Why do I think the crane collapsed in Halifax?

I’m not surprised the crane collapsed in Halifax during Hurricane Dorian, and an initial hypothesis of cause is easy.

The crane was set up for construction of a multistory building next to The Trillium, 1445 South Park Street.  A friend of mine happens to live in The Trillium.

In collapsing on September 7, the crane just lay down against the street side of the approximately 12 story, unfinished building.  It then went over the top and down the side facing The Trillium, the top of the crane scraping the side of The Trillium on it’s way down.

It looks like a kinked, yellow ribbon thrown over the multistory building.  I counted at least six kinks in the ribbon/crane.  It would speak well for the structural design of the multistory building if it hasn’t been damaged structurally on being whipped by the falling crane.  It seemed to resist the horizontal push of the falling crane quite well.

Google crane collapse Halifax for excellent photographs and video of the crane draped over the building.

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Cranes are good at lifting vertical loads/weights not in resisting horizontal loads, like wind.  And if the horizontal load on the crane is a frequent gust of wind from different directions – Dorian was characterized by frequent wind gusts rather than a steady blow - then you’ve got an oscillating load, an on-again, off-again load on the crane.  Worst still.

These kinds of oscillating loads caused three, 1.5 metre deep, steel bridge girders, that were connected to a crane, to fail by bending sideways in Edmonton in 2015. (Refs 1 to 4)

The steel bridge girders were new yet they bent under an oscillating load.  The word on the street is that the Halifax crane was rusted and perhaps not so new.  Not good.

But you say, the open lattice-type construction of the crane doesn’t provide much surface for the wind to push on.  Still some, and Dorian’s wind gusts were not light weight by any stretch.  Have you seen a thin, hanging rope, steel chain or cable swinging back and forth in the wind?

Given the preliminary evidence, an initial hypothesis as to why the crane collapsed is wind load in excess of the crane’s capacity to resist.  A wind load characterized by frequent, strong gusts from different directions.

The resulting oscillation of the crane would cause metal fatigue - a well known cause of failure in engineering – and the crane to break at the location of the first kink.  The upper kinks in the yellow ribbon/crane would form as a result of hitting the stronger multistory building.

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I examined the collapsed crane from outside the security fence near the corner of The Trillium.  I also talked with a man who was evacuated from a building near the collapse and another man at The Trillium.

Hands-on examination of the crane and more evidence is certain to result in revision of my initial hypothesis as to cause, but I know I’m close.  Regarding more evidence, it’ll be interesting to learn the condition of the crane – the rust factor you hear on the street.

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This is what scientists do, an initial hypothesis on an issue, a simple thought, sometimes on the basis of the skimpiest evidence.  They’ve got to start somewhere.  Then, based on more evidence, they tweak, revise and modify their initial thought, and sometimes throw out the initial hypothesis completely.

Applied scientists like forensic engineers and medical doctors do this too – ask your doc next time you see him or her about differential diagnosis.

It’s important for clients of forensic engineers and experts to realize that an initial hypothesis is not the last word on cause.  It’s just a good start.

References

  1. Wind, construction crane and inadequate cross-bracing caused Edmonton bridge failure.  An initial hypothesis.  Posted March  27, 2015
  2. Why, in a recent blog, didn’t I seem to consider foundation failure as a possible cause of the Edmonton bridge collapse?  Posted April 3, 2015
  3. Bridge beams that fail are sometimes like balloons filled with water – squeeze them and they pop out somewhere else.  Posted May 20, 2015
  4. Bridge failure in litigation due to inadequate bracing – City of Edmonton.  But, inadequate for what?  Posted March 15, 2016

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