Impact Factors in International Building Code

[smartin]

Does anyone know the correct way to apply the impact factors for machinery listed in Chapter 16 of the IBC? Factors are provided for elevator machinery, light machinery, shaft- or motor-driven, etc. I have seen the computation done several different ways and I'm confused as to the correct way. In designing steel beams to support reciprocating machinery, I have seen some engineers multiply the dead load of the machinery by 1.5 (F=1.5*D)and use that as the total force imparted by the machine. I've seen others use the dead load of the machine and then add the dead load of the machine times 1.5 (F=D+1.5D). Any help would be greatly appreciated.

 

[DHKpeWI]

smartin:

I am not an expert, but I believe your first option is correct. In other words 2006 IBC 1607.8.1&2 and the 2005 ASCE-7 4.7 specify that the you increase the weight of the elevator or machinary by the indicated factor (20%, 50%, 100%) and total load becomes 120%, 150%, 100% of the dead load. This total load is considered a live load.

 

[Bagman2524]

I agree with DHK. The load should be 1.5 DL not 2.5 DL.

 

[smartin]

Thank you both for you input. I have one additional question. If you are going to factor loads for LRFD design, would you incorporate similar to the way it is done for crane rails (vertical impact). Assume dead weight of machine is 15 kips and impact is 50% of the dead weight. Would you do it like this?

F = 1.2D + 1.6L

F = 1.2(15 kips) + 1.6(15 kips)0.50 = 18 kips + 12 kips = 30 kips

or would you treat the entire load as a live load

F = 1.6(1.5)15 kips = 36 kips

 

[BlastResistant]

smartin,

1st question: agree with DHK, except 100% increase is 200% of dead load (1.0D + 100%D = 2.0D).

2nd question: entire load is live load.