The objective of this paper is to provide a unified design method for fatigue loading due to natural wind for highway overhead sign support structures. Whereas the current fatigue design provisions given in the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminairesand Traffic Signals provide fatigue design criteria for natural wind, these provisions are only applicable within certain limitations. This paper provides a comprehensive approach in fatigue design for the treatment of sign support structures, considering dynamic properties of the structure such as material stiffness, mass, frequency, damping, etc. It is applicable for structures where the dynamic response can be approximated by a single degree-of-freedom system. Typical examples include cantilever- and bridge-type overhead sign support structures. The proposed fatigue design approachincorporates these parameters in a simplified step-by-step procedure thatcan be readily used by the engineer. The analytical work performed involved principles relating to random vibration and utilizing the vibration response spectrum (VRS). The fatigue load is selected from the VRS in terms of the natural frequency of the structure, the critical damping percentage (a.k.a. damping ratio), and the annual mean wind velocity of the intended site location.
Samenvatting