Question for the structural engineers

[Tim+]

Why does the Tees/Middlesbrough transporter bridge have a notch in the middle?

Seems to me it's got to be weaker than if it was braced across the gap.

Tim

[John Rumm]

The two halves are designed to be self supporting - they could take the full weight of the car in cantilever, without the other side being there. Hence you only need "enough" of a join to stop the ends wobbling next to each other - there is no structural need for a stonger joint.

[Tim+]

Well yes but materials flex and stretch. When the gondola is in the middle the counterbracing cables will obviously minimise droop, but not eliminate it. Fully triangulating the top beam would surely help to reduce and droop.

So, perhaps more to the point, why would one choose to NOT use a fully triangulated beam? There are many similar (but not identical) designs of transporter bridge but this is the only one with a "notch".

Tim

[Tim Watts]

The University pf York has/had a footbridge like this between Wentworth and Goodricke Colleges (as were - there's been a bit of a relocating of some of the names since).

It was considered a sport to jump up and down on the middle at resonant frequency :)

[soup]

There is no need to entirely eliminate any flex; witness 'boinging' wind loads, earthquake resistance, etc,etc .

There is no (or at least minimal) structure in the middle as it would weigh more and so need more structure so would weigh more....

Nowadays a computer could work out the optimal structure but 'in those days' some 'architect' drew it and said "that looks right" with some 'back of envelope calculations' a construction master would say "nope needs to be stronger here and here can be thinner here and here" they would settle on something that looked right but was thin enough to work used as little material as possible to minimise costs. They didn't always get it right and some times they went completely overboard (witness the Forth bridge built just after the 'Tay bridge disaster' and so well 'over engineered'.

[Syd Rumpo]

It looks like the two halves could swing upwards to allow very tall vessels through.

Cheers

[The Natural Philosopher]

Never underestimate the 'because I did one like that last week and have all the calculations done already' syndrome.

It looks like two standard land crane deigns joined in the middle

Darwin's law is not survival of the fittest, it's lack of survival of the terminally dysfunctional. And that bridge is good enough, not optimal.

[Vir Campestris]

It didn't do that when I was there...

Andy