PORTAL FRAME
A portal frame is disclosed for use around portals in, for example, a light-framed construction. The portal frame includes a pair of vertically-oriented shearwalls, and a header extending between and connected to the shearwalls. The portal frame may be used around a variety of portals formed in a construction, including for example doors, garage doors and windows. By forming a portal frame using a pair of shearwalls connected to a header, the portal frame in embodiments of the present invention is able to effectively reduce the loads exerted on a foundation by the shearwalls in comparison to a shearwall acting alone (i.e., one that is not part of a portal frame).
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1. Field of the Invention
The present invention relates to a portal frame for opposing lateral forces, and in particular to a portal frame including a pair of shearwalls to improve the ability of the portal frame to withstand lateral forces such as those generated in earthquakes, high winds, floods and snow loads.
2. Description of the Related Art
Shearwalls were developed to counteract the potentially devastating effects of natural phenomena such as seismic activity, high winds, floods and snow loads on the structural integrity of light-framed constructions. Prior to shearwalls and lateral bracing systems, lateral forces generated during these natural phenomena often caused the top portion of a wall to move laterally with respect to the bottom portion of the wall, which movement could result in structural failure of the wall and, in some instances, collapse of the building. Shearwalls within wall sections of light-framed constructions provide lateral stability and allow the lateral forces in the wall sections to be transmitted through the shearwalls between the upper portions of the wall and the floor diaphragm or foundation of the building where they are dissipated without structural effect on the wall or building.
One example of a shearwall is disclosed in U.S. patent application Ser. No. 10/734,870, entitled, “Corrugated Shearwall,” which application is assigned to the owner of the present invention, and which application is incorporated herein in its entirety (referred to herein as “the '870 application”). The performance of a shearwall like the one disclosed in '870 application under lateral loads is such that large moment forces may be transferred from the shearwall to the floor diaphragm or foundation on which the shearwall is mounted, at the lower corners of the shearwall. Typically, the load capacity for such shearwalls is limited not by the ability of the wall itself to withstand lateral loads, but rather the ability of the anchorage system and/or the diaphragm or foundation to withstand the large moment forces generated by the shearwall under the lateral loads.
In constructions such as residences and small buildings, portal frames are formed around portals, which may be any opening in a construction such as for example a garage, door or window. A portal frame typically includes vertical studs spaced from each other and affixed to a horizontal top plate, surrounding the portal. A bottom plate may also be included which is typically anchored to the floor diaphragm or foundation. Portal frames are often subjected to larger lateral forces due to the absence of any structural materials within the portal itself. There is therefore a need for a portal frame capable of withstanding large lateral loads, while at the same time prevent large moment forces on the anchorage system and diaphragm, foundation or other base on which the portal frame is mounted.
SUMMARY OF THE INVENTIONEmbodiments of the present invention relate to a portal frame for use around portals in, for example, a light-framed construction. The portal frame includes a pair of vertically-oriented shearwalls, and a header extending between and connected to the shearwalls. The portal frame may be used around a variety of portals formed in a construction, including for example doors, garage doors and windows.
In the embodiments, the header may be a steel tube, but may be other materials such as glulam or other engineered lumbers in alternative embodiments. The shearwalls may be identical to each other, and may include a pair of end sections generally defining the width of each shearwall, and at least one corrugation. A sill plate may be affixed at the top of each shearwall which allows distribution of the compressive and tensile forces exerted by the shearwalls on the header. A base plate may be provided at the bottom of each shearwall.
By forming a portal frame using a pair of shearwalls connected to a header, the portal frame in embodiments of the present invention is able to effectively reduce the loads exerted on a foundation by the shearwalls in comparison to a shearwall acting alone (i.e., one that is not part of a portal frame). In one embodiment, the portal frame is essentially pinned to the underlying foundation at the bases of the shearwalls. In such embodiments, very little, if any, moment demand is taken up at the connection point of the shearwalls with the foundation. Thus the demands on the foundation and anchoring mechanisms may be greatly reduced.
In alternative embodiments, it is contemplated that the portal frame may be fixed at its base. In such embodiments, the base plates and anchor mechanisms used may be sturdier to provide constraint against rotation at the base. In such embodiments, the load on the base plates may be substantially similar to the load on the sill plates at the top of the shearwalls.
The present invention will now be described with reference to the drawings in which:
The present invention will now be described with reference to
The shearwalls 102, 104 may be identical to each other, and the following description applies to both shearwalls 102, 104. Each shearwall may be of the type disclosed in any of the embodiments of the '870 application, previously incorporated by reference, with the exception that, in embodiments, the shearwalls 102, 104 are inverted with respect to the shearwalls of the '870 application. In particular, a sill plate 110, discussed hereinafter, may be affixed at the tops of each shearwall 102, 104, where the sill plate was located at the bottom of the shearwalls of the '870 application. While not optimizing the use of the sill plate 110, it is understood that the shearwalls of the '870 application may be used in their un-inverted position in the portal frame 100 in alternative embodiments.
