US1825237A - Fireproof floor construction - Google Patents

Description

Spl. 29, 3L R. McwlLLlAMs 1,825,237

FIREPROOF FLOOR CONSTRUCTION Filed NOV. 8, 1928 Patented Sept. 29, 1931 UNITED STATES PATENT oFFlcE ROWLAND MCWILLIAMS, OF NEW YORK, N. JANE C. MCWILLIAMS, EXECUTRIX OF SAID ROWLAND MCWIIJLIAMS, DECEASED, ASSIGNOR TO REPUBLIC FIREPROOFING COMPANY, INCL, OF NEVI YORK, N. Y., A CORPORATION OF NEV YORK FIREPR-OOF FLOOR CONSTRUCTION Application filed November 8, 1928.

This invention relates to reinforced concrete constructions of the type commonly known as block and reinforced concrete, and to the composition of the blocks which are to be incorporated in the iioor or wall structures.

According to the established practice, the function of the blocks is to provide channels within which the reinforcement and concrete miX is placed to form, upon the setting of the concrete, reinforced concrete beams. The blocks remain permanently embedded in the structure and, theoretically at least, contributes to the strength of the reinforced concrete beams since the block is lusually of a hardened plastic which can take compression.

An examination of the patent literature will show that various workers in this art have proposed to construct reinforced concrete floors in which the blocks are expected to take their proportionate share of the compressive stresses. Such proposals, while of interest from an academic standpoint, have been of but little or no practical value since the proposed blocks were of such composition and/ or configuration that, with the type of labor and under the conditions actually encountered in commercial building operations, an effective and uniform bonding of all of the blocks to the concrete was not possible of attainment.

It will be obvious that the blocks and the concrete portions of the reinforced beam cannot be relied upon to take their proportionate share of the compression unless there is a substantially perfect bonding of each block with the adjacent concrete of the beam. Furthermore, an initially perfect bonding will not necessarily result in a construction in which the blocks and concrete may both carry their full loading since relative changes in length due to applied loads'or to temperature changes may destroy the bond between the blocks and concrete and result in the overloading of one of the compression resisting elements of the beam. Destruction of an initially satisfactory bond will not take place if the block is of such composition that its modulus of elasticity and coefficient Serial No. 318,010.

of expansion are substantially the same as i the corresponding properties of the concrete.

An object of the present invention is to provide a reinforced concrete and block structure in which the blocks are of such composition that, without requiring a mechanical interlocking of the blocks and concrete, the bond established between the blocks and hardened concrete will effectively unite the blocks and concrete to form a true monolithic structure. A further object is to provide a floor construction in which the blocks are effectively bonded to the concrete to act as structural parts of the reinforced concrete beams, and in which the individual blocks have such load-carrying properties and are so positioned in the floor that the main compressive forces are effectively transmitted directly from block to concrete and from concrete to block, thus avoiding use of the load-distributing slab now customarily employed over blocks and reinforced concrete. A further object is to provide a iioor construction in which the blocks function as a structural part of the floor beams, the blocks being so arranged that any stresses due to a diiference between the moduli of elasticity of the blocks and concrete are distributed locally of the reinforced beams. More specically an object of the invention is to provide 'a monolithic floor construction vin which the blocks are pre-formed concrete bodies which include as aln essential element thereof blast furnace s ag.

These and other objects of the invention will be apparent from the following specification, when taken with the accompanying drawings, in which Fig. l is a diagram or flow-sheet indicating the composition and method of manufacture of the blocks,

Figs. 2a and 2b are side elevations of blocks bonded to poured concrete, the specimens having been tested to destruction to determine the strength of the bond,

Fig. 3 is a fragmentary perspective view of a one-way floor construction embodying the invention, and

Figs. 4l and 5 are fragmentary cross sections of a load-supporting beam and a loaddistributing beam, respectively.

It is a fea-ture of this invention that the blocks to be incorporated in the reinforced concrete structures satisfy three essential requirements, as follows:

a. They must have a high compressive strength.

b. They must be of such configuration and composition that the shear resistance of the bond between the block and poured concrete will be of the same order of magnitude as the shear resistance of the block or the poured concrete.

c. The modulus of elasticity of the blocks must not deviate materiallyr from that of poured concrete.

In addition to these properties of the individual blocks it is essential, in any practical construction, that the blocks, be so pla-ced in the Hoor that the transmission of the main compressive forces through immediately abutting blocks is avoided. It is also highly desirable that the blocks be of such section as to provide compression areas of substantially equal magnitude for positive and negative bendingV moments.

I have discovered that blocks satisfying the requirements may be commercially manufactured from slag concrete, i. e. a.

concrete comprising cement, sand and blast furnace slag. Blast furnace slag, as pre- Y pared by steel manufacturers for use 1n concrete, is of quite uniform composition, is very hard and has a rough pitted surface which facilitates the production of homogeneous tile.

