Building wall for resisting lateral forces

This invention relates to an improved wall for resisting lateral forces imposed on a building that incorporates the wall. Specifically, this invention relates to a wall in a light-frame building having within it a sub-component specifically designed to resist lateral forces imposed on the building such as those caused by an earthquake or by wind loading. The wall is formed with a bottom plate that rests on the underlying structural component of the building. A plurality of vertically-disposed studs connect to the bottom plate, and a top plate is supported by and connects to the vertically-disposed studs. A shear-resisting assembly connects to the top plate and the underlying structural component. The shear-resisting assembly has top and bottom struts and first and second chords and a planar shear resisting element connected thereto.

BACKGROUND

This invention relates to an improved wall for resisting lateral forces imposed on a building incorporating the improved wall. Specifically, this invention relates to a wall in a light-frame building having within it a sub-component specifically designed to resist lateral forces imposed on the building such as those caused by an earthquake or by wind loading. The present invention improves on precedent wall designs in light-frame construction by providing a structure that the designer can confidently predict will resist the lateral forces for which it is designed.

All structures must be designed to resist lateral forces. Current methods for improving the lateral resistance of light-frame construction walls have focused on adding components to a wall built according to conventional practices. In light-frame construction, the simplest such wall consists of a bottom plate, studs resting on and connected to the bottom plate, and a top plate resting on and connected to the studs. Openings for windows and doorways may be incorporated into the light-frame wall.

One of the earliest methods for bracing a wall against lateral forces was to incorporate bracing into the frame of the wall in the form of diagonal bracing members. Another simple means of providing lateral resistance was to provide sheathing to the frame. Plywood sheathing and Oriented Strand Board are common sheathing materials used today in conventional light-frame construction.

As light-frame construction design became more sophisticated, foundation anchors were added to connect the bottom plate of the wall to the foundation to prevent the wall from slipping off the foundation. Later on it was realized that certain walls were light enough to lift up under moment reactions caused by lateral forces and so needed to be further anchored with brackets called holdowns, which attach to the studs of the wall and to bolts set into the foundation.

With proper design and installation, these conventional methods of providing lateral resistance by applying sheathing, foundation anchors and anchored holdowns to conventional walls can provide acceptable resistance to most lateral forces. However, proper installation can be a problem using conventional methods. The division of labor on job cites can result in improper connections. Furthermore, the installer may cut corners and sacrifice resistance to lateral forces in return for ease of installation or aesthetic considerations.

The present invention improves on conventional methods for providing lateral resistance by minimizing the possibility of variation in the installation of the component that will be responsible for providing lateral resistance.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a wall in a building that, as installed, can achieve specific design loads for resisting lateral forces on the wall.

It is an object of the present invention to provide a wall able to resist shearing forces on a building that is easy and economical to construct.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to an improved wall1designed to resist lateral forces imposed on a building incorporating the wall1. The building has an underlying structural component2that supports the wall1. As shown inFIG. 9, the underlying structural component2can be a cement foundation. Often, the wall1will not rest on the foundation directly, but rather on a floor diaphragm resting on the foundation. In this case, the underlying structural component2becomes the floor diaphragm and the foundation. When the wall1occurs at the second or third level of the building, the underlying structural component2is the supporting floor diaphragms, lower levels and the foundation of the building.

The wall1is formed with a bottom plate3that rests on the underlying structural component2of the building. The bottom plate3is connected to the underlying structural component2by means4for connecting the bottom plate3to the underlying structural component2of the building. A plurality of vertically-disposed studs5are disposed on top of the bottom plate3. These studs5are connected to the bottom plate3by means6for connecting the plurality of vertically-disposed studs5to the bottom plate3. A top plate7is supported by and rests on the vertically-disposed studs5. The top plate7is connected to the vertically-disposed studs5by means8for connecting the top plate7to the vertically-disposed studs5.

