A design methodology to predict optimum post-tensioning forces and dimensioning of the cable system for hybrid cable-stayed suspension (HCS) bridges is proposed. The structural model is based on the combination of an FE approach and an iterative optimization procedure. The former is able to provide a refined description of the bridge structure, which takes into account geometric nonlinearities involved in the bridge components. The latter is utilized to optimize the shape of post-tensioning forces as well as the geometry of the cable system to achieve minimum deflections, lowest steel quantity involved in the cable system and maximum performance of the cables under live load configurations. Results are proposed in terms of comparisons with existing formulations to validate the proposed methodology. Moreover, parametric studies on more complex long span structures are also developed to verify existing cable-dimensioning rules and to analyze between HCS bridges and conventional cable-stayed or suspension systems. values arising from previous iteration step or trial values obtained by preliminary dimensioning rules stiffening girder variable pylon variable stay variable hanger variable main cable variable cross-section area incremental cross-section area of the cable half girder cross-section width cable-stayed bridge girder depth dead load configuration material elasticity modulus main cable sag self-weight per unit length pylon height initial main cable horizontal axial force hybrid cable-stayed suspension bridge moment of inertia with respect to the i-axis factor torsional stiffness number of iterations in plane flexural top pylon stiffness lateral span length portion of the main span without stays central span length ith cable length girder total length live load configuration number of cables live load per unit length total cable steel quantity stayed-suspension coupling parameter incremental initial stress in the ith cable cable stress under self-weight loading initial design stress of the ith cable allowable cable stress incremental allowable cable stress suspension bridge component of the displacement field along i-axis longitudinal stay geometric slope maximum allowable displacement stay spacing step maximum longitudinal main cable geometric slope stress performance factor of the ith cable material specific weight strength performance factor of the ith cable cable cross-section optimization factor cable stress optimization factor component of the rotation field around i-axis 
Optimum design analysis of hybrid cable-stayed suspension bridges