As indicated by Fig. l, the mix used in forming the tile comprises, l part of cement, 3 parts of sand and 2%, parts of blast furnace slag of approximately l size, with three gallons of water per sack of ce,- ment (94 pounds). This forms a comparatively dry mixture from which the blocks are molded under heavy pressure and subsequently steam cured, the steam-curing step serving to supply the additionalv water required' for complete hydration of the con-A crete. As indicative of the heavy pressures to be employed I have found that good results are obtained with an eight by sixteen inch block having one closed end and having side walls of one and one-eighth to one and one-quarter thickness, when the pressure is of the order of four and a half to five tons per block.

The ultimate compressive strength of blocks formed in this manner is of the order of 2000 pounds per square inch. The blocks therefore satisfy the first ofthe requirements noted above. The blocks not only' develop the required compressive strength but are relatively light in weight as no internal ribs or reinforcements are employed. Each block preferably takes the form of a rectangular tube having one closed end and preferably the side walls of the block have plane exterior' surfaces for bonding with the poured concrete of a floor structure.

The usual shallow scoring may be employed, if desired, but I have found that the mechanical interlockings of blocks and concrete which prior workers have proposed is not necessary, in commercial operations, to the development of the full strength of the combined block and concrete structure. Due to the fact that a comparatively dry mixture is used the surfaces of the blocks are not perfectly smooth and unbroken but are more or less pitted. lVhile this pitted or indented surface undoubtedly contributes to the strength of the bond established between the tile and poured concrete, it is believed that the composition of the aggie gate has a far greater effect on the bond strength. I am of the opinion that the natural adherent bond between the blocks and concrete is remarkably strong because the chemical composition of the slag aggregate is quite similar to that of Portland cement'. The following table gives an approximate range of the principal components of different Portland cements and a typical analysis, for the same components, of slag used as aggregate:

Whatever the reason or reasons for the strong bond which is effected when the concrete, of the floor is poured, with the usual type of labor and in the usual manner, in the channels between the blocks, it is a fact that the bond established by blocks manufactured in the manner stated above will develop the full strength of the tile and concrete.

Figs. 2a and 2b are side elevations of test specimens which were subjected to shearing stresses in an attempt to determine the ultimate strength of the bond. In each view, the concrete blocks C were formed by pouring concrete against the sides of the block T, the interior of the block was filled with concrete C, and the specimens after hardening, were tested in a compression machine in the usual manner. The dotted lines a indicate the lines of fracture developed when the specimens were tested to destruction and the dotted lines 7) indicate cracks which were apparent after fracture occurred. The specimens did not show any indication of failure at the junction of the block and concrete, the failuresI being due to failure of the poured concrete under combined moment and shear stresses when the shear stress developed at the bond was upward of 250 pounds per square inch, and for some specimens was as high as 37 5 pounds per square inch.

The third requirement for true monolithic constructions in which the blocks carry their share of the load is that the modulus of Y elasticity of the blocks should be approximately the same as that of the poured concrete. The modulus of elasticity of concrete varies somewhat with consistency, but it is evident that the value for the molded blocks will be of the same order as the modulus of elasticity for a poured concrete comprising a 1:2:4 mixture of cement, sand and stone. As will appear hereinafter, the arrangement of the blocks in the floor is such that any shear stresses due to a difference in the modulus of elasticity are taken up locally of the structure.

In Fig. 3 I have shown a fragment of a typical floor construction embodying the invention.

Each block T is of the form shown in Figs. 2a and 2b, and comprises a rectangular tube having one closed end. Each voidforming unit comprises two tile T arranged with their open ends in contact to form a hollow sectional block, these units or hollow blocks being alined in rows to define a plurality of longitudinal channels l in which concrete 2 and steel reinforcing members 3 are placed to form a plurality of load-supporting beams.

It is to be noted that the joints of all blocks in each row are alined in a vertical plane which denes the junction of the two load-supporting beams in which the particular row of blocks is incorporated. 'Ihe blocks of each row are spaced apart to define parallel transverse passages 4 which preferably are normal to the longitudinal channels l. The passages 4 have a width equal to or of the same order of lnagnitude as the width of channels l, and reinforcing members 5 are placed in the passages for cooperation with the concrete Q and adjaA cent blocks T to form load-distributing beams which serve to distribute a concentrated and/or moving live load to a plurality of the load-supporting beams.

The steel reinforcement 5 will, in general, be materially lighter than the reinforcements 3 as the parts are so proportioned that the entire floor load is transferred, by the or supports, and it is obvious that the side supports will carry some part of the load. I have discovered, however, that the dead weight and/or cost of a floor aanel can usually be decreased by so designing one set 0f beams that it will carry the entire load, and designing the intersecting set of beams to distribute concentrated loads transversely of the set of load-carrying beams. Although the floor panel has the same general arrangement as that used when the stresses are distributed in two directions at right angles to each other, i. e., a two-way ioor7 construction, the parts are so proportioned that there is a one-way distribution of the main compressive stresses. The construction is particularly advantageous when the floor panels are not square as the load-carrying beams are designed to extend the short way of the panel and are thus very economical from the standpoint of reinforcement requirements.

