Geoffs
Well-Known Member
Politicians will always understate a problem. For small piece of tarmac, read huge lump.
For a few minor problems read, a complete cock up!
Twin Sails Bridge update
- Thread starter strakeryrius
- Start date
Politicians will always understate a problem. For small piece of tarmac, read huge lump.
For a few minor problems read, a complete cock up!
Boycey
New Member
Small piece of tarmac
With my old engineering hat on I have done some simple maths..
Approx area of tarmac, lets say a carriageway width is 2.5m (conservative) and the lenght of the slab is 4m (also conservative) the area becomes 5m2 as its a triangle. Depth of tarmac usually 75mm and this born out by pictures on BBC
This equates to .375m3
Density of tarmac= 1700kg/m3 so the "small" piece of tarmac weighed a minimum of 637kg or nearly 3/4 of a tonne.
This however presented "no hazard"
I calculate, based on maths above and assumed tarmac area of approx 5m x12m, the weight of tarmac on each side to be approx 7.6 tonnes. Even if you take a 100% error factor in these assumptions it is 3.6 tonnes.
How can 3.6 tonnes of tarmac be expected to cling to a flexible metal surface which is raised to the vertical every hour or so!
Tarmac has great compressive strength, you can pile extreme loads on it eg trucks, this is why motorways are made of it.
However, like concrete, tarmac has virtually ZERO tensile strength, eg you cannot stretch or "pull" it. When the carriageway lifts you an actually see the slight bend as the tip comes off the bump stops. This in turn will create a radius on the top section where the tarmac is and impose significant tensile forces within it. This is bound to cause cracks, and loss of adhesion?
Did they use a fag packet to design this on?
With my old engineering hat on I have done some simple maths..
Approx area of tarmac, lets say a carriageway width is 2.5m (conservative) and the lenght of the slab is 4m (also conservative) the area becomes 5m2 as its a triangle. Depth of tarmac usually 75mm and this born out by pictures on BBC
This equates to .375m3
Density of tarmac= 1700kg/m3 so the "small" piece of tarmac weighed a minimum of 637kg or nearly 3/4 of a tonne.
This however presented "no hazard"
I calculate, based on maths above and assumed tarmac area of approx 5m x12m, the weight of tarmac on each side to be approx 7.6 tonnes. Even if you take a 100% error factor in these assumptions it is 3.6 tonnes.
How can 3.6 tonnes of tarmac be expected to cling to a flexible metal surface which is raised to the vertical every hour or so!
Tarmac has great compressive strength, you can pile extreme loads on it eg trucks, this is why motorways are made of it.
However, like concrete, tarmac has virtually ZERO tensile strength, eg you cannot stretch or "pull" it. When the carriageway lifts you an actually see the slight bend as the tip comes off the bump stops. This in turn will create a radius on the top section where the tarmac is and impose significant tensile forces within it. This is bound to cause cracks, and loss of adhesion?
Did they use a fag packet to design this on?
Lucky Duck
Well-Known Member
Don't most similar lifting bridges have tarmac surfacing?
AdeOlly
Well-Known Member
I think the point is that due to it's unusual 'sail' design there is flex, and that's causing the problem. No flex=no problem?
Lucky Duck
Well-Known Member
Post #42 talks about the bridge flexing when the span comes off the 'bump stops' which I would have throught was pretty much unaviodable.
mm1
Well-Known Member
twin fails bodge!
there was a meeting today has anyone heard anything enlightening,regards mm1.
there was a meeting today has anyone heard anything enlightening,regards mm1.
baily
Well-Known Member
I heard that there is a problem with the lifting rams on bridge has any body know if it is true.
Geoffs
Well-Known Member
Not heard of this, but wouldn't be surprised. Always thought the idea of putting controls below water level, a bad idea.
The other thing, of course, is that if one of the leaves should fail to lift, the whole channel is blocked.
scej
Well-Known Member
I think that is more likely to be a prediction. most likely the day after it opens to traffic whenever that might be
John_Silver
Well-Known Member
Sounds as if there is a positive outcome emerging on the lifts based on the info provided to Cobbs Bertholders this morning:
- 3 lift commitment reinstated for summer
- Bridge being re surfaced completely. Aiming to complete before Easter
- Still to be decided: what the lift regime is until easter. what the lift regime will be from October & thru the off season.
Good news about 3 lifts though,even if its only committed for the summer, effectively that's continuous openings. Better than we had before! Now we just need to get the winter sorted. Its been very restrictive this winter with the 14.30 lift abolished.
yellowspinnaker
Well-Known Member
Reinstating the three lifts is indeed good news for all the CQ berth holders, and indeed other whose 'home' is inside the bridge.
I await the first Bank Holiday weekend with keen anticipation, I'll be there somewhere with a video camera. The 'holding pen' concept is flawed in my opinion, to the point of being dangerous.
Earlier posters have asked if there's a problem with the rams. I don't know, but I was told that the initial stages of the lift (as witnessed on a number of occasions including the public opening) are jerky and painful to behold. The mechanical disadvantage is, of course, immense with this design.
Other rumours going the rounds involve locking, shock absorbing, flexing, problems in wind, lighting being too bright at night, and of course there's the 'small amount of tarmac' business. All rumour, all unfounded, all persistent.
Councillors and Councils have an unfortunate tendency to go for something they can be persuaded is 'Iconic'. We nearly ended up with an eyesore of a Solar Pyramid in Poole, so it could be worse.
The road system that feeds this new bridge is another masterpiece...
I await the first Bank Holiday weekend with keen anticipation, I'll be there somewhere with a video camera. The 'holding pen' concept is flawed in my opinion, to the point of being dangerous.
Earlier posters have asked if there's a problem with the rams. I don't know, but I was told that the initial stages of the lift (as witnessed on a number of occasions including the public opening) are jerky and painful to behold. The mechanical disadvantage is, of course, immense with this design.
Other rumours going the rounds involve locking, shock absorbing, flexing, problems in wind, lighting being too bright at night, and of course there's the 'small amount of tarmac' business. All rumour, all unfounded, all persistent.
Councillors and Councils have an unfortunate tendency to go for something they can be persuaded is 'Iconic'. We nearly ended up with an eyesore of a Solar Pyramid in Poole, so it could be worse.
The road system that feeds this new bridge is another masterpiece...
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