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- To: wai(--nospam--at)euken.com
- Subject: Fwd: Re: [Fwd: Tilt-up roof ledgers]
- From: rlewis(--nospam--at)techteam.org (Richard Lewis)
- Date: 04 Aug 1997 18:16:51 GMT
In a message dated 97-03-19 11:45:05 EST, you write: << I am working on a tilt-up building project and have had several discussions as to what is the current design thinking for roof and floor ledgers. The buildings are one story multi tenent light industrial with diaphragms of approximately 70 ft. by 200 ft. and 22 ft. to top of walls. "Very typical". With small buildings like this I still prefer to use timber ledgers designed using hankinsons formula and seperate HD's for wall ties. I have also been using 300 plf. wall tie back force for several years and am considering increasing this to 500 plf. I have had several engineers tell me that I should be using steel angle ledgers because it avoids the cross grain bending problem and the use of hankinsons formula. I have concerns about the use of ledgers unless prying is considered at the ledger with regards to the angle or channel legder thickness and also the tension loads on the bolts. Seems that the use of HD's would still be a good idea but this defeats the use of the steel ledger. Am I off in left field with an old way of thinking (An old xxxx that need to move forward), or are timber ledgers with HD's still considered acceptable. I have used steel ledgers on large warehouse buildings where the spans were large. Would appreciate some other oppinions. Thanks in advance. Jim Dane, P.E. >> Jim, I would be comfortable with still using the wood ledgers with pairs of holdowns for the wall ties at the roof, but might consider using steel at the floor depending on the live load requirements. By using the steel channel or ledger, I would agree you still need to check for prying action on the bolt due to the vertical gravity load and the lateral load pulling on the horizontal leg of the angle or top flange of the channel. If you check combined shear and tension the bolts obviously have less capacity for transfering shear. I wonder how many engineers check for prying action on the angle installed using a single horizontal row of bolts vs just assuming the connection is in pure shear due to vertical loads. The other question is installation, is the contractor going to make a templete to match the anchor bolt pattern for shop drilling (most likely not) or start burning holes in the web in the field (with weld washers ?) to erect the ledger (or possibly use epoxy anchors for erection through the shop drilled holes). It is much easier to use a wood ledger for matching the embedded anchor bolt pattern and keeps the carpenter happy and reduces costs on the job (less steel) and can be reliable if you design for the proper out-of-plane wall forces. How do you make the connection of the wall ties from the purlin to the channel?, are this bolted straps each side of the purlin welded to the vertical leg of the angle or the web of the channel?. I would think this is more expensive then using the holdowns which I guess could be used instead of the steel straps. I also would think you may still need one bolt through the angle ledger within 6" each side of the purlin to help spread the load into the wall and minmize out-of-plane bending of the ledger. You still need a wood nailer on top of the channel for the plywood attachment. Depending on where the nails are placed relative to the nailer bolts, you can still have cross grain tension on the nailer (nails located between nailer edge away from the wall face and nailer bolts) as the wall trys to pull away so you have not eliminated cross grain tension by using steel. As Brian Cain mentioned, take a look at the SEAOC Blue Book, I think you will be designing for higher out-of-plane forces then 300 plf depending on how thick your wall is. My two cents worth. Michael Cochran Brain L. Cochran Associates Los Angeles, CA. bcase1356(--nospam--at)aol.com --- Internet Message Header Follows --- Received: from server1.seaoc.org (bqe.com [126.96.36.199]) by host1.texramp.net (8.8.5/8.8.5) with SMTP id BAA04947 for <rlewis(--nospam--at)techteam.org>; Thu, 20 Mar 1997 01:03:22 -0600 (CST) Received: from emout11.mx.aol.com by server1.seaoc.org (NTList 3.02.10) id wa010032; Wed, 19 Mar 1997 22:58:18 -0800 Received: (from root@localhost) by emout11.mail.aol.com (8.7.6/8.7.3/AOL-2.0.0) id BAA04926 for seaoc(--nospam--at)seaoc.org; Thu, 20 Mar 1997 01:56:10 -0500 (EST) Date: Thu, 20 Mar 1997 01:56:10 -0500 (EST) From: BCASE1356(--nospam--at)aol.com Message-ID: <970320015610_-935535189(--nospam--at)emout11.mail.aol.com> To: seaoc(--nospam--at)seaoc.org Subject: Re: [Fwd: Tilt-up roof ledgers] Reply-To: seaoc(--nospam--at)seaoc.org Error-To: seaoc-ad(--nospam--at)seaoc.org X-Loop: seaoc(--nospam--at)seaoc.org X-Info: [SEAOC] Owner: seaoc-ad(--nospam--at)seaoc.org X-POP3-Rcpt: seaoc-ad(--nospam--at)seaoc.org X-Sender: seaoc-ad(--nospam--at)seaoc.org Precedence: list X-ListMember: rlewis(--nospam--at)techteam.org [seaoc(--nospam--at)seaoc.org] __________________________________________________ Richard Lewis, P.E. Missionary TECH Team rlewis(--nospam--at)techteam.org The service mission like-minded Christian organizations may turn to for technical assistance and know-how.
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