Would you do it?

[Henarar]

As to answering the question of the thread then it all depends why the weight limit was put there, if it was put there because the bridge is weak then its not a good idea to use it but if it was put there cos a few people want to keep large vehicles out of the village (except when delivering to them of course) then feck it.

 

[Lofty1984]

As to answering the question of the thread then it all depends why the weight limit was put there, if it was put there because the bridge is weak then its not a good idea to use it but if it was put there cos a few people want to keep large vehicles out of the village (except when delivering to them of course) then feck it.

That’s exactly what happened near me no bridges or anything but the 7.5ton signs have gone up and diverted the wagons to another road less suitable

 

[Exfarmer]

As to answering the question of the thread then it all depends why the weight limit was put there, if it was put there because the bridge is weak then its not a good idea to use it but if it was put there cos a few people want to keep large vehicles out of the village (except when delivering to them of course) then feck it.

That is why there are two sorts of weight limit signs
“No HGV 7.5 tonnes”, this means restricted access to all Lorries over 7.5 tonnes. It does not apply to PSVs ( buses) Emergency vehicles, Agricultural vehicles, or HGVs delivering.

Then there is this sign M G W 7.5 tonnes ( or whatever). This means a complete no access to any vehicle over this weight, emergency , delivering agricultural , whatever. This type of sign can and is only placed , on a public highway, when an engineer decides the bridge is only safe for that weight.
Obviously any engineer can make mistakes and he is going to err on the side of safety, but that cannot excuse a gross abuse as is obvious in that picture

 

[7610 super q]

Maybe ELMS money should be diverted to those running Ford 4000's and Weeks 3 ton trailers with bale extensions.

Dissss cusss.

 

[ollie989898]

Maybe ELMS money should be diverted to those running Ford 4000's and Weeks 3 ton trailers with bale extensions.

Dissss cusss.

If the world resorted to Ford 4000s then the signs would change as well:

'Horse and cart only. Driver has to walk'.

 

[michael N123]

Instead of sticking a sigh post next to a dodgey bridge saying ‘weak bridge’ they should knock the decking thing down and build something that can handle modern traffic

 

[hutchy143211]

Speeding is also gross stupidity have you never done it?

strange how it's 7.5t don't you think? They have plenty a suppply of those signs. The point that the locals are supposedly up in arms about it would suggest the theory of people with nothing better to do than complain about hgv's cutting through their village whilst they drive around in a SUV have probably got the area weight limited ( Not a fact)

Even if that was incorrect a engineer, if one was even consulted in such sign or plating of the bridge would allow a lot of tolerance in the weight limit (unlike the normal it's 5kg out) it's going to be set to allow a lot more. obviously doesn't collapse if more than 7.5t goes over it maybe if it become a route for fully loaded hgv's rattling over it at high speed five days a week it would take its toll over time.

But a couple of tractors a few times a year at 20mph (cough) possibly putting 9t on the bridge at it's stress point is it really such a problem

In the nicest way this is a very misinformed view of how the margin for safety is built into structural design and imposed restrictions. I am a semi qualified structural engineer (structural engineering masters degree, half way to chartership) and have some bridge design experience, though buildings is my main field. In my professional and stress my personal opinion, I would argue that the occasional heavy tractor passing over that bridge is possibly the most damaging action that could occur.

A tractor is more than likely going to be well over 9t. If it has a trailer it's likely to be 20t+ and that could very easily be applied to both ends of the bridge even if not all in the middle. This is typically a governing design case that is checked. In addition axle loads on ag machinery is far less controlled than a HGV which is governed by strict axle weight restrictions for this exact region. For example look at a fully loaded muckspreader filled. 14t + 5t with 3t on the drawbar gives 16t on a single axle, double the rough 8t limit on HGVs.

The argument a HGV doing 56mph vs a tractor at 20mph also doesn't tell the full story. Dynamic load amplification is a very complex issue and is a big reason for the safety margin, not the static load itself. On a bridge like this that appears to have a narrow, curved approach a significantly reduced speed will have likely been consider I would guess to a degree that a lorry and tractor could very feasibly be assume to pass over the bridge at the same speed.

Finally, the issue is how the bridge could fail. It's not all about what's the worst case load that can be thrown on there. From the images (very limited view) it looks as though it could be a deck supported on steel sections due to the use of steel parapets and low profile (could be very wrong). To me straight away fatigue could be an issue and that's one of the most dangerous failire types you can have. That 'once in a while' big tractor induces a huge stress cycle on components which is what causes the greatest fatigue damage. The problem is this is very hard to predict and you'll be fine going over numerous times prior, until one time after stress fractures have formed due to this, something will fail. Failure for a bridge like this would likely be sudden and lead to total collapse and potentially fatalities as a result. That's not to go through all the other failures that could occur due to exceeding the weight restriction.

