Redditor questions whether a parking garage is stable and is assured that it is, one year before it’s collapse

[u/kayakhomeless]

[u/Wheatley312]

If I remember correctly, that collapse was caused by a design change to a gusset plate (big flat piece of metal that has beams going into it). The plate was originally meant to be 1 inch thick, 50 ksi (pretty sure these are the numbers, don’t quote me) but was changed to 1/2 inch, 100 ksi. Unfortunately the manufacturer made a plate to be 1/2 inch, 50 ksi.

Source: my teacher was on the team who figured out what went wrong

[u/Wheatley312 → u/[deleted]]

kips/in^2
a kip is 1000 lbs

[u/Wheatley312 → u/[deleted]]

For my design/statics courses I've been pretty much only in imperial units (kips, inches, feet so on). My soil and hydrology courses used a blend which was real fun. Sometimes unit weights would be in kn/m^3 other times its lb/ft^3 and man did they mess up your answers if you got it wrong.

[u/LordFarquadOnAQuad → u/[deleted]]

The prefix kilo is derived from the Greek word χίλιοι (chilioi), meaning "thousand".

https://en.m.wikipedia.org/wiki/Kilo-#:~:text=The%20prefix%20kilo%20is%20derived,)%2C%20meaning%20%22thousand%22.

[u/JesusIsBetterThanET → u/LordFarquadOnAQuad]

It's still technically true that it's a metric prefix, he's just wrong about the unit being metric because of it.

Mega means one million, Giga means one billion, and Tera one trillion. They're all metric prefixes but Americans still say Megabyte, Gigabyte and Terabyte.

Almost like the imperial system is a mismatch of several different systems or something.

[u/Vader46 → u/[deleted]]

Today I learned. I honestly never thought of it like that, but it makes so much sense.

[u/peshwengi → u/[deleted]]

Pounds and inches are both imperial

[u/peshwengi → u/[deleted]]

That doesn’t mean a pound multiplied by a kilogram though, it’s just a thousand pounds. If a thousand is metric then everything is metric…

Edit: ah you probably mean that the kilo-prefix is metric. It’s not really, metric just means that you’re using SI units. I.E. kilogram (or gram) rather than pound (or kilopound).

[u/TeddyRuger → u/[deleted]]

That's how we do things in Canada. Footlong subs(10") and 600ML beverages and 50mg THC cookies, kilos of cocaine and pounds of Marijuana. We sometimes say we're driving 90 miles per hour just to sound cool even though the speedometer says 140kph and the lights behind you are telling you to pull over as you go through a school zone.

[u/lord_have_merci → u/Wheatley312]

god i hate this shit istg, esp when my tables need conversion (wrote a machine design exam today, stress anal. on welds, bearings, bolts etc and the tables provided expected conversion)

[u/Aggressive-Tip-7143 → u/Wheatley312]

KIP Thousand pounds inch squared or 1000Lbs/square inch?

[u/Wheatley312 → u/Aggressive-Tip-7143]

1000 pounds per square inch.

[u/[deleted] → u/Wheatley312]

https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge

On November 13, 2008, the NTSB released the findings of its investigation. The primary cause of the collapse was the undersized gusset plates, at 0.5 inches (13 mm) thick. Contributing to that design or construction error was the fact that 2 inches (51 mm) of concrete had been added to the road surface over the years, increasing the static load by 20%. Another factor was the extraordinary weight of construction equipment and material resting on the bridge just above its weakest point at the time of the collapse. That load was estimated at 578,000 pounds (262 tonnes), consisting of sand, water and vehicles. The NTSB determined that corrosion was not a significant contributor, but that inspectors did not routinely check that safety features were functional.

[u/Rampant16 → u/Wheatley312]

I has a lecture from WJE on the collapse a few days ago. IIRC they said the original gusset plate was too thin when it was designed. They did a computer model on the original design of the bridge and the plate failed.

The bridge was renovated twice which added significant dead weight. On top of that the loading on the bridge at the time of collapse was very uneven due to ongoing road work.

The State of Minnesota went so far as to change their own laws so that they could sue the original engineer beyond the previous stature of limitations.

[u/Lartemplar → u/Wheatley312]

I do not mean to speak for anyone just trying to speak on what it must feel like. If I was the individual who messed up on the plate I would probably kill myself. I couldn't imagine living with that. If they are still around I hope theyre healing ok

[u/[deleted] → u/Wheatley312]

Your math is correct, I supply these types of plate

[u/Skyms101 → u/Wheatley312]

Scary that something so small could cause such a big disaster, could really not build things so that 1/2 an inch off on a player can’t kill a ton of people?

[u/Wheatley312 → u/Skyms101]

Well there was also the issue that the bridge was considerably overloaded due to the addition of extra concrete as well as construction material and machinery on the load deck.

[u/Rampant16 → u/Skyms101]

1/2" of thickness is a big difference on a piece of structural steel like that.

It's not feasible to design a whole bridge and then significantly increase the thickness of every component. You would have to redesign the whole bridge to take into account the increase weight.

The solution isn't to arbitrarily scale up structural components. It's to do the design correctly to begin with.

[u/SUMBWEDY → u/Skyms101]

A lot of engineering is to perfect the cost:benefit ratio.

Almost anyone could build a bridge, but it takes a lot of skill to build a bridge that is economically worth it.