Mitigating fatigue in cantilevered overhead sign structures



  • Cantilevered overhead sign structures (COSSs) are widely used across highways in the United States. Several cases of excessive vibrations and failures caused by fatigue wind loads from natural and truck-induced wind gusts have been reported. Not enough research has included the effect of making structural design modifications on the fatigue performance of COSSs. Under fatigue wind-induced loads, the dynamic characteristics (frequency and damping) of COSSs are important parameters affecting their structural behavior. When frequencies of wind load and the structure match, resonance may occur, causing excessive vibrations, depending on the frequency value. If accompanied fatigue stresses exceed the fatigue endurance limit, failure occurs after a certain number of loading cycles. The objective of this study was to investigate stiffness and mass distribution of COSSs to control the structural frequency, thus mitigating fatigue caused by wind-induced gusts. For this purpose, modifications in the members' shape, arrangement, size, and layout of structure were examined. Three layouts were compared: four-chord, two-chord, and monotube COSSs. These layouts were designed according to the 2013 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals and modeled with SAP2000. Wind pressure power spectral density and time history loading functions were applied to these structures to simulate natural and truckinduced wind gusts, respectively. Results showed that the vertical monotube COSS design with curved end post had the least mass, but fatigue stresses were comparable with the four-chord COSS. The two-chord COSS design had the largest mass and exhibited the highest fatigue stresses.
  • Authors

    Digital Object Identifier (doi)

    Start Page

  • 18
  • End Page

  • 26
  • Volume

  • 2522