M.Z Kabir - Associate Professor
A.E Seif - M.Sc. student, Department of Civil Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Street, Tehran, Iran

This article intends to investigate the lateral-torsional buckling of steel I-beam retrofitted with FRP in an analytical solution considering shear deformation. Primarily, by defining one hybrid element which consisted of isotropic and Classical Laminate Theory (CLT) was used to obtain the stress-strain relation of retrofitted elements of beam. Afterward calculating the total potential energy and applying the Reighly- Ritz method, the lateral-torsional buckling load is achievable. The main contribution of the current study is implementing of first order shear deformation in lateral torsional buckling of retrofitted thin metal section using composite materials and considering large geometry deformation. Considering the out of–plane components of strains and stresses in 3D strain state and regarding the none-linear geometry analysis will lead to obtain the inter-laminar stresses due to the loading to control the debounding of FRP during loading process

Lateral-torsional buckling, FRP retrofitted steel beam, inter-laminar stress, debounding,first order shear deformation