LRFD load factor on elevator impact load?

[AJF1]

I'm designing an elevator pit that will be supported by steel beams and corner columns. Most elevator manufactures provide drawings with impact loads that area already doubled for impact, which takes care of ASCE 7-10 4.6.2 ("All elements subject to dynamic loads from elevators shall be designed for impact loads and delfection limits prescribed by ASME A17.1"). Well, ASME A17.1 doesn't say much about impact loads as far as I can tell. So my question is, is that doubling of the load acting as an LRFD load factor (meaning, it replaces the normal 1.6 multiplier), or do I still need to use the 1.6 factor on top of that? In ASCE 7-10, section 4.6 on Impact Loads also lists 20% and 50% increases for machinery, so that makes me think the 1.6 applies on top of these , since a 20 or 50% increase would be less than the normal 1.6.

Feedback will be appreciated,

Thanks.

 

[CELinOttawa]

Still need both. The first factor (1.6) is for load uncertainty... The second is separately for instantaneous application of a live load. It comes from a rather neat simplification of the long form formula, the most elegant explanation for which I have seen being in Omer Blodgett's Design of Steel Structures. Apply both, as you can still have an instantaneous application of an unexpectedly high load.

Also, just FYI, the two times factor is only appropriate in terms of elevators based on a long history of performance. All the newer "fancy" elevators are using higher factors, since the factor of two is appropriate for instantaneous applications without a drop in height. The factor I have seen is between two point five and three, due to a drop during the time between something going "wrong" and the safety gadgetry grabbing and arresting the fall of the cab.

 

[wannabeSE]

I agree with CEinOttawa. In ASCE 7, impact is a live load in Chapter 4. So, if strength load combinations are used, the impact load is multiplied by the live load factor, 1.6. If ASD is used, the ASD factor for live load is used: 1. If the impact wasn't multiplied by 1.6, the ASD and strength load would be the same.