Referring to
In embodiments of the present invention, each shearwall 102, 104 may be formed of 7-gauge sheet steel (0.1875 inches). Other gauges, such as for example 10-gauge sheet steel, and other materials of comparable strength and rigidity may be used in alternative embodiments. One such alternative material may be expanded metal. It is understood that other shearwalls, for example manufactured by Simpson Strong-Tie of Pleasanton, Calif., may be used in place of the shearwall 102, 104 described above.
In a further alternative embodiment, a pair of chords (not shown) may be affixed to the end sections 114 and 116 of each shearwall 102, 104 to provide additional structural support to the shearwalls 102, 104. The chords may be formed of wood, such as for example sawn lumber from lumber groups including spruce-pine-fir, Douglas fir-larch, hem-fir and southern pine. The chords may alternatively be formed of engineered lumber, such as glulam and wood composites. Sheathing (not shown) may be affixed over the front and/or back surface of each shearwall 102, 104, and affixed by a variety of affixing mechanisms including screws and glue.
As mentioned above, each shearwall 102, 104 may include a sill plate 110 affixed at the top of the shearwall. The sill plate 110 allows distribution of the compressive and tensile forces exerted by the shearwalls 102, 104 on the header 106. Accordingly, sill plate 110 is provided as a flat plate with a relatively large surface area. The plate 110 has a length which may be greater than the width of each shearwall 102, 104, and a width that is greater than or equal to the depth of each shearwall 102, 104. In one embodiment, the sill plate 110 may be 26 inches long and 4 inches wide. It is understood that the length and/or width of plate 110 may be larger or smaller than these dimensions in alternative embodiments.
Sill plate 110 is also rigid enough to allow even distribution of any localized compressive/tensile forces from the shearwalls 102, 104 on header 106. In one embodiment of the present invention, the sill plate 110 is formed of ½ inch to ⅝ inch thick steel. It is understood that sill plate 110 may have thicknesses other than between ½ inch and ⅝ inches in alternative embodiments. The sill plate 110 may be affixed to each shearwall 102, 104 by affixation methods such as welding, bolting and/or gluing.
A base plate 112 may be provided at the bottom of each shearwall 102, 104. As explained in greater detail below, the portal frame of the present invention is able to effectively reduce the loads exerted on a foundation 120 by shearwalls 102, 104 in comparison to a shearwall acting alone (i.e., one that is not part of a portal frame). Thus, in one embodiment of the present invention explained below with respect to
However, in an alternative embodiment shown in
The anchors used in the embodiment shown in
It is understood that portal frame 100 may be anchored to the underlying support surface by other anchors in alternative embodiments. Moreover, other types of anchoring mechanisms may alternatively be used, such as for example strap anchors, mudsill anchors, retrofit bolts, foundation plate holdowns, straps, ties, nails, screws, framing anchors, ties, plates, straps or a combination thereof.
In the embodiment shown in
In embodiments, yield links may be used at the joints between the header 106 and shearwalls 102, 104 to provide a lateral bracing system against the moment forces generated at the joints. Examples of such yield links are disclosed in U.S. patent application Ser. No. 10/847,851, entitled, “Moment Frame Links Wall,” and U.S. patent application Ser. No. 11/959,696, entitled, “Moment Frame Connector.” These applications are assigned to the owner of the present invention and are incorporated by reference herein in their entirety. Yield links may be omitted from embodiments of the present invention.
It is understood that header 106 may be formed of other materials in further embodiments. One such embodiment is shown in
Referring now to
As discussed in the Background section, shearwalls are able to withstand high lateral loads, but they are typically underutilized in that the load capacity for such shearwalls is limited by the ability of the anchorage system and/or the foundation to withstand the large moment forces generated by the shearwall under the lateral loads. By reducing the forces at the base, the portal frame of the present invention is able to utilize the full lateral bracing capacities of the shearwalls 102 and 104.
The foregoing detailed description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
Claims
1. A portal frame, comprising:
- a pair of shearwalls, each shearwall including: a top edge and a bottom edge generally defining a height of the shearwall, first and second ends, extending between the top and bottom edges, generally defining a width of the shearwall, and a corrugated section extending at least partially between said top edge and said bottom edge in between said first and second ends, said corrugated section forming at least one corrugation; and
- a header extending between and mounted to top edges of the pair of shearwalls, the pair of shearwalls and header together defining a frame for a portal of a construction.
2. A portal frame as recited in claim 1, further comprising a sill plate affixed at the top edge of each shearwall and having a footprint at least as large as the footprint of each shearwall.
