Capacity reduction for damaged girder flange 1

[foreng]

I’m looking for some information on dealing with the reduction in capacity of a welded steel girder, due to damage on the tension flange within the middle third of the span. The bridge girder is a fracture critical member (2 girder system) with a 15 m simple span. The bottom flange 19X300 mm has been bent from construction impact and has caused the edge of the flange to deflect approx 10 mm. What is the tolerance for this type of damage? Is there a resistance reduction factor that should applied a this point?

Also, the damage did not produce any fracture in the flange of at the web/flange connection.

 

[BAretired]

If the material has not been cracked, I would think the reduction in strength is negligible. If it has been cracked, it must be repaired.

BA

 

[Stillerz]

I agree...no crack then not a huge issue.
Members that are bent like this can be repaired very easily in the field.
10mm seems like a negligble amount of distortion.

 

[foreng]

Thanks, as there is no section loss I didn't think it was an issue.

 

[SlideRuleEra]

foreng - I totally agree with BAretired and Stillerz, and can offer offer a first-hand experience of the surprising capacity of damaged beams:

As a Bridge Contractor, in the 1970's we used HP 12x53 (A36 steel) as reusable, temporary falsework to support bottom forms for concrete bridge decks. Since an HP 12x53, used as a beam, is a non compact shape allowable stress is 22 KSI. Our crews were splicing (welding) short cutoffs of HP to create 27' long beams. Also there would be numerous holes in both the flanges and webs. Also, the flanges and some times the complete beam would get bent when the forms were removed (wrecked).

Back-figuring the stress in these "tortured" beams revealed a bending stress of 19.6 KSI (89% of rated capacity for new members). Never had a problem... of course we may have been using some of the intended safety margin (and not known it).

The bottom line is that, over time, I gained real "respect" for how well a damaged steel member can perform. They can look very bad and still be quite capable.

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