Please help me figure out the meaning of the following warning: WARNING: Screed Camber, C, is greater than the camber at time of deck casting, D. The girder may end up with a sag.
This warning indicates that for the minimum and maximum timing for creep and camber and the camber variability that you are using in your model, for at least some cases, the camber at the time of deck casting D is less that the amount the girder will deflect downward due to the weight of the wet deck and superimposed dead loads (aka Screed Camber, C). When the downward deflection is larger than the upward deflection, the girder will be sagging.
More information can be found in the PGSuper Theoretic Manual.
Best regards,
Rick
Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office
Using PG super, if my excess camber is a positive number would this mean I have no girder sag. Or if my screed camber, C, is greater than my Lower bound camber (D21), automatically defined in project criteria library, does this mean my girder is not sagging?
I am confused on why I still get this error, I have the latest version of PG super and this project is using TxDOT standards.
If screed camber exceeds the camber at the time of deck casting, the downward deflection due to deck and superimposed loads is greater than the upward camber of the bare girder.
Thanks for the input, I read that information, and I suppose the format on this new version is generating the error that should not be generated. Currently my screed camber is not larger than my camber at time of deck casting. This would also be D120, per the WSDOT manual, which I would assume is a common AASHTO statement.
So my upper and lower bounds on the camber at D(120) is larger than my Screed, yet I am still getting the error " Screed Camber is greater than the camber at time of deck casting. The girder may end up with a sag".
I understand that you have worked this issue out by working directly with TxDOT. I just wanted to follow up here so that future readers don't think there is an unresolved issue or an error in the software.
The D120 is based on an upper bound prediction of camber. However, it is the lower bound D40 value that is causing the warning to appear. PGSuper models both the natural variation of camber and the uncertainty in the construction schedule. The natural variation of camber is modeled by computing upper bound and lower bound values. The uncertainty in the construction schedule in modeled by computing camber at day 40 and day 120 (note, these days can be changed by the user).
The warning is happening for the case of lower bound camber on the 40 day construction scenario.
Rick,
I get this same Sag Warning. Looking into PGSuper TN003, this warning happens when C > D.
C, aka Screed Camber = Maximum downward deflection due to the weight of the wet deck concrete and superimposed dead loads
D = Maximum net upward camber(typically at midspan)immediately prior to deck placement.
In our case, TxDOT Project Criteria is selected and the D value (upward camber at the time of deck casting) is calculated at 21 days. So in the Deflection tables this is the D21 column. Variability between upper and lower bound camber is selected to be 0%, therefore Deflections for Maximum and Minimum timing are the same.
On the Deflection Tables, the C value at midspan is 0.012 in, whereas D21 is 0.22 in. Therefore C is not higher than D, however the program gives this Warning.
Any feedback on what is the reason behind this warning would be highly appreciated.
What is the exact warning?
I bet it is "WARNING: Screed camber (C) is nearly equal to the average camber at time of deck casting, D. The girder may end up with a sag."
The key here is "nearly". This warning happens when C and D are within 0.25" of each other. This is not technically a sag case, but there is variability in the deflections and camber so sag could still happen.
The idea is to get you thinking about the consequences of sag occurring during constriction. What if your modulus of elasticity comes on a little high and you don't get the initial camber and creep growth you expect, and the deck and barriers are a little heavier than you designed for. You could get some sag. Do you need to make an accommodation for this possibility? Is the sag ok? Could there be ponding and drainage issues of you get sag? What about vertical clearance problems? Do you want the margin between upward and downward deflection to be so close?
This warning indicates that for the minimum and maximum timing for creep and camber and the camber variability that you are using in your model, for at least some cases, the camber at the time of deck casting D is less that the amount the girder will deflect downward due to the weight of the wet deck and superimposed dead loads (aka Screed Camber, C). When the downward deflection is larger than the upward deflection, the girder will be sagging.
More information can be found in the PGSuper Theoretic Manual.
Best regards,
Rick
Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office
Thank you Rick.
