CROSS REFERENCES TO CO-PENDING APPLICATIONS
This invention is an improvement upon the inflatable form structures disclosed in the co-pending application of Horrall Harrington, Ser. No. 760,297 and now U.S. Pat. No. 3,619,432, filed Sept. 17, 1968, entitled "Method and Apparatus for Construction of Concrete Shells."
BACKGROUND OF THE INVENTION
Concrete shells have been in use for many years. A substantial body of technical literature on stress analysis and design data is available on structures of this kind and many concrete shell buildings have been erected, primarily in Europe and Latin America. Comprehensive design data for concrete shells is available from the Portland Cement Association.
One technique that has been successfully employed in the erection of concrete shell structures utilizes a comprehensive fabric form, much like an enormous tent, for the complete shell. The form is inflated to afford a continuous cover for the building structure. The concrete is applied to the surface of the fabric form while the form is inflated. The concrete may be applied to the exterior of the fabric form; alternatively, the concrete is applied to the internal surface of the form, as disclosed in United States Patent No. 3,118,010 to Horrall Harrington, issued January 14, 1964.
Another and improved technique for erecting concrete shell buildings utilizes a form assembly comprising a rigid structural frame with a two-layer flexible inflatable form mounted on the frame. The frame has a configuration generally conforming to one segment of the desired concrete shell. The form assembly is aligned with a part of the building foundation and the form is inflated. Metal reinforcements are then positioned on the external surface of the form. Concrete is deposited over the form surface and permitted to set, after which the form is deflated and the form assembly is moved to a new position adjacent the completed segment of the concrete shell to permit construction of the next shell segment. This particular technique, described in Harrington application Ser. No. 760,297, affords substantial advantages with respect to construction of different building shapes and configurations, producing practical, inexpensive, multisegment shell structures.
In the use of inflatable forms constructed of woven or other like flexible material referred to generically herein as "fabric," substantial difficulty may be encountered in securing the edges of the fabric to a frame or other support structure. This is particularly true with respect to the two-layer inflatable form employed in the preferred building method described above. If the edges of the form are fastened down by retaining strips that use nails, bolts, screws, or other fasteners that project through the fabric, there is a tendency for the fabric of the form to tear, particularly on repeated use of the form in constructing multi-segment shells. Moreover, conventional fastening means make it difficult to remove the fabric portion of the form from a supporting structure for re-use in a different construction job, since the edge portions of the fabric are almost inevitably damaged during use or on removal.
SUMMARY OF THE INVENTION
It is a principal object of the present invention, therefore, to provide a new and improved means for mounting a two-layer inflatable flexible form on a supporting structure for use in the erection of a concrete building shell.
A further object of the invention is to provide a new and improved means for mounting a two-layer fabric form on a support structure that permits convenient removal of the fabric part of the form from the support structure for repair or replacement purposes or for re-use on a different support structure.
An additional object of the invention is to provide a simple and inexpensive mounting means for mounting the edge of the fabric of an inflatable concrete building shell form on a support member without requiring the use of screws, bolts, nails or other elements that project through the fabric of the form.
Accordingly, the invention relates to a form assembly for constructing a concrete shell for a building of the kind comprising a wall structure defining the perimeter of a building space and a concrete shell covering that space. The form assembly of the invention comprises a rigid structural frame, conforming to the configuration required for one segment of the concrete shell and having a plurality of form-supporting members extending around the perimeter of the frame. An inflatable form is mounted on the frame and affords a substantially air-tight chamber spanning the space between the form-supporting members, the inflatable form including an outer layer formed of a strong, relatively inelastic fabric. A retainer member is affixed to one of the support members and affords a substantially continuous channel of given height and width facing outwardly of the space spanned by the fabric outer layer of the inflatable form. A rail member is wrapped in the edge portion of the fabric outer layer corresponding to the aforesaid one support member; the rail member has a height smaller than the height of the retainer channel but has an effective diagonal thickness substantially greater than the effective internal height of that channel, permitting ready insertion of the rail member and the edge portion of the fabric outer layer into the retainer channel when the form is deflated for releasable mounting of said outer fabric layer on said frame. The rail member rotates within the retainer channel into locking engagement therewith upon inflation of the form.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view, partly in section, of a portion of a building incorporating a partially completed multi-segment concrete shell erected by means of an inflatable form in accordance with the method described in Harrington application Ser. No. 760,297;
FIG. 2 is a sectional elevation view taken approximately along line 2--2 in FIG. 1;
FIG. 3 is a detail sectional view of a part of the form assembly, taken along line 3--3 in FIG. 2, with the form deflated, illustrating one embodiment of the present invention;
FIG. 4 is a sectional view like FIG. 3 but with the form inflated; and
FIG. 5 is a sectional view, like FIG. 4, of another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the erection of a concrete shell building using an inflatable form, it is first desirable to erect a wall structure defining the building space to be covered by the concrete shell. The concrete shall can start from ground level, in which case the wall structure may comprise simple footings. In many applications, however, it is desirable to use continuous vertical walls or a plurality of columns around the periphery of the building, affording a wall structure that extends above ground level. The term "wall structure," as used herein, is intended to encompass a continuous footing, a continuous wall above grade level, a plurality of vertical columns, or any combination thereof.
