Special Moment Resisting Frames and Steel Eccentrically Braced Frames 1

[Eren Jaeger]

Hi all,

I am new to structural engineering and was hoping to be enlightened regarding moment-resisting frames and braces.
Lets say in a structure, I will be using Special Moment Resisting Frame (SMRF) on one direction (X-axis) and Steel Eccentrically Braced Frames (EBF) on the other direction (Z-axis). So my questions are,

1) What R value will you be using for the said structure? Will there be two different R values: Rx and Rz? This is not a dual system right? It will only be called dual system if the SMRF and EBF are provided and acts in the same direction?

2) For the bracings, how it is supposed to behave? Tension-only or is it allowed to carry compression?

3) Do you satisfy the user note in AISC 360-16 Sec. D1 in actual practice which says, "For members designed on the basis of tension, the slenderness ratio, L/r, preferably should not exceed 300. This suggestion does not apply to rods or hangers in tension."?

4) Do you know any references, manuals, or textbooks I can use to learn more about moment-resisting frames and braces?

Thank you very much! I appreciate your help.

 

[straub46]

1) R-value is based off each orthogonal direction, and the SFRS chosen in that direction, so you'll have 2, although R is the same for SMFs and EBFs. The Omega and Cd factors will vary. See ASCE 7-10 (12.2.2). Correct to both.

2) See #4

3) Yes.

4) You'll need to look at AISC 341-10 "Seismic Provisions for Structural Steel Buildings". It has all the special design and detailing requirements for SMFs & EBFs. The AISC Seismic Design Manual has design examples of all the different seismic force systems.

Go Bucks!

 

[Eren Jaeger]

Thank you straub46! It really helps!