Deck Tension DTT1Z Ties - Are they necessary??

[johnpaul23]

Hello,
New Engineer here. I am having trouble understanding the necessity of deck tension ties. So I understand having them act as hold downs at each end of the deck to counteract a prying force. But I have also seen them called out at every 8'? Why is that? It seems to me like that would be like putting additional hold downs in the middle of a shear wall. Are these tension ties really doing anything at mid diaphragm?
Thanks

 

[jerseyshore]

In nearly every US state code I've worked with, ties are required on decks being supported by the house. It's usually a minimum of two, but sometimes 4 depending on which tie you're using. They are definitely necessary because look up deck failures, tons have failed just by falling off the house.

 

[phamENG]

They serve two purposes.

1) Chord connections for the diaphragm (which I believe is what you're suggesting)

2) connect the deck to the house for lateral loads away from the house. Without them, you're relying on either tension perpendicular to the grain of the last deck board with a nail in the ledger and a nail in the joist (not good) or tension/prying in the joist hangers (also not good).

 

[johnpaul23]

Thank you for the replies. @phamENG, so the big difference in the tension tie is that it connects the joists themselves to the house, instead of the joist to ledger, ledger to house? So we are basically preventing the joists from ripping away from the ledger?

 

[phamENG]

Essentially, yes.