Experimental and numerical evaluation of breakaway luminaire poles supported by a transformer base under vehicular impacts

This study evaluates four steel luminaire poles, ranging from 7.62 to 15.24 m in height and from 126 to 345 kg in mass, mounted on TB1-17 frangible aluminum transformer bases through an integrated experimental and numerical framework. Two pendulum tests characterized the fracture behavior of the base and were used to calibrate LS-DYNA models employing a strain-based erosion criterion. Parametric simulations examined the effects of bolt-circle diameter, handhole orientation, impact speed, impact angle, and impact point on failure mode and occupant-risk measures under the Manual for Assessing Safety Hardware (MASH) criteria. A 13% reduction in the bottom bolt-circle diameter reduced the velocity change imparted to the vehicle, indicating that this dimension governed base release within the investigated range. Handhole orientation had a limited effect on occupant impact velocity, which varied by 5.8% across four orientations, but a pronounced effect on roof deformation, which varied by 33% and exceeded the MASH limit for the right-side opening. Low-speed centerline impacts emerged as the critical TL-3 scenario because of prolonged pole-vehicle interaction. Two full-scale crash tests under MASH Test 3-60 confirmed activation of the breakaway mechanism and acceptable performance of the two tested systems. Discrepancies in the post-fracture pole trajectory and localized roof deformation, however, indicated limitations in predicting secondary pole-vehicle contact. The framework provides a basis for comparative assessment and critical-case selection for steel poles supported by the TB1-17 base.