Optimal design of longitudinal stiffeners of unsymmetric plate girders subjected to pure bending

This paper aims at investigating the optimum positions and the required flexural rigidity (γrq) of a single and two longitudinal web stiffeners of unsymmetric plate girders subjected to pure bending by using gradient-based optimization algorithms. The optimization procedure is performed into two steps: The first step is to maximize the bend-buckling coefficient kb generated from eigenvalue buckling analyses, and then the second step aims to minimize the flexural rigidity of the stiffeners (γ). This procedure is implemented using the Abaqus2Matlab toolbox which allows for the transfer of data between Matlab and Abaqus and vice versa. Based on this research, the optimum locations of the stiffeners are recommended for the unsymmetric plate girders under pure bending. Additionally, equations are suggested to determine γrq of the longitudinal web stiffeners of the unsymmetric plate girders. These proposed equations are more realistic in the practical designs than those recommended by AASHTO LRFD specifications and several works in the literature in which γrq of the longitudinal web stiffeners is determined based on the simply supported plates but not the unsymmetric plate girders under bending. •The optimum stiffener location of the plate with a single stiffener and two stiffeners is at around 0.42Dc and around 0.25Dc and 0.56Dc, respectively, regardless of the asymmetry of the girder section.•γrq obtained according to the AASHTO LRFD requirements is too conservative in cases ϕ> 1.0 but not conservative in cases of ϕ≤1.0.•The formulas for determining the minimum flexural rigidity requirement of a single and two stiffeners are suggested for practical design purposes.