A device for reinforcement of hollow structures such as aircraft boxes, composed of a front panel, an upper panel, a lower panel, and a rear panel, the device comprising a network of reinforcement rods with the ends attached to at least some of the panels comprising the structure. The device comprises at least a first rod and a second rod, both inclined, the first end of the first rod being attached to the internal side of the front panel, the second end of the first rod being attached to the internal side of the upper panel, the second end of the second rod being attached to the internal side of the lower panel, the device comprising in addition a third rod connecting said second ends of said first and second rods, the first, second and third rods thus comprising a reinforcement triangle.