Abstract
This dissertation establishes a reliability-based framework for designing pultruded fiber-reinforced polymer (FRP) beams against lateral-torsional buckling (LTB). The study critically evaluates American (ASCE-74) and European (CEN/TS 19101) design standards, revealing that ASCE-74's simplified approach neglects the significant influence of vertical load position, leading to potentially non-conservative predictions for common top-flange loading conditions. To address this limitation, a modified LTB equation is proposed that incorporates load-height effects within the ASCE-74 format. The equation demonstrates markedly improved accuracy, achieving a mean bias of 1.06 with less than 10% coefficient of variation across all load positions. Probabilistic calibration using both reliability analysis and comparative reliability methods yields a strength reduction factor of φ = 0.75 for the proposed equation, substantially higher than the current ASCE-74 value of 0.5. These findings provide validated, evidence-based design recommendations that enhance both the safety and economic efficiency of pultruded FRP structures.