Understanding and Mitigating the Dynamic Behavior of RICWS and DMS under Wind Loading

Abstract

Dynamic Messaging Signs (DMS) and Rural Intersection Conflict Warning Signs (RICWS) are roadside signs that feature much larger and heavier signs than are typically placed on their respective support systems. There is a concern that the excess weight and size of the DMS and RICWS, in conjunction with their breakaway support systems, may introduce wind-induced vibration problems not seen in the past. The AASHTO 2015 LRFD Specification for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (SLTS) does not yet address vibration design for these nontraditional roadside signs. Research was done to explore the wind-induced vibrations in the DMS and RICWS. The DMS support system, specifically the friction fuse connection, is susceptible to the formation of stress concentrations and potential fatigue issues. A dynamic numerical model was validated with experimental field data and used to evaluate the fatigue life of the DMS support system instrumented in the field. The fatigue life of the DMS instrumented in the field was found to be approximately 23.8 years. Results of the analysis should be expanded beyond the behavior of the specific DMS instrumented in the field to encompass other varieties of the DMS in service. Large amplitude oscillations under wind loading have already been observed in the RICWS. Research was done to explore the wind-induced dynamic behavior of the RICWS and determine suitable modifications to the RICWS support system for reducing the amplitude of the wind-induced oscillations. Based on data collected from a RICWS instrumented in the field and experiments done on a scaled model of the RICWS at the St. Falls Anthony Laboratory, vortex shedding was identified as the predominant wind phenomena acting on the RICWS structure. Modifications to reduce the impacts of vortex shedding, such as fins, appear most appropriate for reducing the amplitude of the wind-induced oscillations. The effectiveness of the recommended modifications requires further exploration with the experimentally validated numerical models of the RICWS.