I recently decided to experiment and make my own SIP.. today i poured concrete in my SIP and it failed at the seams... without boring u all w/ too much detail... what is a good "Seam" connector to join 4'x8' high sheets of plywood (butt joint, not tongue and groove).. walls are a total of 6" thick... the problem i have is when concrete is poured, the most pressure is at bottom.. as it gets higher the pressure decreases... well the wall seperated at the seam and concrete poured out (only made 2 panels)....i need a connector to "Join" the 2 boards so they are flush (tongue and groove is a good connection, but i dont have that) and also a way to secure em tight so that when concrete is poured, it doesnt make the board bow...

thanks for the help..

That doesn't sound like a SIP to me... sounds like a poured-in-place concrete form.  Where is your insulation?  SIPs don't have concrete on the inside, they have insulation on the inside.  If you have concrete on the inside, you might have an ICF (insulating concrete form), but plywood isn't exactly a great insulator.  Unless you're experimenting with expanded/aerated concrete of some sort, which would be somewhat insulating...

Actually... good point.. Poured in place concrete..
its plywood.. w/ 3"concrete made the plywood bow and come out of the seam.. this is my only obstacle... i need to figure out a way to to secure the butt joints of the plywood...
i have spent the last hour and a half reading a ton of posts on this site... this is a spectacular forum.. i really enjoy reading the forums...

i appreciate the help and response...

You need to brush up on concrete construction try "The Contractor's Guide to Quality Concrete Constrction"-  chapter 5 formwork, by ACI & ASCC