4 ms·

> "Steel is springy. Tall steel-framed buildings and bridges routinely sway in wind, which is usually harmless to the structure but annoying to occupants." exa

> "Steel is springy. Tall steel-framed buildings and bridges routinely sway in wind, which is usually harmless to the structure but annoying to occupants." exactly, i recently mentioned my swaying-in-an-earthquake story[0], which was in a class A (steel+concrete) highrise office building. driving steel into the ground doesn't automatically mean it will rot and/or break in the first earthquake/windstorm that hits, even if that's a general possibility, given that engineers do think about that stuff when designing buildings. the gp comment is classic bullshit, plausible sounding but unconcerned with truth. [0]: https://news.ycombinator.com/item?id=29665129 https://news.ycombinator.com/item?id=29665129

rsync 5y ago
You misunderstood my comment about steel in the ground ... I was trying to convince the OP that they don't need to worry about the corrosion since even in terrible circumstances the steel still lasts quite a while. With regard to your skyscraper experience: I'm not sure this is an apples-to-apples comparison. Skyscrapers are not made of skyscraper-height columns - they are a stack of elements that are connected every X height that has a well known flex per connection. It's also (hopefully) a uniform flex at every connection. But a smaller building would, indeed, have unbroken steel members (like a column) and you might "successfully" connect them to one another with an incredible amount of rigidity. It will either be tremendously strong throughout (good for you) or there will be some tiny piece of the chain that isn't as strong and can fail. I would be confident attempting this on a very small building. I would be hesitant to attempt this on a medium, two-story building. I would want wood framing. For aesthetic reasons, I would want that wood framing to be big timbers. I'd rather spend my money on those than on stainless steel roof framing :)
- clairity 5y ago
  gotcha, my bad for misconstruing your point. joint strength relative to span strength is definitely a non-obvious issue to the average home owner-builder. i also vastly prefer wood/mass timber for aesthetic reasons. mass timber has better burn characteristics than steel, and i'd recently read that builders are actually starting to surround steel columns with cross-laminated timber (rather than concrete) for that reason[0], while providing greater strength/flexibility and better aesthetics. that's probably what i'd want if money were no object. [0]: mentioned in this article, but i'd read more about it elsewhere: https://www.vox.com/energy-and-environment/2020/1/15/21058051/climate-change-building-materials-mass-timber-cross-laminated-clt https://www.vox.com/energy-and-environment/2020/1/15/2105805... p.s. - i've also daydreamed about building warehouse style: a separate steel superstructure for the roof integrating solar panels and solar heating, with a simple stick-built house underneath.
  - rsync 5y ago
    "... and i'd recently read that builders are actually starting to surround steel columns with cross-laminated timber ..." Somewhat relevant - might interest you: https://easternwhitepine.org/this-office-buildings-wooden-frame-was-built-without-fasteners-or-glue/ https://easternwhitepine.org/this-office-buildings-wooden-fr... TAMedia office building in Zurich.
    - ethbr0 5y ago
      > ...mass timber... Not sure if this is a regional / language difference, but I've more commonly seen it called "engineered wood" [0]. Which apparently now also includes transparent(?!) wood composite [1]. [0] https://en.wikipedia.org/wiki/Engineered_wood https://en.wikipedia.org/wiki/Engineered_wood [1] https://en.wikipedia.org/wiki/Transparent_wood_composite https://en.wikipedia.org/wiki/Transparent_wood_composite