The wall1, itself, incorporates a shear-resisting assembly9that is connected to the top plate7of the wall1and is also connected to the underlying structural component2. These connections allow lateral forces on the top plate7of the wall1and on the underlying structural component2to be transmitted to the shear-resisting assembly9. The shear-resisting assembly9is disposed between the top plate7and the underlying structural component2. The shear-resisting assembly9has a planar shear-resisting element10. The planar shear-resisting element10, itself, has a proximal face11, a distal face12, a top edge13, a bottom edge14and first and second side edges15and16. The shear-resisting assembly9includes a top strut17connected to the proximal face11near the top edge13of the shear-resisting element10. The top strut17is disposed substantially parallel to the top plate7of the wall1. The shear-resisting assembly9includes a bottom strut18connected to the proximal face11near the bottom edge14of the shear-resisting element10. A first chord19is connected to the proximal face11near the first side edge15of the shear-resisting element10. A second chord20is also connected to the proximal face11near the second side edge16of the shear-resisting element10. The top and bottom struts17and18and the first and second chords19and20are connected to the shear-resisting element10by means21for connecting the top strut17, the bottom strut18, the first chord19and the second chord20to the shear-resisting element10. The top and bottom struts17and18and the first and second chords19and20form a supporting frame for the shear-resisting element10.

The shear-resisting assembly9is connected to the top plate7of the wall1by means22for connecting the shear-resisting assembly9to the top plate7and is connected to the underlying structural component2of the building by means23for connecting the shear-resisting assembly9to the underlying structural component2.

In the preferred form of the invention, the bottom plate3of the wall1, the plurality of vertically-disposed studs5resting on the bottom plate3, the top plate7of the wall1, the shear-resisting element10of the shear-resisting assembly9, the top and bottom struts17and18of the shear-resisting assembly9, and the first and second chords19and20of the shear-resisting assembly9are all made of wood or wood composites. These members can also be made of steel or synthetic building materials.

As shown inFIG. 9, in the preferred form of the invention, when the underlying structural component2is the foundation of the building, the means4for connecting the bottom plate3to the underlying structural component2of the building are foundation anchors in the shape of bolts bent to form a mechanical interlock with the foundation. The inventor has found ⅝″ diameter ASTM A307 or A36 foundation anchors embedded to a proper depth to be sufficient for most foundations. The length of the foundation anchors, the spacing between foundation anchors and placement of the foundation anchors in the foundation are determined according to the forces that are imposed on the wall1and the strength of the foundation. The means4for connecting the bottom plate3to the underlying structural component2of the building can also be strap anchors, mudsill anchors, bolts, retrofit bolts, foundation plate holdowns, straps, ties or a combination thereof. When the underlying structural component2consists of a floor diaphragm and the foundation of the building, the means4for connecting the bottom plate3to the underlying structural component2of the building can be nails, screws, bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof. When the underlying structural component2consists of a floor diaphragm, a supporting wall and the foundation, the means4for connecting the bottom plate3to the underlying structural component2of the building can be nails, screws, bolts, foundation bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof. When the underlying structural component2consists of a plurality of floor diaphragms, a plurality of supporting walls and the foundation, the means4for connecting the bottom plate3to the underlying structural component2of the building can be nails, screws, bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof.

As shown inFIG. 10, the preferred means6for connecting the plurality of vertically-disposed studs5to the bottom plate3are zinc-coated nails, but screws, adhesives, welds, clips, angles, framing anchors, stud-plate ties, ties, straps or a combination thereof can also be used.

As shown inFIG. 10, the preferred means8for connecting the top plate7to the vertically-disposed studs5are also zinc-coated nails, but screws, adhesives, welds, clips, angles, framing anchors, stud-plate ties, ties, straps or a combination thereof can also be used.

