Building construction and method of same

[57] ABSTRACT

A building construction and method which utilizes columns and precast concrete, generally rectangular, horizontal floor slabs. A first set of columns is erected at the building site and post-tensioned. Then the horizontal slabs are lifted up and positioned with the corners thereof resting on the upper ends of the columns. In the preferred embodiment, each slab has a vertically extending pin secured to the slab at each corner. After the slabs are positioned on the columns, a locking ring is dropped over the pins with the upper edge of the ring extending above the upper horizontal surface of the slabs. A second series of columns is erected in vertical alignment with the previously erected and post-tensioned columns. Each column in the second series rests on the upper edge of the corresponding locking ring. This arrangement provides essentially a point support for the column which permits very easy vertical alignment of the column. Once the column has been aligned, the space between the bottom of the column and the upper surface of the horizontal slabs is dry packed. After the dry pack has set, the second series of columns is post-tensioned before receiving the next series of horizontal floor slabs. The resulting connection between the column and slabs provides a “semi-rigid” connection which is suitable for use in buildings that are constructed in earthquake zones.

Claims, 7 Drawing Figures

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PATENTED 0EC2 51973

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SHEET 1 OF 3

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PATENTED DEC 2 51975

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PATENTED DEC 2 51975

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SHEET 3 OF 3

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BUILDING CONSTRUCTION AND METHOD OF SAME

This invention relates to building systems in general and, more particularly, to a building system and method which utilizes post-tensioned columns and precast concrete horizontal floor slabs.

Various types of post-tensioned column and slab building systems are known in the art. A representative example of one such system is disclosed in U. S. Pat. No. 3,260,025 issued July 12, 1966 to Van Der Lely for PRECOMPRESSED VERTICALLY STACKED, PREFABRICATED BUILDING ELEMENTS. In the Van

Der Lely building system, individual column elements are positioned between floor elements with a posttensioning rod-coupling system extending through the columns and floor elements. Alignment of the column and floor elements is achieved by means of complementary, mating surfaces formed in the columns and floor elements. The resulting rigid connection between the columns and floor elements does not provide the desired relative flexibility for earthquake zone building construction. The Van Der Lely system also requires close tolerance manufacturing of the building elements themselves and, more importantly, accurate on-site assembly techniques with a concomitant requirement of relatively skilled and expensive labor.

It is accordingly a general object of the present invention to provide a post-tensioned, column and slab building construction and method which eliminates the relative disadvantages of the prior art systems.

It is a specific object of the invention to provide a building system of post-tensioned columns and slabs which simplifies the erection process and permits the use of relatively unskilled labor.

It is another object of the invention to provide a building system which does not require close tolerance assembly techniques at the construction site.

It is still another object of the invention to provide a post-tensioned column and slab construction which has a semi-rigid connection between each column and slab.

It is a feature of the invention that various building configurations and floor plans can be accommodated by the building system without sacrificing any of the structural and economic advantages of the system.

It is another feature of the building system that the type of connection between the column and slab greatly facilitates the erection and vertical alignment of the columns by providing essentially a point support for the columns during erection.

These objects and other objects and features of the invention will best be understood from a detailed description of a preferred embodiment thereof, selected for purposes of illustration and shown in the accompanying drawings, in which:

FIG. 1 is a view in perspective, partially broken away, showing a multi-story building constructed with the column and slab system of the present invention;

FIG. 2 is another view in perspective and also partially broken away illustrating the corner placement of four horizontal slabs with respect to an interior column;

FIG. 3 is a view in cross-section depicting the posttensioning system for one of the interior columns shown in FIG. 1;

FIG. 4 is a detailed view in cross-section of a typical bearing arrangement for the column and slab system;

FIG. 5 is a view in perspective, partially broken away, showing the relationship of an exterior column with the horizontal slabs;

FIG. 6 is a plan view, partially broken away, of an interior column and slab connection showing a slab reinforcing system; and,

FIG. 7 is a view in perspective, partially broken away, illustrating another embodiment of the column and slab connection.

