Tension Stress Check Failed

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Shoover23
Tension Stress Check Failed

New to PG Super Trying to replicate a design from Leap Conspan and cannot get tension stress check to work. I've tried to match all the design parameters but just won't work.

Also when I accept the proposed design it always groups the debonded tendons all in the center and then gives me an error regarding debonded strand arrangement and I have to go back and space them out?

Thanks for any advice you can give.

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bricer
Tension Stress Check Failed

Many things can be causing the differences in the tension check results.

For analysis interval 2, Prestress Release, the tension check fails because the tension stress limit is 0.2 ksi and the stress at the top of the girder is 0.432 ksi. If adequate tension reinforcement is provided the tension stress limit would increase to 0.588 ksi and the check would pass. The Details Report provides a chapter titled Reinforcement Requirements for Tension Limits. This chapter shows the area of reinforcement provided and the area of reinforcement required to use the higher tension stress limit. In your case 1.331 sq. in. is provided but 3.236 sq. in. is required. I'd start by comparing the tension stress limits between the two programs to see if that's the source of the difference. If so, the next question is why is Conspan using the higher limit? Perhaps they make an assumption that you will provide adequate reinforcement in your design to justify the higher limit. PGSuper does not make such an assumption, it evaluates the reinforcement for adequacy based on the requirements in the AASHTO LRFD and selects the appropriate stress limit.

The second set of tension stress fails are for the Service III check. Since the tension limit is 0.19*sqrt(f'c) = 0.537 ksi my guess is the difference is in the stress demand, not the stress limit. PGSuper reports the stress in the girder due to pretensioning and due to the Service III load combination. Compare these values with Conspan. Details of the stress due to pretensioning is given in the Details Report in the chapter titled Streses due to Prestressing. You will see the effective prestress force and strand eccentricity listed along with the top and bottom girder stresses. The stresses are easy to check with P/A + Pe/S. You can get the effective prestress details in the Prestress Loss Details chapter. You have PGSuper configured to use elastic gains in the stress analysis with a 1.0 live load factor, make sure the other program is doing this as well. You can check the Service III stresses by looking in the Stresses chapter in the Product Load Stresses tables. PGSuper includes the stress in the girder due to deck shrinkage. If Conspan is missing the deck shrinkage stress contribution, that would likely explain the difference. If the stresses due to prestressing and/or external loads are different between the two programs, dig in more deeply and look at prestress losses and the stress due to each individual load. PGSuper provides all the details.

With regards to the debonded strand arrangement - the debonding is grouped in the center of the beam because that's how you have it defined in the girder library. You have every strand marked as debondable. Not every strand can be debonded so don't make them all debondedable. The strand pattern defined in the library defines the sequence in which strands are added to the girder and debonded. Use a more realist strand fill sequence - probably every other stand position starting from the outside of the shape, row by row.

Shoover23
Tension Stress Check Failed

Thanks for the prompt reply. I will dig deeper into the details chapters compared to Conspan. I understand what you are saying about the debond pattern in the library - that makes sense!

bricer
Tension Stress Check Failed

Were you able to reconcile the differences between PGSuper and Conspan? Please share the source of the differences. Other users will benefit from this information.

bricer
Tension Stress Check Failed

Please share what you find out. I think other users would be interested to learn about differences between Conspan and PGSuper.

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