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Re: structures & ethics

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This happens to me a lot, though not in this magnitude (either building size or under-capacity). I usually sit down with the client and point out the structural "difficulties" in the building. I normally don't have calcs to back me up, as I'm normally not under contract at this point. After laying everything out, I offer to either recheck the original design and incorporate the repair into the overall package, or "return the damaged member to their pre-damaged structural condition."  9 out of 10 times the request is for the latter. 

There have only been a couple of times where I have conditioned my work on a repair of the sub-standard construction.  I'd say I only get about 25% of those jobs. Your case sounds awfully close to being in this class (visible creep, overstressed for DL). For me it would probably depend on how the beams are failing - deflection, end bearing, bending, or shear? The first two are annoying, and will prompt other repairs, the last two are more critical (life safety) and need to be dealt with if this is a habitable building.

Jordan

At 09:40 AM 11/22/2004 -0800, you wrote:
Good morning.
 
I was asked to provide repair plans and specifications for an existing roof damaged by a vehicle (sic).  The problem now became not only structural, but ethical, too.
 
THE LAYOUT
 
The building is apparently a former post office (1970s?), with 5 1/8"x 24-3/8"glulam beams @26' o.c. cantilevering 16' off brick wall along one side.   Further into the building, the glulams also bear on wood columns, and then cantilever and support other glulams spanning toward the opposite brick wall.
 
Sawn purlins span about 26' between the glulams at 8-to-9 feet on-center, supporting 2x4 @24", some insulation, lots of electrical conduits and ducts, plywood diaphragm, and the composition roofing.
 
The "fascia" (still 6x12, nominal/typical) purlin of the overhang was apparently hit and broken by the u-turning big rig, with subsequent damage (delamination with lateral offset) to one of the cantilevering glulams.
 
THE PROBLEM
 
I ran the analysis based upon the current codes as well as upon the 1960s and 1970s codes (UBC).  The analysis shows that the undamaged subpurlins, purlins, glulams, and columns are inadequate against DL+LL (70-to-100% overstressed), and even against DL only (with 0.9 factor, overstressed 15%). 
 
For the sawn lumber, I tried even select structural (dense select structural) - did not help...
 
Some of the purlins are visibly sagging.  The glulams look OK.
 
I can just replace the damaged purlin (these are the only ones that are adequate
due to 50% tributary area) and to repair only the damaged glulam to the "preexisting condition" (I can do it with lag screws etc.).  After all, the building may be OK solely by the fact of it existing like that for about 30 years, right?
 
THE QUESTIONS
 
If I am right in my assumptions - how that could happen (don't answer that)?
 
If I am wrong in my assumptions - what am I missing?
 
What should I do within the limitations of common sense, structural analysis, and professional ethics?
  
Thank you.
 
V. Steve Gordin, PhD
Registered Structural Engineer
Irvine CA

 
 
 
 
 
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