SEF Spring Lecture 2026 - Charles Pfeifer’s structural analyses and Henry Flad’s balanced cantilever erection of the St. Louis Bridge, 1867-1874

Henry Flad’s and Charles Pfeifer’s contributions to the conceptual design of the St. Louis Bridge are described in the context of the Coblenz Bridge over the Rhine, completed in 1864. Pfeifer used linear-elastic, non-prismatic beam models and Navier’s moment-curvature equation for curved beams for structural analysis of the arches. Pfeifer combined effects of partial gravity live loads and temperature changes and sized the chords and diagonals. His results are assessed by SAP2000 computer analyses. Flad’s patented system for controlling the principal stay force during the balanced cantilever erection of the arches is explained. Observations are made on the significance of the St. Louis Bridge on American bridge engineering. Learning Objectives -Understand Claude Navier's 1826 derivation of the moment-curvature and displacement equations for curved beams. -Know the use of the moment-curvature and displacement equations for analysis of statically indeterminate beam problems. -Understand active, albeit manual, control of a stay force. 1 CE Credit Presenter: Dario Gasparini