Project Sauron

[patricks]

methinks this would be more at home in the Out There forum

[MortimerV]

Back on topic then. I'm reconsidering suspending the walkways rather than support them in compression. Can anyone suggest a good rule of thumb that compares sizing for compression vs. diameter for tension?

-Mort

[cliff collins]

Rule of thumb:

Consult with Structural Engineer when sizing any structural members, esp. ones holding up suspension walkways---Hyatt Regency, KC, MO ring any bells?

cheers

[MortimerV]

Cliff -

Research indicates the walkways failed due to improperly installed connections - not improperly sized structural members. Lord and Master says the connections sheared off and were not installed in tension.

Please confirm.

Yours truly -

-Mort

[cliff collins]

Common sense says no matter what exactly happened at KC, consult your friendly Struct. Engineer
when throwing around loose terms like "rule of thumb for compression vs tension member sizes".

( This just in: Research indicates that it was indeed a connection failure; however it was an overloaded suspended walkway which had both tension and compression members which failed due to sympathetic vibrations induced by moving pedestrians similar to the Tacoma Narrows Bridge failure.)

Also you can let the L&M know that it also turns out that my Structural Engineering professor when I was in Architecture School was called in as an expert witness on the case, and gave us a lecture highlighting the exact threaded rod suspension (tension member) connection detail which failed.

cheers

[MortimerV]

Well, common sense (and the chart below) tells me that a braided steel cable can suspend more weight in tension (with a far smaller cross section) than a structural column (with a much greater cross section) can hold up in compression.

And since a 2" cross section of wire rope can safely suspend about 32 tons, I'll use that as a starting point.

Beside's, there still plenty of time for a structural engineer optimize the design as well as roll his eyes and tell us all about the time he had to walk up hill, in both directions, to structures class, in 12' of snow, before electricity, before fire, before sex, without shoes, and right after that really cute girl from the Architecture department dumped him for an unkempt and smelly English major.

Anyway - we're thinking about replacing the structural system at the center of the lair with tension cables. Cables might save some money (ahem...not that we don't have unlimited resources), but they wouldn't look as monolithic. Lord and Master also likes the way the structural connections double as light fixtures.

-Mort

[gtarch]

Cliff -

Research indicates the walkways failed due to improperly installed connections - not improperly sized structural members. Lord and Master says the connections sheared off and were not installed in tension.

Please confirm.

Yours truly -

-Mort

Actually as I understand it:

The original design used a single continuous hanging threaded tension rod to support the walkways. Apparently, this proved difficult to build & detail. So a design change was made through a shop drawing. The single tension rod was cut and the rods were offset, and each was connected to a beam/channels section, and there was some distance between them. One rod went up, the other rod went down to the walkway section below.

With the two rods being offset that distance, a shearing/rotation sort of force was set up in the beam. And the thing broke right there at that connection, the beam was not strong enough to take the force.

The change was approved in the shop drawing, and no one really checked it from an engineering standpoint, or noticed that it created a new set of loads on the beam.

Perhaps Cliff Collins will confirm my understanding of it.

[MortimerV]

So stick with the compression system and heavy members or go for the suspended system? And we're looking at steel cable - not threaded rod.

Attached quick rendering with some more artificial lighting (and natural light). Only either side of the stair and the landing are being lit - along with the core area. Not too bad - but the heavy columns decrease visibility.

Anyway - need to go - Wednesday night beer and volleyball. Minions won easily last week and henchman are looking for revenge!

- Mort

[gtarch]

Mort:

I think your place looks an awful lot like a movie or video game set...

[patricks]

hey I bet Revit could have its place in movie set design, if it doesn't already.