I have a few metal building foundation projects coming up. On the last foundation I did for this company, there were 15 to 20 different base plate/edge distance/reaction combinations. For most of these, there were 8 or so wind reactions, 2-4 seismic reactions plus the dead, live and collateral reactions. This is a lot of load combinations to check by hand (I actually set up an excel spreadsheet) and it takes a long time. Is this how most of you go about finding the critical reactions? Is there a way to simplify it? I know you can eliminate some of the LC by inspection, but it is still very time consuming.
Also, I am in a high seismic area. When designing for uplift or shear, if you add enough rebar so the concrete breakout is not of concern, you can assume you have ductile failure of the rebar, correct? I want to be able to avoid having to use the overstrength factor because the seismic loads are high enough already, I don’t want to have to design for double or triple the reaction.
It is precisely because of the myriad amount of load combinations that we insisted that the metal building manufacturer provided the load combinations. They have the ability and the program to do it. They will cry and whine but they will ultimately do it. They can factor the loads as well. You need factored loads because the anchor rod design per ACI 318 App D is based on factored loads. We have found that the metal bldg community has ignored the changes required implicit in App D in regard to edge distance for shear.
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