ACI Anchor checks

[aggman]

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.

 

[SeanMD]

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.