Please read FAQ's before posting

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Pickings
Please read FAQ's before posting

WSDOT has a large list of frequently asked questions (FAQ's) that you might take a look at before posting modeling questions to this forum. The FAQ list is at:
http://www.wsdot.wa.gov/eesc/bridge/software/index.cfm?fuseaction=FAQs&s...
 
Also, PGSuper's help system has a full theoretical manual that has in-depth descriptions about how PGSuper models bridges. Open the help system by pressing the F1 key from within PGSuper. A link to the Theoretical Manual can be found in the Table of Contents.
Please take a look!
Richard

gharrell
Time-dependent shrinkage loss

Shrinkage appears to be too high in the total time-dependent loss, DfpLT. The shrinkage strain computed at the "id" stage is used to figure the loss up to the time of deck placement. The shrinkage strain computed at final is used to compute the "df" shrinkage loss. Shouldn't the shrinkage strain at final be reduced by "id" shriknage to accurately reflect the additional shrinkage occuring between deck placement and final? As it currently reports, the total time-dependent loss includes "id" shrinkage in the "LTid" term, and it includes total shrinkage (made up of "id" and "df") in the "LTdf" term, effectively using 2*eid + edf in the total loss calc. Please verify.

Gregory Harrell, PE
HNTB Corporation

Rick Brice
Gregory,   I’ve reviewed the

Gregory,
 
I’ve reviewed the prestress loss calculations in PGSuper against the LRFD specifications and NCHRP Report 496 (the basis for the LRFD spec). PGSuper implements the calculation procedure accurately according to LRFD.  However, now that I’ve reviewed the LRFD against your assessment, it appears that the LRFD is incorrect.
 
LRFD defines the shrinkage strain with equation 5.4.2.3.3-1. This equation uses the parameter ktd defined in equation 5.4.2.3.2-5. The parameter t used in 5.4.2.3.2-5 is defined as “maturity of concrete, defined as age of concrete between end of curing and time being considered for analysis of shrinkage effects”.
 
PGSuper computes ebdf using t being equal to the total time for girder shrinkage. The total time is the time between end of curing and the time under consideration as prescribed by the LRFD.
 
A review of NCHRP Report 496 confirms your claim. The shrinkage strain between deck placement to final should be computed as ebdf = ebif – ebid. Where ebif is what PGSuper is computing as ebdf and ebid is the shrinkage strain used to compute shrinkage losses on the non-composite girder section.
 
I’ll get this fixed for the Version 2.5 release.
 
If need be, you can adjust the prestress loss calculations by hand and input them as general lump sum losses.
 
Rick
 
Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office

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