 6. It is, however, naturally possible to give the rib-shaped reinforcement 9 a different shape or different dimensions if required than is the ease in the exemplified embodiment shown in FIG- URE 5. In some cases it is possible to provide more than one reinforcing rib 9 between the lower web parts 612.

The section base 7 is considerably reinforced by the middle rib 9 so that the said base in consequence of the shortening of the lever arms as a result of the middle rib 9 is able to take substantially greater bending and torsional In addition, additional accumulation of material beneath the section base 7 gives the possibility of disposing the section base 7 at a particularly high level and hence making particularly small the effective lever arm for the opening-up forces, that is to say the distance from the section flanges 5.

In the embodiments shown in FIGURES 2, 3, and 4, the section ends disposed co-directionally one inside the other are supported in the region of the overlap only between the lower longitudinal edges 8 of the section webs of the inner section 2 and the section base 7 of the outer section. The flanges 5 and the mutually facing surfaces of the section webs of the inner and outer sections on the other band do not touch. In the form of section shown in FIGURE 5, the section ends overlapping one another are additionally supported against the base 7 of the outer section 1 by the rib-shaped reinforcement 9 of the inner section 2. However, in this case as well, the outer and inner sections do not touch either between the flanges 5 or between the webs 6.

Since the lower

longitudinal edges

8 and 10 of the sections webs 6 and of the centre rib 9 are in addition of circular construction, such small contact surfaces are obtained between the inner and outer sections that even in the case of normal tightening of the clamping connections 3 the surface pressure transmitted by the longitudinal edges 8 of the inner section webs to the base of the outer section exceeds the permissible surface pressure so that on the relative displacement of the sections there is no seizure, but, with small material displacements in the region of the small surface zones supported against one another, a sliding with practically constant frictional resistance.

The principle of the invention can naturally also be applied to those sections which are supported against one another additionally by the webs and/or the flanges or only by the webs and/ or the flanges. Thus, for example, FIGURE 6 shows an embodiment in which the sections 1, 2 are supported against one another by the flanges 5 and in addition by the webs 6, while a gap remains between the lower longitudinal edges 8 of the inner section webs and the base 7 of the outer section 2.

FIGURE 2 shows an advantageous embodiment of a clamping connection 3 for those sections which are supported only between the lower web edges 8 of the inner section 2 and the base 7 of the outer section or, if required, additionally by way of a rib-shaped reinforcement 9 of the inner section. The clamping connection consists of two fiat-

iron sections

11, 12, which are bent to correspond to the. section shape and which are clamped together by clamping screws 13. In this case, an arrangement is madesuch that the halvesll, 12 of the clamping connection are subjected substantially to tensile stress. The up per part 11 of theclamping connection is of U-shape to correspond to the distance'between the section flanges 5 in such manner that both the flanges of the inner section 2 and the flanges of the outer section 1 are guided between the side parts 11a. In this way, in spite of the small contact surfaces between the sections 1, 2 placed one inside the other, good guidance is obtained with the relative displacement occurring under the action of the rock pressure. Moreover, this construction of the clamping

stirrup parts

11, 12 gives the effect that the webs of the support sections 1, 2 undergo no bending stresses at all or no appreciable bending stresses. As is apparent from FIGURE 2, the outer section 1 is likewise supported only by the lower longitudinal edges 8 of the section webs against the base 12a of the clamping stirrup lower part 12, so that even between these contact surfaces a surface pressure is obtained which lies above the permissible surface pressure.

