so 15mm then.

Would that need to be 15mm x 4" or 6"

Sorry to be a pain

No worries I was actually just confirming glass thickness.

Here's what I got for you:

First off this analysis may not be correct in actual displacement values as representing silicon seams and dynamic behavior is difficult and unnecessary.

So we start off by seeing what you had before, not intirely sure but my experience shows most of these larger tanks have 18" wide center brace with about a 1" trim around the top:
http://i11.photobucket.com/albums/a1...nterbraced.jpg
This is showing a displacement of 0.26mm and a somewhat unhealthy displacement pattern.

The goal here would be to at least match the displacement, as already stated the actual number isn't important, we just want to come close to matching it.

First lets compare to no bracing:
http://i11.photobucket.com/albums/a1...entnobrace.jpg
This shows max displacement of 2.22mm, so center brace does a lot.

Now lets try a 15mm x 4" Euro Brace, bigger than 4" and it's awkward, any smaller than 4" and the glass shop will be b*tching.
http://i11.photobucket.com/albums/a1...teurobrace.jpg
This shows 0.36mm max displacement and a healthier displacement pattern. This will be good, not much difference from the center brace.

However we'll take it one step further and place in 2 center braces 4" wide. Not ideal but better than the large one in the center.
http://i11.photobucket.com/albums/a1...cewithdual.jpg
Well look at that 0.26mm max and way better displacement pattern than the center brace alone.

I leave the choice up to you, but it's interesting to see, that center brace does a good job no wonder the manufacturers use them, cheap and effective. Just sucks for us.

HTH

Holy Crap!

I can't thank you enough for that. I think I'm going to go for option 4.. I'd rather be safe then sorry.

neat analysis plots

Robb you had 3 400w, seems the brace breaking might have been for the best for positioning your reflectors for coverage (***** about the extra cost and hassle though)

No problem, glad to help.

Yeah in the end I'll be much better off with that brace being gone. But your right, it will be a pain in the !@# getting there.

Wow those stress plots are really cool!! [/nerd]

Ditto!

They helped me make a decision I have been struggling with. Thanks!

They're actually displacement plots, I figured they would be benificial to most people with similar tanks.