As shown inFIG. 1, the preferred means21for connecting the top strut17, the bottom strut18, the first chord19and the second chord20to the shear-resisting element10are 10d common 0.148″×3″ nails, but screws, welds, clips, ties, brackets, angles staples, adhesives or a combination thereof can also be used. As shown inFIG. 1, nails should usually be spaced 2″ apart around the shear-resisting element10near the top and bottom edges13and14and the first and second side edges15and16to achieve maximum shear resistance without causing splitting of the shear-resisting element10.

As shown inFIG. 10, the preferred means22for connecting the shear-resisting assembly9to the top plate7of the wall1are top plate fasteners having a threaded shank portion, but nails, welds, bolts, straps, brackets, ties, angles, anchor plates, clips, framing anchors or a combination thereof can also be used. The preferred top plate fasteners are ¼″×6″ Simpson Strong Drive Screws. The top plate fasteners are inserted through the top strut17of the shear-resisting assembly9and into the top plate7of the wall1. The number of top plate fasteners is dependent on the lateral loads the shear-resisting assembly9is expected to carry and the strength of the top plate fasteners.

As shown inFIG. 10, the preferred means23for connecting the shear-resisting assembly9to the underlying structural component2of the building is a foundation anchor just like the means4for connecting the bottom plate3of the wall1to the underlying structural component2. The inventor has found three ⅝″ diameter ASTM A307 or A36 foundation anchors embedded to a proper depth to be sufficient for anchoring a four foot wide shear-resisting assembly to most foundations. The length of the foundation anchors, the spacing between foundation anchors and placement of the foundation anchors in the foundation are determined according to the forces that are imposed on the shear-resisting assembly9and the strength of the foundation. The means23for connecting the shear-resisting assembly9to the underlying structural component2of the building can also be strap anchors, mudsill anchors, bolts, retrofit bolts, foundation plate holdowns, straps, of ties or a combination thereof. When the underlying structural component2consists of a floor diaphragm and the foundation of the building, the means for connecting the shear-resisting assembly9to the underlying structural component2of the building can be nails, screws, bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof. When the underlying structural component2consists of a floor diaphragm, a supporting wall, and the foundation, the means23for connecting the shear-resisting assembly9to the underlying structural component2of the building can be nails, screws, bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof. When the underlying structural component2consists of a plurality of floor diaphragms, a plurality of supporting walls, and the foundation, the means23for connecting the shear-resisting assembly9to the underlying structural component2of the building can be nails, screws, bolts, retrofit bolts, framing anchors, angles, ties, plates, straps or a combination thereof.

As shown inFIG. 10, in the preferred form of the invention the shear-resisting assembly9rests directly on the underlying structural component2, bypassing the bottom plate3of the wall1.

As also shown inFIG. 10, in the preferred form the first and second chords19and20of the shear-resisting assembly9rest directly on the underlying structural component2. This prevents the bottom strut18from being crushed when moment reactions exert compressive forces on the first and second chords19and20. Because the first and second chords19and20rest directly on the underlying structural component2, 20 gauge steel standoff plates51are preferably attached to the bottoms of the first and second chords19and20to serve as a moisture barrier. SeeFIGS. 6,7A and7B. This is accomplished with two 8d nails, end-nailed through the standoff plates51.

As shown inFIG. 7A, in the preferred form the means23for connecting the shear-resisting assembly9to the underlying structural component2is a foundation anchor anchored to the underlying structural component2. The foundation anchor is designed to transmit lateral forces imposed on the underlying structural component2to the shear-resisting assembly9.

As shown inFIG. 7A, the bottom strut18is formed with an opening through which the foundation anchor passes. Preferably, the opening in the bottom strut18is oversized to accommodate mis-installation of the foundation anchor in the underlying structural component2. As is shown inFIG. 7A, the opening in the bottom strut18is preferably a slotted opening25, the slotted opening25being oriented so that the bottom strut18can slide horizontally and at right angles to the length of the wall1. As is shown inFIG. 11, the opening in the bottom strut18can also be a notch26in the bottom strut18that allows the bottom strut18to slide into place. A washer50and a nut30can be added to improve the connection and provide resistance to uplift forces on the shear-resisting assembly9.

