This study presents verification methods of current shaft foundation design under linear lateral and torsional loads. Shaft is used as a foundation to support mast arm signal pole structure and transfer loads from superstructures to ground. The capacity of current shaft foundation deployed in the State of Maryland is re-verified due to higher sub-structural strength requirement against super-structural fatigue proposed from the AASHTO LRFD Specification (2015). The shaft foundation verification includes embedment length and torsional capacity. For embedment length check, lateral reactions between soil and shaft are verified by comparing analytical method and finite element method. Wind-induced torque is a design concern for the shaft of a single pole cantilever structure. However, torsional capacity of the shaft foundation of signal pole structures is rarely mentioned in the current design specification. By verifying finite element models with analytical method, torsional effect is further simulated to finite element models to evaluate the adequacy of current shaft foundation design. Results show existing design of shaft foundation could meet requirements to resist lateral force under extreme conditions. For torsional effect, current torsional capacity is less than the torque induced by wind load in the worst soil conditions.
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