build a bridge, get over it

[beenthere]

How do you allow for temperature expansion and contraction in the steel that will occur between winter temp and summer temp's? I'm not an engineer, so don't know what that steel expansion will be.

Also, will there not be any ground freezing and thus moving of the concrete abutements? Or will the stream keep the ground thawed under and behind the concrete?

If the concrete moves, will it shear the bolts off?

 

[beenthere]

Anxious to hear how you will fasten the ties down to the I-beams. Also, what will you deck the bridge with, over the ties? Seems there is quite a bit more hard labor that you will be doing to finish this project, but looks like it will be a great bridge when you are done.

 

[Gatorboy]

I think he will have to drill a hole through the tie, and through the beam and then bolt them down.

Here is a picture of a <A target="_blank" HREF=http://www.pbase.com/image/504780>bridge</A> my neighbor built. He used 8x8 ties, and put nothing on top of them. I guess he could have put some 2x8's where the tires would go -- that would reduce the wear on the ties, as well as quiet the ride.

 

[AZMike]

You have the start of a very nice bridge. It appears that you have both sides of your beams bolted down. If so, I would highly recommend that you consider leaving the beams on one side of your bridge able to expand or contract in accordance with your local ambient temperatures. If you don't, its likely the bolts will shear off. It could also severely bend them and/or result in movement of the piers. I recommend you verify your design with the local highway department engineering group. They may suggest a different bolting method as well as placing a pad of some sort, teflon maybe, under the beams to insure reduced friction with they slide. I would hope they could suggest an easy fix as you don't have to comply with highway standards. Good luck!!

 

[MRHURT]

yes i thought about the expansion and contraction, there are some what of a slot cut for the bolts instead of just a hole.
in all the bridge failures i have seen in the past, none were bolt failures, most all were foundation failures.

 

[hazmat]

<font color=blue>yes i thought about the expansion and contraction, there are some what of a slot cut for the bolts instead of just a hole.
in all the bridge failures i have seen in the past, none were bolt failures, most all were foundation failures</font color=blue>

How big are the slots? Did you leave the nuts a little loose, or torque them down tight.

The reason you see a lot of foundation failures is because the weakest link will break. Most bridges are built in the summer, When it gets cold the steel beams shrink and try to pull the concrete towards the stream. This loads the concrete in tension, and it breaks. Concrete is very weak in tension (compared to its compressive strength) that is why you put all that rebar & mesh in it.

Here are some calculations:

Coefficient of Thermal Expansion for A36 Structural steel 6.5e-6 in/(in-deg F)

Lets say your temp range is 100 degrees (you can probably find the actual at your local library or NOAA)

20Feet *12 inchs/foot *100 Degrees * 6.5e-6in/in-degree F = .156" (5/32")

So for 100 degrees you'll see the steel change 5/32", for 200 degrees it would change 5/16". If your slots are big enough, you'll have no problems/w3tcompact/icons/smile.gif. Just leave the nuts loose. They should be just touching the I Beam. You can spot weld them or use nylon lock nuts if you are worried about them vibrating loose. If you tighen the nuts they have a tremendous amount of clamping force, and corresponding friction & therefore won't let the bridge move.

Enjoy the bridge, it looks great/w3tcompact/icons/grin.gif

 

[MRHURT]

ah yes stainless steel nylon nuts to be exact

 

[MRHURT]

bridge with first real test

With all the snow and rain we have had my bridge got its first real test of high water, the water is about two feet deep here and moving very fast. bridge did very good, but this was not as high as flood of 85 would have to add about another foot of water to match that level.

 

[Boondox]

Re: bridge with first real test

I love that bridge. It appeals to the puttering desire to build in me! /forums/images/graemlins/grin.gif Nice work!

Pete

 

[normde2001]

Re: bridge with first real test

Nice job, can't wait to see it finished. If you had not hit solid rock when digging for the foundation, how deep would you have had to go for proper support. I am considering a similar project in the future.