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Structural Question about beam secured to top of proprietary shear wall panel.

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Monday, May 14, 2007

 

To: All subscribers of SEAINT List who are interested in light-framing remodel questions.

Re: Distribution of a reaction at each end of a Parallam PSL 2.0 E header that extends 24” over a proprietary shear panel (Hardy or Simpson) at each end.

 

I need some advice from the structural engineering community;

 

I am doing a small remodel on a one story custom home construction on a slab on grade. The home was constructed in 1997 and is located on a golf course in a gate community here in the desert. There are no plans or analysis as to how the shear was distributed through the building, but it appears that it was distributed to half of the building (the half I am working on) to the exterior walls. There are three shear wall piers – 3/8” OSB with nails (assumed 8d) nailed at 6:6 o.c. with panels vertical on 12’-0” plate height. Panel ends are support by blocking and unsupported edges nailed.

 

Rather than use the current code and finding that the shear in the wall may not comply, I looked up the shear value for an equivalent panel and worked backwards from the panel capacity. The new work requires removing the center panel that is 36-inches wide and is laterally support currently at 8-feet by the existing door headers. The panel capacity was distributed back into the two remaining panels which pushed the shear up to a point that would require panel nailing at 3-inch on center. Rather than tear the walls out to install 3x minimum vertical studs and a 3x minimum sill plate, I decided to use two Proprietary shear walls. The new header will span over an 18-foot opening and will carry a tile roof tributary of 20-feet. There are two truss sections. The patio truss is supported on the 12-foot plate but then drops down the face of the wall to 10-feet for a stucco ceiling. The inside of the home bears another section of truss 30-feet long that bears on the 12-foot plate.

 

QUESTION:

The header is being raised to set the bottom of header flush to 10’-0”. Each end of the new header will extend 24-inches over the top of either a SSW10x24 steel panel (Simpson) or an HF10x24 7/8 (Hardy) panel. The header will have a short pony wall nailed to the top of the header as the plate is 12-feet above the floor and about 10-inches above the top of the header. The panel will be secured to the bottom of the beam by Simpson SDS ¼” Lag Screws and the panels will rest directly on the slab or upon a bearing plate.

 

The reaction on the end of the beam is 3101 pounds live load and 4317 pounds of dead load. If the reaction or end of beam would be placed on a 4x4 column, the load would be concentric on the column and an additional foundation would be needed below the turn-down slab edge (24” sq. x 12” deep w/ (2) #5 each way). The requirement for the new pad below the slab edge continuous foundation is that the existing foundation would require a distribution of the load that exceeds a 4:1 aspect ratio.

 

Here’s the rub; based upon the extension of the header over the proprietary shear walls and the wall connection to the header, can the reaction be distributed over the panel. Theoretically, the connection might be considered a fixed connection. I don’t believe that you can make a fixed connection in a wood to wood connection without the use of a steel connector. For example, if the header was inserted into a tube that is welded to the top of the steel shear wall (Hardy) then I can argue that the connection is rigid, but if the connection is by lag bolt, the connection will have some rotation and the reaction would be transferred to the end of the panel that is closest to the opening rather than distributed over the top of the panel.

 

What is the general opinion on how to locate or distribute the reaction at the end of the header upon a proprietary frame where the end of the beam is secured uniformly to the top of the panel with lag screws and additional weight above from the tributary roof loads? At this point I assume that the end post of the panel closest to the opening carries the full load (or most of it)  and I have added a pad footing as noted above to each end. Did I make the right choice?

 

Dennis