August 3, 2011
House Design Project
This interesting project was for dencity design in Atlanta, GA. It’s an interesting house with multiple cantilevers. Here is a rendering of the house:
The items in red are the steel beams. Notice we have a cantilever deck on one side, and we are cantilevered over the garage. This is not an easy thing to design, the beam sizing is hard, the connections are hard, and so are the baseplates and foundations. To design this, we used Bentley RAM Elements. Here is the rendering from the software:
In the analysis process, RAM Elements solved 132 equations. I could have designed this by hand, but figuring about 15 minutes per solved equation, it would take me 30 hours. Considering I tried numerous alternatives, triple that number, it would be more like 90 hours. Since you can’t just sit and solve equations day in and day out, humans did not evolve to do such things, we’re talking about month to do this design by hand. That’s for an experienced engineer. Of course the chance of error is extremely high in such a complex undertaking too – typically on projects this complex in the days before computers another engineer would have to be assigned just to go over the calcs done to make sure everything was done right.
What was the biggest hassle? There is a bit of a gotcha in the way this house is built. In the first run of calculations, I had all of the deflections (bending) of the beams in accordance with Code, but the end of the house dipped down a couple of inches, which is not a good thing. What happened was the beam deflected ever so slightly, and so did the columns, and it all added up. So, I had to make the beams and columns really beefy to make sure there was next to no deflection. The beneficial effect is the floors feel really solid, which is important in a house with this type of architecture.
Here are some of the pictures of the house under construction: