Detensioning Failure

Question

I have a single span bridge using I-girders that I need close to the max amount of strands in. These are all straight strands, and I've had to debond to 4 different lengths from the end. The longest debond is 25' of my ~90' girder. When I look at the beam results, I'm seeing failures during detensioning that I don't understand. It looks like my beam is failing at the bottom due to tension after the first pair of strands is cut. The first pair cut is the outside of the bottom row, that do not have any debonding. Can anyone explain how this failure is occurring, or is it a software glitch?

Dilip Matange [Bentley] · Accepted Answer

Detensioning is a simulation of strand cutting operation. It represents the state of stress at the top and bottom of the beam as each group of strands is cut or detensioned. Generally this is of importance only to fabricators or consulting engineers designing straight patterns with debonded strands. To resolve the issue you will have to either change the order of the strand group in Strand Pattern > Debond Pull % dialog or increate the concrete strength a little.