Feasible Range for Midtower Lateral Stiffness in Three-Tower Suspension Bridges

This study investigates the structural characteristics of midtowers in three-tower suspension bridges and proposes a direct approach to determining feasible midtower stiffness for preliminary designs. The lateral stiffness analysis of bridges demonstrates the feasible midtower stiffness is located in a range that can be obtained using a simplified multispan suspension bridge model. This study also defines dimensionless midtower stiffness, and a parametric analysis is carried out in it to examine the effects of different parameters, including the sag-to-span ratio, side-to-main span ratio, dead-to-live load ratio, span length, and traffic load, on the range of dimensionless midtower stiffness. The results illustrate that the range of dimensionless midtower stiffness relies mainly on the dead-to-live load ratio and the sag-to-span ratio. The dimensionless stiffness chart derived from the study is generic and provides an estimate of the feasible midtower stiffness of three-tower suspension bridges with different design parameters. (C) 2017 American Society of Civil Engineers.