AASHTO eta factors & deformation

Question

AASHTO eta factors & deformation

jrw501 (Structural)

(OP)

3 Feb 20 21:37

This is the first project I've worked on with a non-unity factor (eta=1.05/0.95) where I've also been tasked with designing joints and bearings. I think the answer is yes, but thought I'd get some confirmation -- do the eta factors apply to deformations/movement ranges?

Thanks!

crossframe (Structural) · Answer 1 · 2020-02-04 15:15:29

Note that the eta factors are usually equal to 1.00 for all but the Strength limit states (AASHTO 1.3.2 - 1.3.5), so I would suggest it depends on the limit states you're using for the joints and bearings. Those are often designed for Service limits states.

BridgeSmith (Structural) · Answer 2 · 2020-02-04 18:03:09

I believe you're incorrect there, crossframe. The eta factor is the "load modifier" and is applicable to all limit states.

Based on Eq. 1.3.2.1-1, I would say the answer question in the OP is yes, the eta factor would be applied to deformation and movement ranges, as well as all other force effects. That's what I do.

Oops. I should have read further before answering. crossframe is correct; the individual load modifiers are all specified as equal to 1.0 for all but the Strength limit state, and should be applied to deformation and movements for the Strength limit state, but not others.

Rod Smith, P.E., The artist formerly known as HotRod10

BridgeSmith (Structural) · Answer 3 · 2020-02-04 18:18:01

As I wipe the egg off my face, I'll caution that while movement and deformation for joints and bearings are typically controlled by the Service or Extreme Event I limits, the design of some components may be governed by the Strength limits.

Rod Smith, P.E., The artist formerly known as HotRod10

jrw501 (Structural) · Answer 4 · 2020-02-04 20:30:57

Perfect, that makes a lot of sense.

Thanks crossframe & BridgeSmith!

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