US2278797A - Building construction - Google Patents

Description

April 7, 1942- H. E. RAYMoND BUILDING CONSTRUCTION Filed March e, r1941 s sneetsLsheet 1` Gtfornegs.

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April 7, 1942. H. E. RAYMOND BUILDING CONSTRUCTION FiledMaroh 6, 1941 3 Sheets-Sheet 2 Ap 7, 1942- H. E. RAYMOND BUILDING CONSTRUCTION Filed March 6, 1941 3 ySheets-Sheet 3 Gttomeg.

Patented Apr; 7, 1942 s l UNITED STATESPATENT OFFICE" I 2,278,797 BUILDNG CONSTRUCTION y Harold E; Raymond, New Orleans, La. Application March o, 1941, serial No. 382,062

5 Claims. l, (VCI. 108-1) The present invention relates to building constructions and more particularly to the arch constructions thereof built of structural steel and the like, and is a continuation in part of my copending application Serial No. 58,146, led J anu-v ary 8, 1936.

It isan object of the present invention to secure an arch form that is eicient under all conditions of loading.

A further object of the invention is to provide an arch in which the curvature is made in the form of a parabola to minimize the stresses produced in the arch members;

A still further object of the invention is to provide an arch form which is of increased i.

In the drawings, wherein like symbols refer to like or corresponding parts throughout the several views. v, Y

Figure 1 is a front elevational ,view of the arch frame in accordance with the present invention and showing the resultant of forces ofthe horizontal and vertical loads.

Figures 2, 3 and-4 are force diagrams take from Figure 1. -v

Figure 5 lis a View similar to Figure 1 with stress diagrams of combined vertical and horizontal loads superimposed thereon.

Figure 6 shows a forcey diagram of the Wind loads alone. n

Figure '7 shows a force diagram of the combined vertical load and resultant-wind loads.

Figure 8 is a front elevational View of the arch and giving the mathematical equations of the parabolic curves. f

` Figure 9 is a sideelevationall view as seen from the left of Figure 8. 1 y y j Figure 10 is an enlarged fragmentary-view showing details of the arch diagonals vshownr in Figure 8.

Figure 11` is a vertical'sectional view taken along the line II-II of Figure 10, and

Figure 12- is a horizontal sectional view taken along the line l2-l2 of Figure 10.

.The invention is particularly directed to the outlines, curves, etc. used in the varch or of the top and/or bottom chords thereof.

In accordance With'the inventionV it will be shown that if'this curvature is made in the form of a parabola, the axis of which is parallel to the direction of the force which is to be restrained, the `stresses produced in the' arch members are at a minimum. n

The inventive concept lies in the fact that the arch is made up of a plurality of parabolic segments, each one being placed with its particular axis parallel to the direction of the load to be restrained in that section. While no'particular claim is made for the use in an arch of the parabolic curvature per se, it is the special manner in which the several parabolic curves,

are combined to form a unit that is the novel concept of the present invention.

The recent development of the welding process in the field of fabrication of structural steel has made this complicated form of arch'economically possible. In order that a clearer understandingof the invention may be had, the details surrounding the workings of an arch in roof construction under normal conditions should be considered. f

Under normal conditions the arch roof is subjected to loads due to the weight of its own construction and those due to snow. These loads are considered tobe acting vertically on the construction. In addition the roof is also required to resist the eiTect of the wind forces which are considered-to be acting horizontally. Now it is an engineering fact that when uniform loads such as those enumerated above act ronfan arch the line of the resultant follows a f parabolic curve, the axis of which 'is' parallel to the line of vaction of the force being acted against.` Accordingly in order to resist these y horizontal and vertical forces above mentioned the axis of curvature of the arch should change from a horizontal to a vertical position as the a vertical axis designated by the line 25--25 and this axis is parallel to the line of action of the forces due to the weightvof the construction and the weight of the snow. The other curve originating at the springing is generated about a horizontal axis designated by the line 2 6-26 and which is parallel to the line of action on the wind.

