Structural Tie-Down Apparatus

Abstract

Top plate tie-down arrangements are used for securing the roof of a structure against uplift and overturning forces caused by high winds, earthquakes, and the like by anchoring the top plate of a wall to a foundation slab. An anchor bolt for use in a top plate tie-down arrangement has an internally threaded head for capturing the sill plate and holding it against the slab. The bolt also has a self-tapping thread on its bottom end that allows it to be threaded into a hole drilled through the sill plate and into the slab.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to arrangements for securing the roof of a structure against damage caused by high winds. More particularly, it relates to top-plate tie-down arrangements usable with frame construction.

2. Background Information

It is known to reinforce a building wall to resist wind and earthquake damage by the use of what will hereinafter be called a “top plate tie down” arrangement in which vertically disposed elongate fastening members that can be loaded in tension (e.g., a threaded metal rod) connect a top plate of the protected wall to an anchor beneath the wall, where the anchor is fixedly attached to a slab or is buried in or otherwise attached to the ground. As described in U.S. Pat. No. 6,161,339, a satisfactory anchor for such apparatus may be set in position prior to pouring a concrete foundation slab. The anchor can then be used both to retain a sill plate and to connect an elongate top-plate fastener to the foundation.

It is also known, for example, to anchor a sill plate to a slab by drilling through the sill plate into the slab and then gluing (e.g., with an epoxy cement) an anchor into the hole formed in the slab. If dust from the drilling operation is not carefully removed from the hole before inserting an epoxy-enrobed anchor, this approach results in an anchor with a very low pull-out strength. Although such an anchor may be satisfactory for retaining a sill plate against lateral forces, it can not safely be used as part of a top plate tie down apparatus. Glued, or otherwise bonded anchors are generally not acceptable for top plate tie down use because of both the high likelihood of there being at least one dust-contaminated and weakened anchor along a wall, and because of the time and expense involved in running a separate pull-out test on each anchor.

In U.S. Pat. No. 6,367,205, the inventor teaches an improved anchor for a top plate tie down arrangement comprising a plurality of elongate vertical fasteners attached between the top plate and respective anchors disposed beneath the wall. Each anchor may comprise a stud having a self-tapping masonry thread extending by an embedment length from one end. The second end of this anchor is threaded to receive a coupling nut used for attaching the stud to a respective elongate vertical fastener.

In using the fastener taught by U.S. Pat. No. 6,367,205 a selected number of holes are drilled into the slab, where each of the holes extends into the slab by more than an embedment length of an anchor bolt, and preferably by about one bolt diameter more than the embedment length. An anchor bolt is then inserted through a throughhole in a sill plate into each of these holes. A connecting nut threaded onto an upper threaded portion of each anchor bolt provides a set of flat surfaces that can be gripped by a wrench and used to turn the bolt into the hole. A washer is placed between the connecting nut and the sill plate before turning the bolt into the hole so as to effectively capture the sill plate between the connecting nut and the slab without deforming the sill plate.

A shortcoming of this arrangement is that an installer must handle and keep track of separate connecting nuts and washers. These relatively small parts can be lost or misplaced, thus compromising the installation of the tie-down system.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is that it provides a top plate tie down apparatus connecting a top plate of a wall to a concrete foundation. This apparatus preferably comprises a selected number of anchors, each of which has a respective portion threadably engaging the foundation beneath the wall along an embedment length. Each of the anchors also has a respective internally threaded upper portion and a respective head at the upper end thereof. Each head comprises a portion extending laterally by a selected width for holding the sill plate against the slab. The tie down apparatus also comprises the selected number of vertical tensile fasteners, each of which is used to connect an anchor to the top plate. Each of the vertical tensile fasteners has a respective threaded portion at least at its ends so that each of the lower tensile members can be threaded into a respective internally threaded upper portion of a respective anchor. In some embodiments the tensile fastener is threaded along its entire length.

