Long structural member and blank material

A long structural member, comprising:

• a top plate part that extends in a longitudinal direction of the long structural member, the top plate part including a first lateral edge and a second lateral edge;
• a first side plate part that extends along the first lateral edge of the top plate part, the first side plate part including a first upper edge and a first lower edge;
• a second side plate part that extends along the second lateral edge of the top plate part, the second side plate part including a second upper edge and a second lower edge;
• a first flange part that extends along the first lower edge of the first side plate part, the first flange part including a first connecting lateral edge and a first open lateral edge;
• a second flange part that extends along the second lower edge of the second side plate part, the second flange part including a second connecting lateral edge and a second open lateral edge;
• a first upper corner part that connects the first lateral edge of the top plate part and the first upper edge of the first side plate part;
• a second upper corner part that connects the second lateral edge of the top plate part and the second upper edge of the second side plate part;
• a first lower corner part that connects the first lower edge of the first side plate part and the first connecting lateral edge of the first flange part;
• and
• a second lower corner part that connects the second lower edge of the second side plate part and the second connecting lateral edge of the second flange part;
• wherein:
• in a transverse section of one part or all of the long structural member in the longitudinal direction,
• the top plate part, the first flange part, and the second flange part are flat,
• the first side plate part, the first upper corner part, and the first lower corner part constitute a first thick-wall part, and a thickness of the first thick-wall part is greater than a thickness of the top plate part and is greater than a thickness of the first flange part, and
• the second side plate part, the second upper corner part, and the second lower corner part constitute a second thick-wall part, and a thickness of the second thick-wall part is greater than a thickness of the top plate part and is greater than a thickness of the second flange part.