Welding method and steel plate deck

A method of welding a deck plate and a closed section rib both constituting a steel plat, wherein

• the deck plate is comprised of a steel plate having a first thickness;
• the closed section rib is comprised of a steel plate having a second thickness, the rib comprising the steel plate thereof bent to define a rib, to define an edge of the steel plate forming the rib, and to define a root portion formed at the edge of the steel plate forming the rib;
• the method comprising:
• working the root portion of the closed section rib to have a flat surface in parallel with a surface of the deck plate, wherein a dimension of the flat surface along a surface direction of the steel plate deck is 5% to 50% of a thickness of the steel plate deck forming the closed section rib;
• and
• welding the deck plate and the closed section rib while making the flat surface of the closed section rib be in contact with the surface of the steel deck plate.