Overweight vehicle permits

[71corvette]

When considering overweight vehicle permit requests, are there are rules of thumb for when a load rating analysis is and is not required for the bridges on the planned shipping route?

Basically, I’m curious to find out when others have and have not completed load rating analysis before granting overweight permits. Any thoughts are appreciated.

Thanks,
Tim

 

[bridgebuster]

There's no simple answer. Your best bet is to contact your state DOT because some states have their own versions of permit vehicles as opposed to states that still use the Type 3-3 and 3-S2 AASHTO trucks or variations of those axle loads.

 

[LittleWheels]

It depends on how overweight the vehicle is and the known history of permit vehicles traversing the bridge. The vehicle arrangement, span length, bridge type, etc all influence the answer. Which country are you in?

 

[71corvette]

This bridge is in the US and the agency doesn't have any set standards. Do any agencies have their standards listed online?

 

[LittleWheels]

Disclaimers: My background for "Abnormal Indivisible Loads" (AILs) is UK based. I don't know what the bridge rating and assessment requirements are in your state.

Searching on "abnormal load" will give some background on the UK legal requirements there but doesn't answer your question.

https://www.esdal.com/public/index.html

is a UK system being introduced that will include appraisal using influence lines for comparison with existing bridge ratings and maximum axle loads.

If I were in your situation, I'd look at the known history of overweight vehicles crossing that structure first. It may have already been 'proof loaded'. If the bridge condition and loading is similar, the effects are likely to be similar.

Have a good idea how the structure is likely to fail under excessive vehicle loading (sagging, hogging, shear, punching shear, transverse bending, etc) and how your overweight vehicle compares to the rated load capacity. Influence lines may give you a quick and dirty comparison method, if required. To deal with this problem, my previous employer had a semi-automated system and, before that, comparison spreadsheets and extensive records of specific loaded vehicles traversing specific bridges.

If you are dealing with something that is a couple of tonnes over a standard vehicle, it would be rare for it to be a problem. If you are shifting 350-450 tonnes of loaded vehicle (eg transformer) over a new route, I would expect that some calculations would be involved.