Generally, a process for new floor construction using post-tensioned concrete slabs requires a gap (also known as a leave out, a pour strip out, etc.) that separates adjacent concrete slabs (also known as pours or castings). Generally, the gap is four feet and more in length. That is, several feet in distance separates the two ends of the post-tensioned concrete slabs. Sometimes the gap distance (the distance which separates the two ends of the post-tensioned concrete slabs) may be called a “width,” but for clarity and consistency, the term “width” is used herein to describe the distance along the direction labeled “W,” and the term “length” is used herein to describe the distance along the direction labeled “L” (e.g., see FIGS. 1-3). Accordingly, ΔL is used herein to describe a change in distance along the “L” axis direction. Generally, the gap is filled in (i.e., lap spliced) with a pour strip at a later time, connecting the slabs together to form the entire floor.
Prestressed concrete is a type of reinforced concrete which has been subjected to external compressive forces prior to the application of load. Prestressed concrete is categorized as either pre-tensioned or post-tensioned.
Pre-tensioned concrete is formed by a process including initial stressing of a wire strand system and then casting concrete around the stressed wire strand system. The stress from the wire strand system transfers to the concrete after the concrete has reached a specified strength (e.g., cured to a set specification).
Post-tensioned concrete is formed by a process of casting wet concrete around an unstressed wire strand system and then stressing the wire strand system after the concrete has reached specified strength (e.g., cured to a set specification). For example, post-tensioned concrete can have a wire strand system which has a wire enclosed in a duct (e.g., pipe, conduit, etc.). Concrete is formed around the duct and the concrete sets and cures. Then, the wire is stressed and grout material (e.g., a mixture of cement, sand, aggregate, and water) is pumped into the cavity surrounding the wire. The grout material bonds the wire to the duct, and the duct is bonded to the cured concrete. Thus, the stress applied to the wire can be transferred to the concrete. The applied stress (e.g., forces applied to the wire strand system) in the post-tensioning process causes a volume change (and/or a length change) to the concrete material. The volume change of the concrete material causes a change in the length of the concrete slab. The length change is a shortening in the direction parallel to applied stress (e.g., the post-tensioning force).
FIGS. 1-2 show schematic diagrams of a floor construction 10 according to a generally known process using post-tensioned concrete. FIG. 1 shows a top-down plan view of the floor construction 10. The floor construction 10 includes post tensioned slabs 12, 14 separated by a gap 16. FIG. 1 shows the “width” direction indicated by “W” and the “length” direction indicated by “L” (FIGS. 2 and 3 also show the length direction indicated by “L”). FIG. 2 shows a side view of the floor construction 10, also showing the slabs 12, 14, and the gap 16. The floor construction 10 is made by a process wherein the post tensioned slabs 12, 14 are each poured separately, tensioned independent of each other after they have sufficiently cured. Thus, the rebars in the post-tensioned slab 12 do not necessarily lineup (e.g., axially) with the rebars in the post-tensioned slab 14.
Each of the slabs 12, 14 changes volume due to their tensioning processes. The typical tensioning process for a typical floor construction uses the gap 16, which is typically four to eight feet in length, for accommodating appropriate tooling and equipment (and also for access by workers) to tension the slabs 12, 14. Further, the gap 16 (i.e., the separation between the two slabs 12, 14) becomes longer (e.g., along direction L shown in FIG. 1) during and after the tensioning of one or both of the slabs 12, 14. That is, the volume changes in the slabs 12, 14 and the slabs 12, 14 become shorter. And because the slabs 12, 14 become shorter, the separation between them, which is the gap 16, becomes longer.
For example, in a typical hotel floor construction, the gap 16 can be about sixty to seventy feet in width and four to eight feet in length. Generally, the gap 16 is left open for twenty to thirty days to allow most of the volume changes (i.e., slab shortening) to occur to the post-tensioned concrete slabs 12, 14. After the twenty to thirty days, the gap 16 is filled in (i.e., lap spliced) with a pour strip 18 to provide a structural continuity of the floor construction 10 required by the final design to resist all required loads.
FIG. 3 shows a close-up schematic view of a portion 20 of the floor construction 10 shown in FIG. 2. The portion 20 shows the first slab 12 having a post-tensioning wire strand system 22 for stressing the concrete 23. The slab 12 includes a steel reinforcing bar 24 (also known as rebar) which reinforces the concrete 23 in the slab 12. Generally, the rebar 24 and other rebar in the slab 12 are somewhat regularly positioned in the slab 12, and extend out from the end of the slab 12 towards the gap 16. The second slab 14, which is also shown in the portion 20, has its own post-tensioning wire strand system 26 for stressing the concrete 27. The slab 14 includes a rebar 28 which reinforces the concrete 27 in the slab 14. Generally, the rebar 28 and other rebar in the slab 14 are somewhat regularly positioned in the slab 14, and extend out from the end of the slab 14 towards the gap 16. In the prior art process of forming the floor construction 10, the positioning of the rebar 28 is not based on or with respect to the position of the rebar 24. Further, prior to the filling in of the gap 16 with the pour strip 18, the rebar 24 extending out from the slab 12 is not connected to the rebar 28 extending out from the slab 14. That is, prior to the filling in of the gap 16 with the pour strip 18, the rebar 24 extending out from the slab 12 is not directly connected to the rebar 28 extending out from the slab 14. That is, prior to the filling in of the gap 16 with the pour strip 18, the rebar 24 extending out from the slab 12 is not indirectly connected to the rebar 28 extending out from the slab 14. Other rebar (s) 30 is (are) positioned, or laid down, inside the gap 16 along the width direction, so that the other rebar(s) 30 is (are) perpendicular to the length direction of the rebar 24 and/or 28. Then, the pour strip 18 is formed around the rebar 24, 28, 30 filling in the gap 16.
Referring back to FIG. 1, in a multi-level building construction having one or more floors, the floor construction 10 can be placed above another floor. These floors are connected to and accessible via a construction elevator 30. Generally, there is only one (or very few) construction elevator 30 that is used during the construction of the building. Accordingly, during the construction of the floor construction 10, the slab 12 area can be accessed via the elevator 30. However, the slab 14 area cannot be accessed easily when a gap 16 four feet and more exists between the slabs 12, 14. That is, construction equipment cannot easily be moved to slab 14 from slab 12. Thus, generally, the construction process requiring access to slab 14 waits the twenty to thirty days until the pour strip 18 is poured to splice the slabs 12, 14 together. Further, the gap 16 allows significant weather conditions to intrude into the floor beneath the floor construction 10. Such weather conditions can also prevent work from being performed in the floor underneath the floor construction 10. Despite these disadvantages of having long gaps in post-tension concrete construction, waiting and time delay are generally an accepted part of the-process in the field of construction.
USPTO Backgrounds
USPTO Backgrounds