AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
(OP)
Question about the following provision of the AASHTO LRFD Bridge Design Specifications:
Referring to the bolded portions above, this seems to say that this check only need be made at the bottom of the beam location (i.e. the Precompressed Tensile Zone for typical prestressed beams). However, it is conceivable that tension could occur in the top of the beam at the ends at service load, but this is not the "Precompressed Tensile Zone", and therefore the tensile stress check would not apply to the ends of the beam.
Is this generally how others have interpreted this provision (i.e. only check service load tension at the bottom of the beam)?
Section 5.9.4.2.2 - Tension Stresses
Table 5.9.4.2.2.-1 - Tensile Stress Limits in Prestressed Concrete at Service Limit State after Losses, Fully Prestressed Components
Table 5.9.4.2.2.-1 - Tensile Stress Limits in Prestressed Concrete at Service Limit State after Losses, Fully Prestressed Components
Other Than Segmentally Constructed Bridges--> Tension in the Precompressed Tensile Zone Bridges, Assuming Uncracked Sections
Referring to the bolded portions above, this seems to say that this check only need be made at the bottom of the beam location (i.e. the Precompressed Tensile Zone for typical prestressed beams). However, it is conceivable that tension could occur in the top of the beam at the ends at service load, but this is not the "Precompressed Tensile Zone", and therefore the tensile stress check would not apply to the ends of the beam.
Is this generally how others have interpreted this provision (i.e. only check service load tension at the bottom of the beam)?





RE: AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
My interpretation anyways.
RE: AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
RE: AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
What I think AASHTO is trying to say is that in prestressed members subjected to tension, the allowable limit is a certain value. They don't want someone to apply this provision to a regular reinforced concrete section that doesn't have a prestressed component.
I don't have the code in front of me, but I think they probably say something similar about the compression limiting stress.
RE: AASHTO LRFD Prestressed Concrete Allowable Tensile Stresses
Brandon: I also interpret it the way you do, based on AASHTO's definition of the Precompressed Tensile Zone: Any region of a prestressed component in which prestressing causes compressive stresses and service load effects cause tensile stresses. So in most cases, yes, just the bottom of beam.
BridgeEI: Don't forget about the eccentricity of your prestressing strands. Generally, they are located at the bottom of the beams, causing tension at the top. Also note, the table 5.9.4.2.2-1 is for prestressed concrete components, so hopefully these provisions aren't being applied to a regularly reinforced section!