The spot-welded
thin-walled beam, a component of automobile body structure, can be supposed as a half-closed-section beam
composed of interval series (closed-section parts and opened-section parts). It is proposed to apply general theory of torsion based on the warping torsion theory (solution of H. Wagner) to this kind of thin-walled box beams with spot-welded joints. Considering the elastic character of weld spots on the thin-walled spot-welded beam, a continuous shear-spring with character of shearing deformation is used for replacing the weld spots on the beam. After a study on this hypothesized spring beam, a method for analyzing warping torsion on spot-welded thin-walled
box section beam has been presented. The accuracy and rationality of the method are proved by comparing theoretical analysis and experimental testing results. This method can be applied to solve for torsional rigidity of the double-hat beams, and the effects of binding warping of double-hat beams on the torsional rigidity was also clarified. The research lay the theoretical foundation for later studies on solving real warping problems with multiple restraints.