US2223418A

US2223418A - Concrete dome for buildings

Info

Publication number: US2223418A
Application number: US297779A
Authority: US
Inventors: William S Hewett
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-10-04
Filing date: 1939-10-04
Publication date: 1940-12-03
Anticipated expiration: 1957-12-03

Description

w. s. HEWETT 2,223,418 CONCRETE DOME FOR BUILDINGS Filed oct. 4, -1939 2 sheets-snee; 1

w. s. HEWETT 2,223,438 CONCRETE DOME FOR BUILDINGS Filed Oct. 4, 1939 2 Sheens-SheerI 2 Patented Dec. 3, 1940 I UNITEDy STATE anni s PATENT Aorti-cr;

.coNoReTe none: Fon BUILDINGS William s. neweteelmhurst, r11.y 1 Application catcher 4, waaserin No. 297,779 v 10 claims. (o1. 10s- 4) The present invention is directed `primarily to a concrete dome for astructure which is circular, or substantially so, such a dome being the most "economical and satisfactory typeof roofwhich `'has ,yet 4'been devised where a permanent and 'reproofroof is desired for vstructures of this character. However, in the past it has been the practice in the building of'such domes to employ forms which are very expensive and are uselessr after the structure `is built,Y and which moreover 'are expensiveto remove` Great saving will therefore result if the dome can bepre-cast in sections in a plant provided for that purpose land thenlbrought to the building site: and assembled on light form work.

In the building of small domeswhich are cast in the eld according to'` present methods, the thickness of the slabsproduced is ordinarily much greater than the strength'requiredto `compensate for `the stresses encountered, which results in a waste of material, as well as excessive weight which must be'ad'equately supported. f

Domes constructed in accordance with the `practice of the present invention may be precast in `sections of properly computedthickness with- '.out waste of `material and adequately supported in such a manner astopreventY the development of `stresses which might resul-t in cracking or dis-` integration.

In all domes, howsoever constructed,the middle or peak portion of the dome is in circular com- 4pressiongwhile the outeror. marginal `portion is in circular tension, and the point of change from tension to `compressiony will depend upon the shape of the dome. All domesare subjected to a slightbending on radial lines `under uniform loads, `butwhen`properlydesigned the bending lis so 'slightthat `itis easily `resisted by a thin section. W'herepartial `or concentrated loads are encountered, however, the dome slabs are subjected to both-radial andicircular bending.

Inthedomeof the present invention due account is taken of alloftheselfactors and the design is intended to compensate against .circular `tension in the outer or `marginal portion of the domein such a .way asto i'corine .the circular -compression to .that'rportion'of the dome slab which is .computed Y to be in 'circular fcompression in-the analysis of' the stresses* and .alsoto conne vthe circulartension to that `portion ofthe dome `slab which istcomputed to beintension." Failure ito `take due .account of these `factors results. in heavybending stresses intheslabfand results in an` unsafe and unsatisfactorystructure. i

'Further objects and details wllappear'lfrom `a c the completion of the structure.

Isively broad in lthe :outer courses.

description of the invention in conjunction with fthe accompanying drawings, wherein,

on line Fig. 6 is ari-enlarged view of a portion of the exterior of the dome looking downwardly toward the exposed circular stress rods; and

Fig. 7 is a fragmental sectional View showing the positioning of the forms employed in the pouring of concrete to embed the `stress rods in The dome as a whole consists of concentric rows of'slab sections extending fromthe center cap IU to the margin I -of the dome, the outer edge of each row overlapping'the inner edg'eof the next adjacent row of the series. As shown, the rows are designated fromthe interior outwardly as'l2, i3, I4, l5, IB, and Il, although obi viously a greater 4or lesser number of rows may be employed, depending upon the size and character of the structure.` f r 'The outer or marginal row l1 is the one which embodies the principal features of the present invention and which is in the greatest degree subjected -to the expansive thrust occasioned by the weight of the inner portion of thedome and is hence subjected to a circular tension stress which 'is counteracted by the structural features presently tobedescribed.

'Each ofthe circular rows or coursesis cornposed of a plurality ofintertted pre-cast concrete sections of inwardly tapering formation,

'which sections inthe respective rows orlcourses may be convenientlydesignated as l2a, 1321,' Ma, laylafand lia. r The width of the sections in the-progressively enlarging vrows will Vary, as shown, by subdividing the outer rows or` courses to such an extent that none of the sections Awill be exces- Thus the number of sections in rows i3 and I4 will be double the number in row l2, and the number .of sections in rows l5, 16,'and Il will be double v`the number in rows i3 and 14.

