i wish you could give me more details.when the bark falls off is there alot of sawdust or some pest larvae?how old?is there an excretion of sap in places?-this can be borers or pests.if it is just dying from old age(some oaks can live over 100yrs)and bark is peeling while dead branches are falling i would have the tree removed and put something in to replace it so it doesnt become a danger.if you see signs of pest damage,ID the pest ,prune all diseased dying dead limbs,treat it and hopefully it will thrive.if it is from old age the it is dying from inside out and shrinking back from the bark because the living sapwood is dying and there is nothing you can do