Bridge weight capacity 3

You haven't posted enough information. What type of bridge?

You may also be over the legal road weight which may require you to obtain a special transportation permit for your load.

Contact the DOT where your project is located and inquire about a permit and the bridge capacity.

Huge load difference... more axles may not help...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

It's a complicated problem. We simplify things by load posting bridges for a certain tonnage but it says nothing about the axle spacing. Bridges are typically posted in the US for what is known as Legal Loads. This group of trucks have their own axle spacing and load distribution. What you are talking about sounds more like an overweight Permit truck. You can typically put more weight on a bridge for a permit truck than for a Legal truck because you can play with the axle spacing, speed of the truck, and possibly provide traffic control on the bridge to ensure that only the Permit truck is present at the time of crossing. However, the only way that you are going to know whether or not you can cross is to apply for an overweight permit for your truck. Whoever owns/regulates the bridge should be able to check this. The permit application sometimes covers their expenses. Another way may be to hire a local structural engineer who specializes in bridge design to check it and submit supporting calculations as evidence that it will pass. Being in a developing country, it may unfortunately may be more difficult to get your permit.

The 42.5 T rating doesn't say much. It could be the equivalent of the AASHTO Inventory Rating or the Operating Rating. It could be some sort permit vehicle.

It could be a somewhat iterative process to arrive at an answer. Are you the trucker who is shipping this thing? Does this fit on a trailer or do you need dolleys? Once you have a scheme for shipping the load, analyzing the girder is easy. You can adjust your load factors if the truck will be the only one on the bridge. If the analysis shows the girder can't support the initial axle road, look at a different trailer with more axles and repeat the analysis.

Australia?

I think StrctPono has the most direct answer --

You'll either have to ask the government body responsible for the bridge and/or hire an experienced local bridge engineer to check for you. (Experienced because it's not a straightforward problem to solve efficiently, local because they'll likely need to inspect the bridge). 42.5t to 80t is quite the stretch, but depending on the bridge and methods allowed, not impossible.

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just call me Lo.

What do you mean by "a total of" 80T?

One load/ trailer or?

You will need more axles anyway for the road axle limit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

"Developing Country" raises all sorts of alarm bells to me:

See, you have (correctly) identified (a single) bridge load limit that you need to exceed - by twice its normal rated load. The other comments above (correctly) address ways to be able (maybe) safely get over that one bridge.

But your load is threatened by EVERY other bridge, under-strength culvert, railroad crossing, raised roadbed, gravel or old embankment, pothole and sink hole, diversion ditch or side road and buried pipe UNDER every road between loading point and job site. Look also at overhead clearances and dangling wires between loading point and job site. Developing countries are notorious by "locally stringing" (illegally tapping power lines or overloading and bending telephone/power poles alongside and across the road itself.