Decks, Patios, Porches and Docks - shaky deck

My deck is 15 years old and shakes a bit sideways when someone walks on it. I put 'V' type boards from the posts to the beams (deck is on 2nd floor) to stop this action but didnt seem to help. I cant see any sign of movement under the deck but it still shakes. Any ideas on types of bracing I might add? Or?

Welcome to the forums! Is there a deck below this one? Maybe you could post a couple of pictures from different vantage points on a site such as photobucket.com so we can look at the structure and hopefully give better advice.

There is no deck underneath. It is held up with 4X6 posts under 4X10 beams and 2X10 joists with 2X6 decking. Posts are 6' apart and the joists are 16" oc. There are a set of beams 10' from the house and another set of beams 14' from the house. The deck is 48' X 16'. I dont have any pictures but will try to get some. The inspector asked if I was building a parking structure so I think the supports are solid enough but am just concerned about the lateral action. Thanks for your time...

How high is the deck? It probably needs some diagonal lateral bracing, from bottom of post up to the top of post or beam.

Yes, I suspect that Dooer is right.

Your deck extends up to the second level of your home and is it secured to the house in any way or just to the support posts?

If it is secured to the house then you need to add cross-bracing to the outside posts. Run a 2x6 from the bottom of one post to the top of the post closest to it. Then on the other side of the post do the same but opposite direction, so that when you stand in the yard and look back at the house it looks as though you made a big X.

Do this on all of your posts. It'll look like this:

XXXX - see what I mean?