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- To: <seaint(--nospam--at)seaint.org>
- Subject: wood posts & joists
- From: "Andrew D. Kester" <andrew(--nospam--at)baeonline.com>
- Date: Mon, 10 Mar 2003 08:30:13 -0500
(sorry if this posts twice) Wood Column Tables: I have the complete set of the APA ASD books and I never remember seeing tables for axial loaded members like AISC has, in terms of KL. I have seen them in proprietary catalogs for glulam members. This is a pretty easy solution once you set up a template in Mathcad or something similar, using compressive stresses parallel to grain from APA, along with the proper KL and all the other factors and formulas. If you are going to do any wood engineering design I would reccomend ordering that complete package from APA and have a good wood text book on hand, I use and like my college book, "Design of Wood Structures" 3rd Ed by Breyer. With those two sets of refs you can design most wood structures. I forgot the resident APA expert on the SEA list, but I am sure he will chime in soon, he knows his stuff. I don't think most of the residential and park deck and dock structures you see are built according to any engineered design. Most are built by carpenters and contractors who base their designs on experience, books and manuals, and other empirical methods. We have done some engineered designs for parks and many times they ask us to match the existing. I do the calcs and they are way over built. I have a project right now for a park for a 6ft wide deck, with 8ft spans, and they used 8.5" diameter piles!!! I am not too worried about failure in compression or buckling of the piles, but I will do the check if for nothing else for my own entertainment to see what their allowable capacity actually is. To illustrate my point I ran a quick calc on a S. Pine 4x4 , unbraced length = 5ft, the Pallow=13800+ lb! Try to load up a deck post with that. You would need 10ft worth of lag screws to make the connection work. Your stringers will control the design, or your connections, not your posts (unless you are really high off the ground). For deck design, the thing to worrry about is deflection (and probably connections and hand rails). You do not want a bouncy or "spongey" feel to your deck. Good luck finding a reasonable criteria from a reference for this though. I built a wood walkway at my house and spaced the supports about 20", 2x6 decking simply supported. I have stood on one board and jumped up and down and felt no give at all, and I weigh 245lbs. This is not scientific , but try to determine on paper if 1/10" of deflection is ok for a deck. Rules of thumb may say 16" o.c but this is way too small, I think. 20-24" seems fine for comfort levels. USE SCREWS for the decking, this will stiffen it up and you won't have nail heads popping out after a few years. Some wood adhesive (comes in a caulking container) is another good addition for any connections, especially decking. Wood Joists Cantilevering off wall: Call the manufacturer's engineer, they will need to solve that for you (or be involved as a part of the solution) and are usually happy to do so. Not that you cannot do it, but they have a pre-engineered product that can have some unusual properties you may/may not be aware of, like shear, concentrated loads, reverse bending, etc. They can run quick checks via software and offer you typical details and such. It will be a time saver. I have dealt with an engineer from TJI and he was extremely helpful. Just my humble opinions... Andrew Kester, EI Longwood, FL ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
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