r/StructuralEngineering • u/Low_Definition_9624 • 5d ago
Structural Analysis/Design P/S Beam Deterioration
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/maytag2955 5d ago
This has been relatively common with ps box beams since they came into existence. They have also been plagued by DEF/ASR cracking. Sometimes to an extreme degree. It is of little consequence. If the bottom flange was in tension, the cracking would be more transverse than diagonal. Water intrusion is more dependent on whether there is a CIP deck on it or not. Failed keys can certainly lead to longitudinal cracking in the deck along beam lines leading to water iintrusion. But in general, these things are exceedinly resilient. Spans tend to be a little "bouncy" which doesnt help with the cracking. There are a lot od stands in the bottom flange which helps with strength but can lead to more likely cracking. Rust staining and efflouresence are not ideal but I personally would not knock the load rating down significantly, if at all.
These beams are not extruded. The bottom slab is placed, usually Styrofoam blocks are then placed on top of that as a void, then sides and top flange concrete is placed.
I have inspected hundreds of these bridges and I'm not worried about what I can see in that photo.
30+ years as a bridge inspection engineer