Patent Application
20060053714
The present invention relates to a connector for anchoring a first building structural member to a second building structural member. The connector works in conjunction with a separate anchor member that is received or attached to the second building structural member and with fasteners for attaching the connector to the first building structural member.
Earthquakes, hurricanes, tornadoes and floods all impose forces on a building that can cause structural failure. To counteract these forces, it has become common practice to add or strengthen ties between the structural members of a building in the area of the building where these cataclysmic forces may be concentrated. For example, framed walls can be connected to the foundation rather than merely rest on it. Connections between the framed walls of each floor can be strengthened. And joists can be connected to both their headers and the walls that support the headers. One of the most common connectors designed for these applications is commonly called a holdown. Holdowns are commonly used to anchor framed walls to the foundation. Holdowns restrain wall posts or studs against uplift, particularly uplift at the ends of shear walls that occurs as a result of lateral loads being applied to the top of the shear wall. When lateral loads, such as may be caused by earthquakes and high wind, are applied to the top of a shear wall, the shear wall tends to overturn rather than collapse, because it is reinforced against lateral shear loads. The overturning moment tends to lift the trailing side of the shear wall.
Early holdowns were constructed from two or more separate pieces of metal that were welded together. Welded holdowns had to be painted to prevent rust. They were heavy and costly to produce, in particular because of the additional labor involved in welding and painting.
State of the art holdowns are made from galvanized sheet metal formed on progressive die machines. Recently, strong and light cast materials such as aluminum have also been used. Ideally, state of the art holdowns require no welding or painting. These advances have reduced the cost of making holdowns while increasing their ability to withstand tension forces. Severe earthquakes in California and Japan demonstrated that holdowns that are capable of being mass-produced and installed inexpensively should be made even stronger for many connections.
Typical holdowns work in conjunction with a separate anchor member and are attached to the side face of the first building structural member, which is generally a vertically-disposed wall stud. In these holdowns that attach to the side of a stud or post, the anchor member is attached at the seat of the connector. The seat is connected to a back member and the back member attaches to the side face of the stud or post. Often, these holdowns have one or more side members to increase the strength of the connector or to connect the seat member to the back member.
Another style of holdown attaches to the bottom end of the stud or post. A patented example of this type of holdown is found in U.S. Pat. No. 6,513,290, granted to William F. Leek on Feb. 4, 2003. The advantage of a holdown that attaches to the bottom end of a post or stud is that it can remove any eccentricity from the connection. Eccentric connections introduce bending stresses into the post or stud. Thus, as a shear wall moves back and forth under shear loads, the post or stud attempts to rotate about its base. Prior art holdowns, as described above, do not allow post rotation at the bottom, and bending stresses are introduced into the post above the holdown during shear wall movement. Concentric holdowns tend to allow a degree of lateral rotation because the holdown and the supported post are in line with the anchor bolt and the axis of rotation is generally on that line. The point at which the holdown is restrained to the anchor bolt is where rotation will tend to occur, if rotation is possible. Prior art holdowns, however, have not allowed rotation to occur at that point, but have instead permitted bending in the wood post at the juncture of the top of the holdown and the supported post. Eccentric holdowns tend to resist rotation in one direction only because they are attached to one side of the post and therefore to one side of the natural axis of rotation. In the present invention, the axis of rotation is below the post or stud and immediately below the point at which the holdown is restrained to the anchor bolt.