The arch as shown is laid out for an assumed load of 30#- per square foot vertically and 25# horizontal wind pressure. Accordingly with Vthe columns two feet deep and the arch three feet deep at the crown thereof, the equation of the parabolic curves become:

For the axis of the arch at the center segment 2=B01/, the top chord :c2=77.7y and for the bottom chord x2=83y for the equation of the axis of the springing y2=10.r, for the top chord y2=11.7 and for the bottom chord y2=8.66. These parabolic curves intersect and become tangent at the third point of the span. The constants are all worked out directly from the assumed conditions, which have been determined from practice.

In Figure 1 the broken line above the top chord indicates the line of the resultant of the vertical loads which have been marked Rv and for the horizontal loads which have been marked Rh, each starting at the axis of their respective parabolic curves and extending to the point of intersection and tangency of the two curves.

It will be noted that the above mentioned resultants follow the curvature of the arch almost exactly. In practice, this means that the resulting force produces almost no eccentric load but only direct compression in the member. This is the most economical condition possible and it has been achieved by the present unique combination of parabolic curves. At this time it should be mentioned that the eccentricity Vof the line of action of any force from a frame is a direct measure of the intensity of the stress produced in the frame members by that force. Thus' it follows that the closer the line of action the force to the member under load the smaller will be the stress induced in the member of the frame.

It should be noted that each resultant Rv and Rh exert a thrust at its apex in a line tangent to the arch. At the center section this'thrust is counteracted by that of the other half of the arch. At the springing this thrust produces direct compression in the supporting column 32.

At the point of intersection P. I., the resultants Rv and Rh may be resolved into two cornponents, one as a thrust and the other as a direct force, perpendicular to each other. Thus the thrust of Rh will be vertical and counteracted by the direct force of Rv and the thrust of Rv Will be horizontal and counteracted by the direct force of Rh. These counteractions take place to the extent of the magnitude of the small force. While this action is not apparent on the face of the combined stress diagram nevertheless its effeet is reflected in the resultant.

The forces acting on the arch frame do not remain the same at all times. The force due to the wind may act from one side or may act from the other side or may not act at all, and similarly there may or may not be any load due to snow. When there is no wind force to be taken into account of, the equilibrium polygon for the vertical forces alone is shown as Rv in Figure l, which is the resultant of all loads.

Accordingly it is desirable to secure an arch form that is efcient under all conditions ofv loading. The combination of parabolic curves of the present invention in an arch secures that efciency under all conditions as shown by the small eccentricity of the acting force.

Referring more Particularly to Figures 5, 6 and '7, these show the arch with the stress diagrams of the combined horizontal and vertical loads superimposed thereon and marked Re. Fw shows the force diagram of the wind load alone. The force diagram of the combined vertical load and resultant wind loads is shown as Fc. The column reactions are shown for the resultant wind force as R'n and R"n, andthe column reaction of the vertical load are shown as Rv and Rv. These combined column reactions are shown as RL and Rw. The eccentricity of the combined resultant Rc from the members of the top and bottom chords are shown as X and X' respectively.

The loadings are here considered the same as in Figure 1 with the horizontal wind force on the side wall also considered. The base of the column is considered fixed against inward or outward movement, or both. It is thought unnecessary to go into detailed description of the manner in arriving at the resultants as they are obtained in the usual way. The normal component of the horizontal wind pressure is combined with the vertical load and applied as one load to the roof on the windwardside, the vertical load alone acting on the leeward side. The equilibrium polygon was constructed for the loads over the entire combined frame.

In the preferred form of the invention and as shown in the various figures, the arch comprises top chords 21 and bottom chords 28 suitably connected together by means of diagonals 29. 'Ihe lateral portions of the arch are designated by the numerals 30 while the central portion intermediate these lateral portions is designated by the numeral 3|. The lateral portions may be made continuous with columns 32 supported in footings 33. In Figure 9, purlins 34 are shown carried by the chord members.

