Learning Forum

[binc]

Hi Ansys community, I am modeling a prestressed concrete wall with an unbonded post tensioning tendon. I am getting a big distortion on the anchored steel plates that are placed at the ends of the tendon. Any suggestions to eliminate the stress concentration on the end plates? Thank you!

The prestressing force (104 kips) was applied to a link180 element using INISTATE to apply 113 ksi in tension. The anchorage plates used structural steel NL model with a yielding tensile strength of 60 ksi. The dimension of the steel plates was 5 in x5 in, and the resulting stress on the plates from prestressing force is much lower than the yielding strength. However, a stress concentration was developed on the plate surface, and the resultant prestress force in the tendon was incorrectly only half of the applied force.

Bonded contact was defined for the concrete-steel plate contact region, and a joint with fixed 6 DOFs was defined between the plate face and the end node of the tendon.

[dlooman]

Does your geometry have a zero radius (90 degree re-entrant corner)?  That's a singularity and the stress will approach infinity with mesh refinement.  Or perhaps the end of the link180 is connected to a single node of the plate. That's a singularity also since the attachment has zero area.  Such stresses can usually be ignored.  It's expected that the deformation of the model will unload the post-tension somewhat.  You'll just have to double the initial stress.  Or you could use the actuator element, link11.  You can apply the axial force to "face" 2 of the actuator element as a "pressure" with  SFE,element number,2,PRES,,104000

[binc]

Thank you so much for your reply and suggestion. I doubled the initial tensile stress in the tendon, the tensile force was still reduced and reversed to be in compression as deformation increases. However, the tendon needs to be allowed for elongation when the lateral force is applied, which means that as the horizontal displacement (total deformation) increases, the tensile force in the tendon should also increase. Could you suggest on how to apply the prestressing and external force in steps in order to transfer tension in the line element to concrete as compression through the steel plates? 

Currently, I constrained the top node of the tendon in z direction in all load steps as the concrete and tendon are already constrained in x and y direction along the tendon length. How to remove this constrain during the first load step while still be assigned in the inital state? The screenshots below are the current setting for constraints in load steps. Thank you!