Document Information

Document Type: FAQ

Product(s): LEAP CONSPAN/Precast/Prestressed Girder

Version(s): All

Original Author: Bentley Technical Support Group - VM

QUESTION: How to get rid of high stresses for Precast Top - Negative moment envelope condition at Bearing Location?

ANSWER:

For a continuous span structure, CONSPAN checks the stresses at bearing location due to negative moments. If there is an tension overstress at top of beam due to the loading (negative moments) and there is possibility that sometimes it is not possible to rectify the situation by adding additional strands at the top of the beam.
This is because of CONSPAN methodology of considering an effective area of prestressing steel (reduced area, starting at 0 at beam end, and linearly varying to 100% at transfer length).

So no matter how many strands user adds, the prestress force/area is negligible at bearing location, and therefore the overstress is always flagged.

Generally the tensile stress at the top of the beam is a concern typically at transfer. Harping of strands is done to address this. At final  the deck steel should be able to control the crack widths over the pier. If there are high tensile stresses at the top of the beam and they must be reduced the only options would be increase the beam depth or concrete strength. Accounting for the transfer length is the right approach.