Impact loads

[awa5114]

ASCE 7-10 Section 4.6.3 states:

"For the purpose of design, the weight of machinery and moving loads shall be increased as follows to allow for impact: (1) light machinery, shaft- or motor-driven, 20 percent"

I'm confused, is this in ADDITION TO or INSTEAD OF the 1.6 LRFD factor for Live Loads? Also if I calculate an amplification factor using energy methods for impact loading (see page 4

http://www.pdhcenter.org/courses/s164/s164content.pdf)

does that mean I need to increase the impact load even more? or can I use this factor as a substitute for one of the above?

To clarify, I have 3 factors:

Factor 1: 1.6 (ASCE 7-10, Eqn 2)
Factor 2: 1.2 (ASCE 7-10, Sec 4.6.3)
Factor 3: 6~7 (page 4 of

http://www.pdhcenter.org/courses/s164/s164content.pdf)

Which ones should I use? Using all of them would be excessive, IMO.

 

[mike20793]

If you have light machinery or shaft or motor driven equipment, then your live load is increased 20 percent and then factored for design. If you don't have either of those types of equipment, then the procedure outlined in that paper is acceptable. If you're unsure what you have, calculate both ways and use the worst case.

FWIW, the impact factor for AASHTO bridges, which is used to account for vehicle bouncing as it travels over small imperfections in the road surface, is a 33 percent increase in the live load.