Let me tell you about a small project I needed to review in my second year out of college. It was a small aluminum greenhouse type building designed as a lean-to addition to your home. A restaurant that I was doing a remodel on was planning to use one as an indoor/outdoor seating area. The engineer used by the manufacturer did not have a stamp for our state so the firm I worked for agreed to review the drawings and calcs for a cover-letter.
The greenhouse structure was designed as a 3-hinge arch and the calcs had a full Risa model of each bent with lots of calculations. [oooh, shiny]
After looking through the design package for about 10-minutes I took it all to our senior principal and told him what I was doing and said I think there is a problem with this detail. after looking at it for a few minutes he said, "what's the problem?" to which I replied, "where is the flange?" In a about a second, he said "Oh shit!"
The splice detail for a tube section built up from face-to-face aluminum channels with a couple of splice plates that bolded to the web of each channel. The plates were about 50% thicker than the web which looked good.
The problem was that this connection will always be at the point of max moment and the splice was a shear connection with very limited moment capacity because there was an air-gap between the ends of the flange of the section.
I asked him what he wanted to do about it and was told, "you found it, Give the Engineer that designed it a call." Not a fun call as a green junior EIT to call a senior Structural Engineer who had signed off on the design of thousands of these structures which had been built all over the world that he had a fundamental problem with his design. I did the same scenario as I had with my principal only over the phone only his response was different. He sort of convulsively hyperventilated for about 5 seconds and then said, "I'll get back to you" and hung up.
After about an hour I had worked up a simple modification of his design that could be retrofitted the detail that would work for the loads on the one he had sent to us and said "This should work for ours.
I do not do designs for mass produced items. I have done Royalty designed where I get a percentage fee for each build similar to what phamENG described but only for limited quantities.
