US2332990A

US2332990A - Foundation pile

Info

Publication number: US2332990A
Application number: US445159A
Authority: US
Inventors: Collins Tappan
Original assignee: Carnegie Illinois Steel Corp
Current assignee: Carnegie Illinois Steel Corp
Priority date: 1942-05-30
Filing date: 1942-05-30
Publication date: 1943-10-26
Anticipated expiration: 1960-10-26

Description

Oct. 26, 1943. T. COLLINS FOUNDATION PILE Filed May so, 1942 fv. V`

Patented Cet. 26, 1943 f,"

FOUNDATION PILE Tappan Collins, Dormont, Pa., assigner to Carnegie-Illinois Steel Corporation,

of New Jersey a corporation `Application May30, 1942, Serial No. 445,159

2 Claims.

This invention relates to improvements in foun dation piles, the present application being a continuation-impart of my prior application, filed August 2, 1940, Serial No. 349,931.`

Foundation piles are dependent principally upon 'the frictional hold thereof in the ground for their'bearing capacity, and while their use involves some indeterminate factors due to unknown underground conditions, there are certain predeterminable enabling characteristics which `may be embodied in the design of such piles to enhance their efficiency.

The prime considerations uin the design of such piles include (l) mechanical strength, (2) rigidity under load, (3) surface extension, and (4) surface disposition. Volumetric displacement is not properly a primary consideration, since While -it is true that the pile must not have such a crosssection as to unnecessarily disturb the ground upon penetration, I have found that a proper dei termination of the design based upon the four characteristics above will produce a pile having a suitable volumetric displacement.

i insofar asI am aware, prior foundation piles have not possessed the foregoing essential characteristic values insufficient` degree to obtain maximum efiiciency.- In the ease of steel foundation piles, `prior designs have provided excessive cross-sectionland `weight to obtain rigidity, but in fact the same tends to destroy the bearing capacity by undue disturbance and displacement lof theground by the largecross-section, and unnecessarily increases the cost. c

My invention contemplates providing afoundation pile properly shaped and proportioned for maximum eiiiciency and economy of material for a given loading. l

Additional objects and advantages of my invention will become apparent from the following description taken in connection with the accompanying drawing wherein Fig. 1 is a vertical sectional view of an application of my invention, showing one form of my improved pile in elevation;

Fig. 2 is a top end view of the pile of Fig. 1;

Fig. 3 is a view Vsimilar to Fig.A 1, showing a modification; and,

Fig. 4 is a top end View of the pile of Fig. 3.

Referring to the drawing, the cross-section of my improved pile is in the form of a Y having three equi-spaced radial legs or flanges 2 of equal length and cross-sectional area extending from a central body or core 3, each flange or leg 2 having 'parallel sidefaces a, thus providing legs or flanges of uniform thickness throughout.v `The faces a of adjacent fianges or legs are merged at the apex of the reentrant angle formed thereby by a fillet or radius b.

The equilateral section thus formed lends itself readily to production as a rolled steel member, making it possible to producesteel piles by standard rolling equipment, and as hereinafter pointed out, the steel pile so produced may be provided as a minimium section with increased load bearing capacity in comparison with the standard rolled steel pile sections now being employed in the art.

In the form of Figs. 1 and 2, the pile `A having the described cross-section ispreformed of proper length and is preferably pointed at its lower end 4 for starting. In this form, the legs or flanges 2 are longitudinally parallel throughout the pile,

`providing a construction which may be easily driven and embedded for receiving and supporting the load. For example, as in Fig, l, the pile A may be employed as a direct foundation for a tubular pier or column B, thelatter including a tubular casing 5 lled with concrete 6 embedding the upper end of the driven pile for connection therewith. Y l

A foundation pile having the aforesaid crosssection and vertical disposition possesses optimum functional characteristics producing maximum eiiiciency'and economy `of material in comparison with piles now in use of the same cross-sectional area and minimum allowable thickness of material. l

The advantages of any improved designare readily seen from a comparison with a representative group of standard sections including practical rectangular, round and H-beam foundation pile sections, compared as follows on the. basis of the four prime considerations hereinbefore` set forth.

(1) A foundation pile must have the mechanical strength to withstand the imposed load,

which characteristic is dependent upon the cross-sectional area and material of the pile, and for the sake of economy, the cross-section should not greatly exceed the safe minimum for a total axial compression equal to the design load. Hence, the mechanical strength is determinative of size only and not of shape or conguration, and in the present comparison of sections of predetermined equal area and minimum allowable thickness of material, no advantage is apparent for one section over another.

(2) A consideration of rigidity under load shows a substantial Iadvantage for the present invention over other piles, which advantage is of prime importance to both the` efficiency design provide a section having a maximum value of its minimum radius of gyration to thereby enable the greatest length of pile to be used.

The maximum and least radii of gyration of my improved section are equal, and the least radius of gyration thereof is greater than that of any other section of equal area and minimum allowable thickness of material, including the ypractical rectangular, round and H-beam sections, or any other section of which I am aware.

