Las Vegas Monorail 2

[Blooongeey]

Is anyone monitoring this? Is there a current thread related?

 

[phamENG]

What happens in Vegas, stays in Vegas...unless it's a monorail collapse. That'll be on the news.

Yikes. That doesn't look good. But as of 7 or 8 years ago, they had it handled...

 

[3DDave]

Reminds me of the saying "Don't do crack."

Huh -

https://www.lasvegashowto.com/getting-around-world-of-concrete

Maybe those guys can take a shot at it.

 

[IRstuff]

Perhaps the concrete is more decorative than structural; the connection appears to operate more in tension that compression, since the section doesn't appear to flare enough to transfer the loading through compression.

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[dik]

Connection looks really bad...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[1503-44]

Optics failure for sure.

 

[bugbus]

Not to worry, says Las Vegas Monorail spokeswoman Ingrid Reisman: "We have a company who monitors all of our guideways, and all of our columns and beams, because these are large, concrete structures. They’re all superficial cracks [that you saw] but we continue to monitor them, just like we perform regular maintenance on our trains and the rest of our structure."

Nothing about those diagonal cracks looks superficial to me.

 

[LockeBT]

Based on how those cracks propagated, can we say that this is a shear failure of the...double sided corbel (or short catilever beams if you will).

 

[MIStructE_IRE]

Aren’t these things normally concrete encased steel sections?

 

[bugbus]

 

[hokie66]

MIS,

If it were concrete encased steel, I don't think they would have gone to the trouble of tapering the soffit.

Those cracks certainly have the appearance of diagonal tension cracks, propagating from reentrant corners. Would be interesting to see the detail, as the concrete above the bottom of the stringer would appear to serve little purpose.

 

[LockeBT]

hokie66,

Diagonal tension cracks are what we describe as shear cracks no? Plus that zone is in compression due to the cantilever nature.

 

[hokie66]

Yes, but there are several types of shear. Diagonal tension, direct shear, torsion...

Normal to the crack, there would be tension for most of the distance, and a bit of compression at the bottom...I think.

 

[dik]

I seem to recall that the retired 'head' or whatever of the California engineers association has said that the Millennium towers is safe... I'm not so sure about that either...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

that cracking looks bad to me and they are in the 'right spot'; they also appear to be fairly wide. From the symmetry, you would think the loads would be similar, too.


I wonder what sort of disclaimers they have in their agreement to monitor...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

looks like a classic example of the ol' diagonal tension stuff to me.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bugbus]

From what I can glean from various sources and some quick calcs, the total force on each of the two corbels is around about 72.5 tonnes (~700 kN, ~160 kips). This does not include any load factors or dynamic factors. The girders are said to be hollow core concrete planks and appear to be simply supported at the piers (not continuous), not sure on the dimensions but just guessing from the photos maybe 1000x500 mm with maybe a 500x250 hollow core (just a guess?). Maximum span seems to be about the same as the monorail length, which is about 40 m.

Bombarder Mark VI Monorail (4 cars) - 28 tonnes total, but about 75% going to one pier in the worst case = 21 tonnes
240 passengers (@75 kg each) - 18 tonnes, same distribution as above = 13.5 tonnes to one pier
Girders - assuming 40 m span with above dimensions, 38 tonnes

Total ~ 72.5 tonnes


As for the strength of the corbel? I wonder if there are any drawings floating around.

 

[Ingenuity]

Found some info on the existing structural framing from this paper: A Unique Rapid Transit Project for a Unique City by Thomas J. Stone, Ph.D., P.E. , Carlos A. Banchik, P.E. and Jeffery B. Kimmel, Esq.:

Link​

The guide beams:

Spans for the guide beams, which both support and guide the monorail vehicles, average approximately 30 meters (100 feet), with the longest span being about 36.6 m (120 feet). The slender 660 mm wide (26 inch) haunched beam section varies between 2.1 m (7 feet) deep at the column supports to 1.5 m (5 feet) at midspan. Guide beam spacing is typically 4.2 m (14 feet) on centers, increasing to 4.5 m (15 feet) when approaching crossover switches, and wider when entering center platform stations.

The supporting crossheads:

The crossheads typically are tapered from 1.2 m (4 feet) at the tip to 1.8 m (6 feet) at face of column, and are 5.1 m (17 feet) wide. The typical column has a rectangular section, 1422 mm x 812 mm (56 inches by 32 inches). A series of reveals and colored sealer provide the columns with an attractive architectural look. The typical guideway section is shown in Figure 4. The typical cast-in-place column supports two guideway beams over the 1.2 m (4 feet) deep crossheads. The beam-column connection contains a structural steel support and steel hanger detail, that coupled with external supports, will allow the beams to be positioned properly during construction. The assembly is such that guideway adjustment and super-elevation can be adjusted before pouring.

 

[rbenz]

I noticed this while finishing a beer and lighting up a stogie as a monorail passed overhead. Looked up and was shocked at the obvious shear fracture - through the entire column width. What was more disconcerting is that every single support structure from the convention center to the Westgate had similar diagonal cracks as shown. I'd ask the LV convention center for any engineering analysis pertaining to their supposed "monitoring" of the "superficial" cracks but have yet to receive a response.

 

[dik]

to reiterate... to these aging eyes, it looks bad... and the cracks appear to be 'closed' at the compression side.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik