Negative Moment Capacity - Str I Postive Region

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Negative Moment Capacity - Str I Postive Region

My Spec Check Report indicates that there is not sufficient Negative Moment Capacity under Strength I Final with LL. The failures occur in the postive moment region. As I see it, my results for phi*Mn indicate a sufficient capacity (i.e. a larger number than Mu), which are both postive values.

However, the output report states that these checks fail. I'm wondering if the check for negative moment is looking for negative values of phi*Mn less than negative values for Mu, which would be correct for negative moment regions. The same check for postive regions gives a fail because the phi*Mn is not less than Mu, but according to design practice the phi*Mn should be greater than Mu.

Have I misinterpreted my report output? If not, one possible solution in future releases would be to compare absolute values of phi*Mn to Mu in the Negative Moment Capacity checks.


Brent Whitcomb

Rick Brice
Brent,   If you send me your

If you send me your file, I can look at the specific issue. A fail usually occurs in this situation when the moment capacity does not exceed the minimum required moment capacity. That is, Mu is greater than phi*Mn, however phi*Mn is less that Mn-min which is 1.2Mcr or 1.33Mu.
Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office

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