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Estimation of bridge load carrying capacityHelpful Member! 

phaadu (Civil/Environmental) (OP)
4 Mar 09 1:44
In the absence of design data, I will appreciate some help with some non-destructive tests to assess the load carrying capacity of a one span reinforced concrete bridge. Many thanks.
msquared48 (Structural)
4 Mar 09 2:45
How you goin' to determine that without knowing the reinforcing grade, size, pattern, and placement, plus the concrete and subgrade strength and capacity?  

Do you have access to specialized testing equipment to determine that, or is this where your question is really going?

Mike McCann
MMC Engineering

phaadu (Civil/Environmental) (OP)
4 Mar 09 3:07
Thanks Mike, I really could not lay my hands on the design data or as-built drawings and want to know if there are simple load tests which are of course non-destructive that can help to assess the load carrying capacity. The load that we want to move accross the bridge is 80 Ton
fattdad (Geotechnical)
4 Mar 09 8:52
Hire a structural engineer.

f-d

¡papá gordo ain't no madre flaca!

SlideRuleEra (Structural)
4 Mar 09 9:25
phaadu - Your problem can be solved, but not with a simple "pass-fail" test. This sort of thing is done all the time, but you have to get into the details...

1. How the load is distributed to the pavement is more important than the total weight (say the number of tires, tire spacing - transverse & longitudinal, weight distribution on the tires, weight of the transporting vehicle).

2. Length of the bridge (if it is "short" perhaps the full load will never be on the bridge at one time).

3. Approximate age of the bridge (if it was designed in the 1950's, or earlier the bridge is probably deficient in shear capacity (for heavy loads) since shear in reinforced concrete was not well understood then).

There are a lot of other factors, but try those for starters.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

Helpful Member!  Ron (Structural)
4 Mar 09 9:41
phaadu...we have done this several times using dynamic strain monitoring equipment while load testing the bridge using a loaded truck, typically a heavily loaded dump truck. While it is nice to have design data, it isn't absolutely necessary.

From the strain data, you can back into the capacity or anticipated capacity based on the load response.

Essentially bonded strain gauges are placed at various points on the bridge structure (primarily extreme fiber stress points in bending, but not the only locations), then the load testing is done with a moving truck load.  Data evaluation include developing load response curves and then fitting perceived design data back into the mix.  

You should also use some nondestructive measures to get rebar locations (R-meter, Rebar Scan, radiography, etc.) and determine the compressive strength of the concrete with cores if possible.  Most nondestructive concrete strength methods have to be correlated to cores for accuracy anyway.
BigH (Geotechnical)
4 Mar 09 10:27
You might wish to contact Dr. Andrezej Novak at Nebraska University.  When he was at Michigan, I know that he did such load tests of bridges - using M70 tank.
kslee1000 (Civil/Environmental)
4 Mar 09 15:38
Ron has covered all aspects of testing (very interesting).
Prior to that, you should do some research on design code used at the time of original design (could be AASHTO, or local/rural code), and estimate lane load. From which you can develop procedures and check against testing results.   
beton1 (Civil/Environmental)
4 Mar 09 22:42
Topic has been covered well with all the posts. The question I have, is you want to move a 80t load across; is this a one time thing as opposed to, say, getting a 'rating' of the bridge? Rural area? If the bridge is not strong enough, based on the methods noted, what is your option. Re-route or reinforce?  
Drumchaser (Civil/Environmental)
5 Mar 09 6:53
I agree with Ron.

(The original, or as-built plans would help.)
oldestguy (Geotechnical)
9 Mar 09 19:11
Now suppose you find the bridge can't take it, I'll bet these guys can advise on simple reinforcing on a temporary basis.

Depending on the structure's value, etc. can you get by having deformed it?  Going to yield in the steel?
kslee1000 (Civil/Environmental)
9 Mar 09 19:22
There are a few ways to temporarily support a bridge to carry the overload. For example - shoring, plating (thick steel plate or strips) in conjuction with lane & speed restrictions. All depends on how much is the overload, duration, and frequency of occurance.
jheidt2543 (Civil/Environmental)
12 Mar 09 11:21
Ron:

A corollary question, what is a ball park cost for a study of this kind?
civilperson (Structural)
12 Mar 09 13:30
$10,000 for a capability study and reinforcement plan. (Small simple bridge)
Ron (Structural)
12 Mar 09 16:37
jheidt2543...depends on the size of the bridge, but typical is about $10,000 to $12,000 but that does not include any remediation plan...just the data and analysis.  Anything over about 3 spans and the cost goes up quite a bit.  Further, if the water beneath the bridge is relatively fast, you will need a flat barge, which can easily double the cost.  Also does not include the cost of the loading vehicle, though that's not that much.  We've typically used a dump truck with approximately H18-H22 loading.

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