As shown inFIG. 7A, epoxy27can be inserted within the opening in the bottom strut18to ensure close contact between the foundation anchor and the bottom strut18.

As shown inFIG. 7B, in the preferred form of the present invention a toothed plate28, having teeth29, is used to eliminate play between the bottom strut18and the foundation anchor due to the oversized opening in the bottom strut18that receives the foundation anchor. The toothed plate20receives the foundation anchor and connects to the bottom strut18with the teeth29. A nut30is fitted onto the foundation anchor and tightened down, forcing the teeth29of the toothed plate28into the bottom strut18. A washer50can be added to improve the connection.

As shown inFIG. 10, in the preferred form the shear-resisting assembly9also has first and second anchor bolts31that are anchored to the underlying structural component2and are disposed near the first and second chords19and20. The first and second anchor bolts31are received by first and second holdowns32. Nuts33, fitted onto the first and second anchor bolts31, engage the first and second holdowns32. The first and second holdowns32are connected to the first and second chords19and20by means34for connecting the first and second holdowns32to the first and second chords19and20.

The first and second anchor bolts31should at least be ⅞″ diameter ASTM A307 or A36 anchor bolts31embedded in the foundation at proper locations and a selected depth to ensure sufficient resistance to the loads the shear-resisting assembly9is designed to carry.

As shown inFIG. 7A, the bottom strut18is preferably formed with anchor bolt openings through which the first and second anchor bolts31pass. Preferably, the anchor bolt openings in the bottom strut18are oversized to accommodate mis-installation of the anchor bolts31in the underlying structural component2. The anchor bolt openings in the bottom strut18are also preferably slotted openings36, the slotted openings36being oriented so that the bottom strut18can slide horizontally and at right angles to the length of the wall1.

As shown inFIG. 7A, the first and second holdowns32are preferably formed with slotted openings38that are oriented in the same direction as, and are in general alignment with, the slotted openings25in the bottom strut18when the first and second holdowns32are attached to the first and second chords19and20, the slotted openings38receiving the first and second anchor bolts31.

As shown inFIG. 11, the anchor bolt openings in the bottom strut can also be formed as notches37in the bottom strut18that allow the bottom strut18to slide into place. When the anchor bolt openings in the bottom strut18are formed as notches26and37, portals39should be formed in the first and second holdowns32that allow the shear-resisting assembly9to slide into place.

As shown inFIG. 10, the means34for connecting the first and second holdowns32to the first and second chords19and20are holdown fasteners having threaded shank portions. Preferably, these holdown fasteners are ¼″×3″ Simpson Strong Drive screws, although they can also be bolts, nails, screws or adhesives.

As shown inFIG. 10B, holdown fasteners are preferably inserted only a selected distance into the first and second chords19and20without passing all the way through the first and second chords19and20. This allows the shear-resisting assembly9to fit closely between the studs5of the wall1.

As shown inFIGS. 4 and 5, the means21for connecting the top strut17, the bottom strut18, the first chord19and the second chord20to the shear-resisting element10are preferably edge fasteners having shank portions41. Preferably, these edge fasteners are 10d common 0.148″×3″ nails. Preferably, the first and second chords19and20and the top strut17are attached to the shear-resisting element10by two rows of nails. The rows of nails are spaced ½″ apart. Within the rows, the nails are spaced 4″ apart. As is best shown inFIG. 8, the nails between rows are staggered approximately 2″ apart. Preferably, the bottom strut18is attached to the shear-resisting element10by three rows of nails. The rows of nails are spaced ½″ apart. Within the rows, the nails are spaced 4″ apart. Between rows, the nails are staggered approximately 1.3″ apart. Nails should be spaced at least 0.357″ from the top and bottom edges13and14and the first and second side edges15and16of the shear-resisting element10to reduce splitting.

