Abstract
More than 80% of the steel truss bridges inventoried in the United States are structurally deficient and or functionally obsolete. Posttensioning these bridges using different posttensioned tendon layouts can be a cost-effective method to strengthen them to meet current and future loading and traffic requirements. A method for the structural stiffness analysis of posttensioned trusses is suggested. The stiffness matrices of straight, one-drape, and two-drape tendon layouts are developed. The tendon layout need not coincide with the truss members. However, it can be externally or internally attached to the truss. A closed-form solution for the relationship between the cross-sectional area, posttensioning force of the tendon, and the desired final member stress after posttensioning is derived for a statically determinate truss. Posttensioning enlarges the elastic range, increases the fatigue resistance, increases redundancy, and reduces deflection and member stresses. Thus, the remaining life of a truss bridge can be increased relatively inexpensively.