Replumb the barn so it is true and straight. The first and most simple step requires the addition of horizontal boards to the outer sides of the barn. Treated 2-by-6 lumber can be attached to the barn poles using exterior wood screws. Beginning at the bottom of the poles and attaching one complete run of boards will begin to strengthen the barn, but for a greater effect, run several boards horizontally and space them 4 feet apart up the barn poles. Continue this all the way around the barn until the structure is completely stable.
Next, add cross-bracing on the inside of the walls. Begin at the bottom of one wall corner and extend a 2-by-6 to the top of the opposite corner of the barn wall. Do the same for the top and bottom of the other side to form an X on one single wall of the pole barn. Repeat this bracing on as many walls as you wish--the more, the better.
Lastly, adding angle bracing to the top corners, where the poles meet the roof beams, will further strengthen the pole barn. This intersection creates a 90-degree angle. The bracing boards are shorter--only 24 to 36 inches in length. Cut both ends of the brace and place it into that angle, one side against the horizontal edge of the ceiling line and one side against the vertical side of the support post. Do this in all corners where the vertical posts intersect with the horizontal roof beam.