Structural response under combined bending (M) and torsion (T) of pultruded Glass Fiber Reinforced Polymer composite hollow circular and square sections has been investigated, using unique experimental facility for combined loads. Prior to determining combined response, bending and torsional strengths at failure were found separately for all test sections. To evaluate structural response, strain gages were attached at 6 to 12 critical locations of each specimen. For each cross-section, three samples were tested under combined load combinations, i.e. (0.25 M_max, T_Failure), (0.50 M_max, T_Failure) and (0.75 M_max, T_Failure). The results have been presented as M vs , T vs , and M/MmaxvsT/Tmax. Local bending effect are found to be significant under point loads, even though they are distributed over a small area. The interactive plots exhibited three distinct zones, i.e. bending moment dominated zone, torque dominated zone, and transition zone. The failure modes revealed a distinct pattern with crack initiation sites and propagation directions. The potential energy method of bent and twisted specimens of isotropic thin-walled sections has been extended to thin-walled orthotropic members. Finite element analyses using ANSYS-SHELL181 was carried out to develop torsion-bending interaction response and compare with experimental data. Principal strain to failure predictions under combined loads, except under pure bending, resulted in a constant strain to failure for a given fiber architecture.