As best shown inFIGS. 3,4and5, in the preferred form of the shear-resisting assembly9, what the inventors call boundary edging members42are used to strengthen the connection between the shear-resisting element10and the top and bottom struts17and18and the first and second chords19and20. The boundary edging members42are disposed on the shear-resisting element10at the top and bottom edges13and14and the first and second side edges15and16. The boundary edging members42are pierced by the shank portions41of the edge fasteners.

Preferably, the boundary edging members are u-shaped channels, having a pair of legs43joined by a central member44, that embrace the shear-resisting element10. The shank portion41of each of the edge fasteners passes through the legs43of the u-shaped channels. The boundary edging members42are preferably formed from galvanized20gauge sheet metal. The legs43and central member44of the boundary edging members42can be of varying widths to accommodate various nailing configurations and shear-resisting elements10of varying thickness. Preferably, 0.125″ diameter holes52, spaced 1″ apart are formed in the central member44. These holes52allow moisture to escape from the top and bottom edges13and14and first and second side edges15and16of the shear-resisting element10.

When the shear-resisting assembly9is sufficiently wide, the shear-resisting assembly9is preferably made with intermediate studs45disposed between the top and bottom struts17and18of the shear-resisting element10. These intermediate studs45are preferably formed from 1.5″×3″ machine stress rated (MSR) Southern Yellow Pine studs. These intermediate studs45are connected to the top and bottom struts17and18by means46for connecting the intermediate studs45to the top and bottom struts17and18. Preferably, the means46for connecting the intermediate studs45to the top and bottom struts17and18are 20d 0.150″×5.5″ nails. Also, in the preferred embodiment the intermediate studs45of the shear-resisting assembly9are connected to the shear-resisting element10by means47for connecting the intermediate studs45to the shear-resisting element10. As best shown inFIG. 1, in the preferred form the means47for connecting the intermediate studs48to the shear-resisting element10are 10d common 0.148″×3″ nails spaced 12″ apart.

As shown inFIGS. 4 and 5, in the preferred embodiment the first and second chords19and20of the shear-resisting assembly9are formed from two elongated wood members48, laminated together. Preferably, these elongated wood members48are dried 1.5″×3.5″ MSR Southern Yellow Pine. The wood members48are glued together and then trimmed to a dimension of 2.875″×3″. Preferably, the top strut17is formed from this same material and in the same manner from two elongated wood members53laminated together. The bottom strut18is preferably 2.5″×3″ pressure-treated Southern Yellow Pine. At these dimensions, the shear-resisting element10can be 15/32″ wide and still fit within the profile of a wall1formed from 2×4 members. The shear-resisting assembly9is designed to fit within a wall1without interfering with the construction of the wall1. Electrical and plumbing conduits can easily be run through the wooden first and second chords19and20, and paneling and sheet-rocking can be carried out without interference from the shear-resisting assembly9.

The shear-resisting assembly9can be formed in a variety of dimensions to fit various spaces. In some instances, the shear-resisting element10will comprises a single structural panel49. SeeFIG. 1. In other instances, the shear-resisting element10will be so large that the shear-resisting element10will need to be formed from a plurality of adjoining structural panels disposed in a single plane, forming joints between the structural panels. Structural panels49are preferably Oriented Strand Board (OSB) 15/32″ APA Rated Structural 1 Sheathing, 32/16, Exposure 1. The structural panels49can also be formed from plywood, wood and synthetic laminates, wood and steel laminates, gypsum and steel laminates, synthetic materials and steel.

When the shear-resisting element10is constructed from a plurality of structural panels49, intermediate studs45and means46for connecting the intermediate studs45to the shear resisting element10can be used to join the structural panels49together at their joints. Preferably, the means46for connecting the intermediate studs45to the shear-resisting element10are 10d common 0.148″×3″ nails.

