Cantilever Stairstep Construction

Abstract

Reinforcement steel extends forwardly from flange portions of a short length of metal channel stock into a concrete stairstep body. A pair of tabs are bent rearwardly out from the web portion of the channel member. An upper portion of a metal stringer is received between said tabs and the tabs are welded around their free edges to the sides of the metal stringer. Casting apparatus for the stairstep includes a support frame which includes an intermediate undersupport, contoured to follow the under portion of a stairstep form. The form is a pan-type and is supported by the undersupport and by edge portions which rest on the four sides of the frame. The short channel mounting member is placed into the pan and its tabs are directed through slots formed in a wall portion of the form on opposite sides of the undersupport. When the web of the channel member is positioned flat against such wall portion of the form both it and the reinforcement steel connected thereto are properly positioned within the form.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to reinforced concrete stairsteps of the cantilever type, and more particularly to improvements in the manner in which such stairsteps are mounted onto a stringer and in the manner of casting such stairsteps.

2. Description of the Prior Art

It is old to construct a stairway from one or more stringers which extend longitudinally of the stairway and to which precast stairsteps are attached. A stairstep of this general type is shown by U.S. Pat. No. 3,467,220, granted Sept. 16, 1969, to Frank B. Smith and Steffan B. Harley. The stairway shown by this patent includes preformed metal stairsteps which are bolted to the stringer. However, it is old to make stairsteps of this type from reinforced concrete, to embed a metal plate in said concrete, and to attach the stairstep to a metal stringer by welding such plate to the upper edge portions of the stringer.

A disadvantage of welding a flush plate wall to upper edge portions of the stringer is that the welding torch must be directed towards the concrete body of the stairstep. This results in undesirable heating of the concrete which quite often weakens the concrete. Also, considerable care must be taken to support the stairstep in a substantially perpendicular position on the stringer as it is being welded thereto.

SUMMARY OF THE INVENTION

Stairsteps of the present invention include a mounting member having a pair of rearwardly extending metal tabs between which an upper portion of a stringer is received. The free edge portions of the tabs are welded to side portions of the stringer. Therefore, the heat of the welding torch is not directed towards the concrete body of the stairstep.

According to an aspect of the invention, the stairsteps are formed in such a way that the mounting tabs are properly aligned relative to the concrete body of the stairstep, so that when the stairstep is installed onto a stringer the tabs function to correctly align the stairstep, to hold it substantially perpendicular to the stringer. Also, the tabs help to retain the stairstep on the stringer before it is permanently secured thereto by welding.

The stairstep casting apparatus may comprise a support frame having four interconnected side and end members and an intermediate undersupport for a pan-type form which is insertable into said frame. The form includes edge portions restable on the side and end members of the support frame and wall means restable on the undersupport. The wall means includes a pair of parallel slots formed therein which when the form is in the support frame are located on opposite sides of the intermediate undersupport. The slots are sized to receive the mounting tabs which project rearwardly from the stairstep mounting member. When such tabs are located in the slots, and the web portion of the mounting member between the tabs is flat against the form wall, the mounting tabs are correctly aligned with respect to cavity for the concrete so that the finished stairstep will be substantially perpendicular to a stringer received between the tabs. Also, reinforcement steel connected to the mounting member and projecting therefrom into the cavity is properly positioned so that it will provide reinforcement in the finished stairstep where reinforcement is needed.

These and other features of the invention will become apparent from the following detailed description of the illustrated embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmentary isometric view of a cantilever stairway, showing a reinforced concrete step in full line and a skeleton view of a second step;

FIG. 2 is a fragmentary side elevational view of the stairway, presenting a skeleton view of a single stairstep;

FIG. 3 is a cross-sectional view taken substantially along line 3--3 of FIG. 2;

FIG. 4 is an isometric view of an embodiment of the stairstep mounting member;

FIG. 5 is an exploded isometric view of an embodiment of the apparatus for casting the stairstep;

FIG. 6 is a cross-sectional view taken through the casting apparatus, with a stairstep skeleton in place within such apparatus;

