Cable car emergency brake disabled?

Well maybe they did not do any maintenance at all. I suspect that this is yet another case of somebody elses job.

Brian

It didn't. But when the cable did break (for reasons unrelated to the disabling of safety brake), there was nothing to stop the car running away out of control.

The cable that broke would have been a multi-strand cable. That is to ensure that the failure of a single strand does not release the car. It also means that it is very unlikely that all the strands will fail at the same time. I wouldn't be surprised if they found signs of progressive partial failures in the cable, which might be what was triggering the emergency brake.

The purpose of being multi-stranded is so they can be wound round a drum (or generally so they are stronger when flexed because a solid cable would have excessive tension in the outer side even with bending under its own weight). But otherwise I agree the failure *might* have been progressive.

That too :-)

There was a fault with the emergency brake that meant it kept applying when it should not have, so they disabled it. It was disabled for quite a while too, before the time occurred when it was needed to work as intended.

Some cable cars seem to have just one cable that is both support and for pulling. The ones that traverse the Thames only seem to have a single cable.

Andrew

the purpose of stranded cable has nothing whatever to do with being wound on a drum. And everything to do with the failure of one strand nit propagating a stress fracture throughout the whole cable

all suspension bridge cables are multi-element - strands or chain links

- for this reason. They aren't wound on drums

I agree that mitigation was the wrong word.

Suppose that the emergency brake applied itself halfway through the run, with a cabin load of passengers 30 metres up in the air.

Do you evacuate them all by rope and then walk/carry them down to the bottom of the hill?

Or do you disable the brake and run the whole car load down to the bottom?

Neither option is safe, as the evacuation could easily result in casualties. Is it obviously safer to do the evacuation, then move the empty car?

Let them climb out the hatch on the roof and be collected by man attached to a winch on the helicopter - air sea rescue style.

Of course it does.

That is also true, and a benefit, but I would like to see you deploy a "single stand cable" (or steel bar as we might otherwise call it!) that can be strung up through the winding gear for a cable car.

Apart from those that are solid links or rods of course.

Have you ever though of how you would get your solid half mile long "cable" on site when building a suspension bridge if you could not coil it and deliver it on a drum?

Yes I would say that there are two benefits to multi-strand cable:

- gradual failure, where one failure does not cause the whole cable to break

- increased flexibility for coiling on a drum and feeding around pulleys on the linkage between the car and the cable

Which of those two factors is the more important is difficult to say: they go hand-in-hand.

It's why electric cable for installation in conduits of a house can be single-strand (ie solid) but the leads of appliances which are plugged into that wiring have to use multi-strand wires: for increased flexibility (and springing back to a "neutral" un-bent position) and greater resilience against being repeatedly flexed during normal usage.

The other point that all of you have missed is that at least in the case of a winding cable, failed strands are normally at the outside (whether caused by wear, mechanical damage, or corrosion because of inadequate lubrication), and so readily visible in the periodic insurance inspections, not to mention to the operators themselves.

Suspension bridge cables are another matter because corrosion or stress corrosion can cause inner strands to fail. IIRC there are clever NDT methods, also some cables use continuous acoustic monitoring to detect strands snapping.