Preferably, the bottom strut18is made from pressure-treated Southern Yellow Pine, having a cross-sectional dimensions of 2.5″×3″. The bottom strut18can also be constructed in the same manner and from the same materials as the first and second chords19and20with the added step of pressure-treating the materials to protect against moisture intrusion.

As shown inFIG. 10, the top plate7is preferably made from a plurality of individual elongated wood members54joined together by nails or screws to form a double layer.

As described below, in the preferred method of building the wall1of the present invention, the shear-resisting assembly9is installed first and the remaining components of the wall1are built around it. However, sometimes the shear-resisting assembly9will need to be added after the remaining components of the wall1have been constructed and installed on the underlying structural component2. In these instances, the shear resisting assembly9can be slid into place if the bottom strut18is formed with notches26for the foundation anchors, notches37for the anchor bolts and the first and second holdowns32are formed with portals39. SeeFIG. 11. The shear-resisting assembly9could also be tilted into place as is shown inFIGS. 12 and 13. When the shear-resisting assembly9is titled into place, it is best to provide a shim55between the top plate7of the wall1and the top strut17of the shear-resisting assembly9to eliminate any space between the two.

As shown inFIG. 1, additional nails56can be used to connect the top strut17of the shear-resisting assembly9to the first and second chords19and20.

The following is a description of how to make the preferred form of the present invention, where the underlying structural component2is a concrete foundation, as best shown inFIG. 10.

First the shear-resisting assembly9is constructed. Preferably, this is done at a factory by assemblers who specialize in their construction. Slotted openings25and slotted anchor bolt openings36are formed in the bottom strut. The top and bottom struts17and18, the first and second chords19and20and the intermediate studs45are cut to the desired size. The first and second holdowns32are attached to the first and second chords19and20. The top strut17, bottom strut18, the first chord19, the second chord20and the intermediate studs45are placed on a jig. The intermediate studs45are connected to the top and bottom struts17and18with nails driven through the top and bottom struts17and18. Then the first and second chords19and20are attached to the top strut17with nails also driven though the top strut17, forming a frame for the shear-resisting element. Then a shear-resisting element10, fitted with boundary edging members42, is placed on top of the frame. The edge fasteners are then driven through the boundary edging members42and shear-resisting element10and into the frame. The intermediate studs45are also attached to the frame by nails, completing the construction of the shear-resisting assembly9at the factory.

At the construction site, the foundation anchors for anchoring the bottom plate3of the wall1, the foundation anchors for anchoring the bottom strut18of the shear-resisting assembly9, and the anchor bolts31for anchoring the first and second chords19and20of the shear-resisting assembly9are set into the form for the concrete foundation at the predetermined locations. The concrete form is then poured and allowed to cure.

Next, the shear-resisting assembly9is installed on the foundation anchors and the anchor bolts. The foundation anchors are inserted into the slotted openings25, and the anchor bolts31are inserted into the slotted anchor bolt openings36in the bottom strut18and the slotted openings38in the holdowns32. The toothed plates28, washers50and nuts30are then fitted on the foundation anchors. When the shear-resisting assembly9is properly aligned with the foundation, the nuts30are tightened down on the foundation anchors and the shear-resisting assembly9is locked in place. The nuts33for the anchor bolts31are then tightened down so that they bear upon the first and second holdowns32.

Next, the remaining wall1is constructed. First, the bottom plate3is prepared for fitting over the foundation anchors that will attach it to the foundation. This is done by drilling holes in the bottom plate3at selected points. Next, the studs5are attached to the top and bottom plates7and3. Generally, this will be accomplished with the wall1lying flat on the ground. When this stage is completed, the wall1is tilted up and fitted over the foundation anchors. Finally, the shear-resisting assembly9is attached to the wall1by top plate fasteners. The number of top plate fasteners used is dependent on the strength of the top plate fasteners and the loads they will be designed to carry.