The general sectional contour of the dome here shown is best illustrated in Fig. 5, which shows arelatively flat broad dome, although it will be understood that it is equally possible to employ the principles of the present invention in the construction of domes having a higher or more truly circular configuration.

As illustrated in Figs. 2 and 4, each of the slab sections, with the exception of the sections in the marginal row Il, is provided along its outer edge with. an undercut which affords a flange I8 adapted to overlie the inner edge of the sections in the next succeeding row.

As illustrated in Fig. 3, each of the slab sections, including the slab sections in the margi-` `V nal row Il, is provided along oneof its side edges with an undercut affording a flange I9 which overlies the contiguous fla-t edge of the adjacent section in the row, This affords Aan in-4 tertting or overlapping arrangementfor all of the joints throughout the entire dome, and in like manner the marginal edge of the circular cap section I0 is anged to overlie the inner edge of the slab sections in the inner row I2. However, it is preferred to allow space between the adjacent edges for the application of a cement or mortar lling 2l), which lls ,out under the overlap and effectively unitesI and seals the joints.

The above general description `applies to all of the slab sections composing the inner courses from I2 to IS inclusive, but the slabs of the marginal course I 'I are of special construction, which will now be described in detail.

In the relatively flat domek herein particularly illustrated, it will be noted that the sections of the inner courses are relatively at or plane, although formed of slightly increased thickness toward the lowervor outer edgesto provide for the overlap, but the sections composing the marginal lcourse are of curving formation in radial cross section, as well as circumferentially, and constitute the outer or base portion of the dome which, along with its lower edge, rests directly upon the Vcircular wall 2I of the structure which supports the dome itself.

Each of the slab sections has embedded therein a plurality of arcuate reinforcing rods 22 which arepreferably located near the side edges of the sections (Fig. 3), but which may if desired be further supplemented by additional rods spaced at intermediate locations. The reinforcing rods A22 curve upwardly in conformity with the curvature of the marginal slab sections and the rods affordpoints of connection for embedded circumferential rods 23, the ends of which are hooked over the rods 22l as shown in Fig. 3. v

The circumferential rods 23 are arranged in pairs and serve as points of connection for tension loops 24, the inner 'ends of which in each instance are bent around the rods 23 and are embedded therewith in the, slab section when being cast, so that the completed slab section will display a series of rows of inwardly projecting loops for the subsequent insertion of circular tension rods 25. As shown, each section I1a ofthe marginal course presents five rows of loops in spacedv relation to one another and inwardly projecting to receive ve tension rods 25, the uppermost of which'in the present instance is of somewhat greater diameter than the others. f v

Each tension rod 25 extends around the entire interior of the dome at the appropriate level, and theV rows of loops .24 extend inwardly at ktween the courses4 of slab sections.

. would otherwise be subjected.

In order to enable the tension rods to be adequately tightened and put under sucient stress to compensate against the elasticity of the tension4 rods themselves, each of the rods at its meeting ends is provid'edwith right and left screw threads-26 and a turnbuckle 2l' so that the desired tension can be imparted to the rods, which thus tend to contract and draw in on the slab sections With the result that both the tension rods and the slabs with which they are `united are pre-stressed to the required degree,

the rods being tensioned and the slabs compressed.

' The structure is additionally reinforced along the joints by the provision of tie wires 23, which are secured to the embedded rods 23 and extend inwardly from the slab near the meeting edges of the sections, so that their ends may be carried around the downwardly extending ends 29 of alternately spaced radial reinforcing rods 3e, or 3|, the former of which extend upwardly to the center of the domeand are there united, and the latterv of which terminate at an intermediate point as shown in Fig. 1, but which in each case follow the lgeneral curvature or contour of the dome. Although the rods 3|! and 3| are located at the radial joints, as shown, additional rods of like character may be employed along intermediate lines, if desired.

The abovevarrangement of rods and ties constitutes the interior metallic reinforcement for the dome, but in the` completion of the structure these reinforcing elements are embedded in a series of arch beams 32 and intervening circular ribs 33, which ribs, as shown, lie in intervening relation to the arch beams, and the beams `and ribs are of proper dimensions and sufficiently massive to fully embed the metal work and furnish a permanent reinforcing grid or skeleton for the Ventire dome.

In the assembling of the structure, a lightscaffolding`34, or false work (Fig. 5), is built up on the interior of the structure, with the provision of posts or pillars 35 carrying circularly disposed courses of planks 36 properly disposed to underlie the positions occupied by the circular joints be- With the scaffolding thus positioned, the sections of the lower or marginal course are laid in position with their'side edges in overlapping relation. With the sections thus positioned, five rows of tie rods 24 will be presentedvinwardly for the reception of the circular tension rods 25 which will be entered through the loops, forming a row of circular bands standing at varying elevations and in concentric relation with the-vertical axis of the dome.

