As fiber reinforced polymer (FRP) structures find application in highway bridge structures, methodologies for describing their long-term performance under service loading will be a necessity for designers. The designer of FRP bridge structures is faced with out-of-plane damage and delamination at ply interfaces. The damage most often occurs between hybrid plys and dominates the life time response of a thick section FRP structure. In this discussion a model is developed to address delamination in a hybrid beam under fatigue loading. The methodology employs the quadratic delamination initiation failure criteria, in conjunction with a delamination growth law to describe the out-of-plane damage under bending. These phenomena are combined with the critical element residual strength life prediction tool to determine remaining bending stiffness and moment capacity of a pultruded and hybrid FRP 20.3 cm deep structural shape. The model successfully describes the onset of delamination prior to fiber failure and suggests that out-of-plane failure controls the life of the structure.