. Hence, from the standpoint of rigidity and maximum pile-length7 my invention provides a pile having appreciable advantage overv the said standard sections.

(3).'The surface extension of the pile is an enabling property since it is a measure of the ability tov distribute the application of force over the alfected underground. Invother words, the pile must have a substantial surface area in intimate contact with the soil. Such a characteristic is determined by the perimeter of the transverse section of the pile, and assuming that the perimeter does not have small irregularities or inaccessible reentrants, it is possible to provide intimate contact by the entire surface area of the pile. With the exception of an elongate or flat rectangle having one dimension equal to the minimum allowable'thickness of materiall my improved equilateral section has greater perimeter thanV any other known piling section, and since the elongaterectangle referred to is completely impractical, my said section possesses the greatest perimeter of any practical foundation pilesectiorrl n y It should also be noted that the obtuse shallow reentrant angles between the faces a, of my section, and the exposed ends of the legs or flanges 2 provide maximum accessibility to contact with the soil for any known practical section. In this respect my improved section is of material advantage over the H-beam section which produces voids in its deep rectangular reentrant faces,

thus destroying an otherwise appreciable perimeter value.

(4) Since the surface disposition of all compared forms is the same as that of Figs. 1 and 2, i. e., vertical surfaces only, no material advantage or frictional hc-ld may be assigned to the form of the pile A except as noted in (3) above by reason of increased contact area.

From the foregoing comparison it is evident that the form of foundation pile in Figs. 1 and 2 is a distinct improvement in respect to the enhanced contact area and maximum least radius of gyration in comparison with other piles of similar material, equal cross-sectional area and minimum allowable thickness of material. Such a pile may be readily and economically fabricated as a rolled steel section, or from any other ma- `terial employed for foundation piles, and due to its symmetrical form and the symmetrically pointed end 4 thereof, suena pile may be driven surface. resists vertical downward displacement of the pile. In this manner, the pile has increased compressive' resistance in place against vertical loading.

This enhanced property of the pile is obtained without sacrificing any of the other advantageous characteristics referred to, and the pile may be driven in the usual manner, a portion of the driving force being utilized in rotation or a boring action as the pile penetrates the ground. While the angle of the helix may be varied as underground conditions maydictataan angle of up to about 30-degrees to the vertical axis of the pile may be employed with average soil conditions.

A'foundation pile constructed in this manner possesses minimum volumetric displacement, good vertical and horizontal surface disposition, maximum surface extension, as well as maximum rigidity and length for a given mechanical strength determined by the load to be supported thereby. For example, a rolled steel pile so formed 40 feet in length, having an outside diameter of 13 inches, and a flange or leg thickness of one-half inch, twisted one complete revolution for each ten feet of length, hask the volumetric displacement of a cylinder of the same length only 31/2 inches in diameter; the vertical surface area of a L10--foot cylinder 13-inches in diameter; and the vertically distributed downwardly directed horizontal projection of the surface area of a 40-foot truncated inverted conoid whose tip is 31/2 inches in diameter and whose base has a diameter of ll2-inches; thereby illustrating the material advantages of my improved form of pile.

Fig. 3 illustrates the application of my foundation piles in a group and having their upper ends embedded in a concrete slab or pier C, insuring the connection of the piles with the slabs or piers and locking the piles against rotation, thereby obtaining an excellent underpinning and support.

Various changes and modifications are contemplated within the scope of the following claims.

I claim: f

1. A foundation pile having a uniform cross'- section proportioned as to area and minimum allowable thickness of material in accordance with the longitudinal compression loading to be supported thereby, said cross-section comprising a central core and three equi-spaced legs extending radially therefrom, each of said legs having equal length and area and being of `uniform thickness throughout, said thickness being equal to the said minimum allowable thickness of material, the pile having an elongate body adapted to be disposed underground substantially throughout its length, and said cross-section being characterized by having its least radius of gyration greater than that of any other section having the same area and minimum allowable thickness of material, saidpile possessing maximum rigidity under said loading and having maximum length for a given slenderness ratio with respect to4 any pile of said comparable area material. A

2. A foundation pile having a uniform crosssection proportioned as to area and minimum allowable thickness of material in accordance with the longitudinal compression loading to be supported thereby, said cross-section Comprising a central core and three equi-spaced legs extend and thickness of ing radially therefrom, each of said legs having equal length and area andbeing of uniform thickness throughout, said thickness being equal to the said minimum allowable thickness of material, the pile having an elongate body adapted to be disposed underground substantially throughout its length, and saidcross-section being characterised by having its least radius of gyration greater than that of any other section vhaving the same area and minimum allowable thickness 'of material, said pile possessing maximum rigidity under said loading and having maximum length for a given slenderness ratio with respect to any pile of said comparable area and thickness of material, the body of said pile being spirally twisted about its longitudinal axis to provide the legs thereof with helically disposed elements, whereby the embedded pile has increased resistance to downward vertical displacement under said loading. t l

TAPPAN COLLINS.