vibration towing on M1 to GC . Puzzled???!!!!
Submitted: Tuesday, Jan 20, 2015 at 03:08
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Munners5968
Hi All,
Unusual experience with our first BT; having towed it from Rockhampton to Brisbane with absolute ease I took it down to Coomera this morning to store; All was good until the road surface on the M1 seems to change about 20 mins out of Brissie (hadn't really thought about it before). Then I had a horrendous vibration through the coupling - I coudl see the A bar vibrating furiously; reduced speed to 70-80kmhr where it was bearable but still worrying. Hit a few patches of normal bitumen (bridges etc) and it immediately went away....then back onto the other surface and bad vibration again. Off the M1 - back to normal. Am I going mad??!! Anyone else experienced this? Its in a car with air suspension (Range Rover). As I said - none of this all day yesterday (700kms) and it was fine on the "normal" bitumen......really puzzled!!!
Reply By: Sal and John - Tuesday, Jan 20, 2015 at 06:20
Tuesday, Jan 20, 2015 at 06:20
That's usually referred to as structural resonance.
Cure is to avoid the forcing frequency (thumps per second) by driving either slower or faster (faster means you have to get through the resonant frequency both on the way up and then down ... so slower is better).
Plenty of examples (eg aircraft and large structures) where the structure has been destroyed by resonant excitation .. an interesting example was captured on film is the Tacoma Narrows bridge failure in around 1940 .. google search will lead to the film ...
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Reply By: Mobi Condo - Tuesday, Jan 20, 2015 at 07:42
Tuesday, Jan 20, 2015 at 07:42
We have noticed such on that stretch as well as a stretch of the Hume Highway west of Yass. We put it down to the concrete pavement and the necessary construction and expansion joints (I am led to believe at 6m spacing) and the distances between our tug axles and the van axles meaning that at certain speeds there is a harmonic resonance set up. Varying the speed (for us this means slowing) cuts it out and when back onto bituminous concrete (the more common black stuff we call bitumen) with no need for the regularly spaced joints the problem immediately ceases.
Love to hear more from experienced Civil Engineers re the road construction stuff.
Cheers
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Reply By: Munners5968 - Tuesday, Jan 20, 2015 at 08:43
Tuesday, Jan 20, 2015 at 08:43
Thanks guys, appreciate the explanation, never having experienced it before!
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Reply By: Bow & Nan - Tuesday, Jan 20, 2015 at 17:59
Tuesday, Jan 20, 2015 at 17:59
Adjusting the tension on the WDH bars can sometimes solve the vibration problem.
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Reply By: Sal and John - Tuesday, Jan 20, 2015 at 18:27
Tuesday, Jan 20, 2015 at 18:27
WDH - potentially, but may introduce other structural static loading problems - or even fatigue acceleration if local loading is excessive.
Speed control is the quick and dirty solution along with noting such indicators of the forcing frequency as your towing combination may provide to the driver ... which, in turn may allow the driver to be alert to future situations where the forcing frequency rears its ugly head.
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Reply By: Munners5968 - Wednesday, Jan 21, 2015 at 00:32
Wednesday, Jan 21, 2015 at 00:32
Understood, will no doubt learn more as I tow more. The Range Rover has air suspenion so self levelling at the rear and LR dont recommend a WDH. Heaps of debate on this ofcourse on forums, but most Range Rover Vogue, RR Sport, Discovery 3 and 4 owners seem to indicate never an issue.
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Reply By: BT Wanderers - Monday, Jan 26, 2015 at 21:26
Monday, Jan 26, 2015 at 21:26
Hi, It is the road!!! Having lived there during and after construction of the road it has always been there. It doesn't matter what vehicle, towing or not, the bumps are always there. When we go back home we know we are nearly there when we hit them!!
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