Hi John, yes I do theatre and show rigs every week.  Firstly I'd need to know what the SWL & UDL loads are for your rig.  This is so it keeps you right that it cant be over loaded.  For sign off procedures it should be checked at least annually by a competent person (usual and insurance inspector).  It should be checked and signed off each time this is used (I personnaly use scafftags for this and hand a checksheet to the event manager for their file).  If you know the type of anchor fixings used the manufacturer will be able to supply information on what SWL they can take but remember your rig is only as strong as its weakest link.  Depending on how its made up exactly you would need to determine this factor!  Anymore info required you can email me anytime.

brian.campbell@ssearenabelfast.com