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- Thread starter Irish Rover
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Fr J Hackett
Well-known member
23 years old and in need of urgent repair. 
Sandy
Well-known member
All very quaint.
Is this the wobbly bridge that needed to be adjusted so not to upset landlubbers?
Is this the wobbly bridge that needed to be adjusted so not to upset landlubbers?
mjcoon
Well-known member
Just like the luggage label we tie under the Perspex main hatch when it is sometimes closed to warn those emerging that they are about to bang their head...
rotrax
Well-known member
AFAIK, the 'bale of hay' was hung over the centre span of a bridge arch to tell those coming upstream which arch to use in poor light conditions.
Another bale might be used on an arch for downstream traffic, so separating them.
From my River and Canal boating days.
Another bale might be used on an arch for downstream traffic, so separating them.
From my River and Canal boating days.
Irish Rover
Well-known member
I was surprised to read that hay baling was first started in the 1880's.
Concerto
Well-known member
At Rochester Bridge, they have been using a straw bale for donkey's years. Nothing new here except a a wet behind the ears reporter who has never heard of it.
johnalison
Well-known member
Well, I had never heard of it. Where’s that towel?
Irish Rover
Well-known member
Pass the towel please when you've finished.
38mess
Well-known member
I'm next for the towel
mjcoon
Well-known member
Who throws it in?
rotrax
Well-known member
The sometime arcane practices of River and Canal folk can be confusing to seafarers.
I always hang my stern mooring line, permanantly fixed to the narrowboat, over the giggle pin............................................
I always hang my stern mooring line, permanantly fixed to the narrowboat, over the giggle pin............................................
Frogmogman
Well-known member
Looks more like a hay bale to me.
Irish Rover
Well-known member
Definitely straw. If you offered that to a cow as hay she'd tell you moo off.
Snowgoose-1
Well-known member
I'm just about to hoist a traffic cone on the car pointing south to warn everyone on the M25 of the impending doom tomorrow.
johnalison
Well-known member
I used to look forward to the storm cone being hoisted in Mevagissey, and the chance to watch the waves breaking over the harbour wall.
kwb78
Member
Yes, but there was a good reason behind it. The phenomenon that caused it to wobble was unknown prior to the opening of that bridge. Resonance was known to happen with certain circumstances on bridges (eg troops being told to break march and walk), but the resonance on the millennium bridge happened with people just walking independently over it.
What happened was a result of the geometry of the bridge causing the resonant frequency to fall within the range of human walking pace. As people walk they transfer their weight from one foot to the other. This causes an alternating sideways force on the bridge from the feet. This is small, and even though they are not stepping in sync it is not fully cancelled out, and when many people are walking at the same time, there is a resultant force which deflects the bridge sideways. When the bridge returns to its normal position, this imparts a small and imperceptible force on the feet of the people walking.
Although they are not aware of it, people subtly adjust their gait to balance in response to this force, and because it is applying to everyone simultaneously it nudges them into walking more in sync, which caused a positive feedback loop, amplifying the movement of the bridge until it could be seen and felt to wobble.
The fix was to add damping for the sideways movement to reduce the movement and modify the resonant frequency so it was less affected.
Fr J Hackett
Well-known member
Well I never! Our company secretary my boss for a very short time had an office very close to it so I got to test it out quite often.
had an office very close to it so I got to test it out quite often.
Bristolfashion
Well-known member
The current "recreational users guide" refers to a bale of straw. It's still current practice. Not the worst thing to hit!
rotrax
Well-known member
The bale rarely hangs below the bridge arch-it would hit passing vessels and would soon be destroyed. It is above the arch, supported to its rear by the bridge structure.
You dont want to hit that, straw bale cushioning the blow or not......................................