For a generally rectangular building having vertical side and end walls, the basic foundation structure may be as illustrated in FIG. 1, comprising two side walls 20 and 21. Walls 20 and 21 may be of any conventional structural material, including concrete, steel, or wood, so long as they have adequate strength for supporting the concrete shell that is to cover the building. Walls 20 and 21 may be supported upon suitable footings below the ground surface, as illustrated in FIG. 2. A floor 22 extending between walls 20 and 21 may be formed before the shell is constructed, as a part of the foundation structure. On the other hand, floor 22 may be constructed after the shell has been completed. In the building shown in the process of erection in FIG. 1, no end walls between the side walls 20 and 21 have as yet been erected; the construction of the end walls for the building has been deferred until after erection of the shell.
In the erection of the concrete shell, a form assembly 23 is employed. Form assembly 23 comprises a rigid structural frame 24 including four peripheral form support members 25, 26, 27, and 28. For the particular building shown under erection in FIG. 1, the support members 25-28 of frame 24 are of linear configuration, conforming to the required configuration for the front and rear edges of each segment of the particular concrete shell that is to constitute the building roof. For other shell shapes the form support members, particularly members 25 and 26 extending between walls 20 and 21, may be of arcuate or other non-linear configuration. Two concrete shell segments 29 and 30 have already been completed, in the building illustrated in FIG. 1. The support members 25-28 may be formed of steel, laminated wood, or any other suitable structural material or combination of materials affording sufficient strength to hold the shape of a fabric form; steel is preferred for a part of the support members as described more fully hereinafter.
Form assembly 23 further comprises an inflatable form mounted on and spanning the space between the support members 25-28 of frame 24. As shown in FIGS. 2, 3 and 4, the inflatable form comprises an outer fabric layer 31 and a lower deck 32 across the support members. The fabric layer 31 and deck 32 afford a substantially air-tight chamber 33 between them. It is not essential that the chamber 33 be absolutely air-tight. In fact, pressure venting may be desirable to facilitate maintenance of a constant pressure within chamber 33 during use of the form assembly 23. Furthermore, small tears or other holes in either fabric layer 31 or deck 32 can be tolerated and can be compensated by providing an adequate supply of air.
In the building under construction, as illustrated in FIG. 1, the two side walls 20 and 21 are parallel to each other. The frame 24 of form assembly 23 spans the space between the two building walls 20 and 21 and the inflatable form 31,32 covers the entire space between the support members 25-28. Thus, frame assembly 23 spans a complete segment of the building between the two walls 20 and 21 and extends into close conjunction with the walls.
The frame 24 of form assembly 23 is supported upon a series of jacks 35, as generally indicated in FIG. 2. Jacks 35 may be of conventional construction. Preferably, frame 24 is mounted on wheels (not shown) positioned to support form assembly 23 when jacks 35 are not in use, to facilitate movement of the form assembly to a new location.
