Preliminary Investigation on the Compressive Strength of Built-Up Compression Members of the Original Champlain Bridge

This study describes a preliminary evaluation of the compressive resistance of built-up members used in steel trusses of an old long-span bridge. This study is part of the research and development programs on the deconstruction of the original Champlain bridge initiated by Jacques Cartier and Champlain Bridges Inc. (JCCBI). Finite element analysis was performed on 14 built-up truss member specimens to be extracted from the Champlain bridge to determine their compressive behaviour and ultimate strength under compression loading. The examined members are made of two face-to-face channels, or four angles connected by batten plates. The analyses accounted for material and geometric nonlinearities. Local and global geometric imperfections were also considered; however, residual stresses were not incorporated in this preliminary exploratory investigation. All members were assumed to be pinned at their ends to reflect the conditions that will be imposed in the planned experimental program. The compressive behaviour and ultimate capacities from the numerical simulations are compared with the predictions from the equations for built-up members that are provided in the 2020 AASHTO LRFD bridge Design Specifications in the U.S. The comparison shows a good correlation for most of the members examined. In the case of built-up members with slender elements, significant differences were observed between the numerical simulations and the code predictions, which is attributed to the fact that local buckling and its interaction with other buckling modes are not well addressed in current code provisions for this type of members.