Hello--
Does PGSuper calculate the secondary effects due to creep and shrinkage on multi-span bridges at the piers? And to what extent are PGSuper's capabilities in regard to the secondary effect?
Am looking for the positive and negative moment demands at the girder ends due to creep and shrinkage. Is this reported in PGSuper? Am looking at the negative moment demands over the piers, and it is not clear if creep and shrinkage are considered.
Thanks
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 End Moments | 26.5 KB |
The short answer is that PGSuper doesn't directly support these secondary effects, however they can be modeled through the use of user defined end moments.
The current AASHTO LRFD has a bunch of requirements about age of girder when continuity is established (90 day rule), degree of continuity at various limit states, and exceptions when secondary effects can be ignored. Bridge Owner policies regarding this are varied.
The method of predicting restraining moments is not a clear standard either. Many like to use the RMCalc program described in "Resolving Restraint Moments: Designing for Continuity in Precast Prestressed Concrete Girder Bridges" Jul/Aug 2003 PCI Journal (https://doi.org/10.15554/pcij.07012003.104.119)
AASHTO has adopted new provisions for restrain moments that eliminate the 90 day rule. The new provisions are based on Tuan et. al. (https://doi.org/10.15554/pcij63.4-04). We will implement this method when AASHTO publishes LRFD 10th Edition.
Thank you for the clarification.
Following up on this discussion. I have placed end moments and it does not look like they are correctly superimposed onto the entire girder. I only see a point spike at the supports from the additional end moments for the negative moment demands (see attachment, added to main post above).
The positive moment demands seem to have been properly superimposed, but can you verify this is the case?
I am currently still using version 6.1.0.0 so to not change workflow. Side question, is PGSuper fully backwards compatible between versions?
Thanks
This is a rarely used feature so there may be a problem. I'll look into this and get it fixed if needed.
For file compatibility, you can always open a PGSuper file created with an older version in a newer version, but not the other way around.
I've been looking into modeling restraint moments in PGSuper - this is something that isn't standard WSDOT practice and doesn't get much attention. By our design practices, we don't need to satisfy the requirements of LRFD 5.12.3.3.
Here is some information about how PGSuper addresses the requirements of 5.12.3.3
https://www.wsdot.wa.gov/eesc/bridge/software/Documentation/PGSuper/7.0/...
Using concentrated moments for restraint moments works, but with a caveat. The concentrated moments need to be applied at the deck casting event (typically Event 5). That is the best quick fix we could come up with for the 7.0.2 release (releasing week of Nov 7).
The entire concept of restraint moments will be revisited and the implementation will be updated for AASHTO LRFD 10th Edition based on the references I cited in an earlier post.