Crane Load Combos

[vandede427]

Ok, Ok, I know cranes have been a hot topic lately, but I think I've got something new to ask.

AISC design guide 7 Part 2 (the section about cranes) page 51 gives combos for 3 load cases in Section 13.7. I've got questions about these.

Case 1 says dead should not be included yet it gives D in the combo. Am I missing something? If D isn't included why is it listed, and how can you not include D in some fashion?

Case 3 states "the total load of combined effects may be multiplied by 0.75." This seems comparable to the ASCE combon of D + 0.75(L+Lr+W), but surely they don't want 0.75 applied to D as well. Also, they're using 1.0E instead of 0.7E.

Case 3 (4) could be written 0.75(D+L+Lr+Cd+E) based on the verbage, but I would think it would be more like
D+0.75(L+Lr+Cd+0.7E).

 

[ToadJones]

In Case 1 it sounds like AISC is disagreeing with AISE on the inclusion of D.

I think in the other cases they may be allowing the user to use the 0.75 factor on the total combined effect because of how extreme the combinations already are.

for example in Case 3.1

full Dead + Full Live + Full snow + Full vertical crane (crane weight + hooked load) + Crane impact + Wind.

This would amount to Armegeddon.

 

[vandede427]

My thoughts too.

I'll throw the 0.75 on everything else, but not D. and I'm also using 0.7E so it boils down to 0.525E in the end.

1.0Dead + 0.75Live + 0.75Snow + 0.75Crane + (0.525Quake or 0.7Wind)

 

[ToadJones]

As with any load combinations that are code prescribed, they are minimums. You are free to use what you like in excess of the code...as long as the owner is happy.

My experience with combining crane loads with building loads is that they can get extremely hairy if you try to use a wholesale approach. I have blindly included all of the wind, live, dead & snow with crane loads on stepped crane columns and wound up with literally hundred of combinations.