The present invention improves on the prior art by lowering the axis of rotation below the top of the anchor member that connects the holdown to the second structural member, or foundation. It is advantageous to have the axis of rotation as low as possible. Under gravity loads, the post pushes down on the concentric holdown below it along a load line of action. When the post is perfectly vertical, the load line of action passes through the middle of the holdown. When the post is rotated and compressed, as under racking deformation during an earthquake, the load line of action follows the line of the post and the projection point at which it intersects the underlying structural member moves away from the center of the holdown base. The higher the axis of rotation, the further the line of action moves for any given degree of rotation. If the line of action moves beyond the holdown base, the holdown base will tend to be pushed over because the top of the holdown base will be pushed toward a point beyond the bottom of the holdown base. Although the holdown base will tend to be pushed over, it is restrained, primarily by the anchor bolt. As the load line of action moves away from the center of the holdown, the compression stresses on the underlying structural member become increasingly non-uniform. This is undesirable because it tends to rupture the progressively bending upright post member and to damage the underlying structural member, usually a concrete foundation, which both supports and anchors the structure above it. The present invention lowers the axis of rotation so that the load line of action passes through the holdown base substantially away from its edges, keeping the bearing stresses on the underlying structural member as uniform as possible.
Recently, it has become apparent that simply increasing the strength of holdowns does not necessarily result in the best connection for the most common installation, between a frame wall reinforced for shear resistance and a concrete foundation. The greater the simple strength of the holdown, the more rigid its connection. It is possible to design and manufacture holdowns that are so strong and rigid that failure is bound to occur elsewhere in the connected structure, such as in the load bearing wood member above the holdown. By transferring failure entirely out of the holdowns, the risk of catastrophic failure of the connected structure is increased. It has therefore become desirable to design holdowns that maximize resistance to uplift forces, but which allow a small amount of rotation to occur at the connection to the second structural member or foundation.
The present invention improves on the prior art by allowing for rotation as close as possible to the point of attachment to the underlying structure. This means that there will be very little bending in the post or stud to which the holdown of the present invention is attached. This allows the post or stud to be smaller and of a lower stress grade. Because the post or stud bends very little, the attachment of the post or stud to a shear-resisting member, particularly to a panel by many small fasteners such as nails, works better, distributing and dissipating shear forces more evenly and effectively throughout the panel. This results in more gradual and predicable failure. The holdown of the present invention provides a hinge joint at the base of the holdown that improves on prior art rigid holdowns that raised the axis of rotation and tended to transmit additional tension forces into the anchor bolt when the shear panels levered up on their lateral corners. Without the hinge of the present invention, the tension forces acting on the anchor bolt and the prior art holdown are greater than the uplift force of the post or stud alone when the post is subject to an overturning moment. When prior art eccentric or concentric rigid holdowns resist post or stud rotation, additional tension forces are created in the anchor bolt.
The most preferred form of the present invention is superior to prior art rotating concentric holdowns because the present invention does not rely on a relatively weak horizontal pin connection for both rotation and the transfer of both post uplift forces (by shear) and compression forces (due to gravity or overturning moment) between vertical plates embedded in the post or stud and a base that is connected to the anchor bolt. The present invention transfers compression forces by direct bearing of one contact surface on another, as in the most preferred embodiment in which a standoff base and channel slide between the bottom surface of a floating washer and the upper surface of a support base, from post to standoff base to strap to support base to foundation. The present invention transfers uplift forces directly to the anchor bolt in tension (aside from the post to strap connection). In its most preferred embodiment, the present invention achieves rotation with sliding surfaces rather than a pin connection that, if damaged or bent, could lead to failure of the gravity load system or rotation system.
The holdown connector of the present invention improves on the prior art by providing a holdown that withstands very high tension loads with minimal deflection, while allowing for rotation about an axis lower than the top of the anchor member, and being economical to produce.
The present invention is a connection between a wall stud or post and an anchor bolt embedded in a concrete foundation, using a holdown connector that attaches to the anchor bolt and supports the wall stud or post above it. The holdown connector has a tapered bottom that allows it to rotate laterally, allowing the connection to act more purely in tension than is possible with a rigid connection.
An object of the present invention is to reduce bending moments in the wood wall stud or post at the juncture of the top of the holdown connector and the wall stud or post.
The present invention is a connection with a support base that provides a bearing surface that the bottom of the connector can move against instead of the underlying foundation.
