Institute for Transportation

About the research

Cantilevered traffic sign support structures are subject to wind and truck-induced gusts, which generate torsional and flexural forces that are transferred to their foundations. To standardize the design and construction of these foundations, the Wisconsin Department of Transportation (WisDOT) has developed pre-designed foundation plans.

Focusing on the transmission of moment and torsional forces, this study examined the loads transferred to the foundations of cantilevered traffic sign structures under wind loading conditions. The primary objective was to evaluate whether the current foundation designs are adequate or potentially over-designed.

Two test structures with drilled shaft foundations were subjected to both static and dynamic loading. The investigation analyzed load transfer from the superstructure to the foundations, assessed foundation behavior, and explored opportunities for optimized design. This was accomplished through a combination of geotechnical testing, instrumentation-based data collection, finite element modeling (FEM), and structural health monitoring (SHM).

Model validation was achieved by comparing results from free-vibration and static pull tests with EM outputs. A parametric study further informed the optimization of foundation designs. The results suggest that the current foundation designs, while structurally effective, may include conservative assumptions, particularly in terms of foundation depth, relative to the actual service-level demands observed in testing and modeling. The analysis indicates that it may be possible to reduce foundation depth while still maintaining acceptable performance limits, thereby supporting opportunities for more efficient foundation designs in future practice.