It is particularly to be noted that the construction differs essentially from proposedL one-way floor structures in that the blocks do not extend continuously from end to end of the beams. In the present floor structure, the main compressive forces are transmitted from a block to the concrete which was poured against the side of that block, and from the concrete to the next block in the beam. In prior constructions it has been proposed to transmit the main compressive forces through the dry joint formed between two abutting bloclrs. The present invention places the dry joints in the line of the main compressive forces, and, for uniform loading of the beams, no compressive forces will be established in planes transverse to the beams. In actual practice, such transverse force will doubtless arise, but the load-distributing ribs of concrete between adjacent series of transversely alined dry joints are alone sufficient to resist the relatively small compressive forces which may be set up transversely of the load-sup porting beams.

The spacing apart of the blocks along the load-carrying beams is particularly advantageous in a construction in which the blocks carry their share of the load, since any stresses due to a difference in the modulus of elasticity are taken up by the individual blocks and cannot be concentrated upon a single block near the end of the beam.

In a floor construction of this type, and employing two 8 x 16 slag aggregate concrete blocks with walls ll/S-ll/L inch thick to form each unit, the concrete need not be extended above the level of the blocks to provide a cover layer or slab for the floor. Vood flooring or ornamental plastic flooring of negligible structural strength may be applied directly over the tile and beam assembly. The fact that, in commercial construction, the blocks possess such strength andare so incorporated in the floor as to render a: cover layer or slab unnecessary has been proven in actual construction work, and the proper authorities in a number` of the larger cities of this country have approved the usey of floor structures embodying the present. invention.

Tests by the testing laboratories, department of civil engineering, Columbia University, on a floor slab such as illustrated in Figs. 3, 4 and 5 have demonstrated that the. blocks function not only as void-forming bodies but as structural elements of the floor.. In one such test, the extreme fiber stress in the concrete at the instant of failure was computed-on the assumption that the concrete beams carried the entire compressive stress-to be about (3,000 pounds per square inch. It is obvious that the concrete did not carry the entire load, particularly since the average of six compression tests on the concrete was only 1,074r pounds per square inch.

1t is to be noted that the value of the blocks l as structural parts of a monolithic system is not dependent upon a peculiar mechanical interlocking of the blocks and concrete or upon a particular coinposition or method of placing the concrete. The strength of the block and its strong adherent bonding to ne7 cement of usual composition and consistency is inherent in slag aggregate block manufactured in the manner described herein.

The composition of the slag concrete and the high pressure of molding are comparatively critical factors which determine the ultimate strength and the bonding properf ties. llhile some variation is of course permissible, l have determined that any substantial deviation from the composition and the method of manufacture which are described above will result in blocks of inferior strength and/or bonding properties.

Although the invention has been described in connection with a one-way floor, it will be apparent that blocks embodying the invention may be employed in two-way floors such as described in the patent to Burchartz, No. 1,149,180, August l0, 1915.

I claim:

1. A hollow block adapted to serve both as a. void-forming body and as a compression-,resisting element of a reinforced concrete structure, said block having substantially plane surfaces for engagement with and bonding to the poured concrete of said structure, and consisting of concrete substantially identical with that obtained by steam curing a block molded under highr pressure from a relatively dry mixture of cement, sand and blast furnace slag.

2. A hollow block having substantially plane surfaces for bonding with poured concrete of a oor structure, saidl block comprising cement and an aggregate molded under heavy pressure, the aggregate comprising the high temperature product of a niaterial rich in alumino-silicic compoundsand the said plane surfaces of said block having a physical texture and chemical composition which develop, when poured concrete hardens against said plane surfaces, a bond having a shear resistance not less than that of the concrete.

3. A hollow block having substantially plane surfaces for bonding with a poured concrete of a floor structure, said block consisting of a cement, sand and blast furnace slag concrete molded under heavy pressure, and the said plane surfaces of said block having a physical texture and chemical composition which develop, when poured concrete hardens against said. plane surfaces, a bond having -a shear resistance not less than that of the concrete.

t. The invention as set forth in claim 3, wherein the relative parts, by volume of the cement, sand and slag, are 1, 3 and 2%, respectively.

5. In a floor construction, a plurality of hollow blocks alined in rows to define. channels, adjacent blocks of each row being spaced apart to leave passages therebetween, reinforcing members in said channels above the level of the lower surfaces of said blocks, and concrete filling said channels and passages, said concrete terminating in planes substantially flush with the upper and lower surfaces of said blocks having substantially plane surfaces engaging said concrete and each of said blocks being formed of a dry mixture of cement, sand and slag molded under heavy pressure and having such prop-v erties that concrete hardened against the surface thereof develops a bond strength of the order of the shear resistance of said concrete and said blocks.

In testimony whereof` I affix my signature.

ROWLAND MCWILLIAMS.

Images