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- To: seaint(--nospam--at)seaint.org
- Subject: Re: higher loads or better details.
- From: Sleiman Serhal <mony(--nospam--at)destination.com.lb>
- Date: Fri, 04 Sep 1998 15:05:06 +0300
> My boss, just brought up an interesting idea, > > Here in Hawaii, we have just been exposed to the 1997 UBC. We noticed that > the Base shear has increased by about 30 percent for the 1997 codes. > > My boss mentions that it is not the load that will make the building stand up, > you can increase the load as much as you want but if you do not detail it > correctly, larger load is no good. > > Making sure that your load flows through your connection correctly is very > important, I think a lot of people getting out of school lacks that > experience. Included with the Steel, Concrete, and Timber design, there > should be a special class called connections. > > I just recently graduated and I think it was sad that we only spent about a > week in connections. > > Professional Engineer's opinions welcome. > > Marlou B. Rodriguez > Robert Englekirk Inc. > Honolulu, Hi I agree with your boss 100% especially when the structure is so irregular that the computed lateral loads are highly uncertain. Seismic detailing can increase ductility, doesn't add cost that much, doesn't take too much not-so-well-renumerated-and-appreciated structural engineering time and its results are probably more guaranteed than the calculations of lateral distribution of loads. If you compare the Rw factor for RC frame structures with shear walls, it dropped from 8 in the UBC 91 to 5.5 in the UBC 97, a 45% increase in base shear load ! This illustrates how much uncertainties there still are in computing the lateral loads. Last week I was inspecting a construction site (a 4 story Villa) down here in Lebanon, middle east, and the site engineer started criticizing the high number of column stirrups and the 135° hook requirement. When I told him that it was a good seismic detail, he asked me if I had computed the exact lateral loads, and I said no because the structure is so irregular that it will be very hard to accurately compute the lateral loads ... So he told me that he had done a building which was "exactly" designed for earthquakes and where the stirrups in the columns were much fewer than in my design and did not have the 135° hook, and if I wanted to he could give me the plans so I can "learn" how to do an "exact" design. I tried to explain to him that there was no "exact" seismic design even in the opinion of the very best such as Nigel Priestly and the likes, but he kept on going until he reached a peak in ridicule when he told me, and I swear I'm not making this up, that he had gone to a seminar on seismic design where he understood that "the single most important consideration is to have a low height to width ratio which determines whether there will be resonnance or not. And in case there is no resonnance, the building doesn't have to be designed for earthquakes." After hearing this statement, many things ran through my mind such as continue arguing with the guy and waste my time, jump off a cliff, change to an interior decorator, re-evaluate all the time spent on readings and teachings and seminars and internet discussions and dynamic analysis attempts on STAAD, SAP, ROBOT... I guess the moral of the story is that it's a strange world out there, and structural engineering time and effort is most often unappreciated even, most unfortunately, from peers. Moni Serhal MSCE UT Austin, reporting from Lebanon.
- higher loads or better details.
- From: MRodrig273
- higher loads or better details.
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