Turning now to the drawings and particularly to FIGS. 1 through 6 thereof, there is shown a posttensioned column and slab building system constructed in accordance with the present invention and indicated generally by the reference numeral 10. The building system utilizes four major components which comprise: a plurality of laterally spaced, vertical columns 12; a plurality of generally rectangular, horizontal slabs 14 which rest on the upper ends of the columns, a posttensioning system, indicated generally as 16; and a connecting system 18 for connecting the columns and slabs together in a “semi-rigid” connection.

Before discussing the building system components in detail, it will be helpful to briefly describe the general erection techniques employed in constructing the building system of the present invention. Looking at FIG. 1, the first level of columns 12 is erected on a base support or cast-in-place footing and piers (not shown) with the columns positioned in laterally spaced, vertical relationship. After erection, each one of the vertical columns is post-tensioned by means of the posttensioning system 16. The columns are now ready to receive the first horizontal floor slab system. The generally rectangular horizontal slabs are lifted and placed into position with the corners of the slabs resting on the upper ends of the column. The slabs each have chamfered corners 20 which define a central opening 22 when the slabs are positioned on top of the column as best shown in FIGS. 2 and 6. The central opening 22 provides a space for the post-tensioning system 16 and the column-slab connecting system 18, each of which will be discussed below in detail.

With the horizontal slabs correctly positioned on top of the first level columns, another plurality of laterally spaced columns is erected above the slabs and in vertical alignment with the corresponding first level columns. The second level columns are then posttensioned and, thereafter, the same erection sequence is repeated for each additional level.

In the preferred embodiment of the present invention, both the columns 12 and four slabs 14 are formed from pre-cast concrete. Edge reinforcements (not shown) are used in the slab to provide a “beam band” within the slab. Representative dimensions for these two major components are as follows: columns, 8 feet long, 14 inches square; slabs, 12X18 feet and 8 inches thick.

Referring to the detailed and enlarged cross-sectional views of FIGS. 3 and 4, each column 12 has a centrally located cylindrical tube 24 positioned along the longitudinal, vertical axis of the column. Typically, the tube comprises a 2 inches O.D. galvanized steel tube which defines an interior bore 26 within which is positioned a threaded steel tensioning rod 28. The tensioning rod 28 is threaded at both ends and, as shown in FIG. 4, the upper threaded end of the rod extends through a castin-place metal plate 30, a smaller metal bearing plate 32, a post-tensioning nut 34 and into the central open3,780,480 ing 22 defined by the slab corners 20. Each column is post-tensioned after erection by tightening the posttensioning nut 34.

Each column has a grout tube 36 which communicates with the interior bore 26 of the tube 24. A suitable grouting material is injected into the space between the post-tensioning rod 28 and the interior walls of the tube 24 through the grouting tube 36.

An interior threaded coupler 40 is screwed onto the upper threaded end of the post-tensioning rod 28. The coupler 40 is designed to receive the lower threaded end of the post-tensioning rod 28 from the second level column, as shown in FIG. 4. The coupler-tensioning rod system provides a structural connection between the two vertically aligned first and second level columns.

In the preferred embodiment of the invention, the slab corners 20 each rest on a bearing pad 42 which is positioned between the bottom surface of the horizontal slab 14 and the upper end of the column 12. Typically, such a bearing pad can be formed from the material sold under the trade name “FABREEKA”.

Looking now at FIGS. 3, 4, 5 and 6, a cast-in Cshaped channel member 44 is located on each corner of the horizontal slabs. A corresponding vertical pin member 46 is welded to the upper portion of the channel member 44. As best seen in FIG. 4, the upper end of the vertical pin member 46 is flush with or if desired, below the upper horizontal surface of slab 14. After the horizontal slabs 14 are positioned with the corners of the slabs resting on the upper end of the column, a vertically open ring 48 is dropped down over the comer slab pins 46 thereby holding the horizontal slabs in a predetermined horizontal position on the top of the columns. This temporary holding of the slabs is desirable from a safety standpoint since it prevents the accidental dislodgement of the slabs from the top of the columns before post-tensioning of the overlying column.

