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  1. RustyTools

    Putting a new spread footing over an thin spread footing

    Thanks for your feedback. I just put the 3' x 4' x 1' footing under the existing spread footing. Due to its high viscosity, it was quite difficlt to get the concrete under the the existing footing. In retrospect, cutting the old footing out probably would have been easier. In terms of...
  2. RustyTools

    Putting a new spread footing over an thin spread footing

    A few builders in the area have continuous footings. They do it because they are not sure exactly where they are going to put the columns. It is difficult to cut the old footing because I can't find an electric saw that goes 10" below the slab. You are talking gas powered when you get that...
  3. RustyTools

    Flow of hot gases in ducts and stacks

    I did consulting in this area for years. Check power plant publications for papers on this. The pressure drop is from the hydrostatic head inside the stack. You need to do a thermodynamic balance to calculate the temperature drop inside the stack according to that pressure drop. Don't forget...
  4. RustyTools

    Free convection

    You need to calculate the vertical sides seperate from the top & bottom surfaces. THen add up the conductivities using formulas for parallel resistances. "Advanced Heat Transfer" by Rosenhow & Choi has simplified formulas for upward facing, downward facing and verticla surfaces in contact with...
  5. RustyTools

    Putting a new spread footing over an thin spread footing

    When the house was built in 1992, the builder ran a 2' wide spread footing down the center of the basement (70' long) but only made it 6" thick. He located colums about every 6' on this footing. He poured a 4" thick unreenforced slab over the footing and the entire floor. From my calculations...
  6. RustyTools

    Torque for NPT connections

    I have been using 1/8" NPT and 1/4" NPT Parker and Swagelok stainless pipe fittings for years, but when I went to modify a natural gas line, which was 1/2" steel NPT, I overtightened it and the male part snapped after sitting a couple of days. I never got the feeling the torque was increasing...
  7. RustyTools

    Residential spread footings rebar

    The original design was #5 rebar 12"O.C. That was done by rule of thumb, not by calculation. The 3000 psf is based on coarse, granular sand and that the builder built the rest of the neighborhood based on that
  8. RustyTools

    Residential spread footings rebar

    I have to add 2 spread footings to the center of my house, one to hold 9,000 lbs and the other 23,000 lbs. I have a spread footings design using a rebar size I can't get, so I am looking for advice on how to do the footings using 1/2" diameter rebar. The soil capacity is 3000 psf. The...

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