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Broken plate or broken casting?

Broken plate or broken casting?

Broken plate or broken casting?

(OP)
Take a look at the attached photos; two things are bothering me. Last week during a bridge deck demo operation four adjacent brackets failed in the same manner. The “plate” that failed was bolted to the girder to hold the bracket in place. There’s a photo of each; Photo 5 is a rotated close up of Photo 1.

First, based on the photos, the “plate” looks like a casting. I spoke to the manufacturer and was told that their plate and the mating washer (two serrated surfaces) are made of 1081 steel. I was also told that if the mating washer wasn’t in place the plate can fail in bending. Second, it doesn’t look like a bending failure to me, more of a brittle fracture. The capacity of the plate is based upon the capacity of the brackets; the brackets were rated for about 4k working load.

I’m not tasked with investigating the failure. It was sent to me for an opinion. No one knows how much load was on the demo shield, or what was going on at the time, or if the washer was in place - looks like Sgt. Schultz was on the job - and no one has gone out to look for the broken pieces.

Thanks for your opinions

RE: Broken plate or broken casting?

Hi bridgebuster

Looks like a brittle fracture failure to me too, if it were ductile I would expect to see some distortion.

It would be interesting to see where the bolts were positioned in relation to the cracked plate any chance of that and possibly a sketch of how the bracket and plate are orientated at the time of failure with some indication of where the load was acting at the time.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Broken plate or broken casting?

A flat plate wouldn't normally be a casting, but in a couple of those pictures, you can see that it is not a plate, but a 3-dimensional piece to allow a bolt to run at right angles to the other bolt hole, and there, it does indeed look like a casting.

I'd wonder if you maybe you and the manufacturer weren't talking about two different pieces or whether somebody had substituted parts or something like that.

The manufacturer said it was 1081 steel- did they say if it was cast or forged or what?

RE: Broken plate or broken casting?

bridgebuster - The photos look like "overhang brackets" for supporting forms for the bridge deck outside the outer most beam. If the brackets were overloaded, they may have pivoted about the lower contact point causing the plate (in the red rectangle) to fail in shear:

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RE: Broken plate or broken casting?

(OP)
Thank you for your thoughts.

I may be at the job site this week for another issue. If so, I'll try to make my way to that part of the project to get some more info. To me it's potentially serious issue because there's about 2000 LF of deck demo in that section; there's several hundred brackets in place. I was able to get my hands on the shielding design. The "plate" has a ultimate capacity of 8k with a FS =2; maximum vertical load on the plate is 3k.

desertfox - when I first saw the photos I was thinking back to strength of materials lab, we had to test a lap joint - with a single rivet - in tension. The plate failed along the rivet shank but I recall it was distorted.

jstephen - the manufacturer said it's a machined plate not a casting. It wouldn't surprise me if the contractor pulled a fast one.

SRE - that's the location of the failure. I like your theory about shear failure. I was looking a images of Charpy tests and there is a similarity in the appearance along the failure plane. Perhaps there was a sudden loading and they didn't have the mating washer in place it may have caused the plates to shear.

I hope the field staff investigates this thoroughly

RE: Broken plate or broken casting?

(OP)
I saw the report today on the failure:
    It was a brittle fracture,
    It was a casting, and
    It was a bracket from a different manufacturer than shown on the plans

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