Form assembly 23 also includes means for introducing air under pressure into the chamber 33 formed by fabric layer 31 and deck 32. This air pressure means may comprise a simple hose or other conduit 51 mounted in deck 32 and connected from chamber 33 to a blower 53 mounted in frame 24 below deck 32. Only a relatively small blower is required; commercially available centrifugal blowers are adequate for use as blower 53. In most applications, a five to ten horsepower centrifugal blower is adequate to maintain the appropriate pressure for inflation of the form. One or more individual relief valves or other pressure control valves may be incorporated in either fabric layer 31 or deck 32 to provide a means for maintaining a uniform pressure within chamber 33 when the form is inflated.
In considering the erection of a concrete shell segment, a starting point may be taken from the position of form assembly 23 shown in FIG. 1. From the illustrated position, the form assembly is moved into alignment with the already completed shell segment 30. This movement is accomplished with the frame 24 of the form assembly lowered, by means of jacks 35, so that there is a clearance of at least one or two inches below the projecting edge 55 of shell segment 30. Moreover, the movement of the form assembly into position is preferably accomplished with the form 31,32 deflated. The form has been shown inflated in FIG. 1, merely to correlate its shape with the completed shell segments 29 and 30; when deflated, fabric layer 31 lies flat across deck 32 (see FIG. 3).
When form assembly 23 is aligned with the previously completed shell segment 30 and is also aligned with the portion of the wall structure (walls 20 and 21) that is to be spanned by the next shell segment, the form assembly is blocked in position by any appropriate means. Blower 53 is then actuated to force air under pressure into the chamber 33 intermediate fabric layer 31 and deck 32, inflating the fabric form to the condition illustrated in FIGS. 1, 2 and 4.
After the form is inflated, metal reinforcing members (not shown) are positioned on the external surface of fabric layer 31. Once the metal reinforcing members are in place on and supported by the inflated fabric form, a layer of concrete is deposited on the external surface of the fabric form, covering the reinforcing members. This concrete layer usually extends beyond the edge of form 23 as indicated by the dash line 56 in FIG. 4. Along support members 27 and 28, the outer extension of the concrete tops walls 20 and 21, so that the concrete rests on and and bonds to the wall structure of the building. Wet mix pneumatic application is most effective for depositing the concrete although, with proper care to avoid damage to fabric 31, conventional crane and bucket application can be used. Even on steeply sloped surfaces, pneumatic placement is made possible by application in layers not exceeding one inch in thickness. For more nearly horizontal surfaces, thicker layers may be employed.
Once the concrete has set, the shell segment is complete and it is time to move the form assembly into position for the next shell segment. The form is deflated to release the upper fabric layer 31 from the concrete. This can be most effectively accomplished by changing the connection to blower 53 and using the blower to exhaust chamber 33, affording a relatively small vacuum within the chamber to assist in separation of the fabric from the concrete of the shell. The jacks 35 are then used to lower form assembly 23 enough to assure clearance from the shell segment that has just been formed, and the form assembly is rolled out from under the completed shell segment. It is then ready to be aligned with the leading edge of the completed shell segment and the steps set forth above are repeated to form the next shell segment.
FIGS. 3 and 4 illustrate the mounting assembly of the present invention, utilized to secure the edge portion of fabric layer 31 to support member 25 in frame 24. As shown in FIGS. 3 and 4, support member 25 comprises an elongated steel plate 61 mounted on a major structural element 62 of the form assembly 24. Member 62 may comprise a conventional wood beam. A plurality of bolts 63 extending downwardly through plate 61, adjacent beam 62, and through a mounting plate 64 on the bottom of the beam, being threaded into the nuts 65. Plate 61 is similarly secured to other structural elements of the main frame 24 of form assembly 23; other suitable mounting arrangements may be employed if desired. Beam 62 is also one of the supports for the deck 32 that constitutes the bottom layer of the inflatable form as described above in connection with FIG. 2.
A retainer member 66 is affixed to the steel plate 61 of support member 25. As shown in FIGS. 3 and 4, retainer member 66 preferably comprises a steel angle member welded to plate 61 along one edge 67. Retainer member 66 extends for the full length of support member 25 and affords a substantially continuous channel of given height and width facing outwardly of the space spanned by the outer fabric layer 31 of the inflatable form. A series of brace members 68 may be mounted upon plate 61 in engagement with the back of the angle retainer member 66 to brace the retainer member against the forces applied thereto when the form is inflated.
