Elevator at John Hancock Center in Chicago

Question

Elevator at John Hancock Center in Chicago

TomBarsh (Structural)

(OP)

20 Nov 18 22:32

John Hancock Center is one of the tallest buildings in Chicago (okay, I guess its name was officially changed earlier this year).

One of the express elevators to the restaurants and observation level at the top of the building experienced broken cable(s) this week. A number of news articles have referred to it "plummeting 85 stories". I find this to be incredible and think "surely the news accounts are somewhat exaggerated" about plummeting 85 floors. But this description seems to be in numerous news sources, even those I trust (eg: not the National Enquirer).

Can this really be so? ASME has a strict code for elevator safety and inspections. And there are numerous safety devices on these systems. How could a car drop 85 floors? Perhaps it was decelerating for most of that drop? It came to a stop at the 11th floor, what if the cables had broken while the car was 12 stories lower than where they actually failed? it would have dropped to the basement.

Any insight or comments on this event?

ETA: I suppose it might be assumed by people (not engineers) that the car started free fall immediately at its top level...it came to a stop at floor 11, therefore "it fell 85 floors". But the catastrophic break of the cable(s) might have occurred at any point, maybe even floor 12.

BridgeSmith (Structural) · Answer 1 · 2018-11-20 23:50:53

In this story from the Chicago Tribune, one of the passengers is quoted as saying "We were going down and then I felt that we were falling down and then I heard a noise–clack clack clack clack clack clack." So, the cable (one of several) broke at some point during the descent, and it was free falling for a little bit until the emergency brakes engaged (breakaway tabs at regular intervals producing the "clack" sound as it broke each one?), bringing it to gradual stop, as it's supposed to. My hunch is that whatever system is used is set up to slow it more aggressively near the bottom of the shaft. They may not have had all the fancy computer controls that we have today, but elevator design has always been the domain of some of the sharpest engineers anywhere.

miningman (Mining) · Answer 2 · 2018-11-21 00:01:08

When something similiar ocurrs in a mineshaft , we rely on automatically applied dogs to arrest the fall. The action of dogging is sufficiently severe that at the very least all personnel end up on their knees and broken ankles are not unknown. Clearly the clack clack mechanism was a bit more gentle!! Regardless I also would be interested to read an accrate summary of what happened and how the safety mechanisms did what they were designed to do.

BridgeSmith (Structural) · Answer 3 · 2018-11-21 00:07:06

I suspect, miningman, that this one has a similar system to what you describe, but it doesn't get to the point of the more aggressive deceleration you describe unless it's necessary (it gets close to a hard stop).

MintJulep (Mechanical) · Answer 4 · 2018-11-21 00:19:10

So then this is an engineering success.

Maintenance failure.

TomBarsh (Structural) · Answer 5 · 2018-11-21 03:15:09

RE: Elevator at John Hancock Center in Chicago

TomBarsh (Structural)

(OP)

21 Nov 18 03:15

MintJulep, I now agree.

itsmoked (Electrical) · Answer 6 · 2018-11-21 06:42:52

And, probably quickly followed by a housekeeping success.

Keith Cress
kcress - http://www.flaminsystems.com

ashtree (Bioengineer) · Answer 7 · 2018-11-21 08:03:52

I am going from memory here.
When the World Trade Center was struck in 9/11 i think it was reported that at least one elevator suppossedly crashed to the bottom. I guess one of the aircraft strikes must have damaged the lift shaft and cut the cables.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

thebard3 (Computer) · Answer 8 · 2018-11-21 11:19:02

Quote (MintJulep)
So then this is an engineering success.

Maintenance failure.

Yes, and assuming the elevator is original to the building it is 50 years old.

Brad Waybright

It's all okay as long as it's okay.

ornerynorsk (Industrial) · Answer 9 · 2018-11-21 14:43:31

One of the news articles reported the occupants reporting dust infiltrating into the cab as it was descending. Possibly from the safety brakes engaging. I was in Taiwan at the time the Taipei 101 was being topped off, and I remember articles their about the new ceramic materials that are being used in elevator brakes. Doubtful that these older installations would have been re-fitted though. It will be interesting to hear at which floor the cables actually broke, as TomBarsh alluded to. If they had time to recognize and acknowledge a sensation of falling, it was probably "loose" for at least a couple of floors or more.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

cranky108 (Electrical) · Answer 10 · 2018-11-21 19:04:15

Assuming the safety system was designed to require a few floors to engage, and the break took place on floor (in this case we know it did not) 2, they would not have time to engage. So the springs at the bottom, or something else must be able to take care of that, or there might have been an assumption that is unlikely to happen and if it does too bad.

That said, the breaks must be able to slow down the car to a point the bottom springs can handle the impact, and if they stop the car the better.

This is all just my thoughts, but from what I know, how could a cable break happen if the elevator was up to date in the inspections? Was the inspection not done right, or missed? Or something else like a payoff?

I am guessing right now their is some type of finger pointing game going on.

BridgeSmith (Structural) · Answer 11 · 2018-11-22 02:11:17

cranky, if a cable fails 2 floors from the bottom of the shaft (assuming the car ever gets that close to the actual bottom of the shaft during normal operation) and free falls, it doesn't take much deceleration distance to avoid serious injuries.

waross (Electrical) · Answer 12 · 2018-11-22 04:54:27

I have seen the emergency braking setup on a couple of construction skips. The supporting cables are attached to brakes that grip the vertical rails The brakes are held off by the weight of the car on the cables. In the event of a cable failure the brakes will apply immediately. There may be a cam action so that the weight of the car helps apply the brakes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

HamburgerHelper (Electrical) · Answer 13 · 2018-11-28 17:34:53

Isn't this an engineering success and not a disaster? To paraphrase the quote about airplane landings, a good elevator is one that doesn't kill anyone. A great elevator is one that gets everyone to the floor they were trying to get to.

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Elevator at John Hancock Center in Chicago