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RE: Seismic mass[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Seismic mass
- From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
- Date: Wed, 08 Feb 2006 15:39:24 +0000
Mark,I did not participate on the development of the OSHA Subpart R, but I am personally acquainted with some of the participants and I know some of the reasons for the provisions. Following is the section on Erection Stability which contains the 4 anchor rod provision (AISC PC version of anchor bolt;>). I have included my comments. By the way the OSHA web site links to official inquiries and interpretations.
http://www.osha.gov/pls/oshaweb/owastand.display_standard_group?p_toc_level=1&p_part_number=1926 Subpart R General requirements for erection stability. 1926.755(a)(1) All columns shall be anchored by a minimum of 4 anchor rods (anchor bolts). [This provision happened for 3 reasons.First structural engineers were traditionally very hesitant to participate in the development of erection plans. It is that methods and means thing that drives insurance carriers nuts. Secondly, iron workers were getting killed and hurt due to column instability. Thirdly, the iron workers needed a solution to the problem of erection stability that did not require an "engineered" solution. I understand that the 4 anchor rod minimum is limiting to designers, but the iron workers needed a solution TODAY and not a study for the next several years. I had to do a presentation to some iron workers shortly after a column stability failure that caused death and injury to several of my former colleagues (iron workers) and defend the lack of action of my current colleagues (engineers). To say that the iron workers were hostile is to put it mildly. I understand their frustration, and I understand the trepidation of engineers to design an erection plan. This is the land of risk, liability, and low reward. But it is the reality in which buildings have to be constructed. The 4 bolt requirement is not the answer to all iron worker hazards, but it will have to do until structural engineers get into the methods and means. ]
1926.755(a)(2)Each column anchor rod (anchor bolt) assembly, including the column-to-base plate weld and the column foundation, shall be designed to resist a minimum eccentric gravity load of 300 pounds (136.2 kg) located 18 inches (.46m) from the extreme outer face of the column in each direction at the top of the column shaft. [This is indeed to characterize an iron worker tied off to the top of a column. This may or may not be greater than a wind construction load ASCE 37-02. ]
All of Subpart R was an issue that needed to be forced for the safety of iron workers. If we structural engineers don't like it, it is incumbent on us to become involved in developing a solution. But if we want to add a provision for structural engineers to develop erection plans, we had better check with our insurance carriers first. Frankly, those of involved in EPC construction can't avoid the liability (as a company), so I have no problem in developing erection plans. But the general consulting industry may have some barriers.
I agree that Subpart R may provide a false sense of security, and is not an ideal solution. But it is the best that could be developed by those that saw a problem and acted to effect a solution.
If interested reference: AISC Design Guide 10 - Erection Bracing OSHA 1926 Subpart R ASCE 37-02 Design Loads on Structures During Construction LPR Steel, Loveland, CO Regards, Harold Sprague
From: Mark Gilligan <m_k_gilligan(--nospam--at)yahoo.com> Reply-To: <seaint(--nospam--at)seaint.org> To: seaint(--nospam--at)seaint.org Subject: RE: Seismic mass Date: Wed, 8 Feb 2006 00:35:16 -0800 (PST) The OSHA standard is flawed in several ways. First by requiring 4 anchor bolts they create problems in some situations where there is not room for 4 bolts in the completed structure. A more reasonable provision would make provision for engineering special erection procedures. When I have had this problem I have indicated that the contractor could provide an erection aid so the column could be erected with 4 bolts. Later the extra bolts could be removed. More critically the OSHA standard provides a false sense of security.. I am aware of situations that comply perfectly with the standard yet would be unsafe with out special precautions. The erectors have to step up to the plate and look closely at the individual circumstances before erecting steel. Please note that wind loads and loads resulting from the erection process can be many times greater than the OSHA mandated loads.
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