Patent Application
20070261324
The present invention relates to manufactured stair treads which are precast and then transported to a remote construction site and secured in place to two spaced stair frames. The stair tread is formed of a self-supporting slab of concrete having weight reducing recesses.
With the increasing cost of fuel, it is a primary objective of the construction industry to reduce fuel expenditures by reducing the weight of transported products. However, the strength and integrity of the product cannot be affected by the reduction in weight.
One aspect of the construction industry particularly affected by increased fuel costs is the construction of stairways for apartment buildings, parking garages, stadiums, etc. Typically, component parts of the stairway are manufactured close to a source of concrete materials. Individual component parts are then transported to the remote construction site for installation. Due to the inherent weight of concrete material, any reduction in the amount of concrete material used would be a significant benefit by a reduction of transportation costs.
Therefore, there is a need in the construction industry to reduce transportation costs while maintaining the structural integrity of the concrete product. In addition, by the use of less concrete, the production costs are reduced.
Accordingly, it is an object of the present invention to provide a reduced weight stair tread having satisfactory structural integrity.
The object of the present invention is realized by a stair tread having a width of 10, 11 or 12 inches. The tread length varies from 32 inches up to 60 inches. The thickness of the tread will usually be 2¼ or 3 inches thick, with a draft of ¼ inch and exposed edges having a ⅜ inch radius.
A significant reduction in weight is obtained by forming two elongated recesses or four segments of recesses in a bottom surface of the stair tread. On a tread having a thickness of 2¼ inches, the depth of the recesses is 1¼ inches deep. On a tread having a thickness of three inches, the recesses have a depth of two inches. Therefore, the depth of the recesses will be at least 50% of the thickness of the tread.
The length of the recesses will vary from 25½ inches for each of two recesses in a 32 inch tread length to a length of 53½ inches for each of two recesses in a 60 inch tread length. Typically, one of the two recesses will have a width of three inches while the width of the other of the two recesses is two inches.
At opposite ends of the stair tread are two ⅜ths inch bolts which are zinc plated. The head and shaft of the bolt is buried in the concrete slab with the threaded portion of the bolts extending out from the bottom surface of the slab. The exposed thread portions of the bolts serve to anchor the treads to spaced apart stair framing at the construction site. Alternatively, weld plates are anchored in the treads instead of bolts.
Extending lengthwise for a majority of the length of the tread are three pieces of #3 rebar. One of the pieces of rebar extends centrally through the slab. The other two pieces of rebar are located towards the front surface and rear surface of the slab, respectively. The pieces of rebar are positioned so that, in the center of the slab, the rebar lies between the two recesses. The rebars at the front surface and the rear surface lie between the external surfaces of the slab and the recesses in the slab. All surfaces of the pieces of rebar are surrounded by at least a ¾ inch radius of concrete in all directions to secure the rebar in the slab and to strengthen the stair tread.
By the described arrangement of recesses and rebar, a 30% to 40% reduction in weight is obtained for a stair tread as compared to a stair tread lacking the incorporated recesses. The weight loss is attributable to 20% to 30% reduction in weight by the presence of the recesses and approximately 10% of the weight loss is attributable to the use of lightweight gravel.
Therefore, the stair tread according to the present invention is made of concrete materials and has properties which comply with the requirements of a Division #3 Section “Cast-in-place Concrete” for normal weight and light weight, ready-mixed concrete with a minimum 28-day compressive strength of 5,000 psi and a total air content of not less than 4% or more than 6%. The tread has a flexural strength of 2,500-3,000 psi in accordance with ASTM C293. There is a 3% to 4% absorption in accordance with ASTM C67. The aggregate has a report sieve analysis in accordance with ASTM C136. The reinforcing bars meet ASTM A615 standards for grade 40 bars. The tread complies with freeze-thaw tests in accordance with ASTM C67. The tread supports a uniform load of 100 pounds per square foot.