The present invention is a connector with substantially arcuate, or curvilinear, tapering portions which allow the connector to rotate more smoothly than with angularly tapering portions.
The present invention is a connection in which the tapered support surface of the support base conforms to the registering tapered portions of the connector, allowing the connector to rotate smoothly against the support base.
The present invention is a connection in which the connector slides smoothly on the support base below it, accommodating rotating through matched slip surfaces rather than a pin connection or deformation of the holdown connector.
The present invention is a connector with a channel that encloses and supports a standoff base that, in turn, supports the wall stud or post.
The present invention is a connection in which the wall stud or post is inserted between the upright arm of the channel and stands on the upper surface of the standoff base. The sides of the channel are connected to the wall stud or post with fasteners such as nails, screws or bolts. The sides of the channel include fastener openings.
The present invention is a connector in which the support base is a flat-bottomed plate than rests on the planar concrete foundation surface.
The present invention is a connector that has a standoff base that is made with an upper portion, an open portion and a lower portion, the upper portion being open to permit access to the top of the anchor bolt, which comes up through the bottom and terminates in the open portion below the supported wall stud or post, which stands on the upper portion. The open portion has two sides that connect the top and bottom portions and elevate and support the wall stud or post.
The present invention is a connector with a channel that has a back member, so that the supported wall stud or post is enclosed on three sides. The back member is then connected to the wall stud or post with fasteners.
The present invention is a connector with a floating washer that rests on the inner bottom surface of the standoff base and remains level when the rest of the connector and the wall stud or post rotate. The floating washer slides, but remins in full bearing contact with the inner bottom surface of the standoff base. The anchor bolt comes up through the channel, the standoff base and the floating washer, and is restrained on top of the floating washer.
The floating washer has a substantially arcuate bottom that matches the substantially arcuate bottoms of both the standoff base and the channel, providing surfaces that ideally are sections of circles around the axis of rotation.
The anchor bolt openings in the standoff base and the channel are laterally oversized to allow the standoff base and channel to rotate, sliding relative the support base and the floating washer while the support base and floating washer remain level and relatively static.
Thus, as the wood post or stud rotates, only a minimal bending force in transmitted to the vertical anchor bolt in the concrete foundation.
As shown in
The first building structural member 2 includes a first side face 43 and a bottom end 44, the bottom end 44 having a width 45, as shown in
The connector 7 includes an upper portion 47 and a lower portion 48, at least partially located between the bottom end 44 of the first building structural member 2 and the upper surface 46 of the second building structural member 3.
The upper portion 47 includes a first structural attachment member 8, the first structural attachment member 8 including a first side 15 that is attached to the first side face 43 of the first building structural member 2.
The lower portion 48 further includes a first standoff member 49, a first anchor attachment member 11, and a bottom portion 51 located between the bottom end 44 of the first building structural member 2 and the upper surface 46 of the second building structural member 3 and not extending beyond the width 45 of the bottom end 44 of the first building structural member 2. As shown in
The first standoff member 49 includes a first bearing surface 50 that supports the first building structural member 2 above the second building structural member 3. The first anchor attachment member 11 interfaces with the first anchor member 4 and restrains the first anchor member 4 from withdrawing from the connector 7. The bottom portion 51 includes a first anchor member opening 52, as shown in
In contrast, the axis of rotation 12 of a prior art holdown connector 7 would occur at some point above the bearing surface 50, even in prior art holdown connectors 7 that are designed to permit rotation, and above the structural attachment member 8 in prior art concentric holdown connectors 7 that are not designed to permit rotation.
As shown in
Preferably, the first and second tapered portions 53 of the connector 7 are substantially arcuate. Preferably the first support surface 22 of the support base 10 conforms to the first and second tapered portions 53 of the connector 7. Preferably, the bottom portion 51 of the connector 7 slides on the first support surface 22 of the support base 10 when the connector 7 rotates relative to the second building structural member 3.
