The invention relates to a flat position single-seam symmetrical 
welding method for an orthotropic plate U-shaped rib corner 
welding seam 
robot. The method comprises the following steps that A, U-shaped rib groove 
processing, compression and 
bridge deck plate blanking are carried out for obtaining a U-shaped rib plate unit through 
assembly; B, the U-shaped rib plate unit is horizontally placed on a reverse deformation turning moulding 
bed, and the position of the U-shaped rib plate unit is regulated so that the center line of the U-shaped rib plate unit is coincident with the center line of the turning moulding 
bed; C, the U-shaped rib plate unit is clamped and fixed, in addition, reverse deformation is carried out, the 
turning angle of the reverse deformation turning moulding 
bed is regulated so that a U-shaped rib to be welded is positioned in the horizontal position, and in addition, an angle scale is used for detection; D, the 
welding program and the welding specification parameters are input into a 
robot automatic welding 
system so that two welding hands arranged on a 
robot cantilever respectively and simultaneously carry out flat position single-
seam welding on the angle welding seams of the two sides of the U-shaped rib. The method provided by the invention has the advantages that the U-shaped rib is assembled on the platform, the assembling precision is high, and a gap between the U-shaped rib and a 
bridge deck plate can be enabled to be within 0.5mm. The robot automatic welding hand has the 
electric arc tracking function, the change of the welding current and the 
electric arc voltage is sensed through swinging in the 
welding process, and the small deviation of a weld pass is corrected.