In order to study the distribution of welding residual stresses in single-sided and full penetration double-sided welded U-ribs, numerical and experimental investigations were carried out considering different deck thicknesses. The birth–death element technique and the heat transfer analysis method were utilized to obtain the welding temperature field and the stress field. The accuracy of the numerical simulation was verified by using the ultrasonic method and the hole-drilling method. The proposed formulas of residual stresses as a function of the weld length in full penetration double-sided welded U-ribs were regressed. The results show that the stress distribution of double-sided welded U-ribs is consistent with that of single-sided welded U-ribs, but double-sided welded U-ribs produce more complex and adverse residual stresses. With the increase of deck thickness, the peak value of the residual stresses in the weld has no significant change and is stable at about 380 MPa. But the residual stresses in the region around double-sided U-rib welds are generally larger than those of the single-sided U-rib welds, and they decrease with the increase of the deck thickness. When the thickness increases to 18 mm, the maximum decrease reaches about 80 MPa. In addition, the calculation errors of new formulas are very small. The accuracy and reliability of numerical simulation results has been verified.