Preferably, the central opening 22 is filled with grout- ⁴⁰ing material before erection of the second level column. The overlying column is lifted into vertical position over the ring and then gradually lowered down until its bottom surface engages the upper surface of the ring element 48. Since the diameter of the ring is approximately 5 inches and the bottom of the column 12 is 14 X 14 inches, the ring 48 acts as a point support for the column 12. This arrangement greatly facilitates the positioning and vertical alignment of the column 12. After the column has been aligned, the space between the bottom surface of the column and the upper horizontal surface of the two horizontal slabs 14 is packed with a dry pack 50 as shown in FIG. 4. The dry pack material conforms to the cavity shape and compensates for any irregularities in the planar bottom surface of the column. Once the dry pack 50 has been forced into position between the slabs 14 and the overlying column 12, the column 12 is post-tensioned by tightening up on the post-tensioning nut 34 (see FIGS. 1 and 3).

The preceding description has been directed primarily to an interior column-slab configuration in which four slabs rest upon the upper end of the column as shown, for example, in FIG. 2. However, it should be understood that in the case of an outside column such as that shown in FIG. 5, only two slabs will rest upon the column and that the locking ring 48 encloses the corresponding two vertical pins 46 and the posttensioning rod 28. The joint 52 between the two slabs shown in FIG. 5 is filled with grout after the slabs have been positioned on the column. The joint 52 and the 5 similar slab joints shown in FIGS. 1-4 and 6-7 have been depicted in open form for purposes of clarity. However, in practice the bottom slab edges almost touch each other while the upper edges remain open for pouring in the grouting material.

It is also possible to construct the connection shown in FIG. 5 by utilizing a single, generally rectangular slab having no joint 52, but instead, a notch formed in one edge with the two vertical pins 46 secured to each side of the notch. This configuration can be employed to 15 obtain a cantilevered end treatment on a building.

It will be appreciated from an inspection of the drawings, and in particular the enlarged cross-sectional view of FIG. 4, that the pin-ring-grout connection between the slabs and columns is a “semi-rigid” connection and 20 that the connection will provide some degree of flexibility when subjected to lateral forces. This type of semi-rigid connection is especially suited for building construction in earthquake zones. Given the lateral loads placed on a building as a result of an earthquake, 25 the semi-rigid connection shown in FIG. 4 will “open” between the dry pack 50 and the overlying column 12 to permit movement or “knee action ” between the slabs and columns. The already tensioned column rods 28 will be further tensioned as the rods bend under the ³⁰ lateral load. However, when the load is removed, the tensioned rods 28 will return to their minimum tension condition which is, of course, the post-tensioned straight line configuration shown in the drawings.

Looking now at FIG. 6, the column-slab connection is shown in plan view and partially broken away to illustrate the use of a reinforcing rod 54 that is welded to the inside of the corner channel 44 and which extends through a portion of the pre-cast concrete, horizontal floor slab 14. Although the reinforcing rod 54 is not required, it can be used to obtain maximum strength for bearing.

Other connection systems can be employed to obtain the desired “semi-rigid” connection between the horizontal floor slabs 14 and the vertical columns 12. Referring to FIG. 7, each slab corner 20 is provided with a generally C-shaped, vertically extending, cast-inplace channel 56. The temporary mechanical attachment of the floor slabs 14 to the vertical column during ₅θ erection is obtained in the embodiment shown in FIG.

by means of a threaded hook member or eye-bolt 58. A nut 60 is screwed onto the threaded portion of the eye-bolt 58 so that the nut will fit within the channel 56 when the eye-bolt is dropped over the tension rod cou₅₅ pier 40 as shown in FIG. 7. The nut 60 has an exterior dimension which is larger than the outwardly facing opening of channel 56, but smaller than the inside dimension of the channel. In the operative position, nut 60 is forced against the inside wall of the channel open₆θ ing by means of a spring 62.

Having described in detail a preferred embodiment of our invention, it will be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the inven₆₅ tion as defined in the following claims.