How do you calculate beam and/or column with an overstrength factor? What do I do with omega? Multiply all loads with omega? Can anyone share an example?
Typically the process would be something like:
- Select a structural system (ductile frame in this case)
- Assume target ductility (say, 3)
- Model frame with appropriate loads etc as per Code and assuming ductility of 3
- Design a beam with capacity closely matched to your demands from the above
- Check that with your specified beam capacity you actually achieve a ductility of 3 (this requires formation of a full ductile failure mechanism i.e. a beam hinge mechanism in this case)
- If you don't match your assumption then input loads as per your actual achieved ductility, redeisgn beam, re run failure analysis, calculate actual achieved ductility - keep going until this converges
Once you've converged the failure model then you get to the overstrength bit
Take your beam capacity from above and multiply the moment capacity of the section by the various overstrength factors as required by your code (omega)
This is the maximum credible force transmitted from your beam to the beam column joint/column
Design the column for the loads resulting from this overstrength beam force
Jesus that sounds complex...you see what I mean about your question being highly vague?
Do you have a picture?
I am going to have to tap out here, I am only really familiar with steel and concrete, timber frame is a bit beyond me, though I imagine the principles are broadly the same...
First you need to define the irregularities and discontinuities in the system per ASCE 7 Chapter 12.
Once you have identified these conditions you must follow the rest of the requirements of the chapter to determine which elements need to be designed with load combinations including overstrength.
Then you need to apply the load combinations according to chapter 12 as well. There are special combos for seismic effects including overstrength.
The overstrength factor is a factor applied to the EQ load case in these load combinations.
For a discontinuous column that is part of the lateral system, the supporting beam and connection should generally be designed for load combinations including overstrength.
Vertical In a plane discontinuity type structure, wood framed. I am attaching a sketch. Need to calculate beam below the shear wall that has a discontinuity. Shaded area are shear wall. I know how to apply dead and live loads but am not sure how to apply earthquake loads. Do I apply as a point load? Do I apply horizontally or vertically, and if so, where in the beam do I apply? mid point? Do I use both lateral loads from above and at the same level as the B1 beam? How do I convert lateral load to per foot? I was wondering if someone could help me, solve this example, or at least answer my questions above. Thank you in advance.