Testing

In order to characterize and to determine the preferred form of the present invention, individual shear-resisting assemblies were constructed and tested.

The shear-resisting assemblies were tested in Brea, Calif. at the Simpson Strong-Tie Co. Laboratory on a machine designed to simulate their behavior when inserted in a wall during the cyclic (reversing) lateral forces that would occur during an earthquake.

The tests determine the strength and stiffness of the shear-resisting assemblies. Stiffness is measured in terms of the force that is required to displace the top strut a given lateral distance. Strength is described in these terms as well. Strength is also described by what level of displacement force was being exerted on shear-resisting assembly when there was complete failure—the point at which the shear-resisting assembly no longer provided any meaningful resistance to lateral forces.

Test results are reported in Tables 1, 2 and 3 for a number of different shear-resisting assemblies. Results are reported in terms of the force required to displace the top of the shear-resisting assembly 0.5″ (Load at 0.5″) under cyclic loading conditions and 1.0″ (Load at 1.0″) under cyclic loading conditions. Also reported is the load at which complete failure occurred (Maximum Load).

The tests were conducted according to a protocol developed by the Joint Technical Coordinating Committee on Masonry Research (TCCMAR) in 1987. See Porter, M. L.,Sequential Phased Displacement(SPD)procedure for TCCMAR Testing, Proceedings of the Third Meeting of the Joint Technical Coordinating Committee on Masonry Research, US-Japan Coordinated Earthquake Research Program, Tomamu, Japan.

The TCCMAR procedure hinges on the concept of the First Major Event (FME), which is defined as the first significant limit state which occurs during the test. The FME occurs when the load capacity of the wall, upon recycling of load to the same wall displacement increment, first drops noticeably from the original load and displacement. FME for all tests was assumed to occur when an 8 foot high shearwall can be displaced 0.8 inches at its top.

The TCCMAR procedure consists of applying cycles of fully-reversing displacement to the shearwall at various increments of the wall's assumed FME. SeeFIG. 15.

In the first phase, three cycles of fully-reversing displacement are applied to the top of the shearwall at 25% of FME. The first phase continues by then applying three cycles of fully-reversing displacement at 50% of FME. Then, three cycles of fully-reversing displacement are applied at 75% of FME. Then, the fully-reversing displacement is increased for one cycle to 100% of FME. This is the maximum displacement for this first phase. Next, “decay” cycles of displacement for one cycle each at 75%, 50%, and 25% of the phase-maximum are applied in that order respectively. Then, three stabilizing cycles of displacement at the phase-maximum (100% of FME) are applied to the top of the shearwall. These phase-ending cycles stabilize the load-displacement response of the shearwall, prior to the next phase of testing.

In the second phase, which follows immediately according to the test frequency, one phase-maximum cycle of fully-reversing displacement is applied at 125% of FME. Next, “decay” cycles of displacement for one cycle each at 75%, 50%, and 25% of the maximum for that phase are applied in that order respectively. Then, three stabilizing cycles of displacement equal to the phase-maximum for the phase (125% of FME for the second phase) are applied to the shearwall.

In the third phase, one phase-maximum cycle of fully-reversing displacement at 150% of FME is applied to the shearwall. Next, “decay” cycles of displacement for one cycle each at 75%, 50% and 25% of the phase-maximum for the phase are applied. Then, three stabilizing cycles of displacement equal to the phase-maximum (150% of FME for the third phase) are applied to the top of the shearwall.

Successive phases are continued in a like manner as the second and third phases at increased increments, as shown inFIG. 15. The incremental cyclic load-displacement phases are continued at phase-maximums of 175%, 200%, 250%, 300%, 350% and 400% of FME, or until the wall exhibits excessive displacement, or until the wall displacement exceeds the capacity of the test equipment, which in this case was ±3.0 inches. In all trials, the lateral load capacity of the shearwall had greatly diminished by the time the shearwall was displaced 3.0 inches.

