16 Jul 12 14:49
I am doing the analysis of a 9-story building using a dynamic analysis. The building is a residential complex, built using steel. In one direction, concentrically-braced frames (limited ductility) are used and in the other direction, excentrically-braced frames.
In the principal vibration mode for a given direction (X for example), the distribution of base shear for each story seems a bit odd. As I understand it, the shear for a given story is the ratio between (Story weight*Story elevation) / (sum of (Story weights*Story elevations)), am I right?
In other words, for the same weight, the higher level will have a higher story shear than the lower one.
Here is my lateral shear distribution (sorry for the bad formatting):
Is this a reflection of the effect of the building height? When I look at the story drifts, I can't understand really well what's happening:
Story Average Total Drift (mm)
With this drift distribution, I would expect the story shears to be at least all in the same direction. Am I missing something here? How can one level have little to no shear?