ASCE-31 - Force/Deformation Controlled Actions 1

[SKIAK]

I am performing a Tier 2 evaluation of an existing structure and I have a question about determining whether a component is force controlled or deformation controlled. I feel like I am just getting too bogged down in the interpretation of the text.

Am I to assign whether a component is force controlled or deformation controlled based on what components and actions I deem are acceptable to yield? So, for example, we would allow the diagonal member of a steel braced frame to yield in tension, so I would assign it as a deformation controlled component in P (axial force) and I don't want the columns or beam in a braced frame to yield, so I assign those as force controlled action in P (axial force). Would that be correct?

Do I understand correctly that this assignment has nothing to do with actual expected performance based on calculated loads, only what I deem which components and actions are allowed to yield and which are not?

 

[MrHershey]

Don't know about ASCE-31, but ASCE 41-13 (which combines the old ASCE 31 and ASCE 41 into one standard) provides sample material load/deformation curves for different 'Types' of materials in 7.5.1.2. Basically you look at your component's load/deformation curve, determine which 'type' it is, and then match some key points up versus the sample curves and compare ultimate/yield deformation ratio to the benchmarks in 7.5.1.2 to tell if you're force or deformation controlled.

Sounds like a lot, and it is. Thankfully, if you actually dig into the material chapters they'll actually tell you which actions are force-controlled and which actions are deformation-controlled for whatever system you're looking at (typically in the 'acceptance criteria' section). So, taking concentric braced frames as an example, you'd be looking for 9.5.2.4 which tells you:
Axial tension and compression in braces - deformation controlled
For beams columns under 10% of axial strength - depends, kicks you into another section
All connections - force controlled unless you explicitly model them and can prove otherwise (using the curves of 7.5.1.2)

General rule of thumb is similar to your thought process above. Look at it like you would any seismic system. If an individual component is intended to yield so it can dissipate energy, then it's deformation-controlled. If not, then it's strength-controlled.