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ASD vs LRFD[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: ASD vs LRFD
- From: "Meyer, Jonathan" <JMeyer(--nospam--at)webbersmith.com>
- Date: Thu, 20 Dec 2001 08:21:08 -0500
Title: ASD vs LRFD
I found this discussion interesting, so I will weigh in with my opinions. I was taught ASD and have been designing using ASD all of my career. The vast majority of our facilities are one to two story food distribution/process facilities. Some may have one/two story offices. We did a comparison some years age (~1995) and discovered that LRFD would not save any steel on the buildings we design (in fact, we came up with the same sizes!). While I have attended seminars on LRFD, I have yet to see any benefit to the engineer in our industry in it's use.
I have heard all the propaganda from the AISC on steel savings, more uniform factors of safety, etc, and I am not convinced. Most of our clients have no idea how much they spend on steel and concrete. They are more concerned about the millions they are spending on equipment, and rightly so. In comparison, the steel costs are a minor consideration. Clients also reduce engineering fees as low as they can, so spending additional time during design (i.e. LRFD) may cause us to exceed our budgets. If we put in additional design time we risk losing the project.
We currently do not generally provide reactions on our drawings, although we have in specific cases in the past. We provide designs for all of the non-typical connections and ask that the detailer provide his "design" for the standard connections which we review during our review of the shop drawings. In seminars sponsored by the AISC on connection design, they repeatedly state that more economical connections can be provided if the reactions are provided. I agree with this, but because changes frequently occur after the building is completed, I would rather pay for a full depth connection now than save a couple of bolts during construction and have to change/modify the connection later (when the facility is in production).
We switched about a year ago to 50 ksi steel for all of our wide flange sections. The feedback we got from fabricators was that the steel had dual certifications anyway, so why not design to the higher yield? So we decided to switch to 50 ksi steel in our designs. Of course, this means that we have to watch deflection even more closely, which also works against the economies of LRFD.
I would be interested in learning more about who is using ASD or LRFD and how they perceive the timeliness and economies.
Jonathan Meyer, P.E.
Director Structural Engineering
Webber/Smith Associates, Inc
1857 William Penn Way Suite 200
Lancaster, Pa. 17601
Phone: (717)-291-2024 Ext. 239
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