As shown in
Preferably, the first standoff member 49 is part of a separate standoff base 17, further including a substantially arcuate bottom 18, the bottom 18 of the standoff base 17 being formed to be received between the sides 15 of the channel 13 and resting on the base 14 of the channel 13, the standoff base 17 being formed with an opening 19 for receiving the first anchor member 4, the standoff base 17 being connected to the anchor member 4 by the first anchor attachment member 11. The standoff base is best shown in
Preferably, the first building structural member 2 is received between the sides 15 of the channel 13 and the bottom end 44 of the first building structural member 2 rests on the first bearing surface 50 of the standoff base 49. Preferably, fasteners 28 connect the two sides 15 of the channel 13 to the first building structural member 2. Preferably, the support base 10 is a plate 10 additionally including a flat bottom 23 that rests on the upper surface 46 of the second building structural member 3.
Preferably, the channel 13 is a strap 13 and the sides 15 of the channel 13 each additionally includes an end 26 and a plurality of fastener openings 27. Preferably, the standoff base 17 additionally includes a lower portion 29, an upper portion 30, and an open portion 31 between the lower portion 29 and the upper portion 30. Preferably, the open portion 31 of the standoff base 17 includes two sides 32 that connect the lower portion 29 and the upper portion 30. The channel 13 is best shown in
Preferably, the first building structural member 2 is a wall stud 2. Preferably, the second building structural member 3 is a concrete foundation 3.
As best shown in
As in the other preferred embodiments, in the most preferred embodiment the first and second tapered portions 53 of the connector 7 are substantially arcuate.
Preferably, the first structural attachment member 8 and the bottom portion 51 of the connector 7 are parts of a channel 13 including a base 14, with an anchor opening 16, and two sides 15, the channel 13 additionally including a second structural attachment member 8, the first and second structural attachment members 8 being the two sides 15 of the channel and the bottom portion 51 of the connector 7 being the base 14 of the channel 13.
Preferably, the first standoff member 49 is part of a separate standoff base 17, further including a substantially arcuate bottom 18 and a substantially arcuate inner bottom surface 42, the bottom 18 of the standoff base 17 being formed to be received between the sides 15 of the channel 13 and resting on the base 14 of the channel 13, the standoff base 17 being formed with an opening 19 for receiving the anchor member 4, the standoff base 17 being connected to the anchor member 4 by the first anchor attachment member 11.
As shown in
Preferably, the connection 1 further includes a support base 10 including a first support surface 22 that supports the connector 7 and an anchor member opening 21 through which the first end portion 5 of the anchor member 4 passes.
Preferably, the first support surface 22 of the support base 10 conforms to the first and second tapered portions 53 of the connector 7. Preferably, the bottom portion 51 of the connector 7 slides on the first support surface 22 of the support base 10 when the connector 7 rotates relative to the second building structural member 3.
As shown in
Preferably, the opening 19 in the standoff base 17 and the opening 16 in the channel 13 are larger than the anchor member 4, allowing the standoff base 17, the channel 13 and the first building structural member 2 to rotate relative the second building structural member 3 while the floating washer member 38 remains level.
Preferably, the first building structural member 2 is received between the sides 15 of the channel 13 and the bottom end 44 of the first building structural member 2 rests on the first bearing surface 50 of the standoff base 17.
Preferably, fasteners 28 connect the two sides 15 of the channel 13 to the first building structural member 2. Preferably, the support base 10 is a plate 10 additionally including a bottom 23 that rests on the upper surface 46 of the second building structural member 3. Preferably, the channel 13 is a strap 13 and the sides 15 of the channel 13 each additionally include an end 26 and a plurality of fastener openings 27.
Preferably, the standoff base 17 additionally includes a lower portion 29 occupied by the floating washer 38, an upper portion 30, and an open portion 31 between the lower portion 29 and the upper portion 30. Preferably, the open portion 31 of the standoff base 17 includes two sides 32 that connect the lower portion 29 and the upper portion 30.