We claim:

I. A rolled beam adapted to nest in overlapping relation with at least one similar beam to form at least part of a mine gallery support, said beam comprising a pair of oppositely inclined side walls symmetrically arranged with respect to a longitudinal plane of symmetry and having a pair of outer longitudinal edge portions spaced farther from each other than a pair of inner longitudinal edge portions thereof, and a transverse web integral with and extending between said side walls substantially normal to said plane of symmetry and forming the only connection between said side walls, said web being spaced from said pair of inner edge portions a distance which on the one hand is greater than the thickness of said web and which on the other hand is smaller than half the distance of said pair of outer edge portions from said pair of inner edge portions so that said web forms with said side walls a deep and a shallow longitudinal channel separated by said web, the width between the inner faces of said side walls defining said deep channel and measured normal to said plane of symmetry at any distance from the web surface of the deep channel being greater than the width between the outer faces of said side walls measured normal to said plane of symmetry at the same respective distance used for the first-mentioned width but from said inner edge portions of said beam, whereby when one of said beams is nested into the deep channel of another beam the nested beam will only be supported on said web in said deep channel of said other beam, with the outer faces of the side Walls of said nested beam spaced from the inner faces of said deep channel of the other beam.

2. A beam as recited in claim 1, and wherein the distance between said web and said inner edge portions is between one-third and one-sixth of the distance between said inner and outer edge portions.

3. A beam as recited in claim 1, and wherein each side wall has a thickness which tapers from said web toward the inner edge portion of the side wall.

4. A beam as recited in claim 1, and wherein the thickness of each side wall is greater at the portion thereof extending from said web toward the inner edge portion than at the portion thereof extending from the web toward the outer-edge portion. 7

5. A beam as recited in claim 1, and wherein said web has integrally formed therewith a longitudinal rib located between and spaced from said side walls and having a cross section which tapers from said Web toward the edge of said rib distant therefrom.

6. A beamasrecited in claim 1, and wherein said web has opposed fiat faces parallel'to each other.

7. A beam as recited in claim 1, and wherein the portions of said. side walls which extend between said web and the outer edge portions diverge from each other adjacent said web to a greater degree than adjacent said outer edge portions.

81A beam as recited in claim 1, and wherein said side walls respectively have outwardly directed flanges at the edges of said side walls which are located at said outer longitudinal edge portions, and said web having a thickness greater than the thickness of each side wall inthe region of said flange thereof.

9. A beam as recited in claim 8, and wherein said flanges also are thicker than the thickness of said side walls in the regions of said flanges, respectively.

10. In an arched mine gallery support, in combination, two substantially congruent trough-shaped beams, an end portion of one beam being nested in overlapping relationship in the end portion of the other beam and said beams being and yieldably connected at said end portions for sliding movement relative to each other, each of said beams comprising a pair of oppositely inclined side walls symmetrically arranged with respect to a longitudinal plane of symmetry and having a pair of outer longitudinal edge portions spaced farther from each other than a pair of inner longitudinal edge portions thereof, and a transverse web integral with and extending between said side walls substantially normal to said plane of symmetry and being spaced from said pair of inner edge portions a distance which, on the one hand, .is greater than the thickness of said web and which, on the other hand,

is smaller than half the distance of said pair of outer edge portions from said pair of inner edge portions so that said web forms with said side walls a deep and a shallow longitudinal channel separated by said web, the width between the inner faces of the side walls defining the deep channel and measured normal to said plane of symmetry at any distance from the web surface of the deep channel being greater than the width between the outer faces of the side walls measured normal to the plane of symmetry at the same respective distance used for the first-mentioned width but from the inner edge portions of said beam, said nested beam being supported on said web in said deep channel of said other beam, with the outer faces of the side walls of said nested beam spaced from the inner faces of said deep channel of the other beam.

11. In a mine gallery support as set forth in claim 10, wherein the distance of said transverse web from said inner edge portions is between one-third and one-sixth of the distance between said outer and said inner pair-of edge portions.

12. In a mine gallery support as set forth in claim 10, in which the mean wall thickness of the side wall por tionsbetween said transverse web and said pair of inner edge portions is greater than the mean thickness of the side wall portions between said transverse web and said outer edge portions, and said thickness of the side wall portions between said transverse web and said pair of inner edge portions tapers from said web toward said inner edge portions.

13. In a mine gallery support as set forth in claim 10, in which each of said beams includes a longitudinal rib integral with said web and projecting therefrom into the space between said pair of inner edge portions and in which the thickness of said rib tapers from said web toward the free edge thereof.

