Abstract: In frames composed of thin-walled members, the transformation of warping deformations between beams and columns at beam-to-column joints is incorrectly treated by the software ANSYS and ABAQUS. In this paper, the panel zone is seen as a cross-beam system composed of flanges of beams and columns. The out-of-plane bending and twist of the flanges are considered. Using relations between the flange forces/corner point deformations of the panel zone and the member forces/member deformations, explicit formulas are deduced to relate the bimoments to the warping deformations on the 4 interfaces between the panel zone and the beams/columns. -shaped frames are presented, FE analysis is carried out using shell63 element. The comparison with FE analysis verified the accuracy of the proposed semi-rigid warping model. From the results of the examples, for the beam-to-column joints stiffened with extended flanges in rectangular frames, the relation between the warping deformations of columns and beams at the joint, , is approximately valid.