Beavers usually cut small trees less than eight inches in diameter, but they are capable of cutting down trees over five feet in diameter. So if they wanted to chew through a wooden support, they are physically capable of doing so. However, beavers take down trees to eat and to build their dams and lodges. Pressure treated wood from docks or piers are not suitable for those purposes. It is easy to see the teeth marks in cases where beaver have chewed wood. If you are experiencing damage, and if you send me photos, I can try to identify whether beavers are involved.