PGSplice
3.0
Precast-prestressed Spliced Girder Bridges
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A generalized version of the flexure resistance factor defined in AASHTO LRFD 5.5.4.2.1 is used in this software. The resistance factor is a linear interpolation between the resistance factors for compression controlled and tension controlled sections. A linear interpolation is also made for partial prestress ratio between reinforced concrete and prestressed sections.
This article illustrates the derivation of the generalized resistance factor for flexure equation.
Given:
= Net tensile strain in extreme tension steel at nominal resistance | |
= Distance from extreme compression fiber to the centroid of extreme tension steel | |
= Resistance factor for a reinforced concrete tension controlled section | |
= Resistance factor for a prestressed tension controlled section | |
= Resistance factor for a compression controlled section | |
= Resistance factor for a partial prestressed tension controlled section | |
PPR | = Partial prestress ratio |
The net tensile strain is
The resistance factor for a partially prestressed tension controlled section is
From the graph above, the resistance factor can be computed as
Substituting Eq. 1 into Eq. 3 we get
Simplify
Substituting Eq. 2 into Eq. 5 gives