Harry W. Nice Bridge Replacement – Stability Analysis of Steel Girders
The main spans of the replacement Harry W. Nice Bridge consist of three continuous spans, and the span length is about 282’ for each side span, and 350’ for the center span, as shown in following figure. The superstructure consists of 6 steel girders, whose web plates range from 114” to 144” in height.
The six girders were erected in three pairs (girder pair 1-2, 3-4, 5-6), and the maximum length of girder segments is 238’. The intermediate cross frames and top lateral bracing diagonals within the girder pairs were installed before the lifting and field splicing. Prior to the crane release, temporary cross struts were used to brace the top flanges of adjacent pairs of girders at three locations in each span (at mid-span and two ends) to improve system stability in absence of the cross frame installed between the girder pairs afterwards.
The Skanska-Corman-Mclean JV is the General Contractor, who in turn hired CHI Consulting Engineers to perform stability analysis of the steel girders during the erection.
The erection of steel girder system is a challenging task, as improper erection and lifting procedures often lead to instability incidents compromising the safety and constructability of the structure. CHI performed comprehensive 3D finite-element eigenvalue buckling analyses of the structural system for each erection and lifting stage, with steel thin-walled structures being modeled with high-order shell elements and detailed geometry allowing high-precision capture of its structural behavior. This model identifies potential Global Lateral Torsional Buckling (GLTB) modes and other local failure modes and verifies the adequacy of structure against them.
The stage-by-stage computational stability analysis provided in-depth insight into the safety of erection plans and led to the development of erection plans with more efficient lifting, installation, and bracing procedures that allow improved safety, greater economy, and reduced construction time for the contractor.