tendon as compression steel in calculating stress at tranfer for pretensioned beams
tendon as compression steel in calculating stress at tranfer for pretensioned beams
(OP)
Is it possible/correct to include prestressed tendon as compression steel near the compressive face of pretensioned beam when calculating concrete stress at transfer ? I am aware that the tendon in compression is usually ignored in this calc.
I came across a person who suggested that the flexural stiffness of pretensioned beams can be improved by including the prestressed tenson as compression steel in the section analysis to determine compressive stress at transfer. The reason provided is that since the prestressed tendon is bonded to the concrete, the tendon is capable of resisting compression (through reducing tension), and this is different to applying a compressive strain to a non pre-tensioned tendon which obviously has no stiffness.
I came across a person who suggested that the flexural stiffness of pretensioned beams can be improved by including the prestressed tenson as compression steel in the section analysis to determine compressive stress at transfer. The reason provided is that since the prestressed tendon is bonded to the concrete, the tendon is capable of resisting compression (through reducing tension), and this is different to applying a compressive strain to a non pre-tensioned tendon which obviously has no stiffness.





RE: tendon as compression steel in calculating stress at tranfer for pretensioned beams
RE: tendon as compression steel in calculating stress at tranfer for pretensioned beams
RE: tendon as compression steel in calculating stress at tranfer for pretensioned beams
Are you talking about strands used for pre-tension or tendons used for post-tension?
In pre-tension case use transformed section properties and PS jacking force to calculate stresses at transfer. That's a proper way to account for steel in compression or tensile zones. Alternatively you can use only concrete section properties and calculate prestress losses due to elastic shortening. The results will be identical.
In post-tensioning case during transfer consider duct holes and don't include tendons since they are not bonded yet.
Textbook may describe it better.
Regards,
RE: tendon as compression steel in calculating stress at tranfer for pretensioned beams
Just make sure near the ends of the tendons (last 2-3m) that you consider the reduction in effectiveness of the bond due to the development length of the strand.
RE: tendon as compression steel in calculating stress at tranfer for pretensioned beams
Whether to include the tendon as "compression steel" will likely have to be based on how a pretensioned beam behaves at transfer.