Prestressing as action or resistance

There are two distinct approaches to the design checks of prestressed concrete members - the prestressing can be either treated as resistance (integral part of the section) or as action (load)

Prestressing as resistance

• Considers the prestressing strands as integral part of the cross section, where prestressing operation introduces imposed deformation corresponding the pre-elongation of the active reinforcement.
• Hyperstatic effects must be considered.

Prestressing as action

• Considers prestressing as external loading consisting of a self-equilibrating system of forces in the anchorages and the transversally in the concrete. After transfer prestressing strands are considered as conventional reinforcement, only taking into consideration the pre-elongation.

Treatment in different codes

AASHTO LRFD 2007

• Based on C5.7.1, prestressing is treated as part of resistance

Eurocode 2 (1992)

• Based on article 5.10.1, bullet 2, the effects of prestressing can be considered as an action or a resistance

References

• M. B. Cavalcanti, B. Horowitz: Flexural Analysis of Prestressed Concrete Structures, IBRACON Structures and materials journal, Volume 1, Number 4 (December, 2008) p. 331 - 364, ISSN 1983-4195 - describes two methods that can be used to evaluate capacity of prestressed concrete members; method 1 treats prestressing as integral part of the section, while method 2 treats prestressing as external load.