Design Fatigue Load of Sign Support Structures Due to Truck-Induced Wind Gust

Abstract

This research presents a universal approach for determining the design fatigue load due to truck-induced wind gust for highway overhead sign support structures. The fatigue load is determined on the basis of the dynamic properties of the structure. It is applicable to structures in which 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 developed approach incorporates these parameters in a simplified systematic procedure that can be readily used by engineers. Principles relating to mechanical vibration and utilization of the shock response spectrum were used to determine the load. The fatigue load is selected from the shock response spectrum in terms of the natural frequency of the structure and the speed of the truck. Comparisons were made with the current truck-induced gust fatigue design provisions given in the 2009 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals. Additional comparisons were made with dynamic finite element analysis of a modeled support structure.

Advanced Analytical Methods for Fatigue Assessment of Ancillary Systems in Highway Bridges

“…Wind-induced vibrations, in particular, are the primary source of fatigue damage in highway sign structures, while traffic-induced vibrations can also contribute to fatigue damage. Furthermore, galloping and vortex shedding are two important phenomena that can cause fatigue damage in these structures as well [5][6][7]. Galloping occurs when wind gusts cause the sign structure to oscillate in a twisting motion, potentially leading to high-cycle fatigue damage.…”

Mitigating Fatigue in Cantilevered Overhead Sign Structures

“…Accordingly, it was preferred to shift the structure's natural frequency away from that range. A recent study was performed by Hosch and Fouad to obtain fatigue pressure from TIWG (15). Only vertical pressure was considered and it had approximately equal negative and positive values.…”

“…They were modeled with SAP2000 and designed according to the AASHTO specifications on maximum wind and dead loads. Fatigue loads resulting from NWG were modeled by using wind pressure power spectral density and fatigue loads resulting from TIWG were modeled by using the dynamic time history loading function obtained from Hosch and Fouad (15). Modal analysis was performed to obtain the natural frequencies of COSSs and include them in their response to fatigue loads.…”