Don Bell
Using PG super, if my excess camber is a positive number would this mean I have no girder sag. Or if my screed camber, C, is greater than my Lower bound camber (D21), automatically defined in project criteria library, does this mean my girder is not sagging?
I am confused on why I still get this error, I have the latest version of PG super and this project is using TxDOT standards.
Randy Ehresman, PE
Project Engineer
If screed camber exceeds the camber at the time of deck casting, the downward deflection due to deck and superimposed loads is greater than the upward camber of the bare girder.
For more information look at the FAQs on the WSDOT web site.
http://www.wsdot.wa.gov/eesc/bridge/software/index.cfm?fuseaction=FAQs&s...
Specifically, look at Q32.
Rick,
Thanks for the input, I read that information, and I suppose the format on this new version is generating the error that should not be generated. Currently my screed camber is not larger than my camber at time of deck casting. This would also be D120, per the WSDOT manual, which I would assume is a common AASHTO statement.
So my upper and lower bounds on the camber at D(120) is larger than my Screed, yet I am still getting the error " Screed Camber is greater than the camber at time of deck casting. The girder may end up with a sag".
http://www.wsdot.wa.gov/publications/manuals/fulltext/M23-50/Chapter5.pdf
Also, if I have a positive Excess Camber, then there is not sag, which is also what I have.
Respectfully submitted.
If you post your file, I'll dig in deeper.
Thanks
I understand that you have worked this issue out by working directly with TxDOT. I just wanted to follow up here so that future readers don't think there is an unresolved issue or an error in the software.
The D120 is based on an upper bound prediction of camber. However, it is the lower bound D40 value that is causing the warning to appear. PGSuper models both the natural variation of camber and the uncertainty in the construction schedule. The natural variation of camber is modeled by computing upper bound and lower bound values. The uncertainty in the construction schedule in modeled by computing camber at day 40 and day 120 (note, these days can be changed by the user).
The warning is happening for the case of lower bound camber on the 40 day construction scenario.
A more detailed discussion is available in he FAQs on the WSDOT web site.
http://www.wsdot.wa.gov/eesc/bridge/software/index.cfm?fuseaction=FAQs&s....
Rick,
Sorry for my delay in the response to clarify my resolution with TxDOT.
The newest version has eliminated this error.
Regards,
Rick,
I get this same Sag Warning. Looking into PGSuper TN003, this warning happens when C > D.
C, aka Screed Camber = Maximum downward deflection due to the weight of the wet deck concrete and superimposed dead loads
D = Maximum net upward camber(typically at midspan)immediately prior to deck placement.
In our case, TxDOT Project Criteria is selected and the D value (upward camber at the time of deck casting) is calculated at 21 days. So in the Deflection tables this is the D21 column. Variability between upper and lower bound camber is selected to be 0%, therefore Deflections for Maximum and Minimum timing are the same.
On the Deflection Tables, the C value at midspan is 0.012 in, whereas D21 is 0.22 in. Therefore C is not higher than D, however the program gives this Warning.
Any feedback on what is the reason behind this warning would be highly appreciated.
Thank you
What is the exact warning?
I bet it is "WARNING: Screed camber (C) is nearly equal to the average camber at time of deck casting, D. The girder may end up with a sag."
The key here is "nearly". This warning happens when C and D are within 0.25" of each other. This is not technically a sag case, but there is variability in the deflections and camber so sag could still happen.
The idea is to get you thinking about the consequences of sag occurring during constriction. What if your modulus of elasticity comes on a little high and you don't get the initial camber and creep growth you expect, and the deck and barriers are a little heavier than you designed for. You could get some sag. Do you need to make an accommodation for this possibility? Is the sag ok? Could there be ponding and drainage issues of you get sag? What about vertical clearance problems? Do you want the margin between upward and downward deflection to be so close?
Rick,
Your guess is correct, that is the exact Warning. Your response also clarifies what is triggering this warning.
Thank you very much for your help.