prequalified smf rbs
 

prequalified smf rbs
question regarding prequalified smf reduced beam section connection design:

according to seismic provisions section 9.6, in the equation for mpb for prequalified rbs includes 1.1ry*fyb*zrbs, however, in the aisc 358 section 5.4, it directs you to eq 5.8-5 where mpr = cpr*ry*fy*ze.

why are these two equatons using different values, 1.1 vs. cpr?

check out our whitepaper library.
per fema 350, june 2000, commentary section 3.2.4(see link below), in calculating mpr the coefficent 1.1 was used in the 1997 aisc seismic provisions, however, fema testing determined that for most connection types, the peak moment developed is higher than using 1.1, therefore the cpr factor was developed, limited by 1.2.