14. in a mine gallery support as set forth in claim 13,.

in which said free edge of said rib is located in a plane substantially normal to the plane of symmetryand'passing through said pair of inner edge portions.

15. In a mine gallery support as set forth in claim 14, in which said set of beams engage each other at said nested end portions thereof only along the inner edge portions and said free edge of said rib of one beam and the web of the other beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,713,774 Heintzmann July 26, 1955 FORElGN PATENTS 412,561 Great Britain June 25, 1934 487,826 Great Britain June 27, 1938 697,260 Great Britain Sept. 16, 1953 700,020 Great Britain Nov. 25, 1953 962,879 Germany May 2, 1957 1,034,777 France Apr. 15, 1953 1,196,069 France May 25, 1959 1,042,997 France June 10, 1953 OTHER REFERENCES German patent application B 37691 VI/5c; June 14, 1956, K1. 5c, Gruppe 9/10.

'German patent application 1,003,159, February 28, 1957 (K1. 5c 9/10).

German patent application 1,009,133, May 29, 1957 (K1. 5c, Gruppe 9/10).

Claims

10. IN AN ARCHED MINE GALLERY SUPPORT, IN COMBINATION, TWO SUBSTANTIALLY CONGRUENT TROUGH-SHAPED BEAMS, AN END PORTION OF ONE BEAM BEING NESTED IN OVERLAPPING RELATIONSHIP IN THE END PORTION OF THE OTHER BEAM AND SAID BEAMS BEING AND YIELDABLY CONNECTED AT SAID END PORTIONS FOR SLIDING MOVEMENT RELATIVE TO EACH OTHER, EACH OF SAID BEAMS COMPRISING A PAIR OF OPPOSITELY INCLINED SIDE WALLS SYMMETRICALLY ARRANGED WITH RESPECT TO A LONGITUDINAL PLANE OF SYMMETRY AND HAVING A PAIR OF OUTER LONGITUDINAL EDGE PORTIONS SPACED FARTHER FROM EACH OTHER THAN A PAIR OF INNER LONGITUDINAL EDGE PORTIONS THEREOF, AND A PAIR OF INNER LONGITUDINAL EDGE PORTIONS THEREOF, SAID SIDE WALLS SUBSTANTIALLY NORMAL TO SAID PLANE OF SYMMETRY AND BEING SPACED FROM SAID PAIR OF INNER EDGE PORTIONS A DISTANCE WHICH, ON THE HAND, IS GREATER THAN THE THICKNESS OF SAID WEB AND WHICH, ON THE OTHER HAND, IS SMALLER THAN HALF THE DISTANCE OF SAID PAIR OF OUTER EDGE PORTIONS FROM SAID PAIR OF INNER EDGE PORTIONS SO THAT SAID WEB FORMS WITH SAID SIDE WALLS A DEEP AND A SHALLOW LONGITUDINAL CHANNEL SEPARATED BY SAID WEB, THE WIDTH BETWEEN THE INNER FACES OF THE SIDE WALLS DEFINING THE DEEP CHANNEL AND MEASURED NORMAL TO SAID PLANE OF SYMMETRY AT ANY DISTANCE FROM THE WEB SURFACE OF THE DEEP CHANNEL BEING GREATER THAN THE WIDTH BETWEEN THE OUTER FACES OF THE SIDE WALS MEASURED NORMAL TO THE PLANE OF SYMMETRY AT THE SAME RESPECTIVE DISTANCE USED FOR THE FIRST-MENTIONED WIDTH BUT FROM THE INNER EDGE PORTIONS OF SAID BEAM, SAID NESTED BEAM BEING SUPPORTED ON SAID WEB IN SAID DEEP CHANNEL OF SAID OTHER BEAM, WITH THE OUTER FACES OF THE SIDE WALLS OF SAID NESTED BEAM SPACED FROM THE INNER FACES OF SAID DEEP CHANNEL OF THE OTHER BEAM.