A woven preform used to reinforce a composite structure which includes a central portion (6,10) having a plurality of interwoven layers. The preform also includes first and second end portions (4,12) having a plurality of independent woven layers (50) that are integrally woven with the plurality o interwoven layers in the central portion (6,10) and which extend along the entire length the preform. Interspersed between the plurality of independent woven layers (50) in the first and second end portions are bias plies (26). The first and second end portions can have through thickness reinforcements (71) comprising reinforcement fibers that traverse through the independent woven layers and the bias plies, locking them together.