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Open Web Stl Joist Bridging

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A co-worker asked for my assistance regarding the following. Her project is
the complete architectural, mechanical, sprinkler and electrical upgrade of an
existing one story 30 year old seismic zone 1 building. The roof framing
includes open web bar joists which are laterally braced with diagonal(single
angle) cross bridging. The problem is the mechanical subcontractor has
supported HVAC ductwork, via sheet metal straps, from the cross bridging. I
also noticed a few sprinkler drops also supported by the cross bridging. I
indicated that this was unacceptable since joist bridging is not intended as a
support for mechanical equipment. Naturally, the field response was "show me
where this prohibition is indicated within the CD's". 

  Normally, a project's steel joist specification includes this requirement.
However, no new steel joist installation is required for this project and an
associated spec section was therefore not included within the CD's. Nor does
the project's general mechanical specification does not address this issue.
Our office's mechanical engineer stated that SMACNA does prohibit this type of
support. I also reviewed the SJI spec's and again found no definitive
direction. Can anyone refer to other guidance for this type of situation?

Thanks,

Charlie Canitz, PE
Bel Air, MD