Calculation of long-term deflections of post-tensionsed concrete flexural memebers

[CEcoug]

Anyone familiar with calculations for long term deflections of post tensioned slabs? Specifcally for a parking garage. ACI R9.5.4.3 mentions that the calculations are "complicated", which does not give me much confidence. Any references or something to point me in the right direction would be appreciated.

 

[KootK]

There's some good stuff here: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[rapt]

CEcoug

What it means is that you actually have to do the calculations, rather than taking shortcuts like L/D ratios and long term deflection multipliers as many people do in RC design.

There is no logical L/D ratio as the results are dependant on the amount of prestress used which controls the level of cracking and short term curvature.

And long term multipliers do not work at all (they are actually very inaccurate for RC design as well) as while It could be argued that there is a relationship between creep deflection and short term deflection, long term shrinkage warping deflection is not related to a factor times short term deflection in any way.

So to get a realistic assessment of deflections for a PT member, you have to calculate the effects of cracking, tension stiffening, creep and shrinkage on the member, and they vary at every point along the member. There should be some good articles on it by R.I Gilbert if you want to search for it.

 

[KootK]

This is a good reference in addition to the Gilbert stuff: Link.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CEcoug]

Thanks for the links/explanations. This will be a new challenge for me and should be fun.