FEMA 273

[aladdin76]

Hi all
In fema 273 and ASCE 41, the modelling parameters and acceptance criteria of concrete flexure members are given as rotations.
I do not know what is meant by rotation. is it the rotation of the plastic hinge or the chord rotation of members (Drift/L).

 

[KootK]

Can you reference a particular clause in FEMA 273 for us to comment on? In general, I believe that the criteria are curvatures rather than rotations. Curvature, of course, is a measure of the axial strains induced by flexure.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JAE]

Are you talking about this section:

If so it appears to be a deformation-controlled action as the defining acceptance. So if you establish a plastic hinge at a point on a beam, they are requiring the design to result in a smaller hinge rotation than that listed in the referenced table. This, to me, is the relative rotation of the member on either side of the plastic hinge.



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[JAE]

The image I posted is from FEMA 273 (Oct. 1997 version), section 6.8.2.4.

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[aladdin76]

thanks all for your reply
kootk see Table 6-17

 

[KootK]

Thanks for the clarification aladdin76.

I do not know what is meant by rotation. is it the rotation of the plastic hinge or the chord rotation of members (Drift/L).

You've got two separate items on the table here. In each case, FEMA-273 is attempting to limit curvature, and thus damage, in the members.

1) Curvature for a shear wall plastic hinge, often located at the base of the wall, is indexed to the amount of rotation occurring over the estimated length of the plastic hinge. That's figure 6-2.

2) Curvature for a coupling beam is indexed to the chord rotation estimated in each of the coupled shear walls that serve as the chords for the composite wall, taken at the elevation of the coupling beam. This is figure 6-3.

The key to understanding this, in my opinion, is to realize that curvature is the parameter of interest for members dominated by inelastic flexural behavior. Rotation and chord rotation are just how we get to curvature.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.