Sizing of Steel I-Beams for Bridge

[BB_TX]

<font color="blue"> Pressure treated 2x pine is in no way, ever, good enough for a 2' span between your beams. </font>
Paul-I agree with the 2x and the span. I was thinking some additional support attached to the crossing beams, probably channel, running parallel between the lengthwise I beams. You can stand in the middle of an 8' 2x12 supported at each end with only a little flex. My thinking is that the inside I beams would be at the exact center of my rear tires. That way I could be off center by about a foot either way and the tires would still overlap the I beam. I would have to get well off center to get onto boards only.
I do appreciate yours, and all others, input. Keeps me thinking. Still in the theory stage right now. Have even considered using 6 I beams.

 

[poorboy]

I just floored our bridge last spring. It is 1205ft. long and 14 ft wide and about 50 ft. above water. The bridge was constructed with 4 14inch Ibeams. May be larger now that I think of it. But anyway we used 3x8 white oak timbers as flooring. The design was 4 beams evenly spaced and tied together with angle every 12 foot. these were 4inches below the beam tops. We then bolted 4x4's to the angle which brought the tops flush with the angles and running parallel with the beams. We then layed the decking cross ways and nailed them to the 4x4's. The boards have plenty of strenght for what we use it for. But for added strenght we could have used runners for tracks to even out the load a bit. But then we have to deal with the floor rotting where the lumber meets.

I need a picture it would take less time to explain and probably make a lot more sense.

Patrick

 

[Gatorboy]

I'd like to see a picture of your bridge. What is the load limit on your bridge?

 

[em14]

That's a very large bridge. I would also like to see this one to. Please post a picture. 50 foot above the water is a long way up.
Leo

 

[rtimgray]

It is 1205ft. long and 14 ft wide and about 50 ft. above water.

Is that right - 1205 ft. long supported by 4 14" I-Beams? There have to be a few intermediate supports, right? Or is it indeed a clear span? If so, where did you come up with 1205 ft. long I-beams?

 

[tbuff]

Doc,

everyone is correct on this one, 2" for a deck is too thin.

the USDA Forest Service engineering guide for Timber Bridges specs out a minimum 3-1/2" d nail laminated deck for anything over about a 24" span between beams. Nail laminated means just what it sounds like with2x4s standing on their side face to face. It also requires a higher quality lumber than just pine. Douglas fir-larch, southern yellow pine, or oak are good choices. (oak requires extra work to "nail") These designs usually accomodate a 12,000 lb wheel load.

Also, place additional lumber over the tractor wheel path on the girders. It does a couple of things, 1. protects the deck planks, and 2. defines the proper travel path across the bridge.

One comment on the steel beams, there are various types of steels used for these beams all with different corrosion characteristics and strengths. You should know what you have

To defend the engineering types, it has been my experience that most intented uses of structures change over time.
For example, I have seen a movable construction staging used for personnel installing rubber sheetmembrane get changed over to an installation and storage platform for stacks of 2" thick by 2'x'2 granite panels without anyone thinking about its actual load capacity. Fortuanately the movement mechanism faile dprior to the staging!. Small tractors get upsized to larger tractors, no?

I have also seen 12" steel wide flange beams turned into pretzels. When it does, it happens fast and catastrophically.

The point is, it is wise to hire a knowledgeprofessional for some things, bridge building is one of them. Remember, engineers, like doctors have professional liability $$$

Gatorboy - the last bridge I saw that long had steel cable stays and cost $60 million - of your hard earned taxes!

 

[poorboy]

I still don't have any pictures of that bridge and after that extra 0 in there I guess I never will. Oops! /forums/images/graemlins/shocked.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif

But even with the 125 ft. span there are three uprights in the span. I have to sleeve the one at the water's edge because everthing that comes downstream hit against it. I don't have a rating on it. But if I have have something very heavy we just drive the 5 miles around to the other side. We wouldn't have built one but since it was already there it sure was a buying point since it tied the 2 farms together.

A fellow can sure get in trouble by not previewing their posts! /forums/images/graemlins/blush.gif

Patrick