This research investigates the failure mechanism and inelastic deformation of out-of-plane parts beams wrapped externally with steel thin plates. The retrofitting with thin plates is associated with the geometric discontinuity zone making this zone highly vulnerable to crack initiation, stiffness degradation, stress concentration, and extreme damage. The theoretical and experimental programs were matched by simulating three experimental models developed in a previous study to ensure the finite element analysis procedure could achieve accurate results for this modeling. The results obtained by validation, the maximum load and maximum displacement, as well as the relationship between load and displacement, showed a good agreement. The parametric study involved examining thirteen beams divided into three groups. The first group included examining four under out-of-plane parts beams with a varying number of connected segments. The second and third groups included eight models, partially and fully reinforced by thin steel plates. The results showed that the geometric discontinuity altered the mechanism of force transfer from pure flexural stress to a coupled stress compound. This effect is initiated at the connection region where the shear, twisting, and bending developed which initiated cracks at this region and governed the failure. The strength and stiffness decreased when the number of the connected segment increased. The decreased in the load was decreased up to two time due to the increase in the number of discontinuity points. Retrofitting the members with thin plates partially at the connection zone reduced the stress concentration and redistributed the stress far away from the discontinuity zone. Fully wrapping the beams with steel plates enhanced the load resistance by two times in addition to changing the failure mode from brittle shear-flexural to ductile flexural mode.
