BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the invention will be described by reference to the drawings in which:
FIG. 1 is a plan view of an embodiment of the void form according to the present invention;
FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;
FIG. 3 is a plan view of an alternate embodiment of the void form according to the present invention;
FIG. 4 is a sectional view taken along line 4-4 of FIG. 3;
FIG. 5 is a perspective view of a pile and the void form according to the present invention;
FIG. 6 is a sectional view of a pile and the void form according to the present invention;
FIG. 7 is a sectional view of a pile and the void form according to the present invention, capped with a pile cap;
FIG. 8 is an enlarged sectional view of the top section of a pile having a bar anchor; and
FIG. 9 is an enlarged sectional view of the top section of a pile having a strand anchor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
FIGS. 1 and 2 show an embodiment of the void form 10 of the present invention. Void form 10 is preferably made of a compressible material, such as a hard plastic, which can be formed into a hollow chamber that matches the shape of a pile. The exact outer and inner diameter dimensions of the void form 10, defined by outer wall 12 and inner wall 14, are selected based on the size of the pile, and of the anchor which will be used to post-tension the pile. In order to properly fill a void between a pile and a pile cap, void form 10 should have an outer diameter which is at least as large as the outer diameter of the pile. The inner diameter should be selected to closely match the outer diameter of any sheath or casing which is placed around the anchor.
The void form 10 has upper wall 16, which may be slightly convex, and lower wall 18, which is preferably flat and substantially parallel to upper wall 16. The convex shape of upper wall 16 ensures air initially trapped in the void form 10 may escape as grout fills the hollow chamber 24 of void form 10, as will be discussed later. Upper wall 16 and lower wall 18 may be separated by approximately 2″, depending on the diameter of the pile on which the void form will be applied, the type of soil, and the loading conditions. This approximate thickness allows for some compression of the void form 10 during the post-tensioning process, as will be discussed later, while still leaving room for grout. The void form may be thicker than 2″, but it is preferable to avoid an excessive amount of grout.
The void form 10 includes at least one aperture 20, through which grout may be inserted, and a second aperture 22, which through which air trapped in the void form may escape as grout fills the hollow chamber 24 of void form 10. The convex shape of upper wall 16, which allows air to reach the uppermost point at the aperture 22, assists the escape of trapped air. Void form 10 preferably has extending nipples on each of apertures 20, 22, so that tubes 26, 28 (not shown) may be easily and securely connected to void form 10; however, it will be understood that any suitable means to securely connect void form 10 and tubes 26, 28 may be used.
Void form 10 may be formed with outer wall 12 substantially perpendicular to upper wall 16 and lower wall 18, as shown in FIGS. 1 and 2, or it may have a substantially non-perpendicular outer wall 12. For example, in the alternate embodiment shown in FIGS. 3 and 4, outer wall 12 comprises upper and lower sloped sections meeting at a ridge between upper wall 16 and lower wall 18.
FIGS. 5 and 6 show the void form 10 in place on a constructed pile 30. The method of constructing the pile 30 is similar to those disclosed in the prior art previously discussed. Essentially, anchor hole 32 is made in the ground 34, such as by drilling, to the desired diameter and depth under the ground 34. Anchor 36 is placed in drill hole 32. Anchor 36 may be a bar or strand anchor, as would be most appropriate for the circumstances. One or more centralizers 38 (shown only in FIG. 6) may be used to ensure anchor 36 is properly placed within anchor hole 32. Sleeve 40, of any appropriate material, such as PVC, may be used along any part of anchor 36 to provide a free stress length, which will allow anchor 36 to be properly post-tensioned. The anchor hole 32 is then filled with concrete 42, preferably to approximately level with ground 34. If required, a casing 44, made of a material such as steel pipe, may also be placed around the top of the anchor, to help protect the finished pile against lateral stresses.
Void form 10 is then placed on top of the concrete. Preferably, void form 10 is placed before concrete 42 sets, to ensure good contact is made between the top surface of concrete 42 and the lower wall 18 of void form 10. Tubes 26, 28 may be attached to void form 10 at this point, or may have previously been attached. A ring 43 (shown only in FIG. 5) of compressible material, such as Styrofoam®, may be placed around the void form 10 to compensate for any variation in the diameter of the pile 30 when the anchor hole 32 was excavated. Ring 43 will typically only be used if the pile 30 diameter exceeds the outer diameter of void form 10, as it will allow movement of the pile 30 during post-tensioning and will still permit proper load transfer about the periphery of the pile 30 once post-tensioning is complete. Attachments 45 (also shown only in FIG. 5), such as cable ties, duct tape or similar wrapping, may be used to fasten tubes 26, 28 to the outside of anchor 36, to support tubes 26, 28, to keep tubes 26, 28 free from kinks or bends, and to ensure tubes 26, 28 can easily be located and used during subsequent stages.
Referring now to FIG. 7, pile cap 46 may then be placed over pile 30 and void form 10 by any appropriate method. A recess 48 left in pile cap 46 over the top of anchor 36 will permit later post-tensioning of the anchor 36. The ends of tubes 26, 28 also protrude through the pile cap 46. Once pile cap 46 has been placed and finished, the anchor 36 may be tensioned to the desired test load, and locked off at the specified design load. When the anchor has been tensioned, and the pile is therefore properly post-tensioned, grout or other hardenable material may be used to fill recess 48, securing and protecting the top of anchor 36 from the elements and other stresses.
During the tensioning process, void form 10 is compressed vertically due to upward forces from the pile 30 and downward forces from the pile cap 46. Void form 10 may compress as much as ½″ from each force, and may not compress evenly throughout its area, but the vertical forces do not completely collapse chamber 24. Nor does void form 10 interfere with the movements of pile 30 and pile cap 46. It is therefore assured that the pile has been post-tensioned to the desired test and design loads.
Grout or other strong, hardenable material may then be pumped into void form 10, through tube 26, until chamber 24 is filled. Tube 28 allows air to escape, and will also provide visual confirmation when chamber 24 is completely filled with grout. The present invention therefore eliminates any voids in the vertical direction, ensuring continuous support throughout the depth of the pile 30.
FIGS. 8 and 9 show the two embodiments of the void form 10 in place in a pile 30. In either case, the process to construct the pile is the same.
The void form 10 is versatile and may be used with either a bar anchor 52 (as shown in FIG. 8) or a strand anchor 54 (as shown in FIG. 9). FIGS. 8 and 9 also show a different method of post-tensioning the anchor. In this embodiment, the anchor head 49 protrudes above the pile cap 46, and may be post-tensioned by applying force against bearing plate 50 on the top surface of the pile cap 46. Otherwise, the process for constructing the pile is the same as the embodiment discussed above.
It will be appreciated by those skilled in the art that other variations to the preferred embodiment described herein may be practised without departing from the scope of the invention, such scope being properly defined by the following claims.
Patent Application
20080008539
