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Steel bolted moment frame house

bluesolar | Posted in Green Building Techniques on

Hi all – What do you think of this steel bolted moment frame construction method?

I’m thinking of how it might integrate with ThermaSteel REVPANEL walls.

The bolted moment frame is apparently structurally sound without any studs (!). It just has the corner columns, connected laterally by beams. The beams are connected by cross-beams – I guess they’re technically called joists, which support the roof and floor. The corner columns are the only vertical structures. (See the diagram at the above link.)

ThermaSteel walls are EPS foam sandwiched by steel studs. But in a brilliant move they turned the studs sideways so that there’s no thermal bridging – usually a problem for steel-framed homes. (More info at the above link.)

The ThermaSteel walls are structural, so they’d just sort of be extra structural support given the bolted moment frame. I need to hash all this out with an architect and/or structural engineer.

So what do you think? Do you have any misgivings about the moment frame? (Malcom?)


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  1. Expert Member
    BILL WICHERS | | #1

    Their “moment frame” is pretty much how nearly all steel framed commercial buildings are constructed. Commercial concrete and steel construction pretty much uses four things: tubular or I type columns, I beams, corrugated steel floor pan, and poured slabs on top of the floor pan. Most other parts of a commercial building aren’t structural.

    This type of assembly works due to MUCH MUCH higher allowable stresses in steel connections. If you think about two 2x4s nailed together flat at a right angle, and you twist the connection, the nails will pull through the wood but usually won’t break. This is because the wood fails before the nail does in shear. In a steel structure, the bolted connections to plates welded to the structural members don’t have this problem since the fasteners and the structural members have similar allowable stresses before failure.

    I haven’t seen such an assembly with relatively light formed steel structural members before, but there is no reason that can’t work if it’s engineered correctly.


    1. bluesolar | | #6

      Thanks Bill. The joists are light gauge steel, but the columns are Hollow Structural Sections (HSS), which I understand are a heavier gauge than the studs normally used for residential steel frame. HSS are commonly used in commercial construction.

  2. Expert Member
    Michael Maines | | #2

    It's one way to build a house. It probably won't fall down; the engineering is straightforward. Extremely high embodied carbon. Appropriate it you want entire walls of glazing, which can look good but will waste a lot of energy. Nothing "green" about it.

    1. bluesolar | | #5

      I don't want glass walls.

      Are you saying steel isn't green, or just the glass walls?

      1. Expert Member
        Michael Maines | | #7

        Steel is the opposite of green--every pound of steel represents one to two pounds of carbon emissions. Like concrete and plastic, it's an amazing material in many ways, and not going away. I use steel beams regularly when I need to support large spans. But when a lower-impact or renewable material like wood will do the same job, I choose the lower-impact material.

  3. Expert Member


    No misgivings at all. As Bill said that's how your corner convenience store or fast food outlet was most likely built. It's the norm for small scale commercial structures. Usually it's combined with exterior insulation, and a concrete foundation and slab, but the posts work too.

    The drawbacks are cost, and the lack of familiarity of residential trades with steel construction. You need someone knowledgeable to do a lot of coordination between the structure, wall systems and services.

    Conceptually the problem with steel structures like this is the same one you face with timber post & beam. The studs, SIPs, or other wall systems that form the walls are usually able to support the roof, making the structure redundant.

    1. bluesolar | | #4

      Thanks Malcolm.

      I'm also trying to find out what implications a steel frame or Thermasteel has for the exterior cladding like cement board siding (Hardie Panel, Nichiha, etc.) The specs on steel studs are fascinating. I'm surprised that they're not thicker/heavier.

      I like redundancy in construction, and I'm surprised that it's not common. You would still need studs to mount things inside the house (and perhaps outside). There are so many things that might need to be mounted, from TVs to kitchen cabinets, and they might need to be mounted on exterior walls. And mounting aside, would you build walls without studs if you didn't need them for structural support? How do they stand up? Are the walls in commercial structures not structural, if they have a moment frame? I noticed that there are a range of steel studs that aren't structural, like 20 and 25 gauge, which are 30 and 18 mils thick, I think.

      1. Expert Member
        BILL WICHERS | | #8

        There is a LOT of redundancy in construction. In a typical wood framed house, you can knock out studs, a few joists, all kinds of things, and your house won’t collapse. The reason it’s so rare for serious structural failure in houses, even with crazy DIY “Reno” stuff, is because of all the redundancy.

        Most walls in commercial steel framed buildings are not structural. That includes exterior walls. Nearly all of the load is carried by the columns and girders. Typical commercial walls are there just or provide demarcation between different rooms, basically something to hang drywall from. If you’ve ever been in a commercial building during construction, you’ll see that for much of the construction cycle there are just columns, floors, and an exterior facade. Most of the electrical, plumbing, and ductwork goes in BEFORE walls go up so that the walls aren’t in the way. Towards the end of the project, steel stud walls go up, then drywall, then ceiling grid. Sometimes the walls go up to the structural ceiling and sometimes they stop at the drop ceiling. There is almost always empty space above the drop ceiling for electrical and mechanical services.

        It’s a lot easier to modify commercial buildings compared to residential structures as long as you don’t need to go through a floor. Another general rule of commercial buildings is that no matter how hard you try, columns are always in bad places — that’s why large girders are often used to allow for longer clear spans — it makes floorplans more flexible.


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