I would like to say that I don't mean this to be a personal attack, but want to highlight the severity of the consequences that these actions could have.

 

[Forkdriver]

Bridge weight limits are assessed on knowledge of the structure. Old bridges do not have structural information available, so they're assessed at the lowest limit, even if they have regularly carried 40t without a problem.

 

[Exfarmer]

Bridge weight limits are assessed on knowledge of the structure. Old bridges do not have structural information available, so they're assessed at the lowest limit, even if they have regularly carried 40t without a problem.

Complete bolloc** i have been involved in a bridge structural assessment which involved a series of tests including hanging weights under and passing weights over then assessing the deformation.
It is not possible to safely estimate the carrying capacity of a bridge which is being undercut by a river, as the current can remove the base at a rapid rate

 

[Forkdriver]

Complete bolloc** i have been involved in a bridge structural assessment which involved a series of tests including hanging weights under and passing weights over then assessing the deformation.
It is not possible to safely estimate the carrying capacity of a bridge which is being undercut by a river, as the current can remove the base at a rapid rate

Charming. I too have been involved with numerous bridge weight limits assessments on rivers. That was why I replied.

 

[76masseyman]

Can we take the 25+ tonne Quadtrack over as Case IH say they tread lighter than a grown man in his boots ?

 

[Forkdriver]

Can we take the 25+ tonne Quadtrack over as Case IH say they tread lighter than a grown man in his boots ?

Depends on the speed you go at it

 

[Lincsman]

In the nicest way this is a very misinformed view of how the margin for safety is built into structural design and imposed restrictions. I am a semi qualified structural engineer (structural engineering masters degree, half way to chartership) and have some bridge design experience, though buildings is my main field. In my professional and stress my personal opinion, I would argue that the occasional heavy tractor passing over that bridge is possibly the most damaging action that could occur.

A tractor is more than likely going to be well over 9t. If it has a trailer it's likely to be 20t+ and that could very easily be applied to both ends of the bridge even if not all in the middle. This is typically a governing design case that is checked. In addition axle loads on ag machinery is far less controlled than a HGV which is governed by strict axle weight restrictions for this exact region. For example look at a fully loaded muckspreader filled. 14t + 5t with 3t on the drawbar gives 16t on a single axle, double the rough 8t limit on HGVs.

The argument a HGV doing 56mph vs a tractor at 20mph also doesn't tell the full story. Dynamic load amplification is a very complex issue and is a big reason for the safety margin, not the static load itself. On a bridge like this that appears to have a narrow, curved approach a significantly reduced speed will have likely been consider I would guess to a degree that a lorry and tractor could very feasibly be assume to pass over the bridge at the same speed.

Finally, the issue is how the bridge could fail. It's not all about what's the worst case load that can be thrown on there. From the images (very limited view) it looks as though it could be a deck supported on steel sections due to the use of steel parapets and low profile (could be very wrong). To me straight away fatigue could be an issue and that's one of the most dangerous failire types you can have. That 'once in a while' big tractor induces a huge stress cycle on components which is what causes the greatest fatigue damage. The problem is this is very hard to predict and you'll be fine going over numerous times prior, until one time after stress fractures have formed due to this, something will fail. Failure for a bridge like this would likely be sudden and lead to total collapse and potentially fatalities as a result. That's not to go through all the other failures that could occur due to exceeding the weight restriction.

I would like to say that I don't mean this to be a personal attack, but want to highlight the severity of the consequences that these actions could have.

Are you one of those guys who say St Pauls cathedral wont stay up because the computer says no?

 

[Tarw Coch]

Are you one of those guys who say St Pauls cathedral wont stay up because the computer says no?

Speaking of which, the farm where I grew up had a bridge virtually right outside the farm gate.
When I was a youngster they put a 15 ton weight limit on it because some expert had calculated it should collapse under its own weight. Closing the road wasn’t really an option and as ever, they hadn’t got the money to rebuild it.
40 odd years later it’s still standing there.

 

[Exfarmer]

Are you one of those guys who say St Pauls cathedral wont stay up because the computer says no?

The world is full of masterpieces of ancient engineering which engineers do not know how they stay up.
However , what we do not see is all those which fell down

 

[hutchy143211]

Are you one of those guys who say St Pauls cathedral wont stay up because the computer says no?

I'd like to think not but things aren't as black and white as that in structural engineering. I'd be very cautious as I'm a young and unexperienced engineer relatively compared to my colleagues who've been at it for 20-40 years. Their the ones who make the calls of reasonable judgement when things aren't straight forward.

However, regardless of that every point I have raised is based on engineering fundamentals and a relatively simple structure aren't designed for some ridiculous event to happen and have a point at which they fail.