For the sustainability of today’s infrastructure, it is critical that engineers are capable of developing economical and safe design solutions for structures such as bridges and buildings. Multiple things must be considered for structural design. Structural members must be sized to resist applied loading conditions while satisfying design code capacity requirements. Design is also dependent on geometry, constructability, cost, material, availability, etc. The focus of optimization is to determine the best solution for a problem that is defined by a set of given constraints. For structural optimization applications, typically the problem is set up to determine the member cross-sectional areas that will yield an overall minimum weight or cost. It can also be a beneficial tool to compare different design alternatives quickly, especially in the preliminary stages of a project. Various approaches for solving optimization problems have been implemented in different fields of research. Traditional techniques such as linear/non-linear programming are available and more recently heuristic algorithms, which simulate patterns of natural phenomena, have been developed. For this research a heuristic Harmony Search (HS) algorithm is used to optimize a steel plate girder bridge. The HS algorithm is a more recent optimization concept that has been implemented within structural engineering research for solving many truss and frame optimization problems. There has been a limited amount of research on the HS algorithm for bridge structure optimization problems. For this project, HS algorithm will be used to optimize two steel plate girder bridges with varying cross-section configurations. Finite Element Models of the structures using the optimized properties will be used to verify demand/capacities and adequacy of the optimized design. Results will also be compared to traditional preliminary bridge sizing methodologies and programs. / Civil Engineering