huangyhg

aci anchor checks
i use asd for my steel design, even with the new code. i know how to use lrfd and am fairly comfortable with it if need be. i have a question though with checking anchor bolts. for a typical industrial structure bent frame (non-building) we typically have a light framed (conveyor) supported at elevation. this gives us a typical wind load uplift at the base plate under dl - wl. all other loadings aside (seismic, etc) what load combination are people actually using in the appendix d design method. we used to design the anchors using asd based on the dl - wl case. looking at the lrfd load combinations the only case that gives us the same (dl & wl) only is the 0.9dl - 1.6wl. this is comparable to the 0.6dl - wl case and is more of a stability case. it seems to me that this is really conservative when the anchor would have a fs = 1.67 using the asd method but more like 3.3 using the lrfd method. it seems that their should be another case to use for design of anchorages. maybe i am missing it so i would like to hear from others on their opinions of this. what i have done (i know their will be plenty telling me how wrong this is) is take my dl - wl result, multiply it by 1.5, and then do the appendix d calculations. this is comparable to the comparison on load factors and safety factors between lrfd and asd. doing the calculations in this method gives me similar anchors and i feel like it is reasonable. if this is completly wrong then i guess i have a lot of structures out their that are going to falling down in short order.
i look forward to your feedback.
i generally use asd loads also. i think the 0.6d+1.0wl is not just a stability combination although i know a lot of folks look at it that way. i apply it to the anchors. i take (0.6xdl-1.0xwl) and then multiply by 1.5 to use appendix d.
i think when you use aisc asd,you must use 0.6 d.l+ 1.0 w.l
when using aisc lrfd,you must use 0.9 d.l+ 1.6 w.l
and the ratio of wind/dead is about 0.6 for the two codes.

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