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Crane Impact Loads

Crane Impact Loads

Crane Impact Loads

(OP)
In ASCE 07, Section 4.9, the code reads that the crane impact loads are to be applied to design of runway beams, including connection and support brackets. If we have a crane which is supported from the truss panel point, do we have to design the entire truss members (top chord, bottom chord, verticals and diagonals) for the impact load? Code just says the runway beam to be designed for the impact load. So can we design the truss just for the straight crane loads with no impact.

RE: Crane Impact Loads

I don't know the correct ASCE 7 interpretation, but the way I see it, you either need to:

Provide a complete load path for the crane loads with impact to the end of the structural system
-or-
Justify that once the load has reached certain elements of your truss, that any dynamic/impact effects have been attenuated by the flexibility of the structure (the deflections required should be within acceptable limits).

Which of the two is easier depends on your truss arrangement.

RE: Crane Impact Loads

We always carried the load down the structure as it's considered a live load in ASCE 7 and should be treated similarly.

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

RE: Crane Impact Loads

In the practical application of crane impact loads, the custom has been that the columns carry the rated live load, but you need not consider the additional impact percentage on the column. However, a roof truss is very different from a column, and given the lightness of a truss, as compared to a column, I would think that in this case the additional impact percentage should be carried through the connection to the truss framing.
Dave

Thaidavid

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