Analyzing the Effects of Walkway Attachments on Highway Cantilevered Overhead Sign Structures

Abstract

Cantilevered overhead sign structures (COSS) experience cyclic loading due to stochastic loads such as natural wind gusts (NWG). These wind loads cause large deflections in the cantilever and excessive stresses can develop at the connection between the cantilever and mast where fatigue performance is a concern. Modifications to the sign structures pose further concerns as changes to the aerodynamic properties could have unintended consequences. A design consideration of COSS is serviceability of the sign through the use of a steel grate walkway that workers can use for maintenance on the sign. The steel grate walkways on COSS are rarely used for maintenance anymore, hence are being removed by multiple state DOTs to prevent vandalism. However, the impact on COSS with the removal of the walkways is unknown. The research described analyzes the effect the walkways have on the dynamic and aerodynamic properties of COSS. Computer simulations of 32 different COSS configurations were carried out to see the effect of the grate removal on the natural frequency and the mass of the system. Aerodynamic performance is considered through the use of computational fluid dynamics (CFD) and experimental testing where the wind pressure on the sign in both axial directions and effects of vortex shedding are examined. Findings made by the research include: 1) the walkway has a minimal effect on the system’s mass and natural frequencies, 2) the walkway has minimal effect on the wind-induced force on the sign, 3) vortex shedding is not a exacerbated with removal of a walkway attachment, and 4) walkway removal does not change the fatigue performance of the connection between the cantilever and mast. Based on these findings, the removal of walkways is not problematic for COSS.