I’ve got a job with SDC C and using a steel R=3 system with HSS diagonal bracing. Because R=3 I don’t have to use AISC 341 provisions. However, ACI 318-14 17.2.3 says anchors in SDC C shall satisfy additional seismic provisions. My question is, do I need to amplify my seismic reactions for R=3 to check concrete failure modes for anchoring to concrete (breakout, pryout, etc)? I’m looking at 35 kips shear vs 105 kips amplified shear at a couple of locations
Yes, either overstrength factor must be used, or by ensuring the steel is the failing element and not the concrete. Hilti Profis has all the options built in so you can play around with the different ways to meet the code requirements if you don’t have a different calc already created. When I have done this in the past (low seismic area) the overstrength factor made the most sense.
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