Moving collar ties

[Mcblurter]

I searched the archives and couldn't find info on this so hope it isn't an often asked thing. Barry White gave me a great link to study the terminology so I'm not asking about thingy me bobs and whosiwhatsits.
I am putting some flooring (5m x 3m) in the roof space and the collar ties are at about waist height making moving about quite difficult. Can I move these up? I was hoping I could move them up so they would be half their original length, thinking I could put two on each rafter. Is there any hazards with this, or any advice. Also if I can shift them is nailing okay or better to bolt them, would I need to double up for extra strength or not and is it safe or not to actually remove some altogether?
Cheers
Mcblurter

[Termite]

Collar ties are under compression in a loaded roof, if you move them up then you are moving the support point for the rafter with a high risk of the section below the collar tie sagging.

[journeyman Mick]

Mcblurter,
not something to even consider without consulting an engineer. I'm guessing that if he did okay it the process would entail oversize ties, lots of bolts and some steel pieces to bolt onto the rafters. (Ie probably more work than it's worth.

Mick

[Mcblurter]

Thanks Mick and Termite
Not worth the trouble, good exercise to keep ducking anyway!! Thanks for the advice. So many things just seem so simple that actually aren't.
Cheers
Mcblurter

[Jacksin]

Far be it from me to question the learned folk here, and I guess its a bit dicey, but if he was to put one collar tie lower (possibly made of steel rod, plated and bolted each end) and one higher. would that not stop the rafters spreading, and assuming the underpurlin is adequate I wonder if there would be any 'sag'?

[Termite]

Jack, two things, he wants to move the collar ties up so he can get walk/storage space and also he may be in a situation where there are no purlins. Collar ties are under compression, its the ceiling joists that are under tension.