Vertical Distribution of Seismic Forces ASCE 7-05

[Tinguindin]

Hello;

I have been trying to find out about the "k" factor in the Cvx formula (12.8-12). The ASCE 7-05 states that it is an exponent related to the structure period. But I still do not know where it comes from, is it a factor that relates to the system's ductility?

Please let me know if you have some info on this. Thank you.

J.L.P.Q

 

[JAE]

I believe that it is a factor that corresponds to the overall period of the structure in that a more flexible (palm tree) structure will behave in a different fashion than a less flexible (oak tree) system.

With the flexible system, under a particular seismic event, the response of the structure could be visualized more as a whipping motion where lateral forces would be more significant in the higher stories.

So, the k factor accentuates the effect of the height of the structure with larger values of k for longer period structures.

This simply places more of the "applied" forces higher in the structure.

As to where it comes from - I would think it simply is the result of analysis studies or tests. The commentary doesn't even deal with it.