FIG. 7 is a view like FIG. 6, but showing concrete in the form cavity and showing a leveling member in its path of travel across the top of the casting apparatus;

FIG. 8 is a view like FIG. 6 and 7, but showing the form removed from its support frame and the stairstep being rotated out from such form; and

FIG. 9 is a fragmentary top plan view of the mounting member inside the form, showing the relationship of its mounting tabs to the slots in the bottom wall of the form and to the intermediate undersupport of the support frame.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, the type of stairway to which this invention is directed comprises a longitudinal stringer 10 (or a plurality of parallel stringers) and a plurality of stairsteps 12 which are spaced apart along the stringer 10 and are attached thereto. This type of stairway is generally termed a "cantilever" stairway. It includes rising portions throughout which the stringer 10 is set at an angle, as illustrated, and may include landing portions (not shown) in which the stringer 10 is horizontal.

A rising portion of the stairway is illustrated and a stairstep construction for such portion will be described. However, it is to be understood that the invention applies as well to landing sections of the stairway, and the term "stairstep" as used herein is meant to mean a horizontal stair member within a landing section as well as an individual stair member which is attached to a sloping stringer.

Referring now to FIGS. 2-4 in particular, according to the present invention, the stairstep 12 is formed to include a mounting member 14 which may be constructed from a short length of channel stock. It comprises a web 16 and a pair of flanges 18, 20.

At two spaced apart locations, one side and both ends of an elongated rectangular figure are cut through the web and the material within such figure is bent rearwardly about the remaining side to form a rearwardly extending mounting tab 22. The two mounting tabs 22 are parallel and are spaced apart a distance substantially equal to the width of the stringer 10.

As shown by FIG. 1 and 2, a rectangular loop 24 of reinforced steel is welded to the flange 18 and a length of reinforcement steel 26 that is bent into the form of a shallow V is welded to the flange 20. The general plane of the loop 24 extends at an angle X relative to the web 16 which is the angle necessary to result in the general plane of the loop 24 being substantially horizontal when the member 14 is attached to a sloping stringer 10. Also, the position of the loop 24 is such that its side and end parts are located in the upper portion of the concrete stairstep body, so that they can carry tension forces imposed on such body when a downward force is applied on the stairstep 12.

The mounting member 14 and the reinforcement steel members 24, 26 together form a "skeleton" for the stairstep 12. When such a skeleton 14, 24, 26 is embedded in the concrete body of the stairstep the rear surface of the web 16 is substantially flush with, or forms, a rear surface of the stairstep 12.

Herein, the upper surface of the concrete body is considered to be a forward portion of the stairstep and any portion of the stairstep which is generally on the opposite side of the stairstep from the upper surface is considered to be a rear portion of the stairstep. In the illustrated embodiment it is evident that the stairstep 12 includes a rear surface which forms the base of the step and which is flat against the upper surface of the stringer 10. The rear portion of a horizontal stairstep member may be directed downwardly.

According to the invention, an upper portion of the stringer 10 is snugly received between the mounting tabs 22. The mounting tabs 22 are welded to the side surfaces of the metal stringer 10 along their free edges, as indicated at 28 in FIG. 2. The mounting tabs 22 help locate the stairstep 12 relative to the stringer 10 prior to welding. They maintain it substantially perpendicular to the stringer 10 and make it necessary to only restrain the stairstep 12 against sliding down the stringer 10 in order to keep it on the stringer 10 while the welding is being done.

According to an aspect of the invention, each stairstep is individually cast in a pan-like form 30 which may be constructed from a suitable structural plastic material. The form 30 includes wall means forming a mold cavity and an upper rim portion 32 which rests on side and end members 34, 36 of a support frame 38. The support frame 38 also includes an intermediate under support 40 which is contoured to follow the shape of the form 30 at its location. As best shown by FIGS. 6 and 7, the form 30 includes a rear wall portion 42 which when the form 30 is within the frame 38 rests on a sloping wall portion 44 of the undersupport 40.

