adjustable tie backs

huangyhg

adjustable tie backs
i have a little job at the moment to design a small tied back 'a' frame to support a snatch block.  nothing difficult about it except the client wants the tie back members to be adjustable so they can change the 'a' frame angle to horizontal on site.  this is because the frame has a restricted clear height and the client wants to reduce the risk of it not fitting.  
the frame will be used on platform topside so hot work is not permitted.
i was thinking about using screw jacks for the two tieback members but have been unable to source something suitable.  the loads are pretty low.
could any members offer up some suggestions?
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how about turnbuckles? if not, cleveland city forge may have other products you can use. here is a link to their catalog
you can make your tie backs out of tubular steal and have two sizes so one can slide inside the other with holes spaced 6" apart for a pin for adjustment
if the frame is to heavy for a man to hold while adjusting then you can add a small block&tackle to support and move the frame while the pins are out for adjustments
or you could just use a chain fault with a lock for a tie back that would support and adjust all in one
in an ideal world turnbuckles would be perfect.  however, i expect these tie backs (tie back is probably not the correct terminology) to be under compression hence i was looking at prop shoring type of products.  plenty of shoring equipment out there but nothing that lends itself to integration with structural steelwork.
i have used the two sliding member arrangement before, and it worked fine, but it was on a much smaller   
scp manufacture a range of push-pul propping which may be of interest:-
in follow-up to framermike's suggestion you might look at premanufactured lally columns as a possible frame   
thanks for all the suggestions.