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RE: 1976 Uniform Building Code - liability, insurance, etc.

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Jordan:

I didn't prepare the opinion, but I too have had problems with it, but sometimes it's a tool that's useful.   I haven't told many people to get out of their buildings, but the first one was hard.  Told them on a Friday and it collapsed on the next Monday. 

Had a college building that we investigated that had broken roof trusses which were supporting the suspended 2nd floor.  A couple of my technicians had done an as-built, basically for other problems and when I checked the truss (which was an awful design) found that one of the web members didn't work.   Went out to the school, climbed into the attic and the suspect web member was broken (on almost every truss).   

Of course, the first building was built in around 1890 and the 2nd was in 1870 something.

I don't put much faith in the probability criteria's but do recognize that the code is the minimum with some sort of a factor of safety.   Therefore, when an attorney asks you is the building unsafe (and will collapse) you can't for sure say it's going down tomorrow.  Sometimes you get the chance to "guess" what a reasonable factor of safety might be as to why a structure is still standing when all the calcs say it should be on the ground.   Case in point is a 1910 bridge where I estimated that the additional load that could be put on this bridge was around 20,000 lbs.  (bridge had a scoured pier situation) and I had quoted a factor of safety of 1.02! 

I was then attacked by an extremely prestigious bridge design engineering firm in their own assessment, who stated that the bridge was stable and that it had a factor of safety of 1.5 and that a "local" engineer had provided an alarming report (for free!).   This was even though we knew the bridge was moving around; 2/3rds of the pier support was gone and the remainder (we found out later) was on sand, not rock as "guessed" by all others. 

The bridge had been shut down, but was to be used for some special events, one for runners and the other for horses.    The group I was coordinating with provided a procedure to hold these events with special conditions.  One was to use a tilt meter and to limit the amount of horses at any one time on the bridge.   So we came up with the maximum of six horses and we had a professional engineer monitoring the tilt-meter with instructions of what to do; i.e. earthquake or the possible beginning of a collapse.  (The failure mode was the bridge folding upstream).    Anyway, at about three o'clock in the morning on the day of the race, a dozen horses arrived at the bridge clamoring to go across and in spite of the protestations of the on-duty engineer (who was pretty upset, to say the least) they went on across and the tilt-meter reading spiked!    After they were on the other side, the tilt-meter readings returned to their previous reading.  

In review of the great prestigious bridge designers calculations, we could find nothing that provided a "stability analysis" - (SAP90 output), but we did find some interesting support results buried in the back of the two inch set of calcs and that was the modeled support springs were in tension!   Pretty amazing, since the bridge was, as I said earlier, built in 1910 and they must have had access to a lot of Chance anchors.

So how do you say, with some certainty that something is going to collasped or is possibly harmful to those who use or occupy the structure?  Sometimes a better tool is a push-over analysis  and you might not necessarily be able to do this with a computer program, but will have to do a number of trial and error scenerios to find out what are the structural elements or combination of elements that will prevent the structure from coming down.

On the other hand, it's easy to walk out onto a site and tell the owner he's going to lose his roof when you can't find any connections to hold his roof down.   There's a lot of people on this list who have seen it all -- most of our duty is to keep people from getting hurt and certainly not discouraging engineers from providing reasonable opinions as to what might happen.   We have even told some prospective clients (during a their initial telephone inquiry) that we might come out to their site and condemn their house and do they still want us to come?   (A particular case was a home owner digging his own basement and the house was beginning to move)   Very often, we pawn off some of these inquiry's to our local geotech consultant (and hope to never hear from them again!)

Within the last two years, we've been involved in two cases where one house (partially constructed and things beginning to move around) and one larger building that was just plain not built per the incomplete drawings, were taken down and the contractor's started over.  

Sorry to be so long.

Neil Moore, S.E.
neil moore and associates
consulting structural engineers
shingles springs, california
distressed structures investigations








At 03:17 PM 9/2/2004 -0400, Jordan Truesdell, PE wrote:
At 12:00 PM 9/2/2004 -0700, Neil wrote:
In California, the attorney's general office provided their AG Opinion No. 85-208:

"A registered engineer retained to investigate the integrity of a building who determines, based on structural deficiencies in violation of applicable building standards, that there is an imminent risk or serious injury to the occupants thereof, and who is advised by the owner that no disclosure or remedial action is intended and that such determinations are to remain confidential, has a duty to warn the identifiable occupants, or if not feasible, to notify the local building officials or other appropriate authority of such determinations."


Yes, but what is "imminent risk".  What probabilistic criteria should I apply to the local environmental loads? 2% per year exceedence probability (ASCE 7 typical), 5%, 10%, 100% in 1 day, 7 days, a month, a year?

Most of the residences in my area built before 1980 don't meet the ASCE7 criteria, and I'm sure many built since then don't either, especially for seismic loads. We don't condemn buildings every code cycle simply because they don't comply, and yet the new codes are the "minimum" safe standards for structural purposes, as anything less is considered "unsafe" for occupancy.

I'm not attacking you, Neil, just pointing out that the wording is foolishly incomplete given the requirements that we need to show a number on paper that is either greater or less than 1.0 to determine the safety of a structure.

Jordan



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