A fiber structure woven (10; 20; 40; 60; 80; 90; 110) as a single piece by three-dimensional weaving, the fiber structure having opposite surfaces (10a, 10b) and presenting: • a first portion having a plurality of layers of warp yarns and forming a first portion of the thickness of the fiber structure between its opposite surfaces; • a second portion having a plurality of layers of warp yarns and forming a second portion of thickness of the fiber structure, the warp yarns being arranged in columns each of which includes warp yarns of the first portion and of the second portion; and • in each plane of the fiber structure, a set of weft yarns interlinking the layers of warp yarns of the first portion and of the second portion while leaving at least one non-interlinked zone separating the first and second portions over a portion of the dimension of the fiber structure in the weft direction from an edge of the fiber structure to an end of non-interlinked zone, wherein: • one or more same first weft yarns (t 11 to t 14) interlink layers of warp yarns of the first portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the second portion of the fiber structure beyond the non-interlinked zone; and • one or more same second warp yarns (t 15 to t 18) interlink layers of weft yarns of the second portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the first portion of the fiber structure beyond the non-interlinked zone; • such that the paths of the first weft yarn(s) and of the second weft yarn(s) cross over in at least one transition zone extending in the fiber structure from the end of the non-interlinked zone; and • the transition zone extends in the weft direction over a distance that is greater than the pitch (p) between adjacent warp columns. • a first portion having a plurality of layers of warp yarns and forming a first portion of the thickness of the fiber structure between its opposite surfaces; • a second portion having a plurality of layers of warp yarns and forming a second portion of thickness of the fiber structure, the warp yarns being arranged in columns each of which includes warp yarns of the first portion and of the second portion; and • in each plane of the fiber structure, a set of weft yarns interlinking the layers of warp yarns of the first portion and of the second portion while leaving at least one non-interlinked zone separating the first and second portions over a portion of the dimension of the fiber structure in the weft direction from an edge of the fiber structure to an end of non-interlinked zone, wherein: • one or more same first weft yarns (t 11 to t 14) interlink layers of warp yarns of the first portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the second portion of the fiber structure beyond the non-interlinked zone; and • one or more same first weft yarns (t 11 to t 14) interlink layers of warp yarns of the first portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the second portion of the fiber structure beyond the non-interlinked zone; and • one or more same second warp yarns (t 15 to t 18) interlink layers of weft yarns of the second portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the first portion of the fiber structure beyond the non-interlinked zone; • such that the paths of the first weft yarn(s) and of the second weft yarn(s) cross over in at least one transition zone extending in the fiber structure from the end of the non-interlinked zone; and • the transition zone extends in the weft direction over a distance that is greater than the pitch (p) between adjacent warp columns.