Method for reinforcing a panel and a method for manufacturing a composite panel implementing such a method

Method for reinforcing a panel (P) in the direction of its thickness E, comprising: - a step a) of providing an flexible elongate reinforcing element (1) with two longitudinal ends (10, 11) having a length L strictly greater than twice the thickness E of the panel (P), - a step b) of positioning and holding said reinforcing element (1) on one side of the panel, termed the insertion side, - a step c) of gripping the reinforcing element (1), at its middle, on the insertion side, - an insertion step d) in which said reinforcement element, gripped by its middle, is pulled through a bore passing through the panel, by folding the reinforcing element back on itself, and as far as a final position (Pf) in which the two longitudinal ends (10, 11) do or do not extend beyond the bore on the insertion side (Ci), wherein a loop (12) of the reinforcing element does or does not extend beyond the bore on the side of the panel opposite the insertion side.