oak island bridge collapse

huangyhg

oak island bridge collapse
video of oak island bridge collapse. i haven't been able to find much on what happened. it looks like they were setting girders at a splice and the splice bracket was bumped and gave way.  
here's another link:

apparently the girder was suspended at the splice with a strongback system overhead.  high strength hanger bars were welded at couplers, which compromised the strength of the bars. the bars snapped.
it appears from the photos forwarded to me that the rebar was just tack welded at the couplers. hard to believe that tack ate up all the safety factor.
i think something else was at work - the other hangers from the first girders set didn't fail.

jlnj,
i haven't seen any photos, but tack welds on high strength steel do a lot more damage than just decreasing the area.
i know welds can be very deleterious, but to cut the strength in half?
sorry about the file sizes! maybe i can resize and upload the others i have.
how do those couplers work? are they threaded, or is the weld the only thing holding them?  
jlnj,
it depends on the chemistry of the bars, but tack welding on some types of high strength bars can cause embrittlement, and the tack weld creates a stress riser, essentially destroying the bar.
the bars have a very coarse thread. i presume someone tacked the bars on one end to keep the coupler in place while the bars on the other end were screwed on.

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here's another link:
apparently the girder was suspended at the splice with a strongback system overhead.  high strength hanger bars were welded at couplers, which compromised the strength of the bars. the bars snapped.
it appears from the photos forwarded to me that the rebar was just tack welded at the couplers. hard to believe that tack ate up all the safety factor.
i think something else was at work - the other hangers from the first girders set didn't fail.

jlnj,
i haven't seen any photos, but tack welds on high strength steel do a lot more damage than just decreasing the area.
i know welds can be very deleterious, but to cut the strength in half?
sorry about the file sizes! maybe i can resize and upload the others i have.
how do those couplers work? are they threaded, or is the weld the only thing holding them?  
jlnj,
it depends on the chemistry of the bars, but tack welding on some types of high strength bars can cause embrittlement, and the tack weld creates a stress riser, essentially destroying the bar.