how to get the Braced frame column axial load

[Groszni]

How do I get the required axial force on braced frame column? Doesthe expected strenght of brace in compression acting as an additional load to column?If it does then lets say i have 10 ten story building using chevron v brace with a 682 kips expected compression strength and an angle made from the brace and the beam is about 48°, does it make thelowest column has to withstand 682sin48*9 kips + gravity axial load acting on column ? Is it usual to have an axial load around 5000 kips for 10 stories structure?

 

[calvinandhobbes10]

How I would do it---sum your overturning moment for the entire braced frame, divide by the horizontal column-to-column dimension. Design the column for this axial lateral load (adding dead/live).
In general columns take the bending force couple, the chevrons take the shear. You can model this as a 2D frame to see the actual interaction. Model all connections as pinned, and members as appropriately continuous.
Expected strength (as opposed to required strength) of the brace won't matter unless you are in high seismic which is a different discussion.
5000 kips sounds high unless you are asking a whole lot from this braced frame.

 

[sandman21]

Its the sum of the expected strength of the frame times sin plus gravity loads. Your braces should not be the same all the way up.

 

[Groszni]

@calvinandhobbes10 thanks for the advice! What do you mean by column to column dimention? U mean the length of the bay? im designing one where the seismic design category is D and has an E site class so i have to consider the expected strength right?

@sandman21 yeah thanks for the advice and the correction! And yeah its just an example but about the brace, i found it that i got not so much option in choosing the section of the brace because the restriction of the sections b/t has to meet the 0.3(E/Fy)^0.5 for WF section on the AISC seismic provision

 

[wannabeSE]

Is this a SCBF designed per ASIC 341-10? If yes, have you considered exception 2 in section F2.3. This may reduce the design load om the columns.

(2) The required strength of columns need not exceed the least of the following:
(a) The forces determined using load combinations stipulated by the applicable building code including the amplified seismic load, applied to a building frame model in which all compression braces have been removed
(b) The forces corresponding to the resistance of the foundation to over turning uplift
(c) Forces determined from nonlinear analysis as defined in Section C3

 

[Groszni]

@wannabeSE yes it is. could you help me explain step by step from the point a to c please?

 

[structSU10]

Your best bet is to get a copy of the seismic design manual from AISC. It has worked examples, and explains how to work your way through the code. Its much to extensive of a scope to describe over an internet forum.

 

[Groszni]

@structSU10 i have one, but in the example it doesnt explain about the exception 2 in section F2.3!