How much weight will this carry now? 7

[snapped01]

Hey everyone! I'm Kevin and new to this forum, i'm a mechanical engineer mainly doing sheet metal design, but now i'm finding myself needing the expertise of civil engineers. There is a property with a bridge and it looks to be in pretty weak condition. The plan is to beef it up so that it will allow a dump truck or something similar to pass over to the other side in order to start construction. Can anyone share any input? anything will help.

Here are the details:

Concreted poured foundation on each end of the span. 22” inch exposed above grade and 36 inches deep and 12 feet long. The support beams upright sit on this foundation which is on opposite banks of a creek.
Length of span end to end 250 inches.
Support I Beams on each end as follows:
• Two on one end 8” x 6.5” and 88” tall
• Two on opposite end 8” x 6.5” x 57.5” tall
Cross bean on top of the two support I Beams above.
• One I beam on each end on top of the support I beams that are 6.5 inch by 8” and 153 inches long.
Large Span I beam sitting on top of the cross beams
• 5” wide by 14” tall by 250 inches long
• There are five of these.
Top
• 1.5-inch-thick grates.

Question
• How much weight will this carry now?
• How much would it carry if I did the following:
o Add three more 250 inch long I beams!
o Add two more beefier upright posts and heavier cross brace.
o Add other diagonal bracing.
o The key here is will the footing carry the load of ideally 40 tons or more.

 

[Lomarandil]

The short answer is that you're going to need to hire a local structural engineering company with some experience in bridge inspection or bridge rating. They'll need to be local, because they'll want to get their own eyes on the deterioration, and you'll need someone who understands the local ground conditions (and they'll probably want to perform some testing on-site).

Without that information, I don't think anyone will be able to directly answer your questions about the weight limit of this bridge.

 

[SWComposites]

Agreed. Get a local structural/bridge engineer out there.
I would probably walk across that bridge. No way in **** would I drive a 40 ton truck over it.

 

[PEinc]

Abutment is failing. Beam condition won't matter if an abutment collapses.

http://www.PeirceEngineering.com

 

[LittleInch]

Well I sure wouldn't be standing on the edge of that like your colleague is!

Those main beams look rather weedy to me.

I would paint wheel tracks onto the grating between those two beams. Anywhere else you're using the strength of the grating and its fixing to something. Not good.

At best this is probably 5 tonnes at the moment but don't quote me.

40 tonnes is going to break something. Either the rather agricultural looking facing of the abutmentments, the foundations or the vertical supports.

Who knows if that foundation has any rebar?

Who knows what the backfill is inside the ramp out how rotten all those trees are.

I can understand why you want to try and use what you have but this will simply turn into a money pit. Build a new one from scratch.

No one is going to certify this for anything other than cars or very small trucks.

And I would ban people from walking across it.

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

 

[AS_PEng]

It a simply supported structure with multi girders. It should be easy to evaluate for an experienced bridge engineer, which I strongly recommend retaining to ensure safety for users. One word of caution: without having some information on the piles embedded depth, blow counts during installation or detailed geotechnical investigation, it's unlikely the bridge foundation can be evaluated, and the owner will assume the risk for the buried portions of the structure.

It'll be interesting to see the result of the evaluation. Keep us posted.

 

[SlideRuleEra]

Large Span...
• 5” wide by 14” tall by 250 inches long

With some reasonable assumptions, finding the upper bound of the beams (when new) load rating using the information provided is straightforward:

1) W14s with 5" wide flanges have been around since the early 1970s (first appeared in AISC 7th Edition). The only two sizes are (and have been) W14x26 and W14x22, I'll assume W14x26 @ 20 ft. long.

2) Assuming the structure was constructed between the early 1970's and late 1990's, the steel used was most likely A36. Design could have been LRFD after 1986, but I'll assume ASD (Allowable Stress Design, per AISC 9th Edition).

3) Per photos, only meaningful lateral bracing at mid-span (10.0 feet unbraced length).

From the graphs for "Allowable Moments In Beams", page 2-174, a (new) A36 steel, W14x26 with an unbraced length of 10.0 feet is ok for a moment of 47.5 kip-ft.

That means the beam (when new) is rated for a mid-span point load (simulating a truck tire) of 9.5 kips (47.5 kip-ft = P x 20.0 ft / 4), solve for P.

My advice to the OP, forget this project.

 

[LittleInch]

Also what exactly is actually holding that grating down?

You have a large cantilevered section of grating whih appears to have very little connecting it to the beams??

Even if the panels are bolted togher to form one sheet, that is not a stable platform able to hold any significant load.

I wouldn't even walk on any unsupported bit of grating ever and would strongly advise you to close this bridge to traffic and pedestrians. Removing the grating is the easiest way.

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

 

[IFRs]

 

[LittleInch]

I think the OP has fallen off the bridge...

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

 

[ACtrafficengr]

The short answer is that you're going to need to hire a local structural engineering company with some experience in bridge inspection or bridge rating.

In the second and last photos, is that column out of plumb? Maybe OP should hire an engineer to replace the bridge with a large culvert.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[BAretired]

I agree with SlideRuleEra. No engineer in his right mind would undertake such a project.