3. A portal frame as recited in claim 1, further comprising a bottom plate affixed at the bottom edge of each shearwall and having a footprint at least as large as the footprint of each shearwall, the bottom plates affixing the shearwalls to a surface on which the portal frame is supported.
4. A portal frame as recited in claim 3, wherein a lateral load on the portal frame results in negligible forces between the bottom plates and support surface.
5. A portal frame as recited in claim 1, further comprising a sill plate at the top edge of each shearwall and a bottom plate at the bottom edge of each shearwall, the header affixed to the sill plates and the bottom plates affixed to a surface on which the portal frame is supported, wherein a lateral load on the portal results in substantially equal forces between the sill plates and header on the one hand, and between the bottom plates and support surface on the other hand.
6. A portal frame as recited in claim 1, wherein the header is formed of tube steel.
7. A portal frame as recited in claim 1, further comprising bolts for bolting the header to the shearwalls.
8. A portal frame as recited in claim 1, wherein the header is formed of engineered lumber.
9. A portal frame as recited in claim 8, wherein the engineered lumber is glulam.
10. A portal frame as recited in claim 8, further comprising bolts for bolting the header to the shearwalls, the bolts fitting within recessed holes in the engineered lumber.
11. A portal frame as recited in claim 1, further comprising yield links at the joints between the header and shearwalls.
12. A portal frame as recited in claim 1, further comprising first and second chords affixed one each to said first and second ends of each shearwall.
13. A portal frame as recited in claim 1, wherein said shearwalls are formed of 7-gauge steel.
14. A portal frame, comprising:
- a pair of shearwalls, each shearwall including: a top edge and a bottom edge generally defining a height of the shearwall, first and second ends, extending between the top and bottom edges, generally defining a width of the shearwall, and a corrugated section extending at least partially between said top edge and said bottom edge in between said first and second ends, said corrugated section forming at least one corrugation;
- sill plates affixed at the top edges of the shearwalls;
- a header extending between and mounted on top of the sill plates, the pair of shearwalls and header together defining a frame for a portal of a construction; and
- base plates affixed at bottom edges of the shearwalls, the base plates affixing the portal frame to a surface on which the portal frame is supported,
- wherein a lateral load on the portal frame results in negligible forces between the bottom plates and support surface.
15. A portal frame as recited in claim 14, wherein the header is formed of tube steel.
16. A portal frame as recited in claim 14, wherein the header is formed of engineered lumber.
17. A portal frame as recited in claim 16, wherein the engineered lumber is glulam.
18. A portal frame as recited in claim 16, further comprising bolts for bolting the header to the shearwalls, the bolts fitting within recessed holes in the engineered lumber.
19. A portal frame as recited in claim 14, further comprising yield links at the joints between the header and shearwalls.
20. A portal frame, comprising:
- a pair of shearwalls, each shearwall including: a top edge and a bottom edge generally defining a height of the shearwall, first and second ends, extending between the top and bottom edges, generally defining a width of the shearwall, and a corrugated section extending at least partially between said top edge and said bottom edge in between said first and second ends, said corrugated section forming at least one corrugation;
- sill plates affixed at the top edges of the shearwalls;
- a header extending between and mounted on top of the sill plates, the pair of shearwalls and header together defining a frame for a portal of a construction; and
- one of a first and second pair of base plates affixed at bottom edges of the shearwalls, the base plates affixing the portal frame to a surface on which the portal frame is supported, the first pair of base plates capable of bearing less load than the second pair of base plates,
- wherein a lateral load on the portal frame results in negligible forces between the bottom plates and support surface when the first pair of base plates are affixed to the bottom edges of the shearwalls, and
- wherein a lateral load on the portal results in substantially equal forces between the sill plates and header on the one hand, and between the bottom plates and support surface on the other hand, when the second pair of base plates are affixed to the bottom edges of the shearwalls.
21. A portal frame as recited in claim 20, further comprising a first pair of anchors for anchoring the portal frame to the support surface when the first pair of base plates are affixed to the bottom edges of the shearwalls.
22. A portal frame as recited in claim 21, further comprising a second pair of anchors for anchoring the portal frame to the support surface when the second pair of base plates are affixed to the bottom edges of the shearwalls, the second pair of anchors capable of supporting a larger load than the first pair of anchors.
23. A portal frame as recited in claim 20, wherein the header is formed of tube steel.
24. A portal frame as recited in claim 20, wherein the header is formed of glulam.
25. A portal frame as recited in claim 20, further comprising yield links at the joints between the header and shearwalls.
Type: Application
Filed: Jul 23, 2008
Publication Date: Jan 28, 2010
Applicant: SIMPSON STRONG TIE, CO., INC. (Pleasanton, CA)
Inventor: Badri K. J. Hiriyur (Dublin, CA)
Application Number: 12/178,078
International Classification: E04C 2/38 (20060101);