      - clairity 5y ago
        my impression is that 'engineered wood' is a slightly different aggregation than 'mass timber', with engineered wood including things like plywood, while mass timber is focused on the 'timber' aspect (more structurally focused, usually larger).
- Animats 5y ago
  they are a stack of elements that are connected every X height that has a well known flex per connection. It's also (hopefully) a uniform flex at every connection. The flex is supposed to be in the beams, not the connections. Stress concentration is bad. Here's an intro.[1] Beams are easy to analyze, and tend to meet their specs, while connections are hard to analyze, and are subject to construction mistakes. The January 1994 Northridge CA earthquake caused damage at beam-to-column connections in steel moment resisting frames. That got a lot of attention. Few buildings collapsed, but a lot of joints needed to be fixed or reinforced.[2] Welded flanges with bolts turned out to be weaker than expected. Now, there's a style of construction where all the joints are rotational. That's seen in older truss bridges.[3] In classic designs, all components are in pure compression or pure tension. This shows in the construction; the tension components are flat plates or cables, and the joints are big steel pins. Those are easy to analyze, and if you take a statics class, that's a homework assignment. Popular for railroad bridges. But building skeletons aren't usually built that way. They usually have rigid connections. You do see some buildings with lots of diagonals and pin joints. Long span roof trusses, which are a lot like bridges, are often built that way. Look at buildings with large atriums and you'll often see pin joints. [1] https://www.thestructuralmadness.com/2014/04/possible-types-of-failures-in-steel.html https://www.thestructuralmadness.com/2014/04/possible-types-... [2] https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir5625.pdf https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir5625.pdf [3] https://en.wikipedia.org/wiki/Truss_bridge https://en.wikipedia.org/wiki/Truss_bridge
  - jacquesm 5y ago
    Same with long low steel buildings, they usually have a lot of room for expansion built into them because the tops are close enough to the foundation that the angle of the uprights would change a lot if not dealt with in such a way. For higher buildings this isn't as much of a problem because the parts closer to the foundation will likely be closer to ambient. In one particular case (the steel truss roof of a convention center in Amsterdam) there are many such places where slack was built into it, the structure is many 100's of meters wide and if connected rigidly would put undue stress on the uprights and the foundations.
- ggcdn 5y ago
  Rigidity is good for some things and bad for others. In seismic design, inertial forces tend to decrease as structures become more flexible (Good!). But the consequence is that things move more (Bad!) meaning that all the nonstructural things get damaged - drywall, chimney, ceilings, etc. If things move too much, they also are subject to various types of degradation - yielding, fatigue, etc. The other structural aspect not mentioned in the above discussion is strength. You can trivially get an order of magnitude more strength than required by even the harshest of loads using steel in a small structure like this. The same cannot be said about wood. For instance, a single 3/4" A325 bolt will be able to resist about 40,000lb shear or 70,000lb tension. The entire base shear of this size of structure in a code-design earthquake would be somewhere around 4,000lb.
  - ggcdn 5y ago
    [clarification: I mixed up my unit conversion. A 3/4" A325 bolt resists ~25kip shear or 31kip tension. One of the joys of working in an industry that primarily uses customary units, while codes are written in SI units]