The rear wall portion 42 of form 30 is formed to include a pair of parallel slots 46 for receiving the mounting tabs 22 of the mounting member 14 (FIGS. 6-8). When the form 30 is within frame 38 the inner borders of the slots 46 are substantially aligned with the edges of wall 44. Thus, when the mounting member 14 is set in place with its mounting tabs 22 in the slots 46, the wall 44 is snugly received between the tabs 22. As a result, the concrete that is poured into the form 30 will flow into the spaces above member 44 which were created when the tabs 22 were pushed out from the web 16, but the concrete will not leak out from the slots 44.

Preferably, the slots 46 are made to be slightly longer than the tabs 22. This is so that after the concrete has sufficiently hardened the stairstep 12 can be easily removed from the form 30 by in effect rotating it out of the form 30 in the direction of the arrow 48 (FIG. 8).

When the mounting member 14 is within the form 30, and the mounting tabs 22 are extending through the slots 46 and the web 16 between the mounting tabs is flat against the form wall 42, which in turn is flat against the undersupport wall 44, both the mounting tabs 22 and the reinforcement steel 24, 26 are properly positioned with respect to the concrete body of the stairstep 12. The mounting tabs 22 are substantially perpendicular to the longitudinal axis of the stairstep 12. Hence, when the stairstep 12 is placed on a stringer 10 it is likewise substantially perpendicular to the axis of the stringer. The rectangular loop of reinforcement steel 24 is located in the upper portion of the concrete body so that it can carry the tension stresses put into such upper portion when a downwardly directed force is applied on the stairstep 12 by a person using the stairway. The reinforcement bar 26 is positioned to carry both bending and sheer stresses.

As shown by FIG. 7, a leveling member 50 may be moved across the top of the form 30 to level the top of the stairstep.

An important advantage of the provisions of mounting tabs 22 in the mounting member 14 is that the stairstep can be welded onto the stringer 10 without it being necessary to direct the welding torch directly towards the concrete body. Instead, the torch is directed generally towards the side surfaces of the metal stringer 10. The cutting of the tabs 22 from the web 16 provides an easy way to construct the mounting member 14 or a disturbance to the flanges 18, 20 to which the reinforcement steel 24, 26 is welded. However, in some installations it might be desirable to construct the mounting tabs in some other manner.

It is to be understood that the illustrated embodiment is only one form of the invention and the invention is not to be limited by the details which are disclosed in the drawing and described above, but is to be determined by an interpretation of the claims which follow.

Claims

What is claimed is:

1. In a precast concrete stairstep which includes an imbedded metal mounting member which is weldable to an upper portion of a metal stringer, for connecting the stairstep to the stringer, and from which the stairstep projects in cantilever fashion, the improvement comprising:

said metal mounting member being a length of channel stock having a web and two flanges which project from the web forwardly into the concrete, said mounting member also including two rearwardly projecting elements of plate metal which are tabs bent out from said web, leaving an opening in the web inwardly of each tab and channel stock end portions outwardly of said tabs, and resulting in said tabs having inner side surfaces which are perpendicular to the web, said side surfaces being spaced apart a distance substantially equal to the width of the stringer, to define a space therebetween in which the stringer is received, each said tab presenting edge portions which are weldable to side portions of the stringer, and said web including a plate portion between the openings which rests on the top of the stringer, and said stairstep also includes reinforcement steel which is welded to said channels and projects therefrom into the concrete, said reinforcement steel consisting of a single loop of reinforcement steel which is welded along one side only to the mounting member flange that occupies an upper position on the metal stringer, and which extends over the other flange in a plane that is generally parallel to the upper surface of the stairstep, and a length of reinforcement steel which is bent into the form of a shallow V, and is welded near its middle to such other flange, and which extends upwardly from said other flange in parallelism therewith.

2. Apparatus for casting a reinforced concrete stairstep of a type including a mounting member having a pair of beam straddling projections and a beam top contacting surface between said projections, said apparatus comprising:

a support frame having four interconnected side and end members and an intermediate undersupport;

a pan-type form insertable into said support frame and including edge portions restable on the side and end members of said support frame, and wall means restable on said undersupport having a pair of slots formed therethrough on opposite sides of said intermediate undersupport, sized to receive the projections from the stairstep mounting member.