A rail member 69 is wrapped in the edge portion 71 of the fabric outer layer 31 that extends along support member 25. Rail member 69 is preferably an inexpensive wood rail of rectangular cross-sectional configuration. The rail member has a height smaller than the height of the channel afforded by angle retainer member 66, but the diagonal dimension of rail 69 is greater than the effective internal height of the channel. The wrapping of rail 69 in the edge portion 71 of fabric layer 31 is not elaborate; the fabric is simply passed around the rail one time and the free end 72 of the fabric is laid back across the top of retainer member 66. As is readily apparent from FIG. 3, rail member 69 and the fabric edge portion 71 fit loosely into the channel 70, permitting ready insertion thereof into the channel when the form is deflated, as shown in FIG. 3. This construction affords a convenient releasable mounting of the outer fabric layer 31 on frame 24 of form assembly 23. It also permits convenient removal of the fabric from the frame of the form if there is any damage to the fabric requiring replacement thereof or if use of the form assembly has been completed and it is desired to employ the fabric layer 31 in another form assembly.
After fabric layer 31 is mounted on support member 25, as shown in FIG. 3, it may be desirable to add an auxiliary form, extending beyond the edge of fabric layer 31, to provide for formation of a rim or edge portion on the concrete shell. As shown in FIG. 4, this auxiliary form may comprise a vertically extending form member 73 and a horizontally extending form member 74, both mounted upon a support block or beam 75 that extends parallel to support member 25. The auxiliary form structure is supported upon the beams 62 of frame 24.
When air is introduced under pressure into the chamber 33 between the outer fabric layer 31 and the deck 32, the fabric layer 31 expands to the desired configuration for a segment of the concrete shell, as generally illustrated in FIGS. 1 and 2. The fabric is lifted clear of deck 33 and pulls upwardly and inwardly of the form assembly frame as indicated by arrow A in FIG. 4. A substantial tension force is exerted on the fabric, in the direction of arrow A, since form 31 must be maintained taut enough to support a substantial weight of concrete and steel reinforcement without appreciable deformation and is preferably maintained under sufficient pressure to support workmen and a limited amount of equipment on the fabric during placement of the reinforcement and pouring of the concrete.
The pull exerted upon the fabric layer 31 rotates rail 69 within channel 70. The rotation of rail 69 locks the corners of the rail into engagement with the internal walls of channel 70 and maintains a firm mount for fabric 31 when the form is inflated. Because the fabric edge portion 71 encompasses rail 69, and since there are no nails, screws, or other fasteners extending through the fabric into rail 69 or any other portion of the mounting structure, the inflation of the form does not damage the fabric outer layer. In fact, the form can be inflated and deflated numerous times, in the erection of a building, with little or no damage to the edge portion of fabric layer 31, using the mounting assembly illustrated in FIGS. 3 and 4. Nevertheless, when use of the form assembly 23 is completed, or if fabric layer 31 has been damaged in any way during use, the fabric layer can be rapidly removed from the form assembly simply by deflating the form and pulling rail 69 out of channel 70. Where an edge form, such as the auxiliary form 73-75, is used, it may be necessary to remove the auxiliary form to permit removal of fabric 31, but this would also be necessary with virtually any other mounting arrangement for the fabric.
FIG. 5 illustrates another embodiment of the mounting assembly of the invention in a view similar to FIG. 4, with the form inflated. In the construction illustrated in FIG. 5, the edge support member 125 of a form assembly frame 124 comprises a tubular steel frame member. On the top of support member 125, a steel angle retainer member 66 is welded to the support member. Retainer member 66 extends longitudinally of support member 125 to form a substantially continuous channel 70 of given height and width facing outwardly of the space spanned by the fabric outer layer 32 of the inflatable form.
In the mounting assembly of FIG. 5, two rail members 169 and 171 are used to mount the edge portion 71 of fabric 32 in channel 70. The main rail member 169 is wrapped in the edge portion 71 of fabric 32 in the same manner as rail 69 in FIGS. 3 and 4, with the free end 72 of the fabric extending back into the inflation chamber 133 of the form assembly. Rail member 169 is substantially thinner than the rail member of the previously described embodiment; typically, an ordinary wood furring strip can be used as rail member 169. The auxiliary rail member 171 may also be an ordinary wood furring strip. Auxiliary rail member 171 is inserted into channel 170 below the principal rail member 169 and outside of the edge portion 71 of fabric 32. Thus, the auxiliary rail materially reduces the effective internal height of channel 70.