The embedded stair tread anchor bolts meet ASTM F1554. The anchor bolts are hot-dip or mechanically deposited zinc-coated anchor bolts with nuts for attaching and securing stair treads to stair framing.
It is therefore another object of the present invention to provide a stair tread having a reduction in weight of 30% to 40% as compared with a normal stair tread of the same dimensions.
It is another object of the present invention to provide a stair tread having a reduction in weight of 30% to 40% as compared with a normal stair tread of the same dimensions with a bottom surface of the stair tread including two recesses extending longitudinally to a depth of at least 50% of the thickness of the stair tread.
It is still yet another object of the present invention to provide a stair tread having a reduction in weight of 30% to 40% as compared with a normal stair tread of the same dimensions with a bottom surface of the stair tread including two recesses extending longitudinally to a depth of at least 50% of the thickness of the stair tread and having a centrally located rebar located between the two recesses.
It is still yet another object of present invention to provide a stair tread having a reduction in weight of 30% to 40% as compared with a normal stair tread of the same dimensions with a bottom surface of the stair tread including two recesses extending longitudinally to a depth of at least 50% of the thickness of the stair tread and having a centrally located rebar located between the two recesses, with the rebar being surrounded by at least a ¾ inch radius of concrete.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.
The following drawings illustrate examples of various components of the stair tread with bolts disclosed herein, and are for illustrative purposes only. Other embodiments that are substantially similar can use other components that have a different appearance.
In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.
With reference to the drawings, in general, and to
With reference to its orientation in
A plurality of precast stair treads 10 of the present invention are transported to the construction site for assembly on the stair frames. The stair frames include a plurality of L-shaped anchors 16 for cooperating with anchor bolts of the stair tread 10. Nuts 18 threaded on the anchor bolts secure the stair treads 10 in place on the stair frames 12, 14.
As shown in
In the stair tread shown, the stair tread 10 has a length of three feet (on the upper surface 22 and 2 feet, 11½ inches on the bottom surface 24), a width of one foot (on the upper surface 22 and 11½ inches on the lower surface 24), and a thickness of 2¼ inches. As shown in
The bottom surface 24 also includes a second recess 36 having a length of two feet, 5½ inches, a width of two inches and a depth of 1¼ inches. Edge 36a is spaced 2¼ inches from rear surface 28 and opposed end edges 36b, 36c are spaced three inches from end surfaces 30, 32, respectively. Recess 34 includes interior edge 34d which is spaced from interior edge 36d of recess 36 by two inches.
In an alternate embodiment, as shown in
Positioned within the gap formed by edges 34d, 36d of recesses 34, 36, respectively, or between rows of recesses 50, 52, is a centrally located piece of rebar 38. Located in the gap between edge 34a and front surface 26 is a piece of rebar 40 and located in the gap between edge 36a and rear surface 28 is a piece of rebar 42. As explained with reference to the strength requirements of the stair tread of the present invention, the pieces of rebar 38,40 and 42 are surrounded by at least ¾ of an inch radius of concrete. Therefore, a diameter “d” for each piece of concrete surrounding rebar 38, 40 and 42 is at least 1½ inches.
Opposed end surfaces 30 and 32 are sloped ¼ inch from upper surface 22 to bottom surface 24 for ease of removal from a mold. The interior of the recesses 34, 36 are of similar construction so as to ease removal of a molding form.
Projecting from the bottom surface 24 are zinc plated bolts 44a, 44b, 44c, 44d. The separation between bolts 44a and 44b is 6¼ inches as is the separation distance between bolts 44c and 44d. The separation distance between bolts 44b and 44d is two feet, 7½ inches as is the separation distance between bolts 44a and 44c. Bolts 44b and 44d are spaced 2½ inches from rear surface 28 and bolts 44a and 44c are spaced 3¼ inches from front surface 26.
The foregoing description should be considered as illustrative only of the principles of the invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
