Seismic R Value for Steel Frame With CMU Infill Walls

[mfrad]

What seimic R Value per the IBC 2000 should be used for a steel framed school auditorium with metal deck, steel spandrels and steel columns for vertical load only, but braced laterally by CMU infill masonry. Should the masonry be rigidly placed against the steel columns are flexibly anchored?

 

[MikeE55]

I would call this a Building Frame System with either ordinary, intermediate, or special reinforced masonry shear walls. If you place vertical reinforcing at spacing not to exceed 48", you can use the intermediate shear wall "R" value, which is 4. You have a good question about attachment of masonry to steel. My own philosophy is that if the frame is leaning on the wall (compression), and the amount of potential movement is insignificant, then flexible ties are enough. If I am forced to count on tension between the column and wall, I would provide a different type of anchorage.

 

[JAE]

More important is the connection between the beam over the wall - this is where the lateral shear from the horizontal diaphragm is taken down into the walls. The connection to the columns is not that significant.