Bridges

Square Hollow Section (SHS) and Rectangular Hollow Section (RHS) members are commonly used as column legs and bracing of sign support structures. The AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffics Signals and the VicRoads Bridge Technical Note 014 (V2.1 Nov 2019) identify challenges assessing the fatigue performance of SHS and RHS connections for infinite fatigue life using a nominal stress-based approach. The alternative analysis methods suggested in these standards require detailed finite element modeling and/or laboratory testing that may not be practical for application across large projects with multiple unique geometric configurations of sign gantries.

Austroads Guideline AP-G95-21 Design and Construction Guidelines for the Delivery of Large Cantilever and Gantry Structures provides fatigue assessment methods that have been practically applied on the West Gate Tunnel Project to verify gantry member connection details will achieve an infinite fatigue life. Specifically, Method 1 of the Austroads Guide has been applied. Design engineers have conducted thorough geometric stress assessments using a combination of finite element modelling and design code literature and compared to allowable stress limits at 100 million cycles of fatigue load. This paper covers the challenges and conflicts in current design codes, outlines the solution employed on the West Gate Tunnel Project through application of Austroads Guideline AP-G95-21, and provides details of the specific assessments completed for the analysis of the projectís gantry structures.