Distribution of Seismic Forces in moment frames with rigid diaphragm

[Sanira]

Hi all,

I know that in rigid diaphragms, we distribute the seismic force (which is applied at the CM of diaphram) based on relative stiffness of the vertical elements. However, I find examples of shear wall only in each and every book. I am not sure how to distribute seismic forces in moment frames and braced frames. My question is how do you calculate the stiffness of moment and braced frames for the purpose of horizontal distribution of lateral forces? Anyone can suggest me any book or link for this purpose? Thank you.

 

[phamENG]

Any decent structural analysis book should be able to help you. Essentially, apply a unit load (1kip, 1kN, or whatever unit you like) to the top corner of the frame, and analyze for deflection. Stiffness, like a spring, is force/distance (k/in, kN/m, etc.) That can be used in concert with shear wall stiffness's and other LRFS elements to distribute the diaphragm reactions.

 

[JAE]

Agree with phamENG - put a unit load on the brace at the same level as the diaphragm and determine the deflection at that same point of load.
Your frame stiffness is 1/Deflection.