hoping for 3 photo's here- one of the collar ties, or the bottom brace of the trusses. One of the x braces on the top of trusses. this stops parallelagram like racking. imagine the overhead view of the shop as a square, and the x keeps it square rather than a parallelagram. The final photo should be the angle braces from the bottom of the trusses to the purlins. this also stops racking, but a different direction, it is from running the length of the building, or the tendancy of the trusses to lean over. they also help keep the purlins from bowing under heavy snow loads by using the bottom truss cord strength.