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Re: Engineering judgment[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "Seaint" <seaint(--nospam--at)seaint.org>
- Subject: Re: Engineering judgment
- From: "Dmitri Wright" <dmitri(--nospam--at)cascade-structural.com>
- Date: Fri, 12 Mar 2010 08:19:38 -0800
Erik,I faced many such situations early in my career, and looking back now, I wish I had handled them a little differently. At the time, I would go over the assumptions and calculations a second time with my boss, to make sure he understood how I arrived at my design. If he still requested a change to the design, I would comply, although I was often left scratching my head. In the years since then, I have often come across issues or situations that make my look back and realize what his concerns were (often unrelated to stress calculations). So, while I now appreciate the "why", I still have a problem with the "how". I should have pushed hard for the reasoning at the time. If the boss was too busy to explain it at the time, or felt that I was being difficult, get a promise for an explanation after the project is done, and follow through on it. In many situations, I found much later that the boss had valid reasons for the design changes, but would not or could not articulate them to me. These were substantial missed learning opportunities in a young career. I found that I continued to make similar errors for years, until I figured out the problem on my own.
So, my advice is to be tenacious about getting explanations from your boss (after the fact if it lowers the stress level). It's your career, and only you take responsibility for it. If your boss is unwilling or unable to mentor you, look for someone else who will.
I have a question about engineering judgment or better yet, engineering comfort. Let me explain what I mean with 2 typical examples: 1. A small residential addition where the owner is adding a new roof. The new ridge beam is supported by a new post onto the existing continuous footing. A soils report was conducted and the allowable soil bearingpressure was determined. You know the existing continuous footing size (15"wide x 24" deep) and based on the allowable soil pressure of 2000psf you have determined that the new 4.5k point load onto the existing ftg will be no problem. After your boss reviews your work he tells you to use a new pad ftg under the existing ftg at the location of the new post. You ask why and he tells you that 4.5k is a lot of load for a continuous ftg. You are left scratching your head because by your calculations as the 4.5k spreads out at a 45 degree angle from the top of the ftg the increase in soil pressure will is only 900psf. 2. Another residential remodel, but this time the architect is removing a lot of the existing exterior shearwalls in order to get "the view." You conduct a a full lateral analysis and you determine that a 6ft section of shearwall located on the exterior of the upper floor of a 2 floor home is adequate to resist the designed seismic force. Since the force on theshearwall is close to the maximum allowable shear force for the lowest rated shearwall on your shearwall schedule which is based on the current CBC, youupsize the shearwall and specify a higher rated shearwall. Now your boss reviews your work and he says that he doesn't like the fact that there is only a 6ft section of shearwall along the exterior of this residence, but you show him your numbers and everything checks out. He insists that the architect give up a couple more feet of shearwall, or provide another shearwall along that line.Both situations I am dumbfounded because my numbers make sense and in thesecases I do not understand his reasoning. I have enough experience to know that just because the numbers show onething doesn't mean that the solution is practical, but in these 2 situationsI just can't see the logic. Any comments would be appreciated, and sorry for the long winded email.
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