A motor vehicle bodywork beam having a longitudinal direction and comprising: - a main reinforcement provided with a bottom, two walls (52, 53) forming together with said bottom an angle comprised between 80° and 120°, and two arms (54, 55) that are substantially parallel to the bottom and being inclined with respect to the bottom at a maximum angle of 10°; - at least one secondary reinforcement (6, 60a, 60b) provided with a bottom (61, 610a, 610b) and at least one wall (62, 63, 620a, 620b, 630a, 630b) forming with the bottom (61, 610a, 610b) an angle comprised between 80° and 120°, said at least one secondary reinforcement (6, 60a, 60b) is fixed to the main reinforcement; wherein - the main reinforcement and at least one secondary reinforcement (6, 60a, 60b) are fixed at the level of each wall (52, 53, 62, 63, 620a, 620b, 630a, 630b), comprising at least one of the walls (52, 53, 62, 63, 620a, 620b, 630a, 630b) and/or bottom (51, 61, 610a, 610b) of the main reinforcement and/or of the secondary reinforcement (6, 60a, 60b) a transition part (56, 64, 640a, 640b) such that at least one part of the bottom (61, 610a, 610b) of the secondary reinforcement (6, 60a, 60b) is in contact with one part of the bottom of the main reinforcement, - the vehicle bodywork beam comprises at least one closed cell (7, 8, 7a, 7b, 8a, 8b, 9) formed by the assembly of the main reinforcement and a secondary reinforcement (6, 60a, 60b) and comprising four linear segments (71, 72, 73, 74, 75, 81, 82, 83, 84, 85) formed by elements of the walls (52, 53, 62, 63, 620a, 620b, 630a, 630b) or of the bottoms (51, 61, 610a, 610b) of the main reinforcement and/or of the secondary reinforcement (6, 60a, 60b), at least three linear segments (71, 72, 73, 74, 75, 81, 82, 83, 84, 85) covering at least 50% of the corresponding dimension of the cell (7, 8, 7a, 7b, 8a, 8b, 9), so that two segments (71, 73, 75, 81, 83, 85) have an orientation which is transversal to the bottom of the main reinforcement, and the two other segments (72, 74, 82, 84) are substantially perpendicular to said at least two first segments (71, 73, 75, 81, 83, 85) according to an angle comprised between 80° and 120°; characterized in that at least one of the linear segments (71, 72, 73, 74, 75, 81, 82, 83, 84, 85) comprises a groove or a slope or step. - a main reinforcement provided with a bottom, two walls (52, 53) forming together with said bottom an angle comprised between 80° and 120°, and two arms (54, 55) that are substantially parallel to the bottom and being inclined with respect to the bottom at a maximum angle of 10°; - at least one secondary reinforcement (6, 60a, 60b) provided with a bottom (61, 610a, 610b) and at least one wall (62, 63, 620a, 620b, 630a, 630b) forming with the bottom (61, 610a, 610b) an angle comprised between 80° and 120°, said at least one secondary reinforcement (6, 60a, 60b) is fixed to the main reinforcement; - the main reinforcement and at least one secondary reinforcement (6, 60a, 60b) are fixed at the level of each wall (52, 53, 62, 63, 620a, 620b, 630a, 630b), comprising at least one of the walls (52, 53, 62, 63, 620a, 620b, 630a, 630b) and/or bottom (51, 61, 610a, 610b) of the main reinforcement and/or of the secondary reinforcement (6, 60a, 60b) a transition part (56, 64, 640a, 640b) such that at least one part of the bottom (61, 610a, 610b) of the secondary reinforcement (6, 60a, 60b) is in contact with one part of the bottom of the main reinforcement, - the vehicle bodywork beam comprises at least one closed cell (7, 8, 7a, 7b, 8a, 8b, 9) formed by the assembly of the main reinforcement and a secondary reinforcement (6, 60a, 60b) and comprising four linear segments (71, 72, 73, 74, 75, 81, 82, 83, 84, 85) formed by elements of the walls (52, 53, 62, 63, 620a, 620b, 630a, 630b) or of the bottoms (51, 61, 610a, 610b) of the main reinforcement and/or of the secondary reinforcement (6, 60a, 60b), at least three linear segments (71, 72, 73, 74, 75, 81, 82, 83, 84, 85) covering at least 50% of the corresponding dimension of the cell (7, 8, 7a, 7b, 8a, 8b, 9), so that two segments (71, 73, 75, 81, 83, 85) have an orientation which is transversal to the bottom of the main reinforcement, and the two other segments (72, 74, 82, 84) are substantially perpendicular to said at least two first segments (71, 73, 75, 81, 83, 85) according to an angle comprised between 80° and 120°;