Posttensioned Trusses: Analysis and Design

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.