Structural Analysis and Load Test of a Nineteenth-Century Iron Bowstring Arch-Truss Bridge

Abstract

A structural study examines the oldest remaining metal bridge in the Commonwealth of Virginia, a wrought-iron bowstring arch truss, designed and manufactured by the King Iron Bridge Company. Finite-element analysis is used to evaluate the interaction between the arch and truss, and the results are compared with field measurements from a live-load test. The study reveals that diagonal truss elements decrease arch bending by distributing concentrated vertical loads along the arch toward the abutments in a way consistent with that of modern network arch bridges. When the truss diagonals are absent, the vertical bridge-deck deflection is doubled. Underslung portal frames provide lateral stiffness to the arch, an innovation that accommodates a shallow arch profile conducive to transportation and erection.