rsync 5y ago

You misunderstood my comment about steel in the ground ... I was trying to convince the OP that they don't need to worry about the corrosion since even in terrible circumstances the steel still lasts quite a while. With regard to your skyscraper experience: I'm not sure this is an apples-to-apples comparison. Skyscrapers are not made of skyscraper-height columns - they are a stack of elements that are connected every X height that has a well known flex per connection. It's also (hopefully) a uniform flex at every connection. But a smaller building would, indeed, have unbroken steel members (like a column) and you might "successfully" connect them to one another with an incredible amount of rigidity. It will either be tremendously strong throughout (good for you) or there will be some tiny piece of the chain that isn't as strong and can fail. I would be confident attempting this on a very small building. I would be hesitant to attempt this on a medium, two-story building. I would want wood framing. For aesthetic reasons, I would want that wood framing to be big timbers. I'd rather spend my money on those than on stainless steel roof framing :)

clairity 5y ago
gotcha, my bad for misconstruing your point. joint strength relative to span strength is definitely a non-obvious issue to the average home owner-builder. i also vastly prefer wood/mass timber for aesthetic reasons. mass timber has better burn characteristics than steel, and i'd recently read that builders are actually starting to surround steel columns with cross-laminated timber (rather than concrete) for that reason[0], while providing greater strength/flexibility and better aesthetics. that's probably what i'd want if money were no object. [0]: mentioned in this article, but i'd read more about it elsewhere: https://www.vox.com/energy-and-environment/2020/1/15/21058051/climate-change-building-materials-mass-timber-cross-laminated-clt https://www.vox.com/energy-and-environment/2020/1/15/2105805... p.s. - i've also daydreamed about building warehouse style: a separate steel superstructure for the roof integrating solar panels and solar heating, with a simple stick-built house underneath.
- rsync 5y ago
  "... and i'd recently read that builders are actually starting to surround steel columns with cross-laminated timber ..." Somewhat relevant - might interest you: https://easternwhitepine.org/this-office-buildings-wooden-frame-was-built-without-fasteners-or-glue/ https://easternwhitepine.org/this-office-buildings-wooden-fr... TAMedia office building in Zurich.
  - ethbr0 5y ago
    > ...mass timber... Not sure if this is a regional / language difference, but I've more commonly seen it called "engineered wood" [0]. Which apparently now also includes transparent(?!) wood composite [1]. [0] https://en.wikipedia.org/wiki/Engineered_wood https://en.wikipedia.org/wiki/Engineered_wood [1] https://en.wikipedia.org/wiki/Transparent_wood_composite https://en.wikipedia.org/wiki/Transparent_wood_composite
    - clairity 5y ago
      my impression is that 'engineered wood' is a slightly different aggregation than 'mass timber', with engineered wood including things like plywood, while mass timber is focused on the 'timber' aspect (more structurally focused, usually larger).
Animats 5y ago
they are a stack of elements that are connected every X height that has a well known flex per connection. It's also (hopefully) a uniform flex at every connection. The flex is supposed to be in the beams, not the connections. Stress concentration is bad. Here's an intro.[1] Beams are easy to analyze, and tend to meet their specs, while connections are hard to analyze, and are subject to construction mistakes. The January 1994 Northridge CA earthquake caused damage at beam-to-column connections in steel moment resisting frames. That got a lot of attention. Few buildings collapsed, but a lot of joints needed to be fixed or reinforced.[2] Welded flanges with bolts turned out to be weaker than expected. Now, there's a style of construction where all the joints are rotational. That's seen in older truss bridges.[3] In classic designs, all components are in pure compression or pure tension. This shows in the construction; the tension components are flat plates or cables, and the joints are big steel pins. Those are easy to analyze, and if you take a statics class, that's a homework assignment. Popular for railroad bridges. But building skeletons aren't usually built that way. They usually have rigid connections. You do see some buildings with lots of diagonals and pin joints. Long span roof trusses, which are a lot like bridges, are often built that way. Look at buildings with large atriums and you'll often see pin joints. [1] https://www.thestructuralmadness.com/2014/04/possible-types-of-failures-in-steel.html https://www.thestructuralmadness.com/2014/04/possible-types-... [2] https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir5625.pdf https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir5625.pdf [3] https://en.wikipedia.org/wiki/Truss_bridge https://en.wikipedia.org/wiki/Truss_bridge
- jacquesm 5y ago
  Same with long low steel buildings, they usually have a lot of room for expansion built into them because the tops are close enough to the foundation that the angle of the uprights would change a lot if not dealt with in such a way. For higher buildings this isn't as much of a problem because the parts closer to the foundation will likely be closer to ambient. In one particular case (the steel truss roof of a convention center in Amsterdam) there are many such places where slack was built into it, the structure is many 100's of meters wide and if connected rigidly would put undue stress on the uprights and the foundations.
ggcdn 5y ago
Rigidity is good for some things and bad for others. In seismic design, inertial forces tend to decrease as structures become more flexible (Good!). But the consequence is that things move more (Bad!) meaning that all the nonstructural things get damaged - drywall, chimney, ceilings, etc. If things move too much, they also are subject to various types of degradation - yielding, fatigue, etc. The other structural aspect not mentioned in the above discussion is strength. You can trivially get an order of magnitude more strength than required by even the harshest of loads using steel in a small structure like this. The same cannot be said about wood. For instance, a single 3/4" A325 bolt will be able to resist about 40,000lb shear or 70,000lb tension. The entire base shear of this size of structure in a code-design earthquake would be somewhere around 4,000lb.
- ggcdn 5y ago
  [clarification: I mixed up my unit conversion. A 3/4" A325 bolt resists ~25kip shear or 31kip tension. One of the joys of working in an industry that primarily uses customary units, while codes are written in SI units]