• State Verified Answer
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 111 subscribers
  • Views 2773 views
  • Users 0 members are here

Modeling of a Non post tensioned beam in a post tensioned slab.

Carl Abinader
Offline

Dear Concerned,

I am having an issue regarding the modeling in RAM of a R.C. Beam (With no tendons) inside a Post tensioned Slab.

Both beam and the slab are monolithic so there won't be a cold joint and will act as a unit, however the beam will not have any tendons passing into its depth.
All tendons will be in the slab, hence the design of the beam will be based on an R.C. Beam.
Since it is an unusual case, and not covered by the manual, I would like to ask how I can model such a behavior in RAM.
Also regarding the strips, how do you recommend placing the strips in such a case, Do I follow the T-Beam Requirement or not.
Another major issue is when the beam is set to design as R.C., the design will not include the tendon compression, and The hyperstatic tension forces will penalize the shear and bending capacity of the beam.
   
Regards

Parents
  • 0

    Model just what you have, the beams, the slab the tendons. Place a design strip along the beam for the design of the beam only and in the General tab uncheck the box to "Consider as Post-Tensioned".  The forces in the strip are not affected by this selection, only what code provisions are checked, so the hyperstatic load effects are still present. The strip width should probably include some of the flange (I am not a fan of designing beams trimmed exactly to the stem width).



Reply
  • 0

    Model just what you have, the beams, the slab the tendons. Place a design strip along the beam for the design of the beam only and in the General tab uncheck the box to "Consider as Post-Tensioned".  The forces in the strip are not affected by this selection, only what code provisions are checked, so the hyperstatic load effects are still present. The strip width should probably include some of the flange (I am not a fan of designing beams trimmed exactly to the stem width).



Children
  • 0 Offline in reply to Seth Guthrie

    Thank you for the reply, it was helpful

    However If the tendons are far from the T-beam flanges considering the beam as a T will provide good results, however in the case that banded tendons are spanning along the flange section, I have found it more reasonable to reduce the width of the flange even if it means considering the stem alone, As long as Axial stresses will be considered in the slab the section will be properly designed, the Tension/Compression couple in the T will be considered.

    Please refer to the included sample model. The top beam has 3 tendons passing into that will not be included in the design of either the beam or the slab (because beam is R.C.) and will result in tension in the beam. Hence in the cases where the stem is considered alone the beam will be in compression reflecting actuality and the capacity of the strength will be considered in the slab.

    So in this case would you still recommend a T Section or as a Beam.

  • +1 in reply to Carl Abinader
    So long as the net axial force is considered in the design, you should get a theoretically correct answer either way. This post gets into more details: communities.bentley.com/.../ram-concept-t-beams-and-axial-forces-tn.aspx
    Practically speaking, your sample file is a good one to examine. Even though most of the forces are in the stem, the wider design strip that includes more of the flange requires a few more top and bottom bars, and being rather conservative I tend to like that layout.



    Answer Verified By: Carl Abinader 

Communities
Support and Services
Training and Learning
Social Media