Preferably, the first building structural member 2 is a wall stud 2. Preferably, the second building structural member 3 is a concrete foundation 3.
In an alternate embodiment, the channel 13 preferably further includes a back member 37 joining the two sides 15, and the first building structural member 2 interfaces with the back member 37. Preferably, fasteners 28 connect the back member 37 to the first building structural member 2.
Preferably, the first support surface 22 of said support base 10 conforms to the bottom portion 51 of the connector 7. If the bottom portion 51 is curved, the support surface 22 will have a matching curvature. If the bottom portion 51 has flat portions, the support surface will have matching flat portions. Preferably, the first support surface 22 of the support base 10 forms a concavity 24 that cradles the bottom portion 51 of the connector 7.
Preferably, if the supported post 2 is a double 2×4 stud, the support base 10 is a metal plate that has a flat bottom 23 and a substantially arcuate first support surface 22 that is ¾″ thick at a minimum, forming a concavity 24. The concavity 24 is an arc preferably with a radius of 1¾″. Preferably, the support base 10 is 3½″ long and 3″ wide and has an anchor member opening 21 that is 15/16″ in diameter and centered in the concavity 24. Preferably, there are two flat portions 25 on either side of the concavity 24 and these are preferably ¼″ wide. The support base 10 is preferably steel or cast aluminum.
Preferably, if the supported post 2 is a double 2×4 stud 2, the channel 13 is a U-shaped strap 13 with a base 14 that fits snugly between the concavity 24 of the support base 10 and the substantially arcuate bottom 18 of the standoff base 17. The channel 13 is preferably a length of 3-gauge sheet steel with two sides 15 that stand 18¼″ tall from the lowest point of the substantially arcuate bottom 18 to the ends 26 of the sides 15 of the channel 13. Preferably, it is 3″ wide and its sides 15 are spaced 3″ apart. Preferably, its substantially arcuate bottom 18 has an outside radius of 1¾″. Preferably, both of the sides 15 of the channel 13 have a plurality of fastener openings 27, preferably beginning 7⅛″ from the lowest point of the channel 13 and continuing substantially all the way up the sides 15. The sides 15 are preferably attached to the first structural member 2 with a plurality of mechanical fasteners 28, preferably self-drilling wood screws, but also possibly other types of screw, nails or bolts. The sides 15 might also be attached to the first structural member 2 using chemical bonds or adhesives.
As shown in
Alternate preferred embodiments are shown in
As shown in
In the preferred form, the connector 7 of the present invention is used to connect a first building structural member 2, which can be a double wall stud or post 2 made from two nominal 2×4 lengths of lumber, to a second building structural member 3, which is preferably a concrete foundation 3. The first anchor member 4 is preferably a steel anchor bolt 4 embedded in the concrete foundation. Preferably, the first end portion 5 of the anchor bolt 4 is threaded. The anchor bolt 4 preferably passes through the anchor member opening 21 in the support base 10, through the anchor opening 16 in the base 14 of the channel 13, and through the opening 19 in the lower portion 29 of the standoff base 17. In the preferred form, the anchor attachment member 11 is a nut 11 that is turned down over the threaded first end portion 5 of the anchor bolt 4. The open portion 31 allows the nut 11 to be turned down and tightened on the threaded first end portion 5 of the anchor bolt 4. Alternatively, the anchor attachment member 11 could be a pin 11 that passes through the anchor bolt 4 or the anchor attachment member 11 could be a weld 11 that either closes off the first end 6 of the anchor member 4 or that joins the first end portion 5 of the anchor member 4 to the connector 7.
As shown in
As shown in
As shown in
In another alternate embodiment, shown in
It may be desirable to coat the curved slip planes between the support base 10 and the channel 13 and between the standoff base 17 and the floating washer 38, and the coating could be a dry or liquid lubricant, metal bearing liners, Teflon fabric bearing liners, or the like.
