In this work, the frequently detected damages (cracks) of the tank car for oil transportation are analyzed. The effectiveness of the repairs strengthening in the zone of shaped body support of the tank car is evaluated. During the analysis of the damages of 4-axis tank wagon frames, the key areas of cracking were identified: welding seams of manhole hatch, welding seams of shaped pads, welding seams of discharging device, welding seams of the barrel shell near supports, and welding seams of dome. The finite element model of the tank car was elaborated using CAE programme COSMOSWorks®. During calculations, using the FEM model, the loads and reasons that cause cracks in the researched zones were defined. The variant structural calculations showed that the zones of cracking are zones of stress concentrators. The calculated equivalent (von Mises) stresses in the these zones did not exceed the maximum permissible values of the first extraordinary loading mode; however, if the defects (cavities, cracks, etc.) are formed in the researched areas, the stresses decrease 2,7–3,5 times and may exceed the yield strength of the material. A low-quality repair welding leads to stress increase up to 53 %. After few numerical experiments, the insufficient strength and quality of repaired joints in the zone of shaped body support and its joining with the center sill of tank car were confirmed. A proposal for increasing the strength and quality of repair works (as well as for correction of poor repair) of the tank car in the indicated zones was elaborated. As a result, a new design for the strengthening plate with a truncated form was proposed. The use of the new strengthening plate allows reducing stresses up to two times in the researched zone and does not create new stress concentrators.