The collapse of the I-35W Bridge in Minneapolis, Minnesota has raised questions regarding the performance and possibly safety of steel truss bridges. The failure investigation indicated that the collapse was due to a design error in the gusset plates used to connect the truss members. The findings also recommend that evaluation of truss connections will be needed, which is a deviation from past practice where only members were considered. There are large numbers of steel truss bridge connections that will need to be evaluated. Many connections may be rated as insufficient due to original design or deterioration and effective strengthening and repair methods are needed. However, data in the technical literature are lacking on the behavior and performance of representative large-sized gusset plate connections with complex member interactions and alternative strengthening options. For example, the largest tests reported in the literature are still nearly all less than 1/4 the size of those found in I-35W. In addition, the number of fasteners in these tests is even less, sometimes only 15% to 20% of those found in large, but not uncommon, truss connections. In addition, actual in-situ failure modes, which may be much more pronounced in larger connections, may not be fully understood or captured in tests of smaller specimens. Current work underway at FHWAâ€™s Turner-Fairbank Highway Research Laboratory and at PSU and OSU in Phase I of this project are producing new data on large-size gusset plate performance. However, one area requiring additional investigation is strengthening of existing gusset plate connections.
Experimental and analytical research is proposed. The objectives of this research are to:
1) Develop experimental data for gusset plates strengthened using:
Shingle plates (layered plates)
2) Develop experimental data for repair of corrosion deteriorated gusset plates.
3) Validate analysis techniques or develop new and improved analysis/design methods for effective strengthening of gusset plates based on experimental results.
Both analytical and experimental techniques will be used to meet these objectives. New experimental data will be developed for simulated gusset plates to characterize plate behavior of different strengthening techniques for bridge type gusset plate connections. These data are currently lacking and needed for calibration of the proposed or other analysis methods. Current general purpose FE packages are complex and expensive to run and maintain. Most state DOTs do not have the resources to operate these programs. A directed FE analysis software package under development in Phase I for conducting nonlinear plate analysis with incorporation of the salient geometric and material properties as well as initial imperfections will be modified for implementation of the experimental findings. Results will allow automatic meshing, scripted parametric analyses, visualization of results, and reporting features that present summary results in terms of rating factors, including strengthening alternatives. The analysis results will be compared with industry standard FE packages and also calibrated with available archival and emerging experimental results.