Conveyor Bridge Seismic Design Forces

[larsacious]

I am classifying a conveyor bridge for an industrial facility. The bridge is constructed of tube steel chords and angle diagonals. The structure is classified as seismic design category D. This is a non-building structure with a weight of less than 25% of the combined weight of the bridge and supporting structure so ASCE 7-05, section 15.3.1 applies and directs me to chapter 13. Table 13.5-1 has coefficients for architectural components and none of which seem appropriate. Section 13.1.5 states that if the nonbuilding structure can not be classified in tables 13.5-1 or 13.5-2 then the R from chapter 15 should be used. Since it is a horizontal spanning bridge, I am having difficulty justifying a classification in either Table 15.4-1 or 15.4-2. Is there anyone out there who has run into a similar situation? If so, please let me know how you handled it.

 

[BENDOG]

See attached article from Structure Magazine July 2008. The authors recommend R=2.5 for conveyors.