Racking shear loads were applied to the test specimens through an actuator located at the top of the wall. The actuator was placed so that the actuator did not interfere with any movement of the structural panel. The actuator that caused deflection at the top of the shearwall was computer controlled. Actuator loads were applied to the wall at a frequency of one cycle per second.

The shear-resisting assemblies were attached to the base of the test frame with ⅝″ diameter foundation bolts, passing through the bottom strut, spaced approximately 12 inches on center, and approximately 12 inches from the ends of the shearwall.

The vertically-disposed first and second chords, of the shear-resisting assembly test specimens were attached to the test frame with holdowns and ⅞″ inch anchor bolts that passed through the bottom strut. All tests were conducted with Simpson Strong-Tie PHD8 holdowns, except test F945 which used an experimental holdown formed in accordance with the present invention. The holdowns used for Test F945 are formed with slotted openings for receiving the first and second anchor bolts and attach to the first and second chords by means of ¼″×3″ Simpson Strong Drive Screws. The PHD8 holdowns also attach to the first and second chords by means of ¼″×3″ Simpson Strong Drive Screws, except they are not formed with slotted openings for receiving the first and second anchor bolts.

Lumber used for the tests varied according to the goals of the test. Generally, lumber moisture content at the time of the tests was approximately 20 to 25%.

The top struts were generally doubled 2×4s connected with nails. The top struts for each shear wall were 48″ long. The bottom struts were also typically 2×4s. In addition to the top and bottom struts and the first and second chords, two intermediate 2×4 studs, spaced 16″ on center from each other and the first and second chords, were added and end-nailed to the top and bottom struts with nails according to currently accepted building practices, for most tests.

A variety of chords were used for the vertically-disposed first and second chords. In all tests, except test F498, which reflects current building practices, the first and second chords were approximately 93″ tall. This means the chords sat directly on the test frame. Setting the chords on the test frame eliminates failure of the shear-resisting assembly due to crushing of the bottom strut by the chords, and greatly improves the performance of the shear-resisting assembly. This particular design of using long chords that bypass the bottom strut is especially effective where the shear-resisting assembly sits on the relatively non-compressible building foundation.

Plywood and Oriented Strand Board structural panels were used for the structural panel or shear-resisting element in the tests. All tests were conducted with one 4′×8′ structural panel applied to the framing members with the face grain or strength axis disposed vertically.

Generally, the structural panels were fastened to the top and bottom struts and the first and second chords by steel 10d common nails that were either 2.125″ long or 3″ long. All nails were driven into the framing members to a depth of at least 11 times their shank diameter to comply with the Uniform Building Code. All nails were driven so that the head of the nail sat flush against either the shear-resisting assembly or the boundary edging members. All nails were spaced 2″ on center around the periphery of the structural panel, except where noted otherwise in the tables. Generally, the structural panel was attached to the intermediate studs with 10d×3″ long common nails spaced 12″ on center.

Table 1 represents a progression from a basic shear-resisting assembly built according to the present invention (Test 495) to a shear-resisting assembly that incorporates most of the preferred elements of the present invention (Test 945). Test F945 used the nailing patterns described in the description of the preferred embodiment to connect the shear-resisting element to the first and second chords and to the bottom and top struts. Test F945 also used the preferred material of Oriented Strand Board for the structural panel. As in the preferred embodiment, the chords of Test F945 were long chords. In Test F945, the first and second chords bypassed the bottom strut and rested directly on the test frame. Test F945 also used first and second chords made from individual wood members glued together to form a laminate. Test F945 used “u” shaped boundary edging members. Finally, Test F945 used holdowns having a slotted openings that connected to the first and second chords by means of holdown fasteners having threaded shanks.

Tables 2 and 3 provide as direct a comparison as is possible between shear-resisting assemblies using different materials for the first and second chords. Again, Test F945 is the preferred unit among the compared assemblies.