Study of the effects of wind power and vortex-induced vibrations to establish fatigue design criteria for high-mast poles

Description

Traffic signal and high-mast poles are used by transportation agencies to control and illuminate intersections; their structural design is governed by national specifications. High-mast poles are luminaire supports located near highway interchanges that range from 80 to 180 feet in height. These tall flexible structures are susceptible to wind vibration which may lead to fatigue cracking near discontinuities and base connections. In a previous related study conducted by the University of Wyoming (Phase I), fatigue cracking of traffic signal poles was determined to be related to the average wind speed (Price 2009). However, high-mast data did not indicate the same direct average wind speed fatigue cracking relationship behavior. In this continuing work, the research goal is to gain a more complete understanding of the relation between wind speed and high-mast pole cracking. Surveys were sent to more state bridge engineers to further the data collection of Phase I. It is hypothesized that the cracking of high-mast poles is caused not as much by direct wind speed, rather it is caused by the resonant displacements of vortex-induced vibrations (VIV). The Canadian Standards Association (CSA) code models VIV and was, therefore, selected to complete Phase II of this research. It was used to create a spreadsheet which predicts amplitudes of vibration of a high-mast pole located in Laramie, Wyoming. The output data were compared to field data of a local pole. This sheet was further used to predict base stresses and fatigue life as a function of local wind data. The Phase II analysis process produced high-amplitude predictions compared with local field data; therefore, self-limiting concepts were studied in Phase III. A self-limiting concept for an oscillating member hypothesizes that the natural properties of the pole and the fluid interaction keep amplifications under a predictable maximum.

Subjects

Series Statement

• MPC report -- no. 11-240

Links

• External source