MillR
Structural
- Jan 15, 2007
- 67
Using AISC 41, I am conducting a Tier 1 seismic analysis of an existing hospital building that has previously undergone a seismic retrofit. The original building (1947) used steel moment frames. The retrofit (1981) used concentric braced frames. I am trying to pick the building type for the current analysis. S1 Steel Moment Frames can't be right, it's undergone a retrofit. S2 Braced Frames could be correct, although I don't know if the retrofit was intended to replace the moment frames or augment them, and it seems as though it would be conservative to neglect the moment frames. However, the description of S4 Dual Systems with Backup Moment Frames is very close to the building I have. I know this is ultimately a judgment call based on the best guess for how the building will behave, but as this is my first interaction with AISC 41 any thoughts would be helpful. Thanks in advance.