A multi-sheet beam includes sheets pre-shaped and/or pre-formed to have integral features and to cause a final beam shape with non-radiused corners and optimal impact properties when assembled, including beams with constant or varied cross sectional shapes. The non-radiused corners offer excellent impact strength over radiused corners. The sheets are selected to have desired (different) thicknesses and material properties for optimal impact results and low beam weight. To assemble, the sheets are fixtured together and welded to form box beam, such as a two-tube monoleg beam, preferably using welding processes having low heat-affected-zones around the weld. The multiple sheets can include grades of aluminum with high tensile strength well above extrudable grades of aluminum. Alternatively, the multiple sheets can be any grade of steel, such as high strength and ultra high strength steels. The fixturing and assembly technique minimizes capital expense on extruding machines and/or roll forming machines.