Thereafter the radial rods 30 may be positioned with their lower portions in Contact with the tension rods and the tie wires 28 will be carried around the radial rods and united by twistingor otherwise, thus tying the slab sections of the marginal course of the metal reinforcing rods. The joints between adjacent slab sections may be filled with mortar, cement, or other suitable bond, at this stage or later, and thereafter the upper courses will be laid in successive order until the uppermost course is` laid and the cap is positioned; vThe slab sections of theupper `courses Will be tiedto themetal rods in the-manner heretofore described, land this completes the general assembling of the preformed partsof the dome structure. I

In order to pre-stress themarginal-course of the slab sections before the scaffolding is reexhaust their normal elasticity, but also to impart a compressive stress to the lower `course tocorn- "pensate for the tension or expansive stress 'to `which the marginal course is subjected in resisting the weight of the inner courses of the dome which aire necessarily under compression.`

`After the tension rods and marginal course of slabs have been pre-stressed to thedesired degree,

-suitably shaped pouring forms, such as 31(Fig.

7), are placed in position to enclose' the `metal work, and concrete is poured to properlymold the beams and intervening ribs, which completes'the structure of the dome.l After the `concrete has hardened, the forms and scaifolding can be removed and the dome will stand -as a permanent self-sustaining structure free from a tendency'to crack, sag, or become' otherwise deformed.V If the steel stress rods were not pre-stressed in the manner described, the elasticity of vthe steel under tension would cause tension in the adjacent concrete.

In the design illustrated in the drawings, that part of the dome within the marginal course is in circular compression. If the marginal course were reinforced in the usual manner, the reinforcing would be placed in tension, which in turn would be transmitted to the concrete, so that the entire marginal portion of the dome would be in tension, which would tend to deform the dome as such stress would result in cracks in the concrete and also in placing a large part of the in"- terior portion of the dome in tension. Sincethe total circular tension in thestructure must equal the total compression'it necessarily follows that if a large part of the area of the dome inside of the marginal course is forced into tension, the 'esulting unit compression ofthe remaining portion 4of the dome would be verymaterially in.-

`creased, since in the circumstances stated the Acompression must be zero rat some point within the inner courses of the dome. Such an inequality in circular compression would tend to change the shape of the dome, withresultant heavy bending and stresses impossible ofsolution. By subjecting the marginal tension of the dome to a compressive pre-stressing in the manner described, therewill be no tendency to impart tension to any portion of the inner courses of the dome, which will at all points remain in compression, so that abnormal or deleterious in- @qualities in the distribution of stress will be avoided and the proper weight and dimensions for each portion of the dome properly computed,

for the purpose, which reduces the cost `of erecv `tionfto a nmin'imumfsincethe use of formsiand -th'e pouring "ofconcrete will be 'confinedfsole'ly'to *the fformation 'of 'the `beamsfand ribs which encloseithe -metalj reinforcement. -At the same time theI completed `dome is'entirelyfree from obtrusiveinteriorbeamor truss vwork of an expensive and unsightly character, `since the only breaks in the interior contour of the'dome are of slight depthand offanature which in no -way detracts fromthe vpleasing appearance of the structure.

Although Ithe invention has been described with -particularity,.an'd in relation 'to `the erec- '.tion of a relativelybroa'd flat ldorne, it Will'of course be -understood lthat the principlesy here involved Aare'applicableito domes of any desired;` coniiguratiom v'since the stresses to`which .every portion `of the 'dome is subjected can berreadily Vcomputed and 4adequately provided for.

1 claim: v lL'A dome consisting formed o'f pre-cast adjoiningsections vof plastic `material and inner and upper courses supported uponfand abutting in succession against themar- `ginal course and against one another, an inner `circumferential metal reinforcement positioned within vthe confines of Vthe marginal course exterfnally of the body `thereof and in contiguous relation thereto, connections between the slab sections and said metal reinforcement, the metal reinforcement being undertension and the sec-i tions connected therewith being compressively ,pre-stressed thereby to compensate for. the

weight-factor forces of vthe inner and upper courses tending to impart tension to the'sections `of -the -marginal course.

