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Overstrength applicability for anchor design

Overstrength applicability for anchor design

Overstrength applicability for anchor design

Hello everyone, long time viewer but first time poster. It's just been one of those days and I'm sure I'm overthinking things. 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

RE: Overstrength applicability for anchor design

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.

RE: Overstrength applicability for anchor design

structSU10 explained the case.

I want to add that, for primary SFRS, brittle failure shall be prevented to all costs. This can be assured either with ductile anchorage design or by designing the attachment to undergo ductile yielding at a load level not greater than 75 percent of the minimum anchor design strength ( Anchorage Design for Petrochemical Facilities ASCE report ). When material strength limitations or geometry does not allow such an approach, an overstrength factor to the load case can be applied.

When the anchors embedded in concrete and pulled to failure, failure will be either by pullout of the concrete cone (brttle failure ) or by tensile failure of the anchor (ductile failure). If the yielding of the anchor or the reinforcement or the attachment controls the failure of the anchorage system , this will be a ductile anchorage failure and will result in large deflections, redistribution of loads, and absorption of energy prior to sudden loss of capacity and often preventing structures from collapsing.

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