Spec Check Report - Pretension results

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CSnee
Spec Check Report - Pretension results

Hello, I'm going through my results and was hoping you could help identify what I'm doing differently than the program. I am trying to reproduce the "Pretension Stress" under the spec check report. Below are my values (obtained from program). POI=0.5L Interval 2
L=138.333
St=-15949.3 in^3 (from section properties transformed Non-Comp)
Sb=15823.6 in^3 (from section properties transformed Non-Comp)
A=964.895 (from section properties transformed Non-Comp)
Eff PS=1474.51kip (34-0.6LL Strands; 2.648ksi PS losses)
ecc=25.766in (Is the eccentricity of PS available from program? I am able to obtain this value for PT but not for PS)

Interval 2 Results (0.5L):
Top Flange = 0.854 (Calculated); 0.807 (Program)
Bottom Flange = -3.922ksi (calculated); -3.875 (Program)

Thanks for any assistance,

Happy Holidays

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File WardOC_b4deckPT.spl247.96 KB
Rick Brice
Pretension Results

The best way to see how the stresses and losses are computed is in the Time Step Details Report.

To keep things simple, look at just the location and interval you are interested in. You'll be prompted when you create the report.

You can get the strand eccentricities in the "Bridge Description Details" chapter in the details report. Note that the eccentrics are based on the net, non-composite section. This is because this is the eccentricity you need to compute the effect of the prestress on the net concrete section.

Since your approach is using a transformed section analysis, you can get the CG of the strands, measured from the top of the non-composite girder, based on the transformed section, in the Time Step Details report.

There are a lot of zero values for Interval 2 because time hasn't started yet. For example, concrete strains due to creep and shrinkage hasn't happened yet so all the tables reporting incremental strains will be filled with zeros. This makes the information you want a little difficult to find.

You'll find what you want in the tables labeled "Incremental forces due to external loads and restrained component forces during this interval" and "Incremental component stress". The "Incremental forces..." table shows how the external loads (girder dead load and prestress in your case) are distributed amongst the elements of the cross section (girder concrete, strands, etc) using a transformed section analysis. The "Increment component stress" table resolves the incremental forces on each component into stresses using the component's net properties.

CSnee
Pretension Results

Thank you for the direction.

Could you provide how the program knows when to remove pretensioning strand contributions that are selected as "Temporary Strands" in the strands tab of the girder options.

Thanks,

Christopher

Rick Brice
The program assumes that

The program assumes that temporary strands are removed just after precast segments are erected.

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