Immediately above and below the point of springing as indicated by the line 2li-26 additional cross braces 35 are provided, the lowermost two defining the upper part of the columns 32 While the topmost one defines the beginning of the lateral end portions of the arch 30. It is understood that the point P. I'. defines the point of intersection between the lateral and central portions of the arch.

The diagonals 29 which are shown in detail in Figures 10, 11 and 12 may be of standard structural shapes but are preferably of angles placed at an angle of 45 with the direction of the span of the arch. In this manner the angles nest in one another to form a compact joint easy to weld and at the same time give'additional rigidity against lateral movement of the bottom chord 28.

The top and bottom chords 21 and 28 may be made of any suitable structural shapes such as channels, angles, I-beams, or built up sections which are readily rolled or sprung to the proper curvature. As the radius is great except at the point of springing, very little labor is required in assembly. The chords may be made of long sections, in which only a minimum of joinings will be necessary and which further eliminates labor. Where there is eccentric, as at the springing, cover plates may be used by simply applying a curved rolled plate of the required thickness. No great amount of labor is required to layout the sections as there are no angles to be maintained at the intersection.

Figure 8 shows the arch frame together with the mathematical equations of the parabolic curves of the top chord, center line and bottom chord of the midsection 3| and also the equations of the top chord, center line and bottom chord of the lateral sections 30 and their points of intersection, namely P. I.

It is understood that the arch as above described may be made of individual central and lateral sections joined together in any suitable manner and that the columns 32 may also be separate parts suitably joined and supporting the lateral sections 30 of the arch.

By gradually increasing the depth, the arch may be increased in strength in the same proportion as the stresses on the frame increase.

composed of top and bottom members connected y by diagonal members, having the central portion of the arch in the form of a parabolic arch with its axis vertical and coincident with the center of the span, and lateral or end portions in the form of a parabolic curve, the axis of which is horizontal and coincident with the line of springing of the arch, said parabolic rcurves being so proportioned as to become tangent at their point of intersection.

2. An arch roof construction of structural steel composed of top and bottom members connected by diagonal members, having the central portion of the arch in the form of a parabolic arch with its axis vertical and coincident with the center of the span, and lateral or end portions in the form of a parabolic curve, the axis of which is horizontal and coincident with the line of springing of the arch, said parabolic curves being so proportioned as to become tangent at their point of intersection, and being supported on columns of similar construction and forming a continuation of the lateral portions of the arch, said columns being fixed at their bases.

3. An arch roof construction of structural steel composed of top and bottom members connected by diagonals, having the central portion of the yarch in the form of a parabolic curve, the axis of which is vertical and coincident with the center oi the span of the arch, and lateral or end portions in the form of parabolic curves the axis of which is horizontal and coincident with the springing, and having the said diagonals made of angles set at an angle of 45 with the line of the span of the arch and set' so as to nest together at their joinings.

4. In building construction, an arch comprising a central section of a parabolic curvature generated about a vertical axis coincident with the central vertical axis of the arch, and lateral sections connected to the central section and being of parabolic curvature generated about a horizontal axis at the points of springing of the arch, the curvatures of said parabolic central and lateral sections being proportioned eccentric to their respective parabolic curves to meet at a tangent at their points of intersection.

5. In building construction, an arch comprising a central section of a parabolic curvature generated about a vertical axis coincident with the central vertical axis of the arch, and lateral sections connected to the central sections and being of parabolic curvature generated about a horizontal axis at the points of springing of the arch, the curvatures of said parabolic central and lateral sections being proportioned eccentric to their respective parabolic curves to 'meet at a tangent at their points of intersection,` and having their inner and outer anges spaced proportionally to the eccentricity of the sections for transmitting the thrust of the load vertically at the points of springing of the arch.

, HAROLD E. RAYMOND.

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