Static structures (e.g. – buildings) – Assembled in situ-type anchor or tie – Sheet or wire tie
Reexamination Certificate
1999-09-02
2002-07-09
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Assembled in situ-type anchor or tie
Sheet or wire tie
C052S714000, C052S715000
Reexamination Certificate
active
06415575
ABSTRACT:
BACKGROUND-FIELD OF INVENTION
This invention relates to an invention sent in on Jan. 07, 1999 and is an innovative connector that positively holds down sheathing to create buildings that are resistant to earthquakes, hurricanes, tornadoes, and strong winds.
BACKGROUND-DESCRIPTION OF PRIOR ART
BACKGROUND
Recent studies of hurricane damage on wood-frame buildings indicate that the most extensive destruction to a house by strong winds, was when the roof sheathing was torn off and rain ruined everything in the house.
Roof sheathing ties all the rafters together on a wood frame house, and the roof sheathing tries all the roof trusses together when a masonry or wood-frame house is constructed with trusses. The roof sheathing helps prevent the trusses from racking, or tilting perpendicular to their length.
Sheathing that is tightly secured to the roof and subsequently fastened to the walls, helps transfer uplifting forces to the walls and henceforth to the foundation. If the roof sheathing fails, the trusses collapse, and the walls usually fall down as they can not stand by themselves against strong winds.
Failure and loss of the roof sheathing is common during hurricanes, mainly because of inadequate fastening of the roof sheathing to the underlying structural members. The roof system provides stability to a house by bracing the tops of exterior and interior load-bearing walls.
Sheet metal joints perform better than nailed joints in high winds and during seismic activity. Strong connectors, secured by well placed fasteners, will insure that the major structural members of a house are securely tied together.
HURRICANES
Studies of damage after Hurricane Andrew show several problems with the attachment of roof sheathing that this invention solves. Some sheets of roof sheathing that were blown off houses contained no nail holes, indicating that the sheet was placed in position, but was not nailed down. Some roofing sheets had nails in them that had missed the rafter that they should have been nailed upon. Some sheets had staples or nails that had rusted away, and on some sheets the nails had just pulled out from the rafter.
The engineering staff of the American Plywood Association provided technical personnel to assess the damage from Hurricane Andrew in Florida. The majority of wood structural sheathing failures were attributed to improper connection details, and in every case investigated, the sheathing loss was a result of improper nailing (Keith, 1992).
These problems have not been solved because staples are still used to tie down roof sheathing, and by looking at new construction, nails are still seen poking through the roof sheathing, completely missing the roof rafter. Most conscientious framers would drive another nail when they felt the nail miss the underlying rafter, but with the new powered nail guns, the framer can not tell if the rafter was missed because each shot feels the same, no matter what the nail is being driven into.
EARTHQUAKES
During an earthquake, the floor, wall, and roof diaphragms undergo shearing and bending. The shear forces from the roof boundary members are transferred to the top of the shear wall by way of toenails or blocking to the top plate. To withstand and transfer the shear loads, plywood sheets have to be spliced together to prevent adjoining edges from sliding past or over each other (Gray, 1990).
Butted together on the centerline of a 2×4, 2×6, etc. (nominally 1½-inches-wide), you've only got ¾ inch bearing for each plywood sheet, so the nail has to be ⅜ inch from the edge. This leaves little margin for error, and nailing has to be done with care to avoid splitting the plywood and missing or splitting the underlying member (Gray, 1990).
Tests at the University of California show that plywood secured by overdriven nails, nails that penetrated the plywood beyond the first veneer (usually by a powered nailgun), failed suddenly and at loads far below those carried by correctly nailed plywood panels (Gray, 1990).
Steel connectors, between different components of a wood-frame building's superstructure, provide continuity so that the building will move as a unit in response to seismic activity (Yanev, 1974).
PRIOR ART
A number of connectors have been developed to tie together the structural members of a house under construction. Up until this invention, nobody had seen how to make a compact connector that could tie two or more sheathing sheets together and to the underlying structural members, or could be applied from the top of the roof.
Some prior art prevents uplift, but this invention not only prevents uplift during hurricane-force winds, but prevents lateral movement during earthquakes.
I invented a previous sheathing tie that wrapped around a structural member and attached to the sheathing by a different method. That invention was sent in for patent protection on Jan. 7, 1999 as application Ser. No. 09/227,059.
The Simpson Strong-Tie Co.'s January 1996 catalog (page 62) lists a PSCL Plywood Sheathing Clip. This clip provides a gap and aligns sheathing but does not tie the sheathing to underlying structural members or prevent uplift or lateral movement. No other sheathing ties were found in their catalog, but they do show several seismic and hurricane ties on pages 60-61.
A prior art roof securing system by Llorens, U.S. Pat. No. 5,390,460 ties down a single sheet of roof sheathing to a support beam. This is a good connector, but it is long, and can only tie down one-size of sheathing. It must be hammered around the beam from below, but panels are installed from above the roof. Llorens' 460 can only tie down one panel and provides little lateral support.
Another sheathing strap and alignment guide by Nellessen, U.S. Pat. No. 5,423,156 shows an apparatus for securing sheathing using a long strap, connecting bands, and saddles. This is a good connector, but it is long, complicated, and must be installed from below the roof. With sheathing in place, this is difficult. Nellessen's 156 can only tie down panels of one size.
According to the magazine Fine Homebuilding, October/November, 1998, sheathing courses should begin with either a full or half sheet. The course of sheathing at the top row and beginning row are often odd-size, in order to get a reasonable width of sheathing on the top row.
OBJECTS AND ADVANTAGES
Accordingly, several objects and advantages of my invention are that it helps secure the roof, wall, and floor of a building to keep the building from being destroyed by hurricanes, tornadoes, and earthquakes.
This invention helps prevent the wall of a building from detaching from the wall studs during a hurricane or earthquake. It makes the wall into a stable shearwall, transferring shear forces into the foundation and ground.
This invention helps prevent the roof of a building from detaching from the rafters or roof trusses during a hurricane. It ties the roof sheathing securely to the underlying rafter or roof trusses, transferring lateral and uplift forces to the walls and to the foundation.
This invention helps prevent the floor of a building from detaching from the floor joists during an earthquake. It makes the floor into a horizontal shear wall, and helps the floor resist lateral forces in its horizontal plane. It also makes sure that any forces transferred from the roof and wall can be managed by the floor and transferred properly to the ground.
One object of this invention is to make each sheathing structure on a house into a shearwall, that is, able to transfer forces without breaking or disconnecting. By tying the plywood securely to the underlying structural member, the plywood can reliably transfer and dissipate shear, lateral, and uplift forces to the ground.
During an earthquake or a hurricane, another object is for the building with my invention to move as a sturdy unit, resisting and transferring destructive forces to the ground. Mounted on the roof sheathing and rafter, my invention resists uplift, the most destructive force during a hurricane. Mounted on the wall
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