The mounting assembly of FIG. 5 further comprises a plurality of the small wood wedges 172 that are inserted into channel 70, from the open end of the channel, between support member 125 and rail 171. Wedges 172 are not forced into channel 70 under any great pressure; they may be tapped into place with an ordinary carpenter's hammer. Wedges 172 serve simply to clamp rails 169 and 171 and the edge portion 172 of the fabric into channel 70 prior to inflation of the form. After fabric 32 has been positioned on the form, an auxiliary edge retaining form, comprising form members 73, 74, 75A and 75B, may be mounted on support member 125 to make the form assembly ready for operation. Suitable brackets 76 may be provided to support the outer members of the auxiliary edge form.
In the construction illustrated in FIG. 5, there is no continuous deck for the inflatable portion. Instead, a second fabric layer 231 is provided and constitutes the bottom of the inflatable form. To mount fabric layer 231 on the frame 124 of the form assembly, and specifically on support member 125, a mounting arrangement like that for the upper fabric layer 32 is used. The mounting for the lower fabric layer 231 includes an angle retainer 266 welded to support member 125 and forming a continuous channel 270 that faces outwardly of the inflatable chamber 133. A principal rail 269 wrapped in the edge portion 271 of fabric layer 231, and an auxiliary rail 277, together with a plurality of small wedges 272, serve to mount the edge portion of fabric 231 in channel 270 in the same manner as described for fabric layer 32 and channel 70.
The operational characteristics for the mounting assembly illustrated in FIG. 5 afford all of the advantages achieved by the construction of FIGS. 3 and 4. In assembling the inflatable form, the upper fabric layer 32 is spread loosely over the frame 124. The lower fabric layer 231 may be supported on any desired temporary support; a series of ropes spanning the bottom portion of frame 124 will serve. The edge of fabric 32 is wrapped in rail 169, the wrapped rail 169 and the auxiliary rail 171 are inserted into channel 70, and the rails are wedged in place by wedges 172 as shown in FIG. 5. The fabric is not in tension at this time and the mounting arrangement can be accomplished quickly by a limited number of workmen. The same technique is followed for fabric layer 231, with the edge portion being wrapped around layer 231 and the rails 269 and 271 then being inserted into channel 270 and wedged in place by wedges 272.
The form can then be inflated. The tension on the fabric layers 32 and 231, indicated by the arrows A and B, rotates the rails within the channels afforded by retainer members 66 and 266 and firmly locks the edges of the fabric layers in place, as shown in FIG. 5, without damage to the fabric. Thus, the mounting assembly performs its primary function of affording a secure and continuous anchorage for the fabric layers of the form despite the high tension forces created in the fabric by the inflation air pressure. In addition, the fabric mounts each afford a tight seal against air leakage, in contrast with other mounting arrangements requiring piercing of the fabric. The illustrated mounting arrangements also afford secure maintenance of the fabric edge position during installation and during random movements of the fabric that may occur as air pressure builds up in the inflatable form.
The tension in the fabric layers, indicated by arrows A and B in FIG. 5, pulls the principal rails 169 and 269 against the inner surfaces of their respective retainer members 66 and 266. As a consequence, the edge portion of each of the fabric layers 32 and 231 is effectively maintained in a continuous vise in which the clamping force of the vise increases as a direct function of fabric tension. This action is aided by the high friction restraint at each bend of the fabric around the corners of the principal rails. Wedges 172 and 272 serve only for the temporary purpose of maintaining fabric position during air pressure changes for inflation and deflation.
In both of the illustrated embodiments of the invention, the clamping means for the fabric does not subject the fabric to any cutting or other severe mechanical attrition, facilitating re-use of the fabric after the form assembly is dismantled. The use of wood for the rails 69, 169 and 269, and for the auxiliary rails 171 and 277, facilitates the prevention of damage to the edge portions of the fabric. The use of wood rails for this purpose is also advantageous from an economical standpoint. Furthermore, the wood for the rails is generally available from any lumber yard; ordinary furring strips perform this function quite adequately.