Another aspect of the invention is that it provides a method of attaching a top plate of a wall to a slab beneath the wall. This method uses a selected number of anchor bolts, each bolt extending from a respective tip to a respective head end, each bolt comprising an externally threaded portion extending from the respective tip towards the respective head end by an embedment length, each bolt having a respective internally threaded portion extending from the respective head end toward the respective tip by a coupling length, each bolt comprising a respective head at the head end thereof, each head having a plurality of drive facets. The method involves drilling the selected number of holes into the slab, where each of the holes extends into the slab by more than the embedment length. Each of the selected number of anchor bolts is then inserted through a respective throughhole in the sill plate and into a respective hole in the slab. Each anchor bolt is then turned, by means of a drive tool engaging the respective plurality of drive facets until the sill plate is captured between the respective bolt head and the slab. A lower end of each of the selected number of vertical tensile fasteners is then screwed into to the internally threaded portion of a respective bolt head and a suitable attachment arrangement is provided at the upper end of each tensile fastener to attach the respective vertical tensile fastener to the top plate.

Although it is believed that the foregoing rather broad summary description may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Those skilled in the art will appreciate that they may readily use both the underlying ideas and the specific embodiments disclosed in the following Detailed Description as a basis for designing other arrangements for carrying out the same purposes of the present invention and that such equivalent constructions are within the spirit and scope of the invention in its broadest form. Moreover, it may be noted that different embodiments of the invention may provide various combinations of the recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an elevational view taken perpendicular to a framed wall and showing a plurality of roof framing members transverse to the wall anchored to a foundation beneath the wall by a prior art tie-down arrangement.

FIG. 2 is an exploded, partially sectional view of an anchor bolt retaining a sill plate against a slab, the anchor arranged to have a tensile fastener threaded thereinto.

FIG. 3 is a perspective view of a head portion of an anchor bolt.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Turning now to FIG. 1, one finds a wood framed wall 10 standing on a concrete foundation slab 12 and having a sill 14 or foot member laid thereupon. The wall comprises a plurality of vertically disposed framing members 16 or studs, and a top plate 18 that is fastened across the top of the studs 16. A top plate hold down arrangement may comprise a tensile fastening assembly 46 comprising one or more threaded tensile fasteners 42 connected to a prior art anchor 30 at a bottom and fastened to the top plate 18 by a nut 22 and washer 32 combination. Although a wooden framed wall 10 is depicted, the reader will realize that other sorts of wall construction may also be employed with either a prior art anchor, or an anchor bolt of the invention 34. For example, a metal framed wall, of the type commonly used in commercial building construction could be employed. So, for that matter, could a concrete block or brick wall having a top plate 18 disposed thereupon. Moreover, although the invention is herein described and depicted with respect to an exterior wall of a building, the same arrangement could clearly be applied to an interior wall.

In the prior art anchoring arrangement 30 depicted in FIG. 1, a threaded anchor 24 is turned into a hole 26 drilled into a hardened foundation slab 12 so as to capture a sill plate 14 between a connecting nut 40 and the slab 12. In one particular case the threaded anchor 24 has an overall length of about nine inches. At one end of this anchor there is a embedment length portion 44 about six inches in length that has a nominal half inch self-tapping lead thread formed on it. The lead thread preferably comprises a helical land having a relatively high helix angle and a helical dust relief groove formed in the body of the anchor. At the other, upper, end there is a second threaded portion 38 adapted to engage a connecting nut 40. This portion generally has a length about one half times the length of an associated connecting nut and may, for example, be about three quarters of an inch long with a 7/16.by.12 thread. In some versions of this anchor an unthreaded intermediate portion 49 of the anchor has a length approximately the same as the thickness of lumber used for forming the sill plate 14. The depicted arrangement accommodates a washer 32 between the connecting nut 40 and the sill plate. In the exemplar case, the intermediate portion 49 has a length of about one and three quarters inch. The penetration depth of the anchor into the connecting nut is limited by an internal stop in the middle of the connecting nut, and not by the threaded length of the upper portion, Hence, it is really not important whether the intermediate portion of the anchor is threaded or not. In any event, as long as the hole is deep enough, the overall length of the self threading anchor will be approximately equal to the sum of the penetration depth of the anchor into the connecting nut, the sill thickness and the embedment length.

