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Basement wall restraint by wood[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'SEAINT'" <seaint(--nospam--at)seaint.org>
- Subject: Basement wall restraint by wood
- From: "Jeffery Seegert (x 485)" <jbseegert(--nospam--at)matrixti.com>
- Date: Wed, 25 Aug 1999 16:38:41 -0400
I can agree that designing the walls as cantilevered is not incorrect; nor is assuming it is a tank (with special considerations for long walls). I am shocked that there is even a discussion about the preferred way (not always the best) to design basement walls. First of all, wood diaphrams are not designed to support the walls. The floor joists and blocking are (and in some situations, sub-diaphrams). There was a very good article in SEA a few years ago about such a design. First of all, if setting your joists/trusses on top of the sill plate, special attention should be given the attachment to the sill plate in order to provide the proper restraining force. If the joists or trusses are hung off of the sill plate, the shear connection to the sill plate can be neglected. The code requires a continuous connection of attachment of joists/girders/blocking from one wall to another when designing wood diaphrams supporting CMU walls. This is to assure the support of the walls and to not rely upon the diaphram in tension or compression for wall support. It is a much simpler problem with basement walls in that they only see inward forces. With continuous floor joist/trusses/blocking properly called out, one need not worry about "loading" the diaphram. I'm sure one could argue "what about creep and deformation in the wood joists/blocking". First of all, with manufactured wood products, creep is not an issue. Secondly, calculate the amount of compressive load in a joist/truss at 16" o/c. or blocking at 48" o/c. These loads tend to be very minor resulting in negligible movement. Besides, the tile would continually expand and contract with the house temperatures which would be more of a concern than wood creep. Bottom line : design the basement walls as pinned, give some extra attention to sill plate connections and continuos joist/blocking from wall to wall and save the home owner some money. Any contractor that I required to build the basement walls as cantilevered would soon find another engineer to due their design. Why chase away business when a little detail in the right place solves the problem?
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