Building A Bridge

[Blk88GT]

I'm sorry, but this thread is hilarious.

I have nothing of value to add, other than I'd love to have a bridge and I think it's awesome you're going to use that one.

I'd use it and never look back.

 

[schmism]

In the courtroom:

"Mr. BridgeOwner, did ever contemplate the consequences of this bridge?"

IS that like "if a tree falls in the woods, does it make a sound?"

"i dont understand the question, can you please rephrase" would be the correct answer...

9. A Coal Mine operates a NFPA Class 1, Division 2 Hazardous Area.

Before i was in trusses i worked for Killark designing lighting for hazardous locations. I acutally know what a Class 1 Div 2 enviroment is!

 

[KentT]

My recommendation: Forget the Loads it will handle for now, get yourself a savvy Insurance person, and get it Insured. By virtue of having the insurance, you will end up with the proper safety inspections and documentation.

Why not just jump straight to the lawyer and get his advice -- bypassing another "potential middleman" of the insurance company -- since fear of litigation is your motive?

I'm glad a culvert met my needs, but I guess I should be so concerned that someone will drive off the edge of the driveway crossing it where it's about 6 feet above ground level and doesn't have a guardrail, that I should just require everyone to park on the road and hike in...

Geez.........

 

[sandman2234]

Between the lawyers and the engineers and the insurance people and us, I know why he has been using a low water crossing!
David from jax

 

[pat32rf]

Up here in Ontario the Min. of Nat Resources would soon put an end to that "low water crossing". They would also demand a work permit before the bridge was installed.

 

[koop]

Koop,


Nothing personal, but I think VDOT was crazy to sell that bridge to a private individual for anything other than scrap.

Why?
This bridge was in use up to the day it was moved.
Less than a year ago, VDOT had the bridge inspected and it was given a 7 ton rating in its current condition. One concern mentioned in the report was the condition of the crumbling stone abutments. The report also stated the average traffic volume was 300 - 400 cars per day.

So I ask why is this bridge only good for scrap? It will be repaired, painted and set on brand new abutments. Not to mention, on a heavy traffic day, there might be 6 trips across.

I would like to help clear up some of the assumptions being made.

The bridge weighs approximately 68000 lbs.

Because this bridge spans bank to bank, we should not need a permit, although we are waiting for this to be verified by the appropriate agencies.

The bridge spans the head waters of a small river with average depth of 12" - 18". The bottom of the bridge will be set about 6' - 8' above the river to ensure good flow beneath the structure during high water events.

The low water crossing is sufficient at the moment because it is only used a few times a year.

Perhaps the worst assumption to be addressed is from Kendall69. This forum is a great way for me to hear the perspectives of other members, even if I disagree with them. I really appreciate the input from critical thinkers (Toiyabe). I don’t see the value in those who choose to respond to my questions by assuming I am an idiot who wants to cut corners to hurt my family and friends and that the forum is a useless tool with which to gain information to assist in making a sound decision. You think that in asking my question I am analogous to a drunk driver etc, shows you think the worse of people and Tractorbynet members and that is a shame.

 

[Toiyabe]

I think that VDOT should have scrapped that bridge before letting a private individual get a hold of it for liability concerns. It would be a shame as it is a very nice looking bridge, but it has a great potential to cause harm if used inappropriately.

My wild guess of 50 tons was wrong. Still, the fact that it weighs 34 tons but is only rated for a live load of 7 tons should clue you in to the fact that you are dealing with a structure on a different scale than most people are used to.

There is something sometimes called the "square-cube law". It states that the strength of a structure increases as the square of its length (cross-sectional area) whereas the the weight increases by the cube of the length (volume). So as things get bigger, they get heavier much faster then they get stronger. It isn't strictly true, but is good for mental approximations. The upshot is that big structures don't behave like scale models of themselves, although people often think that way. That way of thinking can lead to big trouble.

This is a very difficult thread to be involved in. I have an ethical requirement to urge you to seek professional advice while not giving you anything that could be seen as professional advice.

 

[Renze]

I have an ethical requirement to urge you to seek professional advice

Some hilarious replies were already made, but this one just tops it









... just kidding.
btw, good point about the square-cube law. Translating it into everyday language, it means that when doubling the span of the beam, the bearing capacity reduces to 1/3 or am i having my maths wrong ??


Do you guys in America have the same standardised hot rolled steel profiles as we have in Europe ?? If you can give me the steel profiles and steel type, i can put it into my construction program... But i dont know what loads should be calculated for bridges as i usually just calculate trailer frames, for which are no prescribed load situations, just common sense.

 

[koop]

Renze,

You have seen the picture, I can give you the dimension of every piece of steel you see. Just let me know. I would love to see what your program comes up with.

It would appear I need to reassure everyone that if your program says 40 ton weight limit that I am not going to invite every tandem axle dump truck with 4 pony axles and 23 tons of gravel to come test your results. LOL

 

[Toiyabe]

The square cube law would state that if you double the scale of a structure, the weight would increase by a factor of 8 (2^3), while the cross-sectional area of the members would increase by a factor of 4 (2^2). Cross-sectional area is proportional to strength for members in pure tension, for members in bending or compression it is more complicated. The actual change in live load carrying capacity would vary based on the ratio of dead load to total load.

The square cube law isn't something to be used in actual calculations. I only brought it up as one reason why extrapolating from experiance with small structures (such as trailers) to large structures is dangerous.

Unless you specify your steel shapes in inches of depth and pounds per foot of weight, I doubt the hot rolled sections are the same in the US as in Europe. Steel grades are also different. Based on the photo, I doubt that it is made from current standard sections.

Computer programs are garbage in garbage out. Unless you know how it works, you are not likely to get the right answer. And without experiance in the field, you won't know what the right answer should look like.