Area of Prestressing Steel on Flexural Tension Side

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Thanh Bui
Area of Prestressing Steel on Flexural Tension Side

I have a 2 span prestressed concrete frame with 11 girder lines. The girder is WF100G with modified section properties.

I’m trying to verify the area of prestressing used in equations 5.7.3.4.2-4 and 5.7.3.5-1 (AASHTO LRFD Bridge Design Spec 8th ED 2017). My understanding from the code is that both Aps in these two equations are on the flexural tension side of the member, so at a certain location, they should be the same. Am I correct on this? As an example, I attached two snapshots from PGSuper’s Details Report for Girder A, Span 1. The area of prestressing differs in each equation. In addition, the area of prestressing used for longitudinal strain is not dividable evenly by 0.217 in^2 (area of strand).

I’ve reviewed the PGSuper design example posted on the website, but I didn’t see any calculations for Aps values.

PGSuper model attached; I’m using version 4.1.4

Thanks

Thanh

Rick Brice
Area of Prestressing Steel on Flexural Tension Side

There are two things you are missing:

1) The longitudinal reinforcement for shear tension side is on the top of the girder when negative moment is larger then positive moment. The deck reinforcement provides the tension tie. Aps does not contribute. You can clearly see the switch from bottom to top tension tie when the capacity reduction factor for flexure changes from 1.0 (prestressed concrete) to 0.9 (reinforced concrete).

2) Near the ends of the beam, the lack of full development must be taken into account. The quantity Aps*fpe must be reduced as described in 5.9.4.3. Since PGSuper reports Aps and fpe (not the product), Aps is reduced. This is why you don't always get even multiples for 0.217.

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