The process of installing the prior art anchor 30 into holes drilled through a sill plate and into a hardened slab generally requires that the installer first place a washer 32 and connecting nut 40 on the threaded upper end of the threaded anchor, and then start the anchor into the hole and turn it with a suitable tool to capture the sill plate between the washer and slab. This process requires the installer to keep track of several separate components and is confounded if one of the relatively small required parts—i.e., the washer 32 or connecting nut 40—is lost or misplaced.

A preferred arrangement for a tie-down system for securing walls and roofs against uplift and overturning forces overcomes the problem of component loss and avoids the installation time required to assemble anchors on site. A preferred anchor bolt 34 comprises an internally threaded head portion 50 having a plurality of external drive facets 52 and a collar portion 54 extending outwardly from an axis of the anchor bolt. With a fastener of this sort, the step of securing the sill plate 14 against a foundation slab 12 involves starting the anchor bolt 34 into a pre-drilled hole 26 and turning it, by means of a socket wrench or other suitable tool acting on the drive facets, into the hole so that the sill plate 14 is captured between the slab 12 and the collar portion 54 of the anchor bolt 34.

Once the sill has been captured against the slab, the process of installing a tie-down system using the preferred anchor bolt 34 proceeds in the same manner as is used with the prior art anchor 30.

Although the present invention has been described with respect to several preferred embodiments, many modifications and alterations can be made without departing from the invention. Accordingly, it is intended that all such modifications and alterations be considered as within the spirit and scope of the invention as defined in the attached claims.

Claims

1. A method of attaching a top plate of a wall to a slab disposed beneath the wall, the method comprising the steps of:

a) providing a selected number of anchor bolts, each bolt extending from a respective tip to a respective head end, each bolt comprising an externally threaded portion extending from the respective tip towards the respective head end by an embedment length, each bolt having a respective internally threaded portion extending from the respective head end toward the respective tip by a coupling length, each bolt comprising a respective head at the head end thereof, each head having a plurality of drive facets;

b) drilling a selected number of holes into the slab, each of the holes extending into the slab by more than the embedment length;

c) inserting each of the selected number of anchor bolts through a respective throughhole in a sill plate and into a respective hole in the slab;

d) turning each anchor bolt, by means of a drive tool engaging the respective plurality of drive facets thereof until the sill plate is captured between the respective bolt head and the slab,

e) threadably connecting a lower end of each of the selected number of vertical tensile fasteners to the internally threaded portion of a respective bolt head, each of the vertical tensile fasteners comprising an attachment means adjacent an upper end thereof, each of the attachment means attaching the respective vertical tensile fastener to the top plate.

2. The method of claim 1 wherein each of the anchor bolts has an anchor bolt diameter and each hole extends into the slab by at least one anchor bolt diameter more than the embedment length.

3. The method of claim 1 wherein the sill is captured between the respective bolt head and the slab by means of a respective washer-like portion of the respective bolt head, the respective washer-like portion extending laterally outward from an axis of the respective bolt beyond the respective plurality of facets.

4. A top plate tie down apparatus connecting a top plate of a wall to a concrete foundation, the wall extending upward from a sill plate disposed on the concrete foundation, the sill plate having a plurality of throughholes therethrough, the apparatus comprising:

a selected number of anchors, each anchor having a respective portion threadably engaging the foundation beneath the wall along an embedment length, each anchor having a respective internally threaded upper portion, each of the anchors having a respective head at the upper end thereof, each head holding the sill plate against the slab;

the selected number of vertical tensile fasteners, each of the vertical tensile fasteners connected to the top plate, each of the vertical tensile fasteners further comprising a respective lower threaded portion at a respective lower end thereof, each of the lower threaded portions threaded into a respective internally threaded upper portion of a respective one of the anchors.

5. The apparatus of claim 4 wherein the length of each of the respective threaded portions of the vertical tensile fasteners is equal to a length of each of the internally threaded portions of the anchors.

6. The apparatus of claim 4 wherein the anchor threadably engages the foundation by means of a self-tapping lead thread comprising a helical land having a high helix angle, the lead thread further comprising a helical dust relief groove formed in a body of the anchor.