Static structures (e.g. – buildings) – Settable material receiving backer fixed to furring – joist,... – Impaling-type fastener
Reexamination Certificate
2001-02-15
2003-12-30
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Settable material receiving backer fixed to furring, joist,...
Impaling-type fastener
C052S454000, C052S443000, C411S480000, C411S482000, C411S441000, C411S546000, C411S155000, C411S156000
Reexamination Certificate
active
06668501
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thin concrete or stucco wall panels. In particular this invention relates to means for securing stucco wall panels to wood frames to improve the shear resistance to cyclic loading such as from earthquakes or wind.
BACKGROUND OF THE INVENTION
In building and structural design, structural elements need to be incorporated in the design to adequately withstand rack shear loads imposed by earthquakes or high winds. Common methods to achieve this shear strength are through the use of moment resistant frames, cross bracing, or through shear resistant structural diaphragms. Wood frame shear walls are a primary lateral force-resisting element in wood frame structures. Their behavior is often considered analogous to a deep cantilever beam with the end-framing members acting as “flanges” or “chords” to resist overturning moment forces and the panel acting as the “web” to resist shear. This analogy is generally considered appropriate for wind and seismic design. The structural elements of the building wall of interest are described by properties such as strength, stiffness, and ductility. Common diaphragm materials would be plywood sheathing, oriented strand board (OSB), or gypsum wall board (GWB).
In certain areas of North America, such as the Western States of the U.S., another material that is commonly used to provide shear strength is stucco cladding. Stucco is a Portland cement plaster that is reinforced with either wire lath, or expanded metal lath.
The stucco is normally ⅞ inch thick and achieves compressive strengths of 1,500 to 2,800 psi.
The lath serves several functions. First, it provides reinforcement for the stucco to provide tensile strength, similar to structural concrete design. Second, it provides the means for attachment of the stucco cladding to the building framework. The lath is attached in a prescribed manner. Usually fasteners are applied every 6 inches vertically on studs and every 6 inches horizontally along the top and bottom plates for each storey. In the case of wood framing, the fasteners are often roofing nails but they may be staples.
With the use of such stucco wall cladding, engineers have been allowed to use a shear value of 180 lbs. per foot to resist rack shear forces in their designs. Following the Northridge Calif. earthquake of Jan. 17, 1994, it was found that some buildings constructed with stucco shear walls suffered premature failures. Subsequently, some building officials have lowered the shear rating for stucco to 90 lbs. per foot in specific seismic areas.
Failure of the stucco cladding was primarily caused by failure of the attachment of the reinforcing lath to the framing. The normal method of attaching the lath is to drive a nail alongside a wire and hold the wire under one side of the head of the nail. Where possible, the nails are driven at the intersections of the wire lath, but the wires are still only held under one side of the nail head. For unidirectional loading, such as wind forces, the fastening is adequate. However, during reversing cyclic loading such as an earthquake, the fastening is inadequate. During an earthquake of high intensity, there is relative movement between the stucco cladding and the building framing. With displacement in the first direction a number of fasteners will disengage from the lath. With displacement in the other direction, more fasteners will disengage. Over a few cycles, the majority of fasteners will be disengaged.
Since the wire sizes in wire laths used in the Northridge Calif. earthquake were relatively small, usually 0.050 to 0.062 inches in diameter, they had limited strength. Under cyclic loading where the nails did not disengage from the wire, the loading broke the wire. On some buildings, construction staples had been used to attach the lath. The performance of staples was worse than the nails, since it was found that each leg sheared with the reversing cyclic loads. Accordingly, there is a need for an improved method for transferring rack shear forces to a building frame.
Wood framing for a wall without sheathing or diagonal bracing is essentially a low strength structure that deforms readily under shear loads. Shear walls have traditionally used sheathing, such as plywood, that is very stiff under shear loads to reinforce the wood framing. The sheathing is fastened to the wood framing by nails using a nailing pattern that meets engineering requirements. Under in-plane shear loads, the nail fasteners are the ductile elements that deform and provides the inelastic behaviour that is essential for energy dissipation in cyclic loading.
Stucco wall panels can provide effective reinforcement for wood framed shear walls if a suitable method is used to attach the panels to the wood frame. Nails, such as used to attach plywood sheathing to a wood frame, are not suitable for stucco. Nails will pull out of the stucco by local brittle fracture mechanism under tension loading. Nails will crack the stucco when the local yield stress is exceeded under shear loading.
The problem of providing attachment between a shear-resisting element and a structure under in-plane shear loading has been addressed by many building structure designers. In 1999, Utzman was granted U.S. Pat. No. 5,870,870 for metal shear panel fasteners to fasten shear resistant diaphragms to framing elements in the construction of framed building. Ulzman claims a special fastener similar to a “duplex” nail for attaching the diaphragms to the wood building frame. The application was to attach metal-faced gypsum wallboard to wood frame construction for shear walls. Although Utzman claims that his invention provides good shear resistance, the system is not suitable for fabricated-in-place stucco wall finishes.
In 1996, Irimies was granted U.S. Pat. No. 5,493,833 for a welding stud used in the construction industry for providing a shear connection between cast-in-place concrete and structural steel. Irimies provided the optimum dimensions for an array, or group, of studs to develop full shear strength when embedded in concrete. The welding stud has applications only in cast-in-place concrete structures that are attached to steel structural members to which the studs can be welded. The objective of that shear connection is to create a joint between the concrete and the structural steel that is stiff and strong. The connection does not, however, provide ductility and is not suitable for wood frame construction.
In 1995, Ruiz et. al. was granted U.S. Pat. No. 5,414,972 for a reinforced structural member to be used in the construction industry for providing a shear connection between a concrete building panel and a reinforcing member that will be fastened to a building structural member. The main application is to attach pre-fabricated building panels to a steel building framework. Ruiz shows a reinforcing member having a multiplicity of projections that embed in concrete to provide full shear strength. As in the Irimies invention, this shear connection is not capable of providing any ductility.
In 1989, Grimaud was granted U.S. Pat. No. 4,841,703 for a connection system to create a composite beam structure from a concrete slab cast over wooden floor beams. The connectors are tubes inserted into the concrete slab and the wood floor beams along the common interface to provide sufficient material to carry the shear loads. The object of the invention is to create an integral structure with no relative motion between components. Grimaud made reference to another connection system that uses vertical nails that are partially engaged in the faces of the wood floor beams and embedded into the concrete during casting. [Godycki et. al. “Verbunddecke aus Holzrippen unde Betonplatte”, Bauingenieur 59 (1984), 477-483, Springer-Verlag, Germany]. Such connectors suffer from limited shear strength and either deform readily or break at the interface, and hence are not suitable for attaching thin vertical panels of stucco cladding to wood frame walls.
The object of the present invention is to provide a
Adebar Perry
Davis Harold R.
Sacks Abraham
Spilchen William
Friedman Carl D.
Oyen Wiggs Green & Mutala
Sacks Industrial Corp.
Varner Steve M
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