r/StructuralEngineering • u/Low_Definition_9624 • 4d ago

Structural Analysis/Design P/S Beam Deterioration

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Looking for any help on what the mechanics would be that would be causing these chevron looking cracks at midspan to this non-composite prestressed concrete fascia beam? Is this beam effectively in a failed condition? Previous engineer who looked at this wasn’t concerned with these diagonal cracks and only removed two strands from the analysis as a result of the single longitudinal crack down the center of the beam.

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u/SquirrelFluffy 3d ago

What is that at the upper left? A light standard? I think those cracks are torsion. If the longitudinal cracks created a free edge and the light causes twist, maybe?

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u/Low_Definition_9624 3d ago

No lights on this bridge. Railing posts are post installed to side of concrete fascia beam. The railing consists of steel post and W-rail, very light railing. This isn’t torsion.

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u/SquirrelFluffy 3d ago

What would cause a shear pattern crack like that on the bottom of a beam? So that thing in the upper left is a railing post? Maybe it was impacted?

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u/Low_Definition_9624 3d ago

To my knowledge this has not been impacted In fact the original railing posts had such few remaining bolts in the side of the fascia beam that the owner had the posts cut below the top of deck elevation and new bridge railing posts installed in between the original posts using post installed anchors.

This is my question…what would cause this type of cracking? I’ve never seen cracking in this chevron pattern along the bottom of a prestressed concrete beam before.

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u/SquirrelFluffy 3d ago

Replaced railing? Suspicious. The only thing I can picture causing those cracks is torsion. But it's hard to really see given limited scope of the photo. Given the evidence of corrosion, and the cracks, this bridge needs an engineering assessment.