2. A circular dome consisting of a marginal Vcourse *formedof .pre-cast-slab sections of plastic cmaterialiarranged in edge-to-edge `abutting relationship and inner courses supported upon and abutting successively against the marginal course@lv and" against one another, -a plurality of tension rings' extending circumferentially around the marginal course externally and on the inner side thereof, .and tying means for securing the sections of the marginalcourse to the tension rings. v `the rings being vunder ytension 'and the-sections connected therewith beingV thereby compressively pre-stressed -to lcompensate against forces tend- 3. A circular dome consisting of a course formed o f pre-cast slab sections 0f plastic material arranged in edge-to-edge abutting relationship and 'innercourses supported upon and abutting Ysuccessively against the marginal coursey and againstoneaanother, a plurality of vtension vrings extending -`circum'ferentially around the of a lmarginal ceirse'` marginal ing-to impart tension to 'the sections of themarginal course.

material adjoined along their edges and inner courses abutting successively against the marginal course and against one another, a plurality of tension rings extending circumferentially along the interior of the marginal course, and tying means for securing the Vsections of the marginal course to the tension rings, the tentying means forsecuring the sections of the gsion` ringsbeing pre-tensioned andthe sections -:connectedrtherewith beingl compressively..v prestressedto compensate against forces tendingto vimpart tension to the sections of the marginal course, radially extending reinforcing rods downgturned at `their outer ends and underlying the fcourses, and tyingmeans for `securing the sections of the courses to the radial reinforcing rods. v5. A circular dome consisting of a marginal course formed of pre-cast slab sections of plastic 'material adjoined along-their edges and inner Acourses abutting successively against the Inar- I;ginal course and against oneanother, a plurality l of; tension ringsV extending circumferentially along the interior of the marginal course, and

marginal course tothe tension rings, the tension rings being pre-tensioned andthe sections connected therewith being compressivelyr prestressed; to compensate against forces tending to impart;v tension to the sections of the marginal coursegrladially extending reinforcing rods down- .turned at their outer ends and underlying the courses, and tying means for securing the sec- 25` tions of the courses to the radial reinforcing rods, arch shaped ribs of plastic material embedl ding'the radial reinforcing rods, and circumfer- 1 entially extending ribs of plastic material embed- Y ding the tension rings.

- 6 TA circular `dome consisting of a marginal course formed of pre-'cast slab sections of plastic material adjoined along their edges and inner coursesvabutting successively against the marginalcourse and against one another, a plurality of tension rings extending circumferentially along theinterior of the marginal course and having their opposed ends oppositely Vthreaded and united by turnbuckles, tying means for securing the sections of the marginal course to thetension rings, the tension rings being pretensioned and the sections connected therewith being compressively pre-stressed to compensate i against forces tending to iin-part tension to the i sections of the marginal course, radially extending reinforcing rods downturned at their outer vends and underlying the courses, and tying rcourse, threading the individual sections of the marginal courseupon an inner split circular tenj sion rod inside' the connes of the dome, and

drawing the ends of the tension rod together to tighten the same and bind the sections of the lmarginal course together to equalize and compensate for the inherent circular compression and tension stresses existing in the marginal and Y inner courses.

8. The method of constructing domes which y,includes assembling a marginal course consisting of pre-cast adjoined sections of plastic material, building up the dome by inner courses standing in circumferential edgewise relation to one another and supported by the marginal course, threading the individual sections of the marginal course upon an inner split circular tension rod inside the confines of the dome,V drawingA the ends of the tension rod together to tighten the same and bind the sections of the marginal course together to equalize and compensate for the inherent circular compressionl and tension stresses existing in the marginal and inner courses, embedding the tightened tension rod completely in an inner ribbing of plastic material and allowing the latter to harden.

9. The method of constructing a concrete dome which comprises erecting a temporary support, positioning upon the support a body formed of plastic material and shaped to provide a dome, slidably connecting a series of split circular tension rods to the dome about the interior thereof at circumferentially spaced points with the rods occupying positions at different elevations within -the confines of the dome, drawing the ends of the split tension rods to reduce `the effective circumference of the tension rods and apply stresses to the dome to compensate for weight-factors existing in the dome, and thereafter removing the temporary vsupport whereby the dome remains sustained independently thereof.

=10. A circular dome comprising a vdome-like body of concrete, a plurality of series of anchors partially embedded in the body and having corresponding ends thereof protruding exteriorly of the body inwardly of the confines thereof, the anchors of each series being spaced from each other circumferentially in substantially the same horizontal plane, each series of anchors occupying different elevations within the dome structure, and a split circular tension rod slidably extending through the protruding ends of all the anchors of each series, and means for drawing the ends of each tension rod to contract the latter and compensate for weight-factor stresses existing in the dome body.

WILLIAM s. HEWETT.