Structural Systems

[cprr0107]

Good day!

I am modeling a 4.4mx4.4m steel braced frame tower like structure, 25m high, with operable machine floor at top.

I have modeled The columns and horizontal members(beams)
to be fixed at the joints(no releases). And with hinge supports.

SAP2000 automatically assign effective length factor k=1 for the beams and braces.

I would like to ask what value of "R" (overstrength factor) is suited for my model referring to table 16-N of UBC97.

and

Can someone please define more the meaning of
1.) Ordinary braced frame
2.) special concentric braced frame
3.) and when is dual systems be used.

can you please provide code references for me also to look at.

thanks a lot in advance!

 

[strucguy]

From what I know "R" is Response Modification Factor, and is dependent of the Seismic Load Resisting System (SLRS) you select. I not so familiar with UBC97. But, I suggest you to read through the following publication for additional guidance.

AISC 341-05, "Seismic Provisions for steel Buildings" including Supplement No. 1

Hope this is helpful.

 

[frv]

The difference between "Ordinary", "Intermediate" and "Special" is the level of detailing required.

Long story short, for moderate seismic acceleration areas, YOU can choose what system you want to use. The whole idea is that the more detailing (read "ductility") you choose to do, the lower the seismic load you need to design for.

For high seismic accelerations, you are limited in your choice of SFRS, and must select one that is permitted by code.

 

[cprr0107]

Thanks alot to all your post!