Timber Utility Pole Fracture Mechanics Due to Non-Deformable and Deformable Moving Barrier Impacts 2011-01-0288

The energy dissipated by the fracture of wooden utility poles during vehicle impacts is not currently well documented, is dependent upon non-homogenous timber characteristics, and can therefore be difficult to quantify. While there is significant literature regarding the static and quasi-static properties of wood as a building material, there is a narrow body of literature regarding the viscoelastic properties of timber used for utility poles. Although some theoretical and small-scale testing research has been published, full-scale testing has not been conducted for the purpose of studying the vehicle-pole interaction during impacts. The parameters that define the severity of the impact include the acceleration profile, vehicle velocity change, and energy dissipation. Seven full-scale crash tests were conducted at Exponent's Arizona test facility utilizing both moving deformable and non-deformable barriers into new wooden utility poles. The vehicle energy was dissipated in a bi-modal event for the non-deformable barrier tests and a tri-modal event for the deformable barrier tests. In the deformable tests, the three modes were identified as 1) deformation of the vehicle structure, 2) fracture and separation of the pole from its base, and 3) acceleration of the pole out of the vehicle path. The analysis associated with these test results provided a better understanding of pole fracture mechanics and corresponding vehicle kinematics as well as the energy dissipation during the full-scale dynamic events.