Another bridge building question...

[LD1]

Holy moly, LD1 -- this fellow Buckeye thanks you for that wonderful tutorial! I truly appreciate it! I missed a few steps due to my unfamiliarity with it, and that makes all the difference.

Based on what these calculations are showing, I'm happy to read your assessment that the beams won't be the weakest link. And I somewhat agree with you that two beams should be enough, but with the way scrap prices are these days, it might not be that big of a hit to the wallet to just keep the extra two. At any rate, it's time for me to sharpen the pencil a little bit and spend some time with a structural engineering firm to figure out our best options.

Thank you so much to all for welcoming a newbie! Any and all ideas are still welcome....and certainly appreciated.

Thanks for the tutorial, it let me check how a beam I have would work for a cider press (very well) and how it would work for another location to help in the house

Aaron Z

No problem. ITs a pretty simple program. The stress, and deflection are both things that arent difficult to calculate by hand and its nice to know how to do it, but this takes all the guess work out. Thing I like most is their pretty extensive list of beams, channel, and angle iron.

And like I mentioned, if you know a little about what you are doing, and know some specs of wood, (or any material for that matter) you can use that program as well.

 

[LD1]

Isn't there a difference between static and dynamic loading?

Don't forget live loads for a bridge with vehicle traffic -- that is an important factor.

Aren't there also buckling considerations that are required?

Yes there is a whole lot more to it than just the static load the beam will hold. I am not worried as he is already said he is talking to an engineer. He was just wanting a little info so he can be better informed when talking with them.

Dynamic loading is impossible to figure. Too many variables. How fast is that concrete truck going to be moving when hitting the bridge, and any sudden elevation changes before/aft the bridge? or a perfect flat transition. Are they gonna have cheater axles down to help distribute the load? Thats why it will usually just be built with a safety factor. Those beams have a safety factor of at least 4x if only using 2. And thats only for 80k trucks. For most of the traffic the bridge will likely see, probably a 40x safety factor.

 

[Streetcar]

An engineer will want to know what material you already have for the bridge and what condition they are in . The live loads and dead loads have different multipliers or safety factors when used in the design calculations. Will your bridge be in the flood plane of the stream. A concrete deck will help with lateral restraint of the beams. Do you have access to both sides of the stream?

 

[RedNeckRacin]

A word of caution to anyone using that beamboy program. It will not tell you everything. It is designed to be used by a competent person who understands the limitations of the program. There are several failure modes that need to be evaluated individually for structural members. Deflection is not the only concern. :thumbsup:

[/rant]

 

[Egon]

I

Yes there is a whole lot more to it than just the static load the beam will hold. I am not worried as he is already said he is talking to an engineer. He was just wanting a little info so he can be better informed when talking with them.

Dynamic loading is impossible to figure. Too many variables. How fast is that concrete truck going to be moving when hitting the bridge, and any sudden elevation changes before/aft the bridge? or a perfect flat transition. Are they gonna have cheater axles down to help distribute the load? Thats why it will usually just be built with a safety factor. Those beams have a safety factor of at least 4x if only using 2. And thats only for 80k trucks. For most of the traffic the bridge will likely see, probably a 40x safety factor.

There is a little more to bridge design than picking a safety factor out of the air.

 

[vtsnowedin]

I

There is a little more to bridge design than picking a safety factor out of the air.

Let's not get too convoluted here. The common safety factor for decades has been three. That allows for a lot of rust and other abuse before failure. Somebody fabricated these beams for the span length they are. Cut them off a bit shorter and you increase the safety factor. Try to weld a couple of them together and increase the span and you might have a problem but shorter is obviously better.

 

[Streetcar]

Let's not get too convoluted here. The common safety factor for decades has been three. That allows for a lot of rust and other abuse before failure. Somebody fabricated these beams for the span length they are. Cut them off a bit shorter and you increase the safety factor. Try to weld a couple of them together and increase the span and you might have a problem but shorter is obviously better.

typically beams like this are salvaged from another structure. You do not know the span length or spacing on the beams originally. There is also the weight of the beams and deck to support. An engineer will review several loading cases to determine what is the controlling factor for your bridge

 

[LD1]

I

There is a little more to bridge design than picking a safety factor out of the air.

That is why the OP is going to talk to an engineer. I dont know what kind of safety factor he is going to require.

But the beams he has, there will be a 4x safety factor for an 80k truck. If the engineer happens to require more than that, he may rate the bridge for less, or offer suggestions.

Engineering a bridge for a specific load certainly aint rocket science. He has some pretty large beams. He is gonna talk to an engineer, come up with a plan for footings and decking, and the bridge will be rated for a given load. Pretty simple.

 

[RedNeckRacin]

That is why the OP is going to talk to an engineer. I dont know what kind of safety factor he is going to require.

But the beams he has, there will be a 4x safety factor for an 80k truck. If the engineer happens to require more than that, he may rate the bridge for less, or offer suggestions.

Engineering a bridge for a specific load certainly aint rocket science. He has some pretty large beams. He is gonna talk to an engineer, come up with a plan for footings and decking, and the bridge will be rated for a given load. Pretty simple.

Its not child's play either. There is a reason engineers have a 4 year school and a 5 year apprenticeship program to get their license to certify these structures. Plugging in numbers is simple. A simple beam calculation is simple. There is a whole lot more that goes into it than that.

 

[Sodo]

There is a reason engineers have a 4 year school and a 5 year apprenticeship program to get their license to certify these structures. Plugging in numbers is simple. A simple beam calculation is simple. There is a whole lot more that goes into it than that.

True, but that allows an engineer to optimize. For example aircraft must be optimized for weight.vs.strength and the difference is payload, range and service life. When you already --- have --- the materials, just about all you need is validation. If the materials exceed the safety factors then it gets pretty simple. Perhaps within the realm of forum engineering. Adequate bridge designs